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SUMMARY OF MAJOR FINDINGS Water. ",<S> ",,,,"',,,,,,'" '1,.' b' "I;;)' AREA. IN SQUARE MILES , I I 20 40 60 KILOMETERS _ _ _ Physiographic province boundary Land use from Fegeas and others (1983) and Hill (1995). The Upper Colorado River Basin (UCOL) of the National Water-Quality Assessment (NAWQA) Program includes the 17,800-square-mile drainage basin of the Colorado River upstream from the Colorado-Utah State line. The study area is almost equally divided between the Southern Rocky Mountains and the Colorado Plateau Physiographic Provinces. Population in the basin is approximately 308,000. The major use of water is irrigation, but transmountain diversions provide water to more than 1 million people in the eastern part of Colorado (outside of the study area). Stream and River Highlights Streams and rivers in the Upper Colorado River Basin (UCOL) are very different in the two major physiographic provinces. In general, streams within the Southern Rocky Mountains are characterized by lower sediment and dissolved-solids concentrations, cooler temperatures, and somewhat higher gradients than streams in the Colorado Plateau. Sediment, salin- ity, and nutrient (nitrogen and phosphorus) concentra- tions increase along the major rivers as the water flows from the upstream areas in the Southern Rocky Moun- tains down through the Colorado Plateau. Coupled with the general differences due to physi- ography and geology are the effects of different land uses. Recreation and urban development are becoming major land-use issues throughout the basin, precious metal mining was historically prevalent in the South- ern Rocky Mountains, and intensive agriculture is located in the valleys of the Colorado Plateau. Most of the streams and rivers sampled within the UCOL met State and Federal water-quality guidelines. Major exceptions to this statement were trace-element concentrations in some streams in the Southern Rocky Mountains and selenium concentrations in some streams in the Colorado Plateau. · In the Southern Rocky Mountains, concentrations of nutrients (nitrogen and phosphorus) were generally low but were greater in urban streams than in streams in areas with minimal development (p. 6). · Urban streams in the Southern Rocky Mountains had greater amounts of algae and a change in the invertebrate community from pollution-sensitive insects to pollution- tolerant insects compared to streams in areas with mini- mal development (p. 6-7). Similarly, in some mining areas of the Southern Rocky Mountains, the invertebrate community was also composed of pollution-tolerant insects, indicating more degraded sites (p. 13). Selected Indicators of Stream-Water Quality Southern Rocky Mountains Colorado Plateau Small Streams Agri- culture Major Outlet of Rivers Study Unit Small Streams Major Rivers Urban Mining Pesticides1 ti) ~ .J,) tit e tJ C) tttt Nitrate2 0_0 ~ t) <; ct ~ c; Total Phosphorus3 Trace Elements4 . Percentage of samples with concentrations greater than or equal to health-related national guidlines for drinking water, protection of aquatic life, or contact recreation Percentage of samples with concentrations less than health-related national guidelines for drinking water, protection of aquatic life, or contact recreation . Percentage of samples with no detection (a Percentage is 1 or less and may not be clearly visible) Not assessed 11nsecticides, herbicides, and pesticide metabolites, sampled in water. 2Nitrate (as nitrogen), sampled in water. 3Total phosphorus, sampled in water. 4Selenium and metals (such as cadmium, lead, and zinc), sampled in water. Summary of Major Findings 1