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Show 8 Water Quality in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1998- 2001 pstream diversions have resulted in increased water temperatures in streams and changed fish communities In the Slate of Utah, the criterion for water temperature in stream reaches designated to support cold- water aquatic life is 20 degrees Celsius (° C). This criterion was selected prior to any continuous monitoring of stream temperature and applies to any point measurement of temperature taken at any time of day. Twenty- one sites on 13 urban streams designated Ito support cold- water game fisheries were monitored for temperature, and at 17 o( these sites the criterion was exceeded at least once during the summer of 2000. Five sites had maximum daily temperatures that exceeded the criterion on more than 75 percent of the days during this time. Most urban sites are in the valley and are exposed to warmer air temperatures; however, these streams historically supported cold- water salmonid species ( Sigler and Sigler. 1996). Thermal pollution in these streams is likely due to upstream diversion of water and subsequent replacement with urban and agricultural runoff. Additionally, the reduction of flow that also results from diversions increases temperatures during the summer due to the loss of thermal mass. Increased temperatures in urban streams have changed fish communities. Specifically, warm- water species, such as common carp, green sunfish, and channel catfish, which are not native to streams in the Great Salt Lake Basins, have populated streams in which temperatures exceed 20° C at least 30 percent of the time. These warm- water species have replaced native cold- water species, such as trout and w hitefish. and cool- water species, such as sculpin and dace, which cannot tolerate the warmer waters. In fact, in streams where the daily maximum temperature exceeds 20° C more than 75 percent of the time, cold- water species compose less than 25 percent of the fish community. 0 0to30 30 to 75 75 to 85 Percent Percent Percent Percent PERCENTAGE OF DAYS THAT MAXIMUM TEMPERATURE EXCEEDED CRITERIA DURING JUNE- AUGUST 2000 D Warm- water species 0 Cool- water species 1 Cold- water species changes in natural flow conditions can result in corresponding changes in the number and kinds of fishes found in a stream. For example, streams with more diversions have less available habitat for fish. With decreased water at low flows, deeper water habitats, such as pools, are reduced, which limits larger species, such as brown trout. Smaller species that are adapted to shallow, riffle areas, such as mountain sucker, tend to dominate in streams with severe dewatering. In addition, streams with less flow had higher water temperatures and higher concentrations of nutrients. These conditions tend to favor warm- water fish species more tolerant of high temperatures and degraded water quality, such as sunfish and catfish. Pumping likely affects the distribution of dissolved solids in the basin- fill aquifer in Salt Lake Valley Pumping from wells accounts for about one- third of the total estimated discharge from the basin- fill aquifer in Salt Lake Valley, Utah, an urban area in the Study Unit ( seepage to streams and evapotranspiration are the other major forms of discharge). Most ground- water withdrawals occur on the eastern side of the valley because of higher well yields ( discharge rates) and lower dissolved- solids concentrations. In some areas on the western side, ground water is withdrawn and blended with water from other sources to improve its quality. Comparison of water in the basin- fill aquifer sampled in 1988- 92 and that sampled in 1998- 2002, shows an increase in the extent of the aquifer containing water with a dissolved- solids concentration greater than 500 mg/ L. Water with less than 500 mg/ L dissolved solids extended to the northwest past the Jordan River in 1988- 92, but was replaced by water with concentrations of dissolved solids greater than 500 mg/ L by 1998- 2002 ( fig. 13). Concentrations of dissolved solids increased in water from some wells near the center of the valley, where the direction of groundwater movement ( gradient) is naturally upward between the basin- fill aquifer and land surface. Withdrawals from the basin- fill aquifer for public supply may have caused gradients to reverse, allowing more mineralized water that was recharged in the valley to move to the aquifer. Land use influences water quality and aquatic community health Undeveloped basins show minimal degradation of water quality and biological communities Water quality and biological conditions are generally better in streams draining forests and rangeland ( undeveloped areas) than in streams draining agricultural and urban areas or areas of mixed land use ( developed areas). |