1.
Arizona's Aquatic Ecosystems
Authors
The reports in this chapter were prepared by the following individuals.
Arizona's Riparian Ecosystems
o Duncan T. Patten, Ph.D., Center for Environmental Studies, Arizona State University
o Robert D. Ohmart, Ph.D., Center for Environmental Studies at Arizona State University
Arizona's Lake Ecosystems
o Richard Meyerhoff, Ph.D., Arizona Department of Environmental Quality
o Edward Ricci, Brown & Caldwell
o Dennis Shirley, Salt River Project
Arizona's Streams and Rivers Ecosystems
o W. L. Minckley, Ph.D., Department of Zoology, Arizona State University
o Dennis M. Kubly, Arizona Game and Fish Department, Non-Game Branch
Introduction
Riparian systems include the ecological part of the landscape that is hydrologically connected with, and dependent on, streams, lakes and other water sources.
In the Southwest, riparian systems compose less than 1% of the landscape, but create habitat that is important to a majority of arid-land species. In Arizona, riparian systems comprise 0.5% of the landscape (Strong and Bock 1990). These systems are extremely sensitive to modifications because of their hydrological connection with water sources. See Map B-1 (Riparian Lands of Arizona), in Appendix B.
Riparian systems in Arizona include a wide variety of vegetation types.
o At lower elevations, these systems are normally dominated by Fremont cottonwood (Populus fremontii) and Goodding willow (Salix gooddingii) trees, with shrubs and herbaceous plants growing near the water's edge.
o At mid-elevations, riparian vegetation is characterized by mixed deciduous trees such as sycamore (Platanus wrightii), ash (Fraxinus spp.) and Arizona walnut (Juglans major).
o At high elevations, shrub willows, alders (Alnus spp.), and grasses are common.
Some riparian areas in Arizona include cienegas, or wetlands, a consequence of stream channel morphology that permits standing water or a shallow water table.
Recent inventories of riparian habitat types (Valencia et al. 1993) provide insight not only to the paucity of riparian habitats in Arizona, but also to the scarcity of perennial streams.
o In Arizona there are approximately 5,032 miles of perennial streams distributed as follows (Valencia et al. 1993):
2,511 miles (50%) are on federal lands
255 miles (5%) are on state lands
857 miles (17%) are on private lands
1,409 miles (28%) are on tribal lands.
o There is a total of 266,786 acres of floodplain or riparian vegetation associated with these perennial streams. Of the total acres, the community types are represented as shown in Table 1.1 (Valencia et al. 1993):
Table 1.1 Community Types on Perennial Streams
--------------------------------------------------------------- | Community Type | Percent of Total | =============================================================== | Saltcedar (exotic) (Tamarix chinensis) | 20 | --------------------------------------------------------------- | Mesquite (Prosopis spp.) | 18 | --------------------------------------------------------------- | Arrowweed (Tessaria sericea) | 15 | --------------------------------------------------------------- | Conifer | 11 | --------------------------------------------------------------- | Mountain meadow | 6 | --------------------------------------------------------------- | Oak (Quercus spp.) | 4 | --------------------------------------------------------------- | Cottonwood/willow | 4 | --------------------------------------------------------------- | Mixed scrub | 3 | --------------------------------------------------------------- | Cattail (Typha spp.) | 2 | --------------------------------------------------------------- | Sycamore | 1 | --------------------------------------------------------------- | Miscellaneous Communities | Less than 1% | ---------------------------------------------------------------
Saltcedar was introduced into the US from the Mediterranean in the early 1800's as a soil stabilizer and ornamental (Horton 1964, Robinson 1965).
It has wildlife values (Anderson et al. 1977, Hunter et al. 1988, Brown and Trosset 1989), but they are much lower than those of cottonwood willow communities.
Breeding bird densities in cottonwood willow habitats reported from Arizona exceed published densities of any habitats in the continental US (Carothers et al. 1974).
The rapid decline of the cottonwoodwillow community in Arizona is exemplified from data on the Colorado River (Ohmart et al. 1977).
o In the mid-1800's there was a minimum of 5,000 acres of cottonwoodwillow habitat along the 275 miles of river between the US - Mexican border and Davis Dam.
o Vegetation inventories in the mid-1970s showed only 500 acres remained (Ohmart et al. 1977)
o Today, less than 100 acres persist along the Colorado River (Ohmart pers. obs.).
The Arizona Nature Conservancy (1987) reports that the cottonwod-willow association is the rarest forest type in North America.
Riparian Systems Values
Riparian systems are valuable to humans and wildlife because of the many services they provide.
o Riparian vegetation creates habitat for fish and wildlife, shades and cools the water along streams, stabilizes banks, and improves water quality by filtering sediments and pollutants.
o Riparian vegetation ameliorates the intensity of flood events while promoting groundwater recharge.
Riparian vegetation extends the return of water to the stream system, which aids in transforming intermittent streams to permanent flows.
o Riparian habitats are vital to Arizonans for supplying drinking and agricultural waters.
o A large percentage of recreational activities occurs in and around these systems (Arizona State Parks Board 1994a).
In Arizona, many of the riparian systems along larger rivers have been greatly altered by water management activities.
In many cases, riparian vegetation has been highly degraded because instream flows have been significantly reduced and some rivers are de-watered.
In other cases, development and agricultural activities have modified or eliminated streamside vegetation, often introducing exotic species and allowing others to expand.
Riparian systems are highly limited in Arizona.
Human health, environmental quality, and wildlife habitat are so significantly intertwined with riparian systems that they should be of primary concern for an environmental risk study.
Environmental Stressors
Accidental Spills
Accidental spills that will affect riparian areas will occur primarily along transportation routes, such as highways and railroads. Occurrences are low and the area that might be affected is a small percentage of Arizona's riparian areas.
When a spill does occur it can have a major impact depending on volume, duration, and toxicity of the material.
The greatest impact will be on the aquatic system and the riparian community immediately adjacent to the stream. Riparian vegetation may absorb spilled toxics but, except for a few compounds, the material may accumulate and not be lethal.
It may, however, prove lethal to higher trophic levels (insects, fish, etc.).
Depending on the toxicity of the spill material, the riparian system will show various levels of resistance and resiliency. The higher the toxicity, the lower the resistance and resiliency.
In most cases, spill effects will be short-lived, but accumulation of toxic materials in soils may extend the spill life. There is little literature on the effects of toxic spills on Southwestern riparian vegetation.
Air Pollution
Low-level air pollution found in most of Arizona has little or no effect on riparian systems, with the exception of riparian areas near high pollution level point sources such as smelters or power plants.
At these sources, air pollution tends to be a chronic impact.
Studies of the response of arid region systems to smelter pollution, primarily SO2, show that many species may be lost (Woods and Nash 1976).
Other studies that include plant riparian species, such as mesquite, reveal the existence of leaf necrosis, but show that the plants appear to recover with each year's new leaves (Gabriel and Patten 1990).
No studies have been done on broad-leaved deciduous riparian plants, but these plants growing near pollution point sources do not show much response to air pollutants.
It can be concluded that most riparian plants in Arizona are relatively resistant to air pollution and that resistance is a result of the development of new foliage. Growth may be limited because of this, but the systems per se are not at much risk.
There is little literature to document the effects of other air pollutants, such as NO2, O3 and PM-10's on riparian systems in Arizona, although the effects of NO2 and O3 in the Los Angeles area have been substantial. These effects are primarily on plant species that are dependent on airborne nutrients, but many other species seem to survive these heavy pollution levels.
Physical Alteration of Systems
Grazing
Domestic livestock concentrate in riparian habitats because there they find water, shade, and lush verdant forage (Skovlin 1984, Platts and Nelson 1985, Goodman et al. 1989).
As much as 100% vegetation removal has been reported by Platts and Nelson (1985) in semi-arid big sagebrush (Artemesia tridentata) riparian habitats.
Livestock impacts to riparian habitats include vegetation degradation, species loss, soil compaction, streambank degradation, and aquatic system degradation.
As the stream channel destabilizes, it downcuts during high flow events, lowering the floodplain water table.
Large elk (Cervus elaphus) populations degrade riparian habitats similarly (Houston 1982, Chadde 1989), and elk concentrations in some areas in Arizona are approaching or have exceeded those population levels (Arizona Game and Fish Department 1993).
As a result, riparian systems have low resistance to grazing by cattle, but light grazing and proper management may improve this resistance.
o For example, winter grazing by cattle on Date Creek Ranch near Wickenburg, Arizona, has allowed woody perennials to recover and persist, although many of the native herbaceous plants have not recovered or show continued signs of heavy grazing.
If grazing is removed from a riparian system, the system demonstrates a moderate level of resilience, but not all components of the system respond at equal rates. Herbaceous species such as grasses, sedges (Carex spp., Cyperus spp.), and rushes (Juncus spp.) begin to recover within a few years to trap sediment and provide some bank stability. Willows and other woody species are slow to recover, and may fail to return if seed sources have been eliminated.
The fibrous roots of grasses and sedges are important for stabilizing soils, while the woody roots of willows and other woody vegetation help to prevent streambank damage in annual floods (Platts 1981, Elmore and Beschta 1987, Beschta and Platts 1986, Clifton 1989). An area in Oregon protected from grazing for 50 years showed a 94% reduction in channel cross-section, and in 1989 "thickly vegetated overhanging banks obscure a narrow and deep channel" (Clifton 1989).
The degradation of riparian habitats has been heavily studied over many portions of the West and grazing impacts are well known (Cottam and Evans 1945; Ames 1977; Davis 1977; Armour 1978; Behnke 1978, 1979; Behnke and Raleigh 1978; Dahlem 1979; Skovlin 1984; Clifton 1989; Elmore 1992; GAO 1988, 1992; Meyers 1989).
Studies conducted in Arizona demonstrate how unmanaged livestock grazing can severely impact both fish and wildlife resources. Krueper (1993) examined avian populations and understory vegetation recovery along the San Pedro River before and after cattle were removed. Dramatic density increases were observed in neo- tropical birds when livestock were removed in 1987.
o The Yellow Warbler (Dendroica petechia) increased six-fold over the five years
o The Song Sparrow (Melospiza melodia) increased 61-fold
In east-central Arizona, Clarkson and Wilson (1991) examined domestic livestock grazing impacts on the endangered Apache trout (Oncorhynchus apache) by sampling 243 stations among 75 reaches of 21 high-elevation streams over a 4-year period.
o Streams were either ungrazed, lightly grazed or heavily grazed, the last having significantly lower trout standing crop values than the first two categories of managed streams.
o Streambank damage by large ungulates consistently explained the greatest variation in total numbers of trout. They concluded that cattle management is essential if the trout fishery potential is to be realized.
o Horning (1994) examined federally-listed species on BLM lands in the West, and of the 76 plant and animal species where livestock grazing contributed significantly to decline, 61 species were riparian-dependent or associated with riparian habitats.
The effects of vegetation change and removal and on erosion by livestock grazing are exemplified in a study by Cottam and Evans (1945) of parallel canyons in the Wasatch Mountains, Utah.
o After approximately 50 years of cattle exclusion, Red Butte Canyon contained 58% more forage per unit area of production. It also had 10 native grasses not present in Emigration Canyon, 66% more palatable shrubs, 12% fewer weeds and annuals, and less sheet and gully erosion.
o Croft et al. (1943) examined erosion from light (City Creek), moderate (Red Butte Canyon), and heavy grazing (Emigration Canyon) and reported a linear response in soil erosion to intensity of grazing. They strongly argue that soil management problems are at least as important as forage management, and the two should be considered together.
Grazing impacts are extensive and long-term.
Biological alterations due to grazing are exemplified by changes in species composition and loss of native species, both plant (Cottam and Evans 1945, Elmore 1992) and animal (Armour 1978, Skovlin 1984).
Resistance to these changes is low, but if grazing is removed, resilience is moderate, controlled in part by the availability of seeds and other propagules of native species (Wolden 1993).
Agriculture
Agricultural impacts to riparian systems are long-term and complete (Conine et al. 1978, Anderson and Ohmart 1982).
Removal of riparian vegetation, soil disturbance, and introduction of exotic agricultural species have prevented riparian systems from demonstrating any level of resistance to this disturbance.
Depending on the type of disturbance, once these lands are abandoned, it takes decades for the riparian system to re-establish. Recovery will be limited, based on the effects of soil disturbance, soil salinity, and groundwater draw-down connected with agriculture.
The area impacted by agriculture is primarily limited to broad floodplain valleys, which represents a small percentage of total riparian areas in the state (Karpisak 1981, Conrad 1982).
Highway construction in riparian areas includes highways that run parallel to rivers and highways that cross them.
The total area of riparian systems impacted by highways is limited, probably less than 1% of existing riparian areas. However, because of the nature of highway construction, the disturbance is relatively complete and long-term, and resistance of the system is very low if it exists at all.
Portions of the riparian system some distance from the river may be lost due to construction paralleling the river. The construction of a highway across a river not only disturbs the immediate area but also modifies stream hydraulics above and below the crossing point. These changes cause direct and indirect impacts on riparian systems.
Highway abandonment, like agricultural abandonment, leaves an area so disturbed that recovery of the riparian system is long-term, and thus the system has a low resilience.
Literature on effects of highway construction on riparian areas in Arizona is limited, although some studies have been done for environmental impact statements. An example is the highway construction across the Verde River from Rio Verde to the Beeline in the Tonto National Forest. Limited studies exist in other states (Patten 1989).
Highway construction requires materials for the roadbed and surface, materials often mined from stream channels. Development of sand and gravel mines and borrow pits within or near river channels often alters stream channel dynamics and may result in degradation of downstream water quality, especially during flows that are above baseline.
Most large stream channels in Arizona have sand and gravel operations, but the total area disturbed is limited. These operations are totally disruptive, thus there is little system resistance. However, if operations are abandoned, and topography is returned to normal channel and floodplain contours, the system may be quite resilient, exhibiting a high potential for restoration. Resiliency is lessened, however, if the topography of the operation's location is not returned to a near pre-construction condition, an almost impossible task with large sand and gravel operations.
Energy Production
Impacts of energy production on riparian systems is limited to air pollution from coal-fired power plants and hydroelectric dams, although diversion of effluent may be considered an indirect impact.
o For example, effluent that normally would have been released from the Phoenix Ninety-First Avenue treatment plant into the Salt and Gila Rivers, and supported a down-stream riparian community, is now diverted to the Palo Verde nuclear power plant for cooling. Dam construction and impoundment development affects riparian systems, both upstream and downstream (Nilsson 1982).
Dam Construction and Operation
The down-stream effects of dam construction and operation are well documented. About 60 percent of Arizona's riparian systems occur downstream of dams. Many of these systems are totally degraded because dams have allowed little or no downstream flow. The existence of the dams makes this a very long-term impact.
Dams may have a direct impact on the riparian system by affecting the stream flow in the following ways:
o Down-stream flows may be eliminated or modified in quality (Ohmart et al. 1988), quantity, and pattern (Williams and Wolman 1984).
o Flood flows may be reduced or allowed with unnatural timing (Fenner et al. 1985, Hunter et al. 1987, Ohmart et al. 1988, Auble et al. 1994).
o Discharges from dams may, however, maintain downstream riparian vegetation, but often insufficient flows are released over a long period, resulting in loss of vigor and even mortality of riparian species.
