ABSTRACT
This chapter summarizes selected findings from a United States Geological Survey water-quality assessment of trace elements in sediment, water, and aquatic biota in the Yakima River Basin. It illustrates the effect of geology and human activity on the distribution of trace element concentrations and loads for suspended sediment and water media. Trace element concentrations were determined from samples of streambed sediment, suspended sediment, filtered water, and aquatic biota. Geologically derived arsenic, chromium, and nickel concentrations in the main stem, although still high, decrease by about a factor of three, by mixing with element-poor stream bed sediment eroded from agricultural lands in the upper basin. In the mid and lower Yakima Valley, the effect of geology is dampened, and human activities increase concentrations of arsenic, cadmium, copper, lead, mercury, selenium, and zinc in sediment and/or aquatic biota. The significance of the trace-element sources was better assessed by temporal measurements of suspended and dissolved trace elements at fixed location sampling sites.
