9343 - Laserfiche WebLink

Home Browse Search

incoming total load left in the reservoir. Copper, iron, manganese, molybdenum, and zinc were analyzed for total (unfiltered) concentration, which allowed the percentage of the overall load occurring in the dissolved phase to be determined (table 6). In the case of copper, iron, and zinc, the entering load had a smaller dissolved percentage than the exiting load. It is likely much of the incoming copper and iron was in the suspended phase and was depos- ited on the reservoir bottom by settling. Manganese showed a decrease and zinc did not show a large increase in dissolved-percentage exiting the reservoir, implying that geochemical processes in addition to sedimentation are acting to contribute loads to Dillon Reservoir. From the load calculations, the stream contrib- uting the largest amount of a given element was identified. Tenmile Creek, which accounts for about 37 percent of the total water inflow, delivered the largest loads of aluminum, barium, and, as one would expect, molybdenum. The Blue River contributed no more than one-third of any trace-element load entering the reservoir, less than the portion of the flow contrib- uted (35 percent of inflow) to the reservoir. The Snake River, generating 28 percent of the total inflow, contributed most of the copper, manganese, and zinc loads. Those streams delivering the largest loads of trace elements to the reservoir also had higher streambed-sediment concentrations, with the excep- tion of barium. The barium load delivered by the Snake River was smaller than the barium loads carried by the Blue River and Tenmile Creek; however, the streambed-sediment concentration of barium was highest in the Snake River. Table 4. Results of Kendall's tau calculations relating trace-element concentrations to core depth in core DNL, collected August 1997 [Ilg/g. micrograms per gram; %. percentage; n. not applicable; value is based on the large sample size approximation described in Helsel and Hirsch (1993)] Element Units Tau p-value Trend Aluminum % 0.099 0.576 No Arsenic Ilg/g 0.111 0.529 No Barium Ilg/g -0.006 1.000 No Cadmium Ilg/ g -0.637 0.000 Yes Calcium % -0.158 0.363 No Chromium Ilg/g 0.333 0.050 No Cobalt Ilg/g 0.287 0.093 No Copper