OCR Text |
Show 12 Water Quality in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1998- 2001 3,000 Figure 18. Nutrients and pesticides are transported to Little Cottonwood Creek in urban runoff, substantially increasing the concentration of these contaminants during storms. because of increased inputs of sodium and chloride from deicing of roadways. For example, the chloride concentration in Little Cottonwood Creek during a 1999 winter storm exceeded 2,900 mg/ L ( fig. 19); conversely, chloride concentrations in Red Butte Creek ( an adjacent, undeveloped basin) remained about 12 mg/ L. Chloride concentrations in Little Cottonwood Creek exceeded the acute USEPA aquatic- life criterion for chloride ( 860 mg/ L) ( U. S. Environmental Protection Agency, 2002a) in 10 percent of the samples, and the chronic criterion ( 230 mg/ L) in 61 percent of the samples collected during December 1999 through March 2000. Elevated concentrations of chloride can cause acute and chronic toxicity in aquatic organisms. Even moderate concentrations can affect community structure, diversity, and productivity ( Environment Canada and Health Canada, 2001). The effects of chloride are particularly evident in Little Cottonwood Creek, where several types of algae tolerant to saline conditions, such as Nitzschia inconspicua and Navicula veneta, are most dominant. Urban storm runoff may be a source of certain VOCs in surface water and ground water. Many of the same VOCs, such as tetrachloroethene ( PCE) and trichloroethene ( TCE), commonly were detected in both storm runoff and shallow ground water from urban areas across the United States ( Lopes and Bender, 1998). In urban Salt Lake Valley, elevated concentrations of gasoline- related compounds ( 1,2,4- trimethylbenzene, xylene, and toluene), chloroform, and TCE were measured during storm events in water sampled from Little Cottonwood Creek. Chloroform and TCE also were detected in shallow ground water. Water temperature is another stream characteristic that is altered by storm runoff. During storms, water • Chloride ES Snowfall USEPA aquatic- life guidelines ( acute 860 mg/ L, chronic 230 mg/ L) z o 20 Z 10; December I January February March 1999 2000 Figure 19. Chloride concentration in Little Cottonwood Creek often exceeded aquatic- life guidelines. temperature in urban streams sometimes increased by 3° to 5° Celsius (° C). Urban streams draining a higher percentage of high- density residential/ commercial land had larger and longer alterations in temperature during storms than streams draining other types of land. Rapid or prolonged temperature changes can alter streamwater chemical characteristics considerably and can adversely affect aquatic organisms that are intolerant to these changes. For example, increased stream temperature can reduce the amount of oxygen available for aquatic organisms while at the same time increasing their metabolic rate and oxygen needs. Elevated levels of pesticides are most common in urban streams Water samples collected from streams were analyzed for 107 pesticides, of which 49 were detected ( Gerner, 2003). At least one pesticide was detected in 23 of the 24 streams sampled. Pesticides ( herbicides and insecticides) are applied in many agricultural and nonagricultural settings in the Study Unit to control unwanted vegetation and destructive insects. On average, samples from streams in basins with predominantly urban or mixed land cover contained more pesticides than samples from streams in agricultural and undeveloped basins ( fig. 20). The number of pesticides detected in individual samples in each stream ranged from none in many samples collected at forest and rangeland sites to 16 in a sample from the Jordan River, a stream whose water quality is influenced by mixed, but predominantly urban, land uses. The types of pesticides detected also differed by land use. Specifically, insecticides- most commonly carba- ryl, diazinon, and malathion- occurred more frequently in urban streams than in agricultural streams. For example, diazinon was detected in about 90 percent of 42 samples from the urbanized Little Cottonwood Creek but in only about 4 percent of 26 samples from the agricultural Cub River. |