For example, minimum releases of 10 cfs from Alamo Dam were considered insufficient to maintain the downstream water table which supported cottonwoodwillow and mesquite forests below the dam (Long and Peck 1988).
o Dams may also increase salinity in downstream water.
o Changes in hydrological regimes below dams may also cause extreme degradation of the riparian system, reduction in growth and maintenance of the riparian vegetation, and loss or reduction in recruitment of new riparian vegetation (Ohmart et al. 1988).
If water is released, and periodic large floods are permitted, the riparian system is relatively resistant to the effects of the dam. More commonly, however, insufficient flows and large releases scour vegetation, or extended high releases drown native vegetation, all degrading the riparian system (Hunter et al. 1987, Ohmart et al. 1988, Rosenberg et al. 1991).
If flows and flooding events were returned to normal, regardless of the existence of the dam, the riparian system would show a relatively high level of resilience. If the dam has been in place a long time and scarce sediment has been delivered down tributaries below the dam, recruitment of riparian vegetation on the remaining cobbles and gravels may be limited.
Impoundment Filling
Impoundment filling inundates the riparian vegetation in the newly formed reservoir, but creates areas of potential habitat along the water's edge for establishment of riparian vegetation. Thus, riparian systems are not resistant to impoundment development, but are potentially resilient to conditions created by the impoundment. However, in the fluctuating reservoirs so characteristic of Arizona, shoreline levels change so dramatically throughout seasons and years that the primary feature around them is a virtually vegetation-less "bathtub ring."
Riparian systems are not dependent on fire and have little history of fire impacts in Arizona.
Fire in riparian habitats below major dams has become an important element in expediting plant community change, primarily because of the invasion and dominance of exotic saltcedar.
o For example, in 1935, after Hoover Dam was implemented on the lower Colorado River, the absence of annual floods allowed litter accumulation; wildfires became common on a 15 to 20-year cycle. Cottonwoods were killed immediately, willows persisted through a few fires, but the exotic saltcedar thrived and expanded in this environment (Ohmart et al. 1988).
It is possible that the riparian sacaton (Sporobolus spp.) grasslands in southern Arizona have changed because of fire suppression, but there is no specific literature on this and these changes are inconsequential compared to other impacts such as grazing or water withdrawal.
Fire suppression has undoubtedly preserved some riparian areas that may have been damaged by exotic plant-enhanced fires.
Mining has had major impacts on systems in Arizona.
Development of mine shafts, open pits, tailings ponds, and overburden waste piles all have affected riparian systems because many of these are in river and valley bottoms. The affected area is limited to a small percentage of total riparian area in the state, less than 4%.
Mining impacts are long-term and riparian systems have little resistance.
o For example, the expansion of the Ray Mine throughout the Mineral Creek Valley totally obliterated the existing riparian zone.
Abandonment of mines and other mining activities and developments does not create suitable sites for re-establishment of riparian vegetation and thus the resilience to mining is low.
Mining has other very significant impacts on riparian systems. Groundwater withdrawal, streamwater diversion, and stream water contamination are also consequences of mining activities.
Streamwater contamination has a greater effect on the aquatic system than the riparian system, the latter often tolerating the contamination as it would a chronic toxic spill. However, collapse of, or spill from, tailings ponds may greatly alter the downstream riparian system as the tailings (often chemically harmful to biota) are laid down equivalent to sediment deposition following normal flooding events.
o An example of a tailings spill is found on Pinto Creek near Miami, Arizona.
Spills similar to this could happen anywhere that tailings ponds fill valleys in watersheds upstream of riparian systems.
The resistance and resiliency of the riparian system is dependent on the amount and toxic level of the tailings spill. For further information refer also to the discussion of highway construction on page 8, regarding sand and gravel mining.
Timber Management
Modifying the watersheds upstream or upslope of riparian areas through timber management has a significant impact on riparian ecosystems.
The majority of Arizona's non-desert riparian systems, about 60% of the total, are found in areas with active forest management. Forest management includes timber cutting which may cause changes in sediment loads and runoff. These directly impact the quality of the riparian habitat, reducing recruitment of riparian plant species.
Depending on the magnitude of timber cutting and the closeness to the riparian system, the resistance of the riparian system will vary. If the cutting is near the stream or downflow in a system, the riparian system is not as resistant to impacts as when cutting is farther away or higher on the watershed.
Because forests grow back, the impacts of proper timber harvest are not long-term and the riparian system will be resilient as the proper conditions return to the channel area.
As was also mentioned in the discussion on highways, an important aspect of timber management is construction of access roads. In many cases these roads are not constructed with any consideration toward preventing erosion or alteration of adjacent systems. Riparian systems may receive most of the impacts of these transportation routes.
Water Transfer
Water transfer is significant to the health of riparian systems only when that water is withdrawn from a stream or groundwater system on which the riparian system is dependent.
The impact of water transfer is similar to the impact from stream diversion or groundwater withdrawal. See page 14 for a discussion of stream diversion, and page 15 for a discussion of groundwater withdrawal.
Less than 1% of the riparian area within Arizona is impacted by inter-basin water transfers, but the potential is great if cities purchase water rights and groundwater in distant basins and transfer the water for urban development.
Transport of Colorado River water in the Central Arizona Project has an unknown effect on the remnant of the riparian community along the Lower Colorado River, but if it is used to recharge groundwater through release into dry streams and washes, it will potentially enhance some riparian systems like Agua Fria River, while biologically altering others like the proposed continued releases into desert washes in Tucson.
Channelization
Most of Arizona's larger rivers have been channelized. This stressor has affected about 60% of Arizona's riparian systems.
Those affected include riparian systems along the Colorado River, Salt River, and Santa Cruz River.
Channelization expedites water movement to reduce duration of flooding and is commonly found through urban areas. Channelization has a long-term impact, but because channels do carry water, riparian systems along the channels demonstrate some resistance to this stressor, as long as flow control is not associated with channel construction as in Phoenix, for example.
Where channelization is accompanied by use of concrete or soil cement for channel lining, riparian vegetation may be totally excluded because shallow groundwater is no longer recharged. There is no resistance and resiliency of the system to this type of channelization. In addition, concrete-lined channels permit urbanization to the edge of the channel, preventing survival or recruitment of any riparian vegetation.
Removal of a constructed channel and restoration of a natural river channel will allow moderately quick response by woody riparian vegetation, but total recovery may be limited because of a lack of native seed sources.
Impacts of channelization have been documented for the Colorado River (Ohmart et al. 1988), Salt River (Graf 1983), and the Santa Cruz River (Betancourt and Turner 1991).
As was discussed for dams on page 10, water diversion usually results from construction of some form of structure across the river, an arrangement which may totally stop any downstream flow, or at least modify flows.
Water diversion reduces the amount of water below the diversion point, often to a level that impacts maintenance of riparian vegetation (Stromberg and Patten 1990).
Water diversion impacts about 60% of Arizona's riparian systems. For example:
o Diversion of water in the Salt River by Granite Reef Dam has eliminated extensive riparian forests that occurred along the river in the early part of the 20th century. These include stands of cottonwood, willow, and mesquite, along with wetland communities of cattail (Typha spp.) and bulrush (Scirpus spp.) (Graf 1988).
o About 90% of summer flow in the middle Verde River between Clarkdale and Camp Verde is diverted. This, along with groundwater withdrawal in the area, is believed responsible for preventing new cottonwood recruitment (Arizona Department of Water Resources 1994).
o A similar situation occurred on the Agua Fria River below Waddell Dam which was constructed in 1927 (Graf 1988).
Diversion is a long-term impact.
o If much of a stream's flow is diverted, riparian system resistance will be reduced because insufficient flow is available to maintain growth.
o However, if diversion is moderate, resistance may be high and riparian vegetation may encroach into the stream channel.
Removal or reduction in diversion will allow a moderate to high level of resilience by the riparian system as appropriate amounts and timing of flows enhance recruitment and recovery of riparian species.
In areas of shallow groundwater (less than 33 feet), groundwater withdrawal by pumping may have a profound effect on riparian ecosystems by removing their "lifeblood." Because of the use of groundwater by cities, agriculture, and mining, about 60% of Arizona's lower elevation riparian systems are impacted.
o The loss of flow in the Santa Cruz River in southern Arizona is a good example (Betancourt and Turner 1991).
o In the early part of the 20th century, groundwater extraction along the Gila River caused a decline in vigor of riparian mesquite bosque trees near Casa Grande National Monument. This reduced vigor allowed the trees to be infested with mistletoe, and the whole bosque community died (Judd et al. 1971).
o Groundwater is now being withdrawn from a depth of over 656 feet in the Casa Grande area.
o Riparian vegetation cover has declined following the practice of groundwater withdrawal from the upper Santa Cruz River for Nogales, but cover is enhanced downstream by Nogales' effluent release near the confluence of the Santa Cruz River and Sonoita Creek (Stromberg et al. 1993a).
o Along the Verde River, 46% - 84% of the Fremont cottonwoods died as a result of groundwater withdrawal by Phoenix, coupled with the effects of natural drought near the Fort McDowell Indian Reservation (McNatt et al. 1980).
In a study along Tanque Verde Creek near Tucson, Stromberg et al. (1992, 1993b) showed that if groundwater withdrawal is limited (a few meters), resistance of the riparian system is high, while deep groundwater withdrawal causes the riparian system to have little or no resistance and, in most cases, the riparian system will be completely lost because the surface flows will have also been lost (Walters et al. 1980).
Resilience of a riparian system to the elimination of groundwater withdrawal will be high only if the withdrawal is limited. If the groundwater is drawn to depths well below the reach of riparian species' roots, elimination of pumping will not allow any riparian recruitment unless surface flows return. Thus, resilience to groundwater withdrawal, in most cases, is low.
Recreation
Only about 2% of Arizona's riparian areas are heavily used by recreationists, for example, the Salt River Recreation Area.
Impacts are short-term and resistance is moderate, with some species showing changes in abundance (Aitchison 1977, Higgins and Ohmart 1981, Turner 1983). However, in areas with heavy use by off-road vehicles or all-terrain vehicles, substrate and vegetation disturbance may be sufficiently intensive to reduce the resistance of the riparian system.
Removal of recreation would, in most cases, probably allow a quick recovery of the riparian system, except, perhaps, in areas that have had major substrate alteration or extensive tree removal.
o An example of changes to flora and fauna was reported (Aitchison 1977) for a developed campground in a riparian habitat in Oak Creek Canyon. Understory vegetation was cleared, roads constructed, toilets installed, and picnic tables constructed. Not only did bird densities and species composition change at the developed site, but mostly larger birds (weight a mean of 48.5 gm) tolerated the changes and camping activities as compared to the control site where mean body weight was less (38.2 gm).
Higgins and Ohmart (1981) examined avian species composition and density in mature velvet mesquite (Prosopis velutina) forests along the Salt and Verde Rivers on the Tonto National Forest where recreation was developed and undeveloped. Where recreation was developed, tree densities were highly reduced and foliage volume was absent between one and ten feet, resulting in an 88% reduction in densities of obligate riparian species.
The Higgins and Ohmart study also predicted loss of Bell's Vireos (Vireo bellii), Cooper's Hawks (Accipiter cooperii), Yellowbilled Cuckoos (Coccyzus americanus), Anna's Hummingbirds (Calypte anna), Yellowbreasted Chats (Icteria virens), and Hooded Orioles (Icterus cucullatus). Woodpeckers and other species would probably be reduced in numbers (Higgins and Ohmart 1981).
Riparian habitats' resistance to recreational use is probably lowest below dams where the vegetation is already stressed because of reduced instream flows.
Urbanization
Urban development has a major impact on riparian zones, but affects only about 5% of the total.
Urban development probably accounts for one of the most long-term impacts of all stressors. Long-term impacts along with near total destruction prevents any significant level of resistance by the riparian system. Resilience does not exist because of the unlikelihood of any reversal to a "natural" system.
Biological Alteration of Systems
Species Introduction
All of Arizona's riparian systems have been influenced by introduction of exotic species (both animal and plants).
These are essentially permanent, long-term changes for which the riparian system has little resistance as exemplified by the introduction of saltcedar (Harris 1966). Because exotics will never be eliminated, resilience cannot be estimated.
Saltcedar has become a major component of most desert riparian systems, its density limited mostly in areas with natural stream flows and little or no grazing.
Global Climate Change
Not evaluated for this report
Land and Soil Contamination
Contamination of the land from spills, deposits or other forms will have indirect impacts on riparian systems. These contaminants will eventually appear in surface water and groundwater and in this way influence riparian species. Refer also to the discussion of surface water contamination on page 18, and of groundwater contamination on page 19.
Natural Hazards
Probably the most influential of natural hazards on riparian systems are floods.
Floods
Floods result from high precipitation events, but they are often compounded by improper watershed management.
Riparian systems evolved with disturbance, usually in the form of floods.
Flood disturbance is necessary for establishing appropriate microenvironmental conditions for plant species' recruitment (Stromberg et al. 1991).
Floods will cause sediment aggradation and degradation in the riparian zone, and in this process may remove or bury riparian vegetation. Vegetation removal and burial are normal features of riparian system dynamics, but they may be exacerbated if floods occur too often because of poor watershed conditions.
Cessation or reduction of flooding because of dams or other water management activities also influences the long-term maintenance of riparian systems. The riparian system has a relatively high resistance and high resilience to floods' normally short- term impact. Except for headwater areas, most of Arizona's riparian systems are influenced by flooding.
Fire
Fire is another common natural hazard in Arizona.
There is little evidence that fire played an important part in riparian system dynamics prior to European settlers and the introduction of saltcedar. (Refer also to Fire Suppression on page 11.)
Insect Infestation
Insect infestation may also be a natural hazard in riparian ecosystems.
Insects such as the tent caterpillar and long-horned beetle may cause major damage to riparian vegetation. Although the system may demonstrate low resistance to these generally short-term infestations, it may sustain a relatively high resilience.
Surface water contamination is caused by non-point sources such as agricultural fields, mines, and domestic livestock grazing (Chaney et al 1990), and from point sources such as a particular industrial site or particular effluent outfall.
Over 90% of Arizona's riparian systems are probably impacted by non-point source pollution, as many are in valleys where agriculture is common, and most are impacted by grazing where waste materials from livestock are carried through the riparian zone by surface runoff to the stream.
Contaminants are often tied to nutrient input to agricultural fields.
Storm drain and urban runoff are also sources of non-point pollution and they often contain hydrocarbons and other organic contaminants (Sommerfeld and Amalfi 1991).
In all of these cases, and usually in the case of effluent inflow, the riparian system absorbs the contaminants when they reach riparian groundwater, except for streamside plants which use surface stream flow (Sullivan 1991).
The effects on riparian vegetation are limited, demonstrating a moderate level of resistance to these short-term impacts, although the plants have a low level of resistance to uptake.
Surfacewater contamination usually has much greater effects on the aquatic system.
Removal of surfacewater contamination will eventually reduce accumulation of contaminants in riparian species. This should occur over a year or two, as the plants shed the contaminated tissue, indicating a moderate level of resilience.
Groundwater contamination tends to be more long-term and chronic, again the result of point and non-point source pollution.
There are fewer locations in Arizona with shallow (riparian-available) groundwater contamination than with surface water contamination.
Where shallow groundwater is contaminated, riparian plants will take up the contaminants and accumulate them in tissues. Because most riparian vegetation away from the edge of the stream is dependent on groundwater, the vegetation cannot resist uptake.
When the contamination source is removed, the system does not readily discontinue contaminant uptake because groundwater will remain contaminated for a long time.
Conclusions
The major stressors of riparian systems in Arizona fall into two categories: water management and land use.
o Water management affects the primary resource that maintains riparian systems.
Because water is managed separately for surface and groundwater in Arizona, coordination of use is non-existent.
As an arid state, Arizona controls most of its surface water for out-of- stream uses. Consequently, most of the lower-elevation riparian systems in the state are lost or extremely degraded.
Although surface water diversion and flow control may be the primary water management stressor with the greatest impact on the largest area of the riparian system, groundwater withdrawal is a close second.
Draw-down of the water table throughout much of the agricultural portions of Arizona has eliminated or greatly reduced riparian systems, especially the extensive mesquite bosques found along larger rivers.
Groundwater withdrawal also has an impact on stream flows throughout much of the state, and consequently affects the associated riparian systems.
o Land use includes physical modification of riparian systems as well as biological change.
Agricultural development has removed extensive riparian stands and kept them from recovering.
Other land uses such as urbanization have all but eliminated local reaches of riparian vegetation.
Grazing, a land use found throughout much of Arizona, has altered most of the remaining riparian systems. Impacts of grazing have been more profound than those of water management. The biotic community that remains following grazing usually does not have the function and structure of the undisturbed riparian system, and therefore does not provide the services expected of these systems.
Often concurrent with grazing and river management and their effects are the introduction, invasion, and maintenance of exotic plant species within riparian systems.
Biological alteration, often a consequence of some type of land use, occurs throughout Arizona and is probably one of the few stressors for which there is no reasonable procedure for eliminating its impacts.
Other stressors play a relatively unimportant role in altering riparian systems, both short or long-term.
o Accidental spills and air pollution have localized effects.
o Construction and mining activities also may cause extreme disruption of riparian systems but on a relatively small scale compared to effects of water management, agriculture, and grazing.
o If policy is to be established that would reduce, or possibly reverse, the impacts of the important stressors on riparian systems, it would have to address the following:
Water requirements (stream flows) of riparian systems;
Long-term degradation of riparian systems by present grazing practices; and
Possible changes in land uses along the riparian corridors of the state.
Lake Ecosystems Stressors
Introduction
A lake may be defined as an inland body of water that naturally serves as a basin for the collection of runoff, or as an inland artificial impoundment that may or may not be constructed in a natural watercourse. Examples include natural lakes, reservoirs, stock ponds and playas.
Because data for Arizona are seriously lacking for playas or stock ponds these types of lakes will not be included in this assessment.
The lake ecosystem is intimately coupled with the land surrounding it in its watershed (Hynes, 1975; Likens and Bormann, 1974).
As waters naturally run downstream to be stored within a natural or artificial basin, the waters transport and metabolize components of the surrounding land to the lake. In addition, waters transport and metabolize dissolved and sediment-attached chemical constituents that may be introduced directly into flowing water courses and lakes.
In this regard, the evaluation of the lake ecosystem should not be far removed from an understanding of the surrounding watershed and contributing stream, river, wash or spring. (See Map B-2 (Watersheds and Major Rivers of Arizona) in Appendix B.) Hynes (1975) provided the following description of this relationship:
---------------------------------------------------------------- | We may conclude then that in every respect that the valley | | rules the stream. | | | | Its rock determines the availability of the ions, its | | soil, its clay and its slope. | | | | The soil and climate determine the vegetation, and the | | vegetation rules the supply of organic matter. The organic | | matter reacts with the soil to control the release of the | | ions, and the ions, particularly the nitrate and | | phosphate, control the decay of the litter, and hence lie | | right at the root of the food cycle. | | | | One could go on and on, building up an edifice of | | complexity, all linked and cross-linked. . . . | | | | It is also clear that changes in the valley wrought by man | | may have large effects. Some [are] obvious... but others | | may be very subtle. | ----------------------------------------------------------------
Typically, lakes are dynamic bodies of water. Natural currents, the overturn of the water column and the flow-through nature of some lakes, especially reservoirs, allow the waters of lakes to continually mix. This mixing process allows the components of the landscape that have entered the system to either pass through, continue to be metabolized or stored.
The retention time for constituents of concern can vary drastically from lake to lake as a result of such things as variation in rates of flow-through, evaporation, precipitation events, and reservoir operations.
The effect of a pollutant on a lake can be much more significant than the effect of that same pollutant on a stream (Hellawell, 1986). When a pollutant is discharged to a stream it is quickly moved downstream, while the pollutant may reside in a lake for a considerable period as the exit pathways are more restricted.
All lakes are temporary systems. Of natural lakes, Hutchinson (1957) stated:
--------------------------------------------------------------- | Lakes seem, on the scale of years or human life spans, | | permanent features of the landscape, but they are | | geologically transitory, usually born of catastrophes, to | | mature and die quietly and imperceptibly. | ---------------------------------------------------------------
Natural processes gradually will convert any lake system, whether natural or man- made, into a terrestrial system. However, the rate at which this change occurs is greatly dependent on:
o Whether the system is natural or artificial
o Which land use activities occur in the watershed
In effect, lakes undergo ecological succession as they age. This is brought about in part by the gradual filling of the lake basin by sediments deposited from the surrounding watershed. As the lake basin fills, the volume decreases and the lake becomes shallower. The net result of this increased shallowness is increased cycling of nutrients and conditions conducive to plant growth. Succession of plant communities then completes the conversion of an aquatic to a terrestrial ecosystem.
Natural lakes differ significantly from reservoirs in terms of size, depth and water retention times (Petts, 1984). Marzolf (1985) documented differences between natural Michigan lakes and Kansas reservoirs. The results are shown in Table 1.2 on the following page (adapted from Marzolf, 1985).
Table 1.2 Comparison of Physical Characteristics of Natural Lakes and Reservoirs in Michigan and Kansas
----------------------------------------------------------------------------- | Lake or Reservoir | Drainage Area/ | Retention Time | Mean Depth | | | Surface Area | (Days) | (Feet) | | | | | | | | (Acres) | | | ============================================================================= | Michigan (natural) | 7.8 | 1622 | 37 | ----------------------------------------------------------------------------- | Kansas (reservoir) | 507.0 | 427 | 18 | -----------------------------------------------------------------------------
These differences may have a critical effect on how a given pollutant might affect a particular lake ecosystem.
Because reservoirs typically drain a much larger area, they are sinks for pollutants from many more activities. However, the retention time for natural lakes is much longer than for reservoirs, and as a result, the effects of pollutants are more difficult to dispel.
The number of lakes on non-Indian lands in Arizona is difficult to quantify because the smallest systems, e.g., stock ponds, are difficult to enumerate (ADEQ, 1994). Not counting privately owned urban lakes and stock ponds, there are 357 significant publicly-owned lakes listed for Arizona that cover an area of 134,040 acres.
A more comprehensive USGS analysis that includes many wetlands, dry playas and stock tanks shows 1,767 lakes with a coverage of 265,802 acres.
Of this number, 172,284 acres are considered perennial (natural lakes or reservoirs) and will be the focus of this assessment. (See Map B-3 (Lakes and Reservoirs of Arizona) in Appendix B.)
Non-point pollution sources contribute greater stress on lakes than point sources.
Lakes serve as collection points, either as basins or as impoundments, along river courses for water quality problems caused by land use activities in the upstream watershed. The effects of many stressors on lakes are indirect via non-point pollution sources such as silt, organic matter, and nutrients (USEPA, 1990). The point sources or direct effects contribute a smaller load of pollutants by comparison and consist of direct discharges to the water body.
The effects of physical, chemical and biological stressors on lakes, whether direct or indirect can be categorized into the following four areas:
o Eutrophication
o Sedimentation
o Deposition of toxic compounds
o Temperature alterations or thermal pollution
Considerable information about these processes and the activities that cause them to occur has been compiled in a number of texts (Burgis and Morris, 1987; Cole, 1983; Cooke et.al., 1993; Haslam, 1990; Hellawell, 1986; Hynes, 1960; Mason, 1991; Omernik, 1977; Petts, 1984, Report of the Committee on Water Quality Criteria, 1972; Resh and Rosenburg, 1984; Thornton et.al., 1990; USEPA, 1988, 1993; Welch, 1992; Wetzel, 1975).
Eutrophication
Eutrophication is the enrichment of a water system by inorganic nutrients, primarily nitrogen and phosphorus (Hutchinson, 1969).
In undisturbed lakes the rate of nutrient and sediment input is in a steady state with the surrounding watershed such that the lake is always in a state of trophic equilibrium (Hutchinson, 1969). This equilibrium is a balance among the edaphic, climatic and morphologic characteristics of the basin.
Natural events such as floods or fire may increase the rate of eutrophication but at a much slower rate, and when the effects of such events end, lakes typically stabilize. Overall, the rate of eutrophication is so slow as to be imperceptible.
More often the process is induced and/or enhanced by land use activities and wastewater discharges to water bodies, and, in contrast to the rate of natural eutrophication, will occur much more quickly, in as little as 10 to 50 years (Welch, 1992).
o For example, Bormann et al. (1969) documented the accelerated deposition rate of nutrients following deforestation around a New Hampshire Lake.
o Longstreth and Patten (1975) found a similar pattern in Arizona where the removal of shrubland vegetation and its replacement with grassland resulted in the erosion of soil nutrients, especially nitrate, from the watershed.
The effects of eutrophication on water quality are numerous (Mason, 1991). These include drinking water with unacceptable taste and odor, water that is injurious to health, the increased treatment of potable water, reduced fishing for sport, increased aquatic plant growth that impedes recreation and reduced recreational opportunities.
The potential effects of eutrophication on drinking water supplies are significant (Cooke et.al., 1993). Two-thirds of the US population obtains its drinking water from surface water sources, and of the 600 largest public utilities (more than 50,000 customers) 68 percent obtain their drinking water from lakes and reservoirs.
In addition to the problems of poor taste, odor and color, drinking water obtained from eutrophic water bodies also has been found with the following problems:
o High concentrations of organic molecules which form possibly carcinogenic and mutagenic trihalomethanes and other by-products of chlorination when raw water must be disinfected (Cooke and Carlson, 1989; Palmstrom et.al., 1981)
o Gastrointestinal disorders associated with consumption of water from reservoirs with blooms of blue-green algae, a typical occurrence in eutrophic waters (Carmichael et.al., 1985)
o The added cost of treating water with high densities of algae (Collingwood, 1977).
With regard to this problem, the American Water Works Association (1987) reported that 61% of drinking water supplies in the United States and Canada had algae (especially blue-green algae) related taste and odor problems.
The effects of eutrophication on the food web vary with the depth of the lake as well.
o In the shoreline area, or littoral zone, wave-exposed areas are less impacted as wave action keeps water well-mixed and oxygen depletion (a typical consequence of eutrophication) does not occur. Food availability increases (increased production) but substrate is often modified.
Changes occur in the biological communities. For example, in the invertebrate community, reductions in pollution-intolerant species (such as mayflies, stoneflies and caddisflies) occur as a direct result of increased organic pollution. Flies and worms, which are tolerant of such pollution, become dominant.
o In the sublittoral zone (deeper than the littoral zone), similar changes in the fauna may occur, but the effects of eutrophication (increased oxygen demand of water and sediments) are usually more severe as increasingly calm water results in less mixing and occasional oxygen depletion.
One of the best examples of this effect was seen on Lake Erie. The normally dominant mayfly population of Hexagenia was decimated when calm waters resulted in severe oxygen depletion at the substrate. It is estimated that 30,000 metric tons of Hexagenia were lost. The mayfly population never recovered and was replaced by the more pollution tolerant invertebrates, worms and flies (Wood 1973, Cook and Johnson, 1974).
o In deep water areas (the profundal zone) of lakes, effects of increased eutrophication are indicated by distinct changes in the invertebrate fauna. This change in the biota is associated with increased tolerance to low or occasionally zero oxygen conditions.
The effects of eutrophication on fish have been well-documented (USEPA, 1993; Welch 1992). Long-term effects include changed species composition, largely a result of reduced dissolved oxygen levels in eutrophic lakes.
In Lake Erie, Beeton (1965) and Beeton and Edmondson (1972) showed that a drastic change in the composition of fish species occurred during the forty-year period that nutrient loading occurred. Popular sports species such as whitefish, walleye and pike were replaced by fish such as carp, perch and drum.
Restoring a lake body to a pre-eutrophication condition is difficult at best and the success of such a process will depend upon many factors including the location, lake size and the nature of the causes of eutrophication (Cooke et.al., 1993).
o For example, in Lake Washington (Washington State) it was possible to stop and generally reverse the eutrophication process because source reduction of nutrients was possible and the retention time of lake water was relatively short.
o In other cases, for example in Switzerland, expensive efforts to decrease nutrient loadings in order to stop eutrophication were only partially successful and efforts to completely restore lakes to a pre-eutrophication condition were unsuccessful. The conclusion from that study was that it is better to prevent eutrophication from beginning in the first place than having to stop and reverse the process at a later date (Gächter and Imboden, 1985).
Sedimentation
Sedimentation is the process by which lake basins are gradually filled by fine sediments transported into the water body from the surrounding landscape either directly or via discharging rivers.
Natural rates of filling depend greatly on the nature of the geology of the watershed. However, human activity can augment rates of sedimentation. Petts (1984) found that large capacity reservoirs or those receiving drainage from hardrock or well-vegetated watersheds are not significantly affected by sedimentation. Rates of storage loss in these water bodies are typically less than 0.01 percent per year.
Reservoirs that receive high sediment loads can fill quickly.
o For example, the Big Tujunga reservoir in southern California lost 70% of its storage capacity in less than four years as a result of high watershed sediment yields (Scott, 1973).
The effects of sedimentation on the nature of lakes are poorly understood. It has been suggested that increased shallowness caused by lake filling changes the trophic equilibrium of the system and can either lead to or accelerate eutrophication (Welch, 1992). As the basin fills, an increasingly large area is available for macrophyte growth. The result is increased productivity and nutrient production in the system and, as a consequence, increased eutrophication. The increased sedimentation and eutrophication result in a shift from an aquatic to a terrestrial ecosystem.
