OCR Text |
Show Major Findings 21 Some of the trace element concentrations in sediment and M fctV fish tissue at urban sites were greater than concentrations for ™ W many urban sites nationwide . Streambed sediment concentra- tributary of the Jordan £ 2 tions in Red Butte Creek, a refer- River, greatly exceeded | PE w 2 7 ence site for study unit streams, were the national median 11 < greater than the NAWQA national values in both sediment | ° o median for cadmium, chromium, and fish tissue. In Little ^ 11 selenium, and silver in urban streams. Cottonwood Creek, 7 of g y < This may indicate that the streams 10 elements in bed sedi- o £ § „ ttgz 2 m the Great Salt Lake Basins Study ment were greater than £ | $ Unit have relatively higher natural the national 90th per- if 0 Bear River Basin 1 Weber River Basin • Jordan River Basin . a Sediment a Fish tissue, liver " • Fish tissue, whole body i lEDI background concentrations than those centile concentration. 1 2 4 5 16 1? 18 SITE NUMBER213 15 16 1? 18 19 found nationally. Trout livers from In fish- tissue samples 1 No fish tissue sample collected at this site. Red Butte Creek in Jordan River Basin from Little Cottonwood 2 No sediment sample collected at this si, e- exceeded the national 90fh percen- Creek, 5 of 10 elements tile ( fig. 35) concentration for nickel exceeded the national 90th percentile. Figure 35. Trace- element concen- and exceeded the national median Arsenic in particular was substantially trations in bed sediment and fish concentrations for arsenic, cadmium, elevated above the 90th percentile. tissue in the Great Salt Lake Basins mercury, and selenium. Concentra- These exceedances are believed to be exceeded the 90th percentile con- tions of trace elements at two sites due mostly to historical mining activi- centration of the NAWQA Program on the Jordan River and two sites on ties before the area became highly Little Cottonwood Creek, an urban urbanized. flow from their mountainous watersheds ( for example, Mill Creek, Provo River) than those without continuous flow ( for example, Little Cottonwood Creek, Kays Creek). Stream temperature was identified as an important factor determining the composition of the biological community. Diversions also serve as barriers to migration of stream organisms, which could reduce diversity. This study identified some of the human- caused factors affecting communities in urban steams along the Wasatch Mountains. It is clear that maintaining flow in the stream channel is essential for the maintenance of biological communities. Reducing water temperatures, improving water quality, and reducing runoff of silt into streams will help maintain the health of the biological community. Such findings may help in the development of useful ecological or other indicators of the effects of urbanization on stream ecosystems, and the uses of these indicators may increase the cost effectiveness of monitoring programs. Elevated concentrations of trace elements in sediment and water are related to natural sources and past mining activities Minerals in rocks are sources of arsenic and radon in ground water Concentrations of arsenic in shallow and basin- fill aquifers in the Great Salt Lake Basins Study Unit were highly variable, ranging from less than 0.4 to 95 ug/ L, with a median of 2.1 ug/ L ( fig. 36). Arsenic, a naturally occurring trace element in ground water within the Study Unit, is derived from geochemical reactions with certain types of minerals. Tertiary volcanic rocks and the Salt Lake Formation exposed near the base of the Oquirrh Mountains may be a source of arsenic on the western side of the Salt Lake Valley that is not present on the eastern side. Water from wells in the western and northwestern parts of the valley generally had higher arsenic concentrations than water from wells in other areas. The median concentration of arsenic in water from relatively shallow monitoring wells, many of which E U" 21 Number of samples at or below this concentration O o o - Deeper basin- fill aquifers tn 0.1 5 Wells sampled Salt Lake Valley Shallow aquifer throughout study area public- supply wells Salt Lake Valley Figure 36. Arsenic concentrations exceeded the USEPA drinking- water standard in about 20 percent of samples collected from the basin- fill aquifers. |