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Major Findings 1988- 1992 EXPLANATION Dissolved- solids concentration, in milligrams per liter, 1988- 1992 and 1998- 2002 1 Less than 250 L © Zl250to500 ^ M 500 to 1,000 •• Greater than 1,000 Approximate boundary of basin- fill deposits in Salt Lake Valley 6 KILOMETERS Figure 13. Dissolved- solids concentration in water from parts of the deeper basin- fill aquifer in Salt Lake Valley increased from 1988- 92 to 1998- 2002. Forest and rangeland cover approximately 70 percent of the Study Unit. Undeveloped basins are sparsely populated and commonly include high, precipitous mountains with narrow crests and forested valleys or broad intermontane basins dominated by arid grasslands and shrublands. Examples of streams in undeveloped areas include the upper Bear and upper Weber Rivers, and Red Butte Creek ( Jordan River Basin). The quality of water and the state of the aquatic community in these streams represents " natural" conditions in the basins ( fig. 14). Figure 14. USGS scientists assess stream habitat at a site on the upper Weber River ( a largely undeveloped river basin). The concentration of dissolved solids in a stream generally indicates . the degree of stream development and human influence on water quality. For example, concentrations in undeveloped streams ranged from 176 to 469 mg/ L, whereas concentrations in more developed and urbanized streams ranged from 67 to 2,750 mg/ L ( fig. 15). Elevated concentrations of dissolved solids in the developed streams generally reflect the return of water to the streams after use for human consumption, industrial activities, and irrigation. Physical habitat, including stream- bed composition, bank stability, water velocity and depth, amount of sunlight received, and protective structures also indicates the degree of stream development and human influence. Physical habitat features often are integrated into one measure, referred to as Habitat Quality Index Scores, which were higher ( better) for undeveloped streams than for developed streams ( fig. 15). Streams with dams and diversions sometimes had lower scores regardless of human influences or land- use activities within their basins. For example, the watershed above the Bear River near Pescadero, Idaho, is largely undeveloped; the Habitat Quality Index Score in this stream reach is low, however, because channelization and flow regulation have resulted in little pool variation or stream sinuosity. Composition of biological communities also indicates degree of stream development and human influence. Specifically, streams in developed basins had aquatic communities that were more tolerant to pollution and habitat disturbances than were aquatic communities in undeveloped basins. Streams in developed basins also had a lower percentage of native fish species such as longnose dace and cutthroat trout, a lower percentage of insect taxa preferring good water- quality conditions such as mayflies, stoneflies, and caddisflies, and a higher percentage of pollution- tolerant algal species, such as Nitzschia inconspicua. n )< g 1,500 IS I I © - © © ~ - 0 - © " t I § 140 u h 100 • © • O O © G • © • © © © Affected by habitat degradation Q O o o O -| 5 © o < ty so ^ j °- h w o "- S ° o LL| Q s < Undeveloped Developed Undeveloped Developed SITE GROUP Figure 15. Aquatic communities and water chemistry in streams affected by urban and agricultural land uses are generally degraded compared to streams in largely undeveloped basins with predominantly rangeland and forest land cover. |