It has also been suggested that sedimentation reverses the process of eutrophication by reducing light transmission through increased turbidity. Reduced light transmission results in less productivity by macrophytes and algae. A study by Warwick (1980) documented this occurrence in Lake Ontario.
o Sediment cores from the lake showed that during a period of extreme logging in the watershed, mineral sediments rapidly accumulated in the lake, as a result of increased erosion in the deforested watershed.
o The fauna changed during the same period from a fauna typical of eutrophic conditions to one typical of oligotrophic conditions (especially low in nutrients). Decreased food availability caused by increased sedimentation is the hypothesized cause.
Deposition of Toxics
Toxic chemicals find their way into lake systems by a variety of means including direct discharges from shoreline or boating activities or indirect discharge from events occurring in the watershed. Toxic chemicals from the watershed may arrive either in the water column or bound to sediments.
The effects of toxic chemicals on a lake ecosystem are closely correlated to the chemistry of the lake. Under certain conditions, toxic chemicals can be bound to the substrate and subsequently buried as sedimentation occurs. However, under other conditions, toxic chemicals may be released from the sediment particles to which they are bound and released into the water column. Habitat variables such as pH, temperature, oxygen, and hardness affect the toxicity of heavy metals.
o For example, pH effects metal solubility. As water becomes more acidic (lower pH), many metals dissolve into the water column and increase in toxicity.
The toxicity of a given chemical may be acute or chronic depending on the concentration of the chemical and the length of exposure to the biota.
Sensitivity to toxicity varies with different types of organisms.
o For short-term acute toxicity tests, it has been shown that aquatic insects are more tolerant to toxic heavy metals than fish or other invertebrates (Warnick and Bell, 1969).
o Under long-term exposure (chronic toxicity tests) some aquatic insects may be equally or more sensitive to the toxic chemicals than fish (Spehar et al., 1978).
Long-term exposure results in effects to all aspects of an organism's life history, e.g., egg-laying, molting, growth, reproduction, behavior, etc., while short-term exposure affects only a specific portion of the life history.
The results of toxic chemical deposition in lake systems are not limited to the lake body in which it occurs. Many toxic chemicals can bio-accumulate in the biological community and may be exported via birds or animals consuming fish from the lake.
o For example, invertebrates take up the chemicals either directly from the water or by consuming food particles adhered to the sediment. Fish consume the invertebrates and birds consume the fish.
At each step in this trophic food chain the toxic chemical is concentrated and made available to the next higher level in the chain (bioaccumulation). These chemicals may have severe consequences for the top consumer such as humans, by affecting growth or reproduction, or even by causing death.
Temperature Alterations
Temperature changes (or thermal pollution) may have serious effects on the biota of water bodies (Mason, 1991; Langsford, 1972).
These effects are not limited to just the types of species that may live in a given temperature regime. The effects may also result in changes in rates of productivity and mineralization processes. The former may affect the rates of eutrophication; the latter affect how toxic chemicals may impact the system. In addition, elevated temperatures cause waters with increased organic pollution to experience greater reductions of dissolved oxygen than waters without that pollution (Mason, 1991)
Water body temperatures may be altered unnaturally in several ways.
o Discharge of cooling water from power plants can elevate ambient temperatures and affect local areas of a lake. The occurrence and severity of environmental effects resulting from these thermal discharges are highly dependent on site and discharge design of the cooling facility.
o Agriculture, forestry, and urbanization affect large areas including entire watersheds (Wurtz, 1969). For example, the loss of riparian vegetation results in elevated stream and lake temperatures from these activities.
Environmental Stressors
Accidental Releases
Accidental spills or toxic releases may be considered a minor component of lake ecosystem degradation, although such incidents have been documented.
Spills or releases result from the direct introduction of a stressor into the water body and, more often than not, are related to midnight-dumper type activities. A recently publicized example of a toxic release into an Arizona lake involved the disposal of batteries over the past two decades into Lake Powell at the Walweap Marina, a practice which caused the accumulation of lead in lake sediments. The impacted area was cleaned up in early 1992.
Direct spills or releases to lake ecosystems are generally limited since large industry, as along the Great Lakes area, is not present on Arizona's lakes. Additionally, Arizona lakes and waterways are not generally used for the transportation of industrial chemicals and waste.
The potential for accidental releases to impact Arizona lakes and surface waters that feed the lakes from storm runoff is evident from data collected in the aftermath of flooding that occurred in January and February 1993.
o During this period, four severe storms occurred within days of each other, causing heavy precipitation and runoff. As a consequence, every major river in Arizona flooded. The excessive precipitation and runoff resulted in widespread contaminant releases to Arizona streams and lakes, releases that ranged from discharge of raw sewage from a number of large municipal wastewater treatment plants, to extensive tailings spills at closed and active mine sites (ADEQ, 1994).
Accidental releases would have a direct and immediate impact to the lake ecosystem and, on a short term and local scale, a chemical or toxic waste release could overcome the ecosystem resistance and cause significant impacts. However, an accidental release is considered to have much less effect when considered over a larger area or longer time frame.
The resilience of a lake ecosystem is considered medium and restorability high.
Indoor Air Pollution
Not applicable.
Outdoor Air Pollution
Pollutants of concern include sulfur dioxide, nitrogen oxides, metals such as lead, selenium, and chromium, mercury, pesticides, and synthetic organic compounds. Industrial point sources and non-point sources along with natural emissions account for these pollutants.
o In Arizona, major point sources of atmospheric emissions include three copper smelters, five coal-fired power generating stations, and various industrial sites primarily located in and around the major urban areas.
o Non-point sources include motor vehicles, agriculture activity, forest fires, and a variety of other small emission sources.
Air pollutants such as nitrogen and sulfur oxides can react in the atmosphere to form acidic compounds. Acid deposition occurs when acidic compounds fall to earth as acidic rain or particulates, and is a serious concern in many parts of the United States. In the eastern United States, many lakes and streams have become acidified to pH levels of 5.0 and lower. Further, for some highly acidified lakes in sensitive regions, fish reproduction does not occur.
The rate and extent of acid deposition and ecological impacts are, however, not well defined because many lakes in North America have complex watersheds where precipitation flows through forest canopies and soils and is chemically modified before entering the lake.
There are no indications of acidification in Arizona lakes.
Indeed, the impacts of acid deposition in Arizona are quite different from other regions of the country. In the majority of the state, the preponderance of calcareous soils and subsequent alkalinity imparted on natural waters provides a buffering capacity to mitigate acidification in the aquatic environment (Kepner, 1988).
The absence of acidification is noted even in high elevation lakes of the White Mountains. This area, located adjacent to the copper smelting activity of southern Arizona and New Mexico, is potentially sensitive to acidification because of its thin, non-calcareous soils, coniferous vegetation and deep snows (Roth et al., 1985). Despite receiving rainfall with a mean annual pH between 4.7 and 5.0, however, most lake waters in the White Mountains have near neutral to alkaline pH levels.
Air pollution may also contribute hazardous and toxic residuals that are transported and deposited as particulates on land surface over a large area. Very little data exist that indicate the accumulation of airborne toxic chemicals or substances in Arizona lakes. Studies, in fact, have failed to show any significant deposition that can be directly associated with atmospheric inputs.
o For example, a recent study of Pacheta Lake in the White Mountains, a high elevation alkaline lake, indicates there are no anomalous metal concentrations in lake sediments deposited over the past 50 to 100 years and consequently no impact attributable to copper smelter activity in the surrounding area (Williamson and Parnell, 1994).
o In another case, a study conducted by the US Geological Survey (1988) indicated that high concentrations of selenium in water, sediment, and biota in the Lower Colorado River region appeared to originate from upstream sources. Further investigation revealed that elevated selenium levels were found, among other areas, in Lake Powell (US Fish and Wildlife Service, undated).
o The US Fish and Wildlife Service is currently conducting an investigation to determine what sources are contributing to trace element concentrations in biota and sediment samples in Lake Powell. However, data from aquatic biomonitoring conducted since the in-filling of Lake Powell have not shown any temporal or spatial association with any particular source in immediate proximity to the lake (Arizona Department of Environmental Quality, 1988).
Due to local, regional, and sometimes global aspects of outdoor air pollution, all lake ecosystems are susceptible to impact. Available data suggest the magnitude of impact is low in Arizona lakes, although there is increasing uncertainty about the impact in the long term.
The resistance of lake ecosystems to the effects of atmospheric pollutants is high.
In general, Arizona lakes are expected to have high resilience to impacts from acidification and acid deposition.
The ecosystem is less resilient to deposition of airborne toxic chemicals such as metals and pesticides due to subsequent pollutant uptake and bioaccumulation. In the absence of atmospheric pollutant inputs, the lake ecosystem is considered highly restorable.
Degradation of Built/Cultural Environment
Not applicable.
Physical Alteration of Lake Ecosystems
The following discussion is a breakdown of the different stressors (physical and biological) that potentially alter the lake ecosystem. For each stressor, the discussion will focus on the direct and indirect effects, and the extent to which the particular stressor is a problem in Arizona's lakes.
Grazing
Domestic livestock activities have a wide range of impacts on water quality (USEPA, 1991).
o Animal wastes increase nutrient inputs to water bodies and may increase bacterial contamination.
o Sediment loads are increased as a result of the loss of vegetative cover and the trampling of streambanks.
These effects are manifested in the lake through increased eutrophication and sedimentation. The effects of grazing on lake ecosystems are primarily indirect whereas primary inputs to the system are from streams discharging to the water body.
Grazing is a common activity along the shorelines of lakes. However, the relative importance of runoff from the lake shore is small compared to the potential for runoff from grazed lands into the many streams that drain a watershed and discharge to the lake. Consequently, the effects of grazing are considered an indirect stressor of lake ecosystems.
The effects of grazing on lake ecosystems are long-term, and resistance varies with watershed size. Clearly, small lakes such as ponds, can tolerate less watershed change than much larger lakes, like Roosevelt Lake, before ecosystem changes occur. Consequently, resistance to change will be less for small bodies than for large bodies. Once the water body is altered, e.g., eutrophication is begun or accelerated, the trophic equilibrium of the lake can be significantly changed and difficult to reverse. As a result, resilience of lake ecosystems to the effects of grazing is low and the restorability of lake systems is difficult at best.
Most of the effects of agricultural activities on lake ecosystems are indirect because these activities occur throughout the watershed and the pollutants are transported to the lakes.
The modification of landscapes for the purpose of agriculture impacts aquatic systems in a number of ways:
o Application of fertilizers and pesticides in support of cultivation activities leads to runoff that is high in nutrients and potentially toxic chemicals.
o Activities associated with soil preparation for planting may lead to increased erosion and deposition of fine sediments to waterways.
o Banks and channels of water bodies are modified to prevent inundation of cultivated lands during flood events.
o Use of canals and ditches to carry runoff from cultivated lands including return flows from irrigation activities results in the discharge of poor quality water to natural water bodies (Lee et al., 1978; Mason, 1991; Omernick, 1977; Porter, 1975; Tomlinson, 1971). Because fertilizers and pesticides are frequently used in cultivation activities, this water can contain high concentrations of potentially detrimental compounds (Hellawell 1986).
Because agricultural activities greatly modify the landscape, it is likely that the effects of agriculture on lake ecosystems will be significant. The degree of effect will depend on the amount of the watershed that is actively cultivated.
The effects will be long-term, as the results of the increased sediment loads and nutrients that come from cultivated lands will lead to accelerated eutrophication in the receiving lake body.
The resistance of lake ecosystems to the effects of agricultural activity will be low as will resilience and restorability, because it is difficult to stop or reverse the process of eutrophication.
Highways
The construction of highways across water bodies results in short-term increased sediment loads to the associated waters. In addition, runoff from highways can lead to increased erosion of sediments into water bodies, especially on highways with poor maintenance.
Vehicle traffic leaves a film of lubricants on the roads over time, and road salting and sanding activities during winter months leave pollutants on the roadway as well. During rain events these pollutants often run off into water bodies.
Clearly, the majority of impacts from roads to lake systems is indirect as few roads ever cross lakes. However, indirect impacts from roads criss-crossing the watershed can be found in lake ecosystems. This indirect impact may be increased in watersheds where frequent stream fords occur on back roads, or increased land-use activity such as timber management, results in significant road building.
The impacts of highway building and maintenance activities typically affect lakes on a short-term basis.
Run-off of pollutants from highways into water bodies is a short-term and localized event that can be quickly absorbed by the receiving ecosystem.
While resistance tends to be medium to high, the resilience and restorability of the systems tends to be high once the runoff or road building activity ceases.
Energy Production
Water bodies may be used in a number of ways for energy production. See Petts (1984) for a review.
o For example, hydroelectric energy production is a common function of many impoundments and water is used as a coolant in the operation of coal- fired or nuclear plants.
The effects of hydroelectric plants are quite different from other types of energy production. For lake ecosystems, the use of water for power generation results in constantly fluctuating lake levels that have detrimental effects on biological communities.
In addition, fluctuating water levels can have a detrimental effect on the integrity of shorelines, resulting in increased erosion (Bodaly et.al., 1984, USBOR, 1994).
Water used as a coolant for power generation by plants other than hydroelectric is often discharged back into the water body from which it was drawn. While this water may be treated for the removal of toxic chemicals to prevent their discharge to the receiving water body, the more significant problem is the release of water with elevated temperatures. Such thermal pollution may have detrimental effects on the resident biological communities (Mason, 1991).
Hydroelectric energy production affects lakes over a long period. Resistance and resilience are moderate, as the normal operation of such a facility will cause continual impacts. Restoration cannot occur without stopping the use of the water body for its designed function, an unlikely occurrence during the lifetime of the water body.
The use of lake water for other methods of energy production has a short term-effect on lake ecosystems as the effects will likely be fairly localized.
Resistance, resilience and restoration are all moderate.
Fire Suppression
Fire suppression leads to increased fuel loads in watersheds, an alteration that can result in the more frequent occurrence of catastrophic fires.
Fires that scorch the landscape rather than just clear the landscape lead to compacted soils and increased runoff. The net result is accelerated erosion and sedimentation of waterways. In addition, the heavier runoff can lead to increased export of nutrients that would normally have been held by the landscape into the waterways. Again, because this is primarily a watershed process, the effects of fire suppression on lake ecosystems are primarily indirect.
The effects of this activity are long-term in nature as when catastrophic fires occur, they can significantly alter the inputs of sediment and nutrients to water bodies.
Resistance and resilience are moderate, as once the policy of fire suppression is removed, natural fire cycles will resume. Human intervention in the form of prescribed burns can lead to a certain degree of restored natural fuel load.
The following types of mining problems affect lake ecosystems (Letterman and Mitsch, 1978; Lundgren et.al., 1976; Mason, 1991; USEPA, 1991):
o Active ore mining (placer or hardrock)
o Abandoned ore mines
o Sand and gravel mining
The extraction of ore from soil and rock has primarily an indirect effect on lake ecosystems, as almost all mining occurs in the watersheds of lakes rather than along the shoreline.
Abandoned mines are considered a greater threat to watersheds than are active mines (Mason, 1991). The physical activity of the mining itself leads to increased erosion of watersheds and sedimentation in waterways.
An additional serious impact of ore mining activity is the release of toxic metals into waterways. This results from the leaching of the minerals from newly exposed rock, or from mine tailings, the spilling of chemicals used in the extraction process itself, and the occasional spilling of toxic laden sediments from mine waste ponds during flood events.
Sand and gravel mining, a common occurrence within the 100-year flood plains of river and streams, results in increased sedimentation and turbidity of aquatic environments. Although this activity almost exclusively occurs in streams and rivers rather than along lake shores, the indirect impacts on lakes can be significant.
Mining activities tend to have short-term effects on lake ecosystems, as the toxic chemicals that are released tend to be localized. Also, the buffering capacity of lakes can mitigate the effects of mining impacts when they reach the lake, although the ability of lakes to resist such impacts can vary widely as a result of local conditions and the length and severity of the chemical impacts.
Because of this variability, resistance and resilience can range from low to high. With regard to toxic chemicals, the restorability of lakes is fairly high, as toxic sediments can be removed from the system, although this approach would be very costly. However, the effects from sedimentation are more difficult to mitigate.
Timber
Timber management activities affect lake ecosystems in an almost entirely indirect manner, as cutting rarely, if ever, occurs along lake shores.
However, there are a number of indirect ways that timber management activities influence watersheds and the water bodies associated with them:
o Harvesting of timber results in reduced soil stability, a disturbance that leads to increased erosion and often increased runoff, especially in compacted soils.
The degree to which this problem affects the integrity of the watershed and consequently the stream ecosystem and subsequently the lake ecosystem depends upon the extent of harvesting activity (the percent of watershed area disturbed), and the method in which the harvesting is done, for example, clearcutting versus thinning. The former has the greater impact on watersheds, while the latter typically causes less damage.
o Road-building associated with timber management activities leads to increased erosion in the watershed.
o In areas that have had timber removed, runoff typically increases. While this might seem beneficial to aquatic ecosystems, it can lead to increased down- cutting and erosion in the stream channels (Fredriksen and Harr, 1979; Gregory et al., 1987; USEPA, 1991).
The effects of timber management activities tend to be long-term. Landscapes, once modified, are difficult to return to their pre-disturbance condition, and because lake ecosystems are so dependent on their watersheds, any activity that affects downstream ecosystems is likely to have a relatively long-term effect.
Initially, lakes are likely have moderate resistance to such a disturbance, although the degree of resistance will depend greatly on the size and type of lake body, for example, natural or reservoir, and the nearness of the activity to the lake.
Because the changes caused by timber management activities can lead to eutrophication, resilience and restorability will both be moderate, as once this process begins, it is difficult to stop or reverse.
Interbasin Water Transfer
This stressor may affect lake ecosystems in several of the following direct and indirect ways:
o Reducing water levels in lakes to the degree that the natural functioning of the ecosystem is severely disrupted;
o Reducing the baseflow of water in streams and rivers that normally function to replenish lakes;
o Causing physical and chemical changes in receiving lakes by discharging water of significantly different quality to the water body; and
o Altering the biological communities of the receiving body as interbasin water transfers can allow the free movement of biological organisms across basins (Hellawell, 1986).
The effects of interbasin water transfers typically are long-term, although this impact will depend greatly on the size of the water bodies involved. The degree of resistance of lake bodies depends on the nature of the water exchange.
o If water is being transferred from the lake, the resistance is moderate, as the transfer will result in the drawdown of the lake and have significant effects on the littoral zone.
o If a lake is the recipient of interbasin water transfer, the resistance of the lake will depend on the quality and quantity of the water received. Clearly, if the quality of the water is significantly different and large amounts of this water are pumped into a receiving lake, then there will be rapid and significant changes to the receiving lake.
Resilience will be high in the receiving lake and/or the providing lake, as once the water transfer stops, the waterbodies will likely revert to their natural states.
Restorability is high, as ending such water transfers will return the basins to their previous condition.
Channelization
The modification of stream channels to minimize the effects of floods, enhance development and provide for more efficient navigation significantly changes aquatic ecosystems (Hellawell, 1986). While channelization activities are most commonly performed on streams and rivers, some channelization of lakes (by dredging) occurs where large shipping passes through reservoirs with lock and dam systems.
Lakes are less often channelized than streams and rivers and, as a consequence, the effects are primarily indirect. If they occur on lake ecosystems, the short and long- term impacts of channelization are high, as the removal of significant quantities of bottom sediments will significantly disrupt the natural processes of the lake ecosystem. This activity will seriously affect water quality, as well as severely impact the biological communities.
Resistance, resilience and restorability of a channelized lake are all low.
If a lake receives inputs from channelized streams or rivers, the effects can be significant.
o Channelized streams can carry significant sediment loads and when carried to lakes during flood events, results in sedimentation of the lake body.
o Stream channelization so completely alters ecosystems that the effects on the receiving lakes are long-term. Resistance is low, as the degree of resilience will depend on how long the process of sedimentation has taken.
Restoration is possible through the use of sediment traps on channelized streams to minimize sediment inputs to the receiving lake. In addition, the sediment could be dredged from the lake body, but, as stated above, this activity in itself could have significant impacts on the lake's ecosystem.
Water Diversions
The primary effect of water diversions is the de-watering of aquatic systems (Hellawell, 1986). This stressor is generally indirect, as the activity primarily occurs in rivers and streams. When it occurs in these systems, it results in reduced water flow to a receiving lake.
Water diversions have a long-term impact on lakes as the lake ecosystem will have to adjust to changing water levels.
Resistance, resilience and restorability are all high.
Pumping
The pumping of groundwater has an indirect effect on lake ecosystems by reducing the water in streams that is available for recharging lake bodies. This activity has the same effect as that of a water diversion as described in the previous subsection. Refer also to Hellawell (1986).
Impoundments
Most lakes in Arizona are artificial impoundments and a disturbance to the pre- existing aquatic and terrestrial ecosystems. However, removing this stressor would result in the loss of many important lake ecosystems in Arizona.
The cost/benefits of impounding rivers are not always clear until after construction has occurred (Turner, 1971).
o For example, the Aswan High Dam on the Nile River has produced 7,000 million kwh electricity annually, has brought 900,000 acres of land under cultivation and has increased national income by $500 million dollars. However, the cost of this project has also been significant.
The rate of occurrence of diseases in newly watered lands has increased markedly.
Changes in water quality and quantity downstream have been linked to a 95 percent loss in the sardine catch in the eastern Mediterranean Sea.
Because the dam traps 100 million tons per year of silt, the loss of this silt to the Nile delta has resulted in:
Significant beach and therefore recreational opportunity losses; and
Greatly reduced silt replenishment for downstream farm lands.
The type of impoundment can have a significant influence on the effects of other stressors on the impounded lake ecosystems. Specifically, the issue of concern here is the type of impoundment that created the reservoir.
For example, how water passes through the dam, that is, surface or bottom, can have important effects on the lake's ecosystem by varying the rates of water retention and nutrient cycling, which are important factors in the process of eutrophication and the fate and transport of toxic chemicals attached to sediments.
Because so many of Arizona's lakes are created by impoundments, the issues of magnitude of impact and resistance, resilience and restoration are not truly applicable to this discussion.
Recreation
Recreational activities throughout a lake's watershed can have indirect impacts on a lake's ecosystem, although these impacts are generally minor compared to the direct impacts.
Direct impacts include:
o Operation and refueling of power boats that a leave film of oil or grease on the water surface;
o Discharge of boat wastes into waters;
o Off-road vehicles damaging shorelines, increasing erosion rates and turbidity of lake water;
o Trash from boaters and campers; and
o Leaching of nutrients from leaks and overflows from septic systems for restroom facilities.
The effects of recreation are either long- or short-term, depending on the nature of the activity. Many activities, like hiking, occasional camping, and fishing, have minimal, if any, impacts on lakes. Other activities, however, like recreational vehicle camping on lake shorelines, can have significant impacts such as the acceleration of shoreline erosion, and the increased inputs of nutrients.
As with other activities, the degrees of resistance, resilience and restorability depend greatly on the length of time of disturbance from these activities. However, all of the ecosystem responses tend to be high.
Urbanization
The urbanization of the landscape increases runoff into waterways, especially during storm events (Wanielista, 1978).
It is not uncommon for storm water runoff to be high in toxic chemicals as the water washes the grease, oils, and chemicals off highways and parking lots into watercourses.
In addition, urbanization increases the rate of runoff that results in flashier flows which increase erosion rates in stream channels. The indirect effects on lakes are increased sedimentation and discharges of toxic chemicals.
Urbanization has a long-term impact on lake ecosystems. Resistance and resilience are at a moderate level, but restorability is relatively high if the sources of the discharges can be controlled.
Biological Alteration of Lake Ecosystems
The biological alteration of lake ecosystems arises almost entirely from recreation and urbanization related activities that promote the development of sports fisheries and lake shore communities (Cooke et al., 1993; Moyle and Cech, 1982).
The management of lakes as sports fisheries dictates the need to stock these waterbodies with exotic species (those that do not naturally occur in a certain environment).
The development of lake shore communities leads to increased manipulation of lake ecosystems for the sake of aesthetics. Such ecosystems are manipulated to reduce natural aquatic vegetation and control pests such as mosquitoes.
Hunting
Not applicable to lake ecosystems.
Fishing
As long as fishing regulations are adhered to, problems with over-fishing will not be a problem in lake ecosystems. However, the illegal fishing of endangered species can cause significant losses to this fauna.
With regard to fishing for sport fish, the effects of over-fishing are very short-term as these fish are often stocked.
Resistance, resilience and restorability are all high.
o However, with regard to endangered species, the impacts of fishing are long-term because once a local population of an endangered species is lost, re-establishment is difficult at best. Resistance, resilience and restorability are all low for this activity.
Illegal Collecting
Not applicable to lake ecosystems.
Species Introductions
Species introductions are either purposeful or accidental (Moyle and Cech, 1982). Those which are purposeful include:
o Introductions in support of sport fishing;
o Attempts to use biological organisms to control disease vector problems like mosquitoes; and
o Addition of exotic species for the control of pests or unwanted species, either plant or animal.
Ironically, the latter introductions become necessary as a result of previous accidental or purposeful species introductions.
Accidental species introductions often result from transfers of materials from one body of water to another. For example, boats transported long distances from one water body to another can accidentally introduce the seeds for the propagation of exotic species, such as aquatic plants, at locations far from their natural habitat.
o Introductions of exotic fish species can have severe impacts on the native fish fauna through predation, competition and hybridization (Minckley, 1973). The introduction of exotic piscivores (fish feeding on fish) disrupts the natural food web by changing the natural balance among fish species.
Under natural undisturbed conditions, the native fauna typically will out- compete any introduced fauna, as the native fauna is better adapted to the natural conditions of the environment. However, once the ecosystem is disturbed, as, for example, the natural habitat of the native fauna is degraded, exotic species may be better adapted to survive in the modified environment.
Hybridization can occur when a closely-related species is introduced and it is capable of breeding with the native species. The results are offspring that are hybrid or intermediate between the two species. The net result may be the loss of the native fauna and the establishment of the hybrid form which is less adapted to the natural conditions.
o The introduction of exotic plant species can have a severe impact on native plants. For example, the introduction of three exotic plant species pose particular problems in Arizona's lake ecosystems (Cooke et.al., 1993; Welch, 1992):
Eurasion water milfoil (Myriophyllum spicatum)
Curly leaf pondweed (Potamogeton crispus)
Hydrilla (Hydrilla verticillata)
Excessive growth of exotic species can result in reduced dissolved oxygen levels when the plants die-off, and cause problems with recreation, either boating or swimming.
Methods for plant removal must consider whether the cure is better than the problem (Burgis and Morris, 1987). For example, using weed killer to kill plants causes them to sink to the bottom of the lake and decompose, which results in reduced dissolved oxygen at lower depths.
Biological control methods such as insect or fish introductions and physical methods of weed harvesting or dredging can be used to solve the problem. The effects of species introductions are long-term as, once these species become established, they can quickly alter the natural biological processes of the ecosystem.
Resistance, resilience and restorability of a lake with introduced species are low to moderate. Often the only way to restore a system with introduced species is to poison the system to remove all fish or plant species and then attempt to reestablish a natural fauna. This process is difficult, can have significant unwanted side effects and can be expensive.
Food and Drinking Water Contamination
Food and drinking water contamination are considered a public health issue and are, thus, not applicable to this ecosystem assessment. Risks posed by agricultural stressors are discussed on page 34, in the section on physical alteration of ecosystems, and beginning on page 24, with the discussion of non-point sources of impacts of surface water contamination.
No commercial fishery exists within Arizona's lake ecosystems, although considerable recreational fisheries exist. In the past, warnings against consumption of fish have been posted at several lakes, including Painted Rock Reservoir, due to the accumulation of chlorinated pesticides in fish tissue.
Much of Arizona's drinking water is obtained from reservoirs throughout the State, including the four Salt River lakes (Roosevelt, Apache, Canyon, and Saguaro), the two Verde River lakes (Horseshoe and Bartlett), and Lake Pleasant on the Aqua Fria River. These reservoirs, in fact, provide about 50% of the Phoenix metropolitan area drinking water. Point and non-point source contamination that may migrate into the reservoirs are of concern because of possible dissolution into the drinking water supply. The greatest chemical constituents of concern are pesticides from agriculture and metals from mining.
Additional areas of concern are related to the water treatment process. Constituents of concern related to water treatment are aluminum from the handling of municipal sludge in the water treatment process, and the trihalomethane compounds, including chloroform, generated during disinfection of drinking water supplies prior to distribution into the water delivery system.
o Aluminum is listed as a constituent toxic to fish, although its origin into the lake ecosystem does not typically occur as a result of the handling of municipal sludges. Aluminum will typically only mobilize under acidic conditions.
o Trihalomethane compounds are seemingly ubiquitous, often found in groundwater supplies as a result of leakage in water distribution systems. The occurrence of these compounds in surface water is expected to be limited due to their volatile nature.
Arizona regulatory agencies have recently focused on the quality of drinking water in rural areas outside large municipal distribution networks. The lack of water treatment and the distribution of naturally-occurring poor quality water has been addressed by Arizona Department of Environmental Quality (ADEQ), and has been identified as a high priority item.
Land and Soil Contamination
Land and soil contamination may contribute to degradation of lake ecosystems.
The primary mechanism for such contamination to enter lakes is via placement of contaminants on the ground surface and subsequent runoff into streams and/or lakes. The impact from land and soil contamination discharges are discussed under the section on non-point sources of surface water contamination on page 47. Additional discussion of the impact from land and soil contamination contributed from point sources is presented in the sections on accidental releases and surface water contamination on page 49.
Land and soil contamination from industrial and domestic sites may also pose an impact to lake ecosystems in areas where seepage from waste disposal sites discharges directly as leachate or indirectly through shallow groundwater into the lake water.
The impact to lake ecosystems from subsurface contaminant discharges is considered minor because, in most cases, few concentrated waste sites lie close to Arizona lakes, and because elevated water levels in reservoirs generally cause groundwater flow away from the lake.
Natural Hazards
Floods
Flooding typically creates inflow and infiltration problems that are manifested in exceedances of water quality standards from municipal water treatment facilities. The January and February 1993, floods created such problems and resulted in water quality violations throughout Arizona (ADEQ, 1994).
Mining is another activity that may result in significant environmental perturbation due to flooding. Tailings' runoff and dam breaches on mining properties were identified in the Pinto Creek, Pinal Creek, Gila River, and Mineral Creek watersheds (ADEQ, 1994). Potential impacts on watershed lakes due to releases from mined areas were discussed under Mining on page 37.
Radiation
Natural occurrences of radon related to area geologic conditions have been widely documented in groundwater supplies throughout Arizona. The most commonly occurring radionuclides are the daughter products of the uranium 238 decay series, including radon.
A mobile gas, radon typically is not found in surface waters due to volatilization. Specific incidents of radioisotope contamination resulting from industrial activity also have occurred.
Residual levels of radioisotopes have been identified in abandoned uranium mine pits that serve as catchment basins for surface water near Cameron on the Hopi Reservation (ADEQ, 1994).
Surface Water Contamination
Activities that produce surface water contamination are generally classified as either point source discharges or non-point source discharges.
Activities that discharge directly into surface waters from point sources include outfalls from industrial facilities such as materials processing, manufacturing, and power generating plants, as well as from municipal point sources such as water and wastewater treatment plants.
Discharges of pollutants into surface waters from non-point sources include runoff from mining, range agriculture, crop agriculture, construction activities, silviculture, and urban activities.
Effluents from the various point sources and runoff from non-point sources can contribute hazardous constituents to surface waters that may cause ecosystem and human health impairment.
According to estimates by the USEPA, non-point sources constitute over half of the nation's water quality problems.
Data compiled by ADEQ (1994) indicates that non-point sources are the likely contributor for the majority of use impairment in those lakes that do not meet their full, designated use. In fact, of the 45,612 lake acres assessed, non-point sources were probable contributors of use impairment on 42,262 acres, or 93% of the lake area acreage assessed.
The largest single category of the various types of non-point sources impacting lake protected uses is agriculture with its associated irrigation, rangeland, animal holding and management practices.
Agricultural practices can contribute pollutants such as fertilizers and pesticides to lake ecosystems by means of runoff that modifies the physical, chemical and biological character of the lake ecosystem. Other significant non-point sources include hydromodification, urban runoff, and recreational land uses.
Pesticides from agricultural use are not widely observed in Arizona lakes and ecosystems. The ADEQ (1994) has indicated that pesticides are the likely cause of impaired use of only 370 lake acres. Pesticides, however, are a prominent environmental concern due to inferred public health effects related to some well- studied compounds.
o For example, studies conducted at Painted Rock Reservoir on the Gila River have identified pesticides including DDT, DDT metabolites, and toxaphene in fish, turtles, and sediments (Earth Technology Corporation, 1993). Consequently, a public health warning has been issued for the consumption of fish.
Although DDT was banned in 1969, and toxaphene banned in 1982, residuals of the persistent compound DDT still occur in varying concentrations throughout the Arizona environment. Pesticides in current use are typically no less toxic, although they generally degrade rapidly in water matrices.
The application of nitrogen fertilizer, as well as the occurrence of nitrogenous wastes produced in concentrated animal feeding operations, or due to human sewage, have resulted in significant nitrate contamination of groundwater throughout various areas of Arizona. Where such groundwater is hydraulically connected to surface water, or where nitrogen is introduced directly into surface water, nutrient enrichment of a lake may occur and eutrophication results.
The characteristics of eutrophication include wide changes in pH and dissolved oxygen with subsequent fish kill potential. In Arizona, eutrophication has been observed in various small lakes that have source conditions similar to those described above. The phenomenon has been noted in small lakes in the Santa Cruz River Basin and in Rainbow Lake, near Show Low (ADEQ, 1994).
Irrigation practices have been observed to cause significant harmful effects to humans, fish, and wildlife.
o For example, return flows from irrigated agriculture in the San Joaquin Valley of California contain high concentrations of dissolved selenium that have adversely affected fish and waterfowl (US Geological Survey, 1989).
Because of the concern for water quality impacts of irrigation drainage, the US Geological Survey conducted a study to identify any water resource and ecosystem impacts in the Lower Colorado River Valley of Arizona, California, and Nevada (1988). The results of this investigation indicate that irrigation return flows were relatively free of organochlorine pesticides, metals and toxic inorganics that might present environmental problems for fish or wildlife.
Urban storm runoff is also viewed as a major source of potential surface water contamination. In Arizona, conditions such as climate and topography may potentially exacerbate urban storm runoff impacts. However, studies conducted over the past five years in Phoenix indicate that urban runoff does not appear to be a major source of toxic organic compounds or contaminant loading to the receiving waters (Salt River Project, 1989; Lhose et al., 1994).
Many ongoing programs administered by the USEPA and the states, particularly those required by the Clean Water Act, regulate point source discharges.
According to law and regulation, all point source emitters of pollutants into "waters of the United States" are required to obtain a National Pollutant Discharge Elimination System (NPDES) permit. ADEQ data indicates that industrial and municipal facility NPDES permits impact approximately 800 acres of protected lake uses in Arizona (ADEQ, 1994).
Major categories of point sources include municipal water and wastewater treatment facilities, natural resources and materials processing plants, and industrial manufacturing operations.
The impacts of sewage treatment generally occur on two levels. One is from septic tank discharges, and the other is from the discharge of primary or secondary effluent from sewage treatment facilities.
Septic releases may affect both groundwater and surface water supplies that are closely located to the septic tanks, or that are hydraulically connected.
o A significant problem resulting from septic tank releases has been identified in the Bullhead City area. This problem directly affected groundwater in the area and potentially affected the adjacent Colorado River. Measures are being taken to bring Bullhead City into compliance.
o Lake Havasu City has been similarly affected recently.
Intense efforts and large sums of money have been historically dedicated to the cleanup of wastewater discharges from municipal wastewater treatment plants or publicly-owned treatment works (POTWs). In most cases, efforts to restore surface waters from POTW discharges represent the success story of US antipollution efforts. Water quality in the nation's lakes and streams has rebounded quickly, even in the most notorious cases, such as Lake Erie.
If not properly treated, municipal wastewater discharges contribute inorganic nutrients, primarily nitrogen and phosphorous, dissolved organic matter, ammonia, metals, and microbial contaminants to the receiving water. These receiving waters are typically streams rather than lakes. When sewage or effluent is introduced to lakes, lake ecosystems may be affected by eutrophication because of the introduction of nutrients, although these are largely incorporated into the biomass of the receiving stream.
Due to their widespread occurrence in Arizona, mining activities represent a large potential point source impact to streams and lakes.
o Of particular concern to ADEQ, and the source of substantial regulatory attention, is the potential impact of mining facilities in the Miami-Globe area on Roosevelt Lake. According to the Mineral Extraction Task Force (1983), overland runoff from old, inactive mining facilities can cause local surface water pollution problems, but has little regional effect.
o It is generally recognized that groundwater contamination from acid mine drainage in the Miami Wash area has migrated into the Pinal Creek drainage. The contaminated groundwater is marked by low pH levels (ranging from pH 2.0 to 5.0) and high concentrations of iron, manganese, sulfate, total dissolved solids, and heavy metals.
Interim groundwater remedial actions conducted under ADEQ oversight are designed to limit the migration of acidic groundwater into surface water that flows toward the Salt River and Roosevelt Lake (ADEQ, 1994).
Monitoring conducted throughout the Pinal Creek drainage basin indicates that, thus far, acidic groundwater has had no impact on the perennial flow reach of Pinal Creek.
Although minor breakthroughs of elevated manganese and sulfate levels have been observed in Pinal Creek surface waters, no significant contamination has been observed in the Salt River. US Geological Survey calculations indicate that significant water quality and ecosystem impacts would not occur even under the worst-case scenario of breakthrough of the most highly acidic groundwater at a time of low surface water flow in Pinal Creek and the Salt River (USGS, 1993).
Geochemical modeling suggests that under this scenario the flux of acidic groundwater into the Salt River would be buffered via mixing with alkaline waters in the Salt River and no sustained impact to Roosevelt Lake would occur. Locally high concentrations of dissolved solutes, such as copper at the Pinal Creek confluence, may lead to possible fish kills.
Solvent contamination of urban lakes has been documented, including McKelleps Lake. Such contamination may stem from the introduction of contaminated groundwater, in this case from the Indian Bend Wash Superfund site, into the urban lakes (ADEQ, 1994).
The available data indicate that non-point source discharges are much more pervasive and represent a longer-term threat than point source discharges.
Ecosystem resistance to impacts from non-point source discharges is thought to be low to moderate, depending on the severity of stressor. It is generally believed that non-point source discharges have a moderate effect on the lake ecosystem resilience and restorability.
Point source discharges represent more cause for concern for short-term and localized impacts on the lake ecosystem. As such, the lake ecosystem would have a low resistance and moderate resilience to the stressor and moderate to high restorability.
Assessment of Arizona's Lake Ecosystems
This section of the ACERP Project Report has used data from the 1994 305(b) Clean Water Act water quality assessment report (ADEQ, 1994) to determine the degree of impairment of Arizona's lakes by physical and other stressors.
As part of this assessment, parameters that indicate impaired water quality were linked with the sources or causes of that impairment. In all, 32% (in terms of acres) of Arizona's perennial lakes were assessed for this report.
Eighty-five percent of the total acres assessed were found to be impaired for one or more water quality parameters. Appendix C lists the acres of lakes within river basins known to be impaired by various water quality problems (ADEQ, 1994).
It is unknown to what degree such processes as eutrophication and sedimentation occur in Arizona's lakes, because such data are not typically reported. However, it is possible to infer whether these processes are occurring on the basis of the types of water quality problems found in Arizona's lakes.
o Low levels of dissolved oxygen, and high levels of dissolved solids/salinity, and metals were identified as the primary parameters indicating poor water quality in the state's lakes.
The regions that experience the majority of these problems are the Colorado River mainstem and the Middle Gila and Salt River basins.
Appendix D summarizes what is believed to be the source of water quality problems in each basin (ADEQ, 1994).
Many of the water quality problems are associated with natural conditions. This is particularly true for the high levels of dissolved solids and salinity and metals, especially arsenic, mercury and selenium. Natural geology in some Arizona basins causes some of these problems.
In addition to natural sources, the two land use activities of agriculture and hydromodification have been identified as primary causes of these water quality problems.
o Agricultural activities result in increased nutrients that can cause low levels of dissolved oxygen. In addition, the return flows from irrigation canals are often high in dissolved solids and once discharged to waterbodies can result in elevated dissolved solids and salinity levels.
Data from the Bureau of Reclamation from the Colorado River mainstem demonstrates this problem (ADEQ, 1994).
o Hydromodification has resulted in the inundation of soils that are high in toxic compounds like selenium. The subsequent erosions of these soils have impacted Arizona's waterbodies, especially along the Colorado River mainstem.
In addition, development of the many reservoirs on the State's rivers has had a severe negative effect on the native aquatic fauna (Minckley, 1973; Minckley and Kubly, ACERP 1995, this report).
The problems associated with the biological alteration of lake ecosystems are widespread in the state. Because Arizona's lakes are frequent sites for sport fishing and boating, the stocking of these water bodies with exotic fish species is an ongoing activity. These introduced species have seriously affected the native fish fauna (Minckley, 1973; Minckley and Kubly, ACERP 1995, this report).
From these studies, researchers conclude from the existence of low levels of dissolved oxygen that eutrophication of the state's lakes could be an ongoing problem.
Turbidity problems in Arizona's lakes are minimal, but are significant in streams and rivers (ADEQ, 1994), meaning that the potential for sedimentation of the state's lakes and reservoirs is high.
The input and deposition of toxic compounds like selenium, arsenic and mercury, is occurring or has occurred in some lakes.
o Selenium is primarily a problem in the Colorado River lakes, arsenic in the Salt and Verde basin lakes and mercury in the Middle Gila and Bill Williams basin lakes.
Problems with mercury are generally associated with historical mining practices in these watersheds.
Based on available data, thermal pollution appears to pose little danger to Arizona lakes.
Conclusions
Burgis and Morris (1987) provide a succinct summary about what society's attitude should be towards the protection of this ecosystem:
--------------------------------------------------------------- | The placid appearance of a lake surface and perhaps our | | unconscious assumption that water is an unreactive | | substance may mislead people into imagining that the lake | | itself is inert. But in practice a lake behaves almost | | like a living creature, constantly sensitive to what goes | | on around it. | | | | The lake responds directly to what is done to it and its | | inseparable partner, the catchment area. Everyone | | understands this principle of 'response to stimulus' | | perfectly well in the treatment of say, a pet dog; it | | would help a lot if lakes were thought of in the same | | vein. | ---------------------------------------------------------------
Streams and Rivers Ecosystem Stressors
Introduction
Early investigations of streams by limnologists and hydrobiologists were directed largely at classification and description, with primary attention given to local phenomena such as water temperature, flow regime, water chemistry and substrate as factors affecting resident flora and fauna.
As knowledge grew and the works of hydrologists, soil scientists and researchers in related disciplines were integrated into the understanding of flowing waters, it became evident that, when considered as ecological units, streams could not be separated from their watersheds (Hynes 1975, Fisher 1986).
With the exception of a small percentage of material decomposed and oxidized in the terrestrial environment, most materials ultimately received and transported by streams are deposited from their catchments (Mullholand and Watts 1982). Therefore, any conceivable noxious or otherwise deleterious material, action, process or organism, whether input at the outer watershed limits or directly into a flowing channel, may have profound effects on stream ecosystems.
The high natural variability in climate and topography in the State of Arizona is reflected by comparable variation in ecology of its streams, and consequently the knowledge concerning stream ecosystems and their responses to the implicated stressors is limited. Thus, uncertainty in estimation of "parameters" is inherently high in natural systems.
When human impacts are superimposed, assignment of numerical values to the attributes of resistance, resilience and restorability of stream ecosystems must be viewed with caution. Variance is remarkably high in the relationships between impacts and ecosystem responses across the range of streams considered.
It may nonetheless be stated that most Arizona streams have suffered major degradation during the last century from the effects of a variety of human activities including those used in the Comparative Risk Project. These changes are chronicled in narrative form and by photographic comparisons in a variety of technical and popular publications (see, e.g., Corle 1951, Hastings 1959, Hastings and Turner 1965, Turner and Karpiscak 1980, Dobyns 1981, Rea 1983, Fradkin 1984, Williams et al. 1985, Humphry 1987, Ohmart et al. 1988, Bahre 1991, Carothers and Brown 1991, Minckley and Deacon 1991, Brown 1994, Minckley and Brown 1994).
Among aquatic organisms, Arizona fishes have been most studied and are thus most useful in interpretation of ecosystem-level impacts of stream alteration.
o A general decline toward extinction of native fishes has been documented by Dill (1944), Miller (1946, et seq.), Minckley (1965, et seq.), Minckley and Deacon (1968, 1991), Miller et al. (1989), Williams et al. (1985, 1989) and others.
o Twenty-four of 31 taxa comprising the original native fish fauna of Arizona are considered imperiled and disappearing.
6 have already been extirpated from the State (some have been reintroduced)
1 species is extinct
17 of the 31 (55%) are federally listed as threatened or endangered
12 (39%) are candidates for federal listing (USFWS 1994a).
o The Arizona Game and Fish Department (AGFD) in 1988 included 23 (74%) of the same 31 taxa as threatened, endangered or candidates for listing.
Environmental Baseline and Limits of Analysis
Based on digitized hydrographic maps, the State of Arizona contains about 150,000 stream miles, of which about 107,500 miles are present on other than tribal lands (ADEQ 1992).
o Within this network exists only about 5000 miles of perennially flowing ( permanent) water (Valencia et al. 1993), the remainder being ephemeral (flowing only after precipitation) or intermittent (with short permanent reaches in an otherwise dry channel), either naturally or as a result of human intervention.
Some stream reaches that remain permanent due to wastewater disposal are included. The estimate of 5000 miles of perennial watercourses is used in this study to approximate existing conditions as an environmental baseline for comparisons of effects of different human activities. (See Map B-4 (Perennial Streams of Arizona), Appendix B.)
It is important to emphasize that excluding intermittent and ephemeral streams from consideration also excludes myriad aquatic communities from coverage in this study.
o Many groups of aquatic organisms, especially those whose terrestrial adults have high dispersal capabilities, are adapted to invade and fulfill their life cycles in temporary waters. There they perform ecosystem functions, for example serving as food for riparian birds for a few months, weeks, or days per year, or for a year out of a number of years.
o Groundwaters percolating beneath the dry beds of ephemeral watercourses also may be inhabited by unique assemblages of organisms, a facultative to obligate hyporheic biota which has only recently been discovered (Boulton et al. 1992).
o Springs are also excluded, mostly because of their relatively small sizes, yet springs and associated habitats such as riparian or stream channel marshlands (cienegas) are notorious in Arizona for their unique, relict and endemic organisms (Hendrickson and Minckley 1985, Minckley et al. 1991, Hershler 1994).
Had these excluded habitats been included along with the formerly permanent reaches already de-watered by damming, diversions and groundwater pumping, or inundated by reservoirs, the miles of stream channels and our estimates of impacts on stream ecosystems would have increased dramatically. The present coverage should thus be viewed as a comprehensive assessment of risks to a selected proportion of flowing water ecosystems in Arizona, to be used as an index of the status and risks to all such kinds of habitats.
Physical and Chemical Alterations of Streams
Natural Sources of Impaired Stream Quality
Toxic materials in streams may originate from natural sources such as ore deposits, metals in soils, or contaminants in spring waters (ADEQ 1994).
o Spring inflows on Chase Creek near Clifton contain high levels of iron and sulfate (Lindgren 1975), and hot springs entering the San Francisco River in Clifton are saline (Rampe et al. 1981).
o Similar examples are the salty Pah Tempe Spring on the Virgin River in Utah, which influences salinity in Arizona reaches, and saline springs on the Black and Salt rivers in central Arizona.
At times of low discharge, either as a result of human depletions or during natural drought, such inflows can be damaging to aquatic organisms.
Accidental Spills and Toxic Releases
Accidental spills and toxic releases have occurred consistently downflow from processing facilities and mining operations since those activities were begun.
o Extractive mining, particularly for metals, is widespread. Early records include those for Chase Creek and the San Francisco and Gila rivers down- stream from Clifton-Morenci, where toxic outflows historically have decimated fishes and also may have negatively influenced irrigated crops and croplands (Chamberlain 1904, Minckley and Sommerfeld 1979).
o The San Pedro River has suffered repeated and severe pollution due to releases of toxic materials entering the United States from mines at Cananea, Mexico (Jackson et al. 1988).
o Pinto Creek, Gila County is a classic example of a stream subjected to periodic toxic releases and chronic inputs from mine tailings and tailings ponds (Lewis 1977, Lewis and Burraychak 1979, AGFD files).
o Potentially toxic materials associated with tailings at a long closed smelter along Aravaipa Creek near Klondyke were exposed by flooding in 1993, resulting in increased concentrations in the George Whittel Reserve (TNC) and Aravaipa Canyon Wilderness Area (USBLM) downstream (Sally Stefferud, USFWS, Phoenix, pers. comm.).
Toxic releases are relatively more common near areas of more intensive chemical production and use, although they occur also during transport and distribution.
o "Fish kills" attributable to toxic releases within and downstream of Phoenix have been repeatedly investigated by AGFD (unpublished files).
In summer 1974, a helicopter applicator turned off a pump without removing connecting hoses, siphoning a tank of pesticide into the Mainline Canal which distributed water throughout the Yuma Valley. The spill killed fishes from upstream of Yuma to the US - Mexico boundary, and likely below (Minckley 1979).
o In another example, an oil spill resulting from a highway accident involving a tank truck on the upper Yampa River, Colorado, was thought to have precluded reproductive success by downstream fish (Woolf 1989). Concern for the potential of a similar event at Cameron, Arizona, has been expressed for the endangered humpback chub downstream in the Little Colorado River (USBOR 1989).
Air Pollution
The Committee views impacts of air pollutants on Arizona's streams as a potentially chronic problem.
Sources include:
o Mining and metal extraction
o Localized industry
o Coal-fired generating stations
o Internal combustion engines, chiefly automobiles
Airborne particles, either directly deposited as precipitation or accumulated biologically through absorption in the watershed, eventually enter streams. Levels are presumably low, but accumulation during prolonged drought may result in high concentrations in runoff following precipitation.
Five ambient air quality monitoring stations, located state-wide, reported no violations of sulfur dioxide or nitrogen dioxide emissions during the period October 1986 to September 1991 (ADEQ 1992). Lack of violations, coupled with the prevalence of well-buffered waters and alkaline soils, suggest a lack of acid deposition problems in Arizona streams.
Emissions from copper smelters in Mexico, however, appear to contribute to acid precipitation (pH 4.7 to 5.0) near the San Bernadino National Wildlife Refuge (Kepner 1988).
Acid precipitation is a suspected contributor to extirpation of the Tarahumara frog from tributaries of the Santa Cruz River (Hale et al. 1976) according to biologists working to re-establish the species (J. Howland, AGFD, pers. comm.). Furthermore, high elevation streams with relatively dilute, poorly buffered waters have been little sampled for potential effects.
Ecosystem-level impacts of overgrazing are transmitted to streams largely through progressive physical and biological degradation of watershed conditions. For example:
o Trampling and vegetation removal lead to heavier runoff, increased erosion and sediment input, arroyo cutting and reduction in groundwater infiltration and storage.
o Nutrient and organic-matter loading from livestock wastes (Chaney et al. 1993).
Concentrated livestock, or any large ungulates, in the immediate environs of a stream results in direct modification of banks and bottoms, with subsequent degradation of water quality (Patten and Ohmart ACERP 1995). Such effects are exacerbated during drought (Hastings 1959, Hastings and Turner 1965, Bahre 1991).
Progressive detrimental effects of domestic livestock on watersheds, riparian zones and stream ecosystems, particularly those in southern Arizona, have been documented first-hand by numerous individuals (Croxen 1926, Dobyns 1981, Bahre 1991, Patten and Ohmart ACERP 1995). It is therefore ironic that there are so few published scientific studies (Szaro et al. 1985, Rinne and Medina 1989, Rinne 1990) quantifying the relationship.
Considerable evidence has been accumulated in other western states (Platts 1991), however, and the American Fisheries Society (AFS) recently published a position statement on the effects of livestock grazing on stream and riparian ecosystems (Armour et al. 1991).
Biological effects of grazing are mostly of watershed scale, resulting in nutrient and organic-matter loading from livestock wastes.
Excessive removal of vegetation through grazing can sufficiently alter the biological composition of watershed cover to result in qualitative and quantitative changes in nutrient inputs to streams. Streamside impacts of trampling and browsing woody vegetation reduce important shading and trophic inputs to the stream from the riparian zone. Grazing exacerbates erosion and loss of fine sediments (Patten and Ohmart ACERP 1995).
The largest direct impacts of agriculture on streams result from practices contributing to flow depletion and water-quality degradation.
o Flow depletion and de-watering are caused by dams, impoundments and diversions storing water for future deliveries or conveying flow away from natural channels, and by pumping from floodplains which lowers water tables.
o Water-quality deterioration results from increased erosion, loss of riparian vegetation and runoff or aerial transport of fertilizers and pesticides.
Direct impacts on floodplains involve:
o Changes in subsurface water relations due to development of subsurface drainage systems where necessary to prevent waterlogging and salinization of croplands;
o Removal of shade and trophic contributions to streams by natural riparian vegetation replaced by crops; and
o Direct alterations of immediate banks (channelization, hardening) to prevent loss of croplands to erosion as, for example, to suppress meander formation.
Temporary levees are commonly constructed to protect agricultural lands. They are quickly replaced after flooding (Seery 1993), often within the channel so that protected areas behind levees can promote accumulation of silt and thereby expand croplands while at the same time constraining and controlling the stream.
Floodplain agriculture places streams in immediate proximity to pesticides, either through inadvertent blow-over or less-than-careful application not only on crops but also on adjacent water surfaces.
Blow-over from the Rio Sonoyta watershed, Mexico, was detected in aquatic habitats in Organ Pipe Cactus National Monument (Kynard 1979). Blow-over into other aquatic habitats is clearly a common occurrence. The example of a toxic spill of pesticides in the Accidental Spills and Toxic Releases subsection on page 57 also pertains here.
Agriculture has been identified by ADEQ (1992) as the "predominant source of contamination in streams" through both direct and indirect effects of range management, irrigated and non-irrigated crop production, and concentrated livestock feeding.
Highways and other transportation corridors (including unsurfaced roads) have both short-term and long-term time effects on streams (Furniss et al. 1991).
Short-term, high-magnitude impacts occur during construction through modification of drainage patterns, disruption of soils, accelerated erosion and alteration of streambeds and channel geometry.
o A clear example of the last exists in Interstate Highway 15 through the Virgin River gorge, constructed directly above the river over much of its length.
Chronic effects persist near bridge crossings or areas of bank hardening, and wherever modified drainage patterns contribute to increased erosion and sediment transport into streams.
Culverts and other structures may act as barriers to upstream movement of organisms, increasing fragmentation of already disjunct populations and disallowing use of extensive, less-than-permanent stream habitats by invasive native species during wet years. This factor may be important to those species which depend upon periodically expanded habitats to maintain variability, which is seriously reduced when populations may become critically small during drought.
Highway and road construction (along with other construction activities) require great volumes of sand, gravel and other raw materials, many of which are extracted from stream channels and floodplains. Extensive removal can destabilize channels and, if intimately associated with perennial streams, can increase turbidity and produce other undesirable impacts.
Patten and Ohmart's review, earlier in this report, of sand and gravel extraction relative to riparian ecosystems applies to streams as well. Refer to the discussion of Highways on page 8 for further information.
All these changes affect physical processes that lead to alterations in hydrological patterns, sediment transport and storage, channel bank and bed configurations, substrate composition and slope stability. Collectively, such changes have widespread, progressive and deleterious effects on stream biota.
Major sources of energy in Arizona include nuclear plants, fossil-fuel-fired generating plants and hydroelectric dams.
Of these, dams have the most direct and pernicious effects on streams.
o Dams block streams, thereby increasing population fragmentation and precluding migration for components of the biota dependent on such movements for completing their life cycles. Dams also alter downstream hydrological patterns, thermal regimes, inputs and outputs of sediments and nutrients and biotic productivity, diversity and taxonomic composition (Ward and Stanford 1979, Petts 1984).
o Production of hydroelectric power from dams often is a secondary purpose to storage and delivery of water. Yet temporal demands for hydroelectric power drive the schedules of water releases on hourly, daily and monthly bases.
Meeting such demands results in large daily discharge fluctuations, considerable difference between weekday and weekend discharges, and major modifications in the seasonal hydrologic patterns characterizing pre- dam rivers. Flood frequencies and magnitudes are changed, negatively influencing natural channel maintenance, and low discharges typically average far higher than before, homogenizing the system (reducing natural variance) even more. Much of the controversy surrounding operations of Glen Canyon Dam upstream from Grand Canyon National Park centers on the influences of discharge fluctuations (USBOR 1994).
Requirements for a sufficient head to generate power also dictates that such structures deliver water from the depths of impoundments. Releases thus are perennially cold and nearly devoid of the seasonal changes in water temperature characterizing unregulated streams. Except for trout, native Arizona fishes are unable to reproduce in the cold waters below mainstem reservoirs (Minckley 1991).
o A third major physical change is the loss of sediment and sediment-bound nutrients through settling in the upstream reservoir. Released waters are clear and erosive; in their passage they remove sediments without replacement, and in so doing modify channel geometry, substrate composition and other features resulting in extirpation of indigenous biota (NRC 1991).
Alterations in physical and chemical habitat features above and downstream of reservoirs and in downstream tailwaters are invariably accompanied by introductions of non-indigenous species for recreational or other purposes or provide habitat for inadvertent establishment of such creatures, as described in the Species Introductions subsection on page 70.
Subsequent extirpation of indigenous biotas is the rule, and these dams are designed and constructed to persist for hundreds of years. When such dams are chained in sequence, as they are in major Arizona streams, the effects are overwhelming. There is little hope for restoration of pre-dam biological conditions without determined effort.
Both short-term and long-term consequences of physical, chemical and biological impacts of hydroelectric dams on stream ecosystems are high.
Arizona contains numerous mineral deposits (ABM 1969), and the extraction of ores, although of undeniable economic benefit, has left a legacy of environmental impacts on both land and water (Follett and Wilson 1969, Lewis 1977, Dobyns 1981).
o Mineral extraction, in particular surface mining, is exceptional in the extent to which it scars the landscape during stripping of overburden, vegetation removal, road construction and dredging or channelization of streams.
o Mining can pollute streams through releases of suspended sediments, toxic heavy metals, and acids. Refer to the Accidental Spills and Toxic Releases subsection on page 57 for more information.
Effects on ecosystems vary with the method used, relative toxicity of metals or wastes present, efficiency of their extraction, and the manner in which mine waste piles, haul roads, tailings ponds, stock-piles and processing plants are developed and operated.
Both short- and long-term impacts result from mining because pollution from abandoned mines, after cessation of extraction activities, may persist for decades.
In recent years legislation has been passed requiring rehabilitation of mine-damaged lands, and posting of reclamation performance bonds for activities on federal lands are required to cover damages.
Rehabilitation rarely is equivalent to restoration to a previous ecosystem state, however, and abandoned mines often escape coverage by existing legislation.
Timber Management
Timber harvesting and silvicultural treatments (planting, thinning, burning, mechanical site preparation and chemical applications) share many features of Grazing (see page 58) and Mining (see page 62) relative to watershed alteration, and Transportation Corridors (see page 60) relative to the impacts of road construction.
Chemicals (pesticides, fertilizers, fire retardants) are applied to protect, rehabilitate or enhance economic benefits from managed timber resources. When they enter streams, such chemicals may affect biotas directly through toxic effects or indirectly through bio-accumulation from lower to higher trophic levels.
Pesticides also may have unintended effects on non-target organisms that have important roles in the trophic economy of streams.
Another major impact of timber operations on stream ecosystems is the opening of access to otherwise remote areas to vehicular, recreational and other uses (refer to the Recreation subsection on page 68).
Fire suppression leading to accumulated debris and subsequent wildfires may result in substantial damage to aquatic habitats when ash and other dissolved and particulate materials enter with post-fire precipitation runoff.
o Substantial loss of aquatic life was sustained in streams along the Mogollon Rim during and following the Dude Fire in 1990 (J. Rinne, USFS, Flagstaff, pers. comm.).
o Populations of endangered Gila trout were lost as a result of wildfire in the Gila Wilderness Area, New Mexico, in 1993 (D. Propst, NMGFD, Santa Fe, pers. comm.).
The Committee knows of four interbasin water transfers in Arizona:
o Between Blue Ridge Reservoir (Little Colorado River basin) and the East Verde River (Verde River basin)
o Between Showlow Lake (Little Colorado basin) and Carrizo Creek (Salt River basin)
o Between Black River (Point of Pines, Salt River basin) and Eagle Creek (Gila River basin)
o Between Lake Havasu on the Colorado River mainstem and central/ southern Arizona (including much of the upper Gila River basin).
The first three have been circumstantially implicated in faunal transfers, for example, occurrence of Little Colorado River sucker in the Gila River basin (Minckley 1973), and appearance of smallmouth bass for which no stocking records exist in Eagle Creek (Marsh et al. 1991).
The CAP Canal, far larger and more substantial than the other three interbasin connections, has created considerable environmental controversy. Included is a USFWS (1994b) Jeopardy Biological Opinion under the Endangered Species Act of 1973, based on projected impacts of non-indigenous fishes carried by the CAP system on the following threatened and endangered indigenous fishes. Refer also to the Species Introductions subsection on page 70, and for an alternative interpretation, see Grabowski et al. 1984.
o Spikedace
o Loach minnow
o Razorback sucker
o Desert pupfish
o Sonoran topminnow
Other factors to be considered are:
o Potential parasite transfers, especially along with non-indigenous trout, as regards the first three interbasin connections;
o Effects of water depletion in contributing streams and enhancement in receiving systems; and
o Questions of just how much water is transferred.
(Minckley and Sommerfeld [1979] discussed Eagle Creek discharge relative to withdrawal of water for mining operations).
In a broader sense, interbasin water transfers between adjoining watersheds in the upper Colorado River system of Colorado and Utah have allowed faunal transfers now implicated (along with stocking of non-indigenous fishes) in increasing problems of hybridization, and contributing to endangerment of the indigenous fauna (A. Hutchinson, Arizona State University, Tempe, pers. comm.).
Elements of this same fish fauna, some of which are already proposed as candidates for listing, also occur in Arizona.
Channelization
Channelization is alignment of stream channels into straight or otherwise artificial configurations. The practice is often accompanied by bank hardening, which forces the stream to maintain a course within a desired channel.
Channelization results in the following (Crandall et al. 1984):
o Removal or subsequent loss of riparian vegetation
o Loss of instream cover
o Altered pool-riffle ratios
o Altered substrate composition
o Increased current velocities and water temperatures
o Divorce of the stream from its floodplain
o Curtailment of meander and oxbow formation
o Incision and rejuvenation that result in increased sediment loads downstream
Environmental consequences, often severe, typically are realized both within the modified reach and at some distance upstream and downstream (Schumm 1977). Channelization is usually associated with other development activities like Agriculture (see page 59) and Mining (see page 62), contributing further to ecosystem degradation.
The Committee estimates channelization has been applied in about 40% of the existing perennial stream miles in Arizona. Effects are documented for the lower Colorado (Ohmart et al. 1988), Salt (Graf 1983) and Santa Cruz rivers (Betancourt and Turner 1991).
The magnitude of negative short-term and long-term impacts is high and stream communities have low to moderate resistance or resilience to this activity. Although recently advocated (NRC 1992), restoration through de-channelization has received little attention in Arizona.
Water diversion was used to irrigate agricultural fields by Native Americans in the Sonoran Desert region long before occupation by Europeans (Dobyns 1981). Their canal systems, although sophisticated, pale in comparison with the networks now supplying agriculture, industry and municipalities.
Beheading streams, by developing impoundments in headwaters (often on ephemeral or intermittent watercourses), results in the following:
o Reduces overall input of water to the system
o Traps nutrients and sediments
o Reduces infiltration into groundwaters at lower elevations thereby promoting negative relationships between streams and their floodplains
o Reduces down-slope variance (changes the pattern) in discharges
Diversions reduce downstream volumes and thus influence all stream functions which depend upon discharge volume and pattern. These relationships further emphasize the impossibility of separating streams from their watersheds.
Water diversions of the magnitude included in the CAP bring up additional questions of a long-term nature, such as the following:
o Water depletion downflow from intake points
o Enhancement of discharges at points of delivery
o Interconnection of watersheds and river basins
o Transport of biological contaminants along with the water
o Fears that new kinds of non-indigenous organisms will be introduced which could use these interbasin waterways for dispersal. Refer also to the Interbasin Water Transfers subsection on page 64, and the Species Introductions subsection on page 70.
Groundwater Pumping
Removal of ground or surface waters is an element contained within the activities of agriculture, mining and urbanization.
A distinction should be made, however, between surface and underground waters, which until 1994 remained absolute in Arizona water law.
Effects of the new recognition that surface waters and groundwaters are inter- connected (General Adjudication of All Rights to water in the Gila River System and Source, Maricopa County Superior Court Nos. W-1, W-2, W-3, W-4 [June 30, 1994]) are yet to be realized, but there can be no doubt in basins with perennial streamflow that floodplain pumping promotes flow from channel to groundwater, reduces flow from shallow aquifers into stream channels, and ultimately has the capacity to obliterate springs and all but flood flows in streams.
Impacts of watertable depletion through pumping, reduction of recharge pathways or any other means are profound and often fatal to aquatic ecosystems.
Resistance and resilience to such events are low and restoration possibilities are remote unless recharge can be rapid, extensive and reliably performed.
Impoundments and Dams
Impacts of impoundments and dams are discussed under Energy Production on page 61, Water Diversion on page 66, and Species Introductions on page 70.
Perennial reservoirs created by dams are sites of multiple recreational activities in Arizona, including fishing, boating and water skiing. Meeting the desires of recreational users promotes introductions of non-native fishes, building marinas with associated problems of waste disposal and storage and sale of petroleum products, among other things.
In most instances, however, storage and release of reservoir waters are governed by downstream water rights of agricultural, municipal and industrial users. Since most impoundments in Arizona were created before the advent of environmental legislation, the needs of native biota are seldom factored into operations of the dams which contain the impoundments.
Water-based recreation in Arizona is closely associated with reservoirs, as is to be expected, so it is tightly bound with development of dams, impoundments and other water-control structures.
Also pertinent is construction of recreational fishing lakes on streams along the Mogollon Rim, in the White Mountains, and in southeastern Arizona in the 1960's and 1970's. These recreational impacts are partially covered under the Energy Production subsection (see page 61), the Water Diversion subsection (see page 66) and in the Ecosystem Biological Alterations section (see page 69).
Off-highway vehicles operating in riparian zones and stream channels, and hiking in the latter, have been implicated in habitat disruptions associated with reduced substrate stability, increased turbidity, and direct effects on fish foods, spawning sites and populations (Minckley and Sommerfeld 1979, Minckley 1981). Some of these impacts may influence downstream reaches as well. Refer to the Hunting and Fishing subsection on page 69 for additional recreational impacts.
Urbanization
Urbanization directly or indirectly involves, and cannot be separated from, a large proportion of the other categories of stressors discussed here, such as demands for power, potable and industrial water, recreational development and so on.
Streams flowing through or near urban zones are typically impounded, diverted, de- watered, channelized, and polluted within the immediate areas, and their indigenous biotas extirpated.
Such systems are altered downstream through desiccation as a result of impoundment, diversion or groundwater pumping, or they may be perennial due to wastewaters discharged from the urbanized zone. In some instances, perennial reaches have even been recreated by wastewater.
Unfortunately, most such stream segments in Arizona are inhabited by non- indigenous plants, fishes and other organisms, and are often so contaminated by toxic materials or domestic wastes as to pose hazards to human health. Hazardous conditions of this type were recorded by ADEQ (1992) in the Gila River downstream from Phoenix Metropolitan area and in the Santa Cruz River below both Nogales and Tucson.
Ecosystem Biological Alterations
Direct impacts of hunting are mostly related to off-road vehicle use for transportation to remote sites (see the Transportation Corridors subsection on page 60, and the Recreation subsection on page 68).
There is little doubt that concentrated fishing with specialized methods can alter any fish population, and, in the past, such removal must have negatively influenced stocks of larger species, especially when they were concentrated for spawning.
Historically, large numbers of fish were also harvested from Arizona streams through use of traps, spears, nets and explosives. It is not demonstrable, however, that any indigenous fish population in Arizona was destroyed by fishing.
Nor does today's recreational fishing have apparent direct impact on indigenous populations. Such may not be the case for indirect influences of stocking non- indigenous fishes and other organisms for recreational purposes (see the Species Introductions subsection on page 70).
In some instances, measures have been taken to suppress or eliminate an existing native fish fauna in order to help ensure the successful colonization of desirable introduced sport fishes (Rinne and Turner 1991).
Purposeful poisoning of "trash" fish populations to prepare streams and lakes (including reservoirs) for establishment of desirable sport fishes, mainly trouts, has resulted in substantial losses to indigenous fish populations in Arizona. In some instances, these losses were only temporary and were followed by recolonization. In others, the effects appear to have been permanent. Ichthyocides are now being used with variable results to renovate contaminated streams for re-introducing Apache trout and other indigenous species (Rinne and Turner 1991).
Illegal Collecting
The Committee knows of no documented instance of illegal (or legal) collecting causing extirpation of a stream-inhabiting Arizona species.
Massive human disturbance of natural aquatic ecosystems and introduction and establishment of non-indigenous species were essentially coincidental in the American West, so separation of impacts of these two major disruptions is difficult.
The extent of the problem is illustrated best by the lowermost Colorado River downstream from Parker Dam, where the only two native fishes remaining are marine species entering from the Sea of Cortez. Otherwise this reach of stream has the dubious distinction of being the only major North American water course populated by an entirely non-native fish fauna (Minckley 1979, 1982).
Appearances of non-indigenous species in nature may be attributable to intentional introductions, unintentional introductions, or unknown sources.
o Non-indigenous organisms were stocked directly for food (carp, buffalofish), sport fishing (basses, catfishes, perches, pikes, trouts, bullfrogs) as forage or bait for sport fish (scuds, opossum shrimp, crayfishes, shad, shiners and other minnows, tiger salamanders), and for biological control of aquatic weeds and insect pests (tilapia, grass carp, mosquitofish).
o Non-indigenous organisms appeared as unintentional contaminants with other organisms (for example, silver carp), or when presumably discarded from home aquaria (sailfin molly, guppy, walking catfish, numerous exotic aquatic plants, snails), or as unused bait and escapees from aquaculture (for example some shiners, other minnows, and the African mouthbrooders).
o One from an unknown source is the Asiatic clam which clogs irrigation canals and conduits at lower elevations.
o An Asian snail lives in the sediment and feeds on fish eggs as well as other sessile organisms.
Some non-indigenous organisms, such as the zebra mussel now spreading rapidly in eastern and central United States, can be transported in any moist container, such as the driveline housing of large boats hauled across the country. Furthermore, fishes and other organisms stocked in adjacent states have ready access through interstate waters such as the Colorado or Gila rivers mainstems. From there they can disperse statewide through artificial interbasin connections like the CAP.
How indigenous fishes are replaced by non-indigenous species remains under debate (Moyle et al. 1986, Douglas et al. 1994). One school of thought supports habitat disruption that enhances habitat suitability for non-indigenous species and reduces it for indigenous kinds as a principal means for replacement (Herbold and Moyle 1986, Ross 1991).
Others advocate direct predation (Arizona examples discussed by Minckley et al. 1977, Meffe et al. 1982, Meffe 1983, 1985, Marsh and Langhorst 1986, Marsh and Brooks 1989, Blinn et al. 1993), competition (Douglas et al. 1994), or some other negative interaction as the contributing factor (see also Courtenay and Stauffer 1984, Courtenay 1990).
In the final analysis, the ultimate cause of extirpation for the indigenous biota likely results from a combination of factors.
In any case, second to habitat loss and disruption from development of water resource structures (now stabilizing after rapid expansion over the past century), introduced organisms have been deemed by some as the most important current danger to what remains of Arizona's indigenous aquatic biota (Minckley 1991a).
Unlike physical and chemical ecosystem changes induced by humans, which can often be corrected or at least ameliorated, naturalized non-indigenous species are difficult to control and essentially impossible to eradicate (Courtenay 1990).
Typically, the resistance, resilience and restorability of ecosystems affected by such biological pollutants all are minimal, except on a local scale and at substantial expense.
Outlook for the Future
This analysis of the effects of human-induced environmental stressors on stream ecosystems in Arizona has concentrated on past and present conditions. Emphasis has been placed on the approximate 120-year period of development and resource exploitation by European colonists and their descendants.
During that time, the human population grew dramatically, to an estimated 3.7 million residents in 1990. Today, only halfway through the decade, approximately 4.1 million people are present, and by the year 2015, some 6.8 million are expected. As population growth continues unabated, or even accelerates, the past merges into the future.
These projections clearly underscore a continuing increase in demands on water resources and even greater challenges in the future to maintain even a status quo for the existing indigenous stream biota, let alone successful recovery or restoration of declining and already extirpated species.
Yet, there may be reasons for hope. The age of dam building may have reached a zenith and plateaued. As evidenced by the Grand Canyon Protection Act and recently completed Glen Canyon Environmental Impact Statement (USBOR 1994), public concern for the effects of hydroelectric dams on downstream ecosystems is resulting in operations that involve fewer impacts on indigenous aquatic species.
Interstate agreements, such as those of state wildlife agencies in the Colorado River Wildlife Council, are slowing the rate of introduction of non-indigenous species and increasing attention to the impacts of those already introduced and established. And broader environmental legislation, such as the Aquatic Nuisance Species Control Act of 1990, has been enacted in response to some problems that have been discussed for Arizona.
The future is uncertain. It has taken a long time to recognize the interdependence of streams, their riparian galleries and their watersheds. Ecosystem views of landscape are becoming understood by a larger proportion of the public, and it seems clear that the opportunity is at hand to reduce the effects of environmental stressors on Arizona's streams.
It is also clear, however, that time grows short for implementation of a successful program of restoration. Time will show the depth of our commitment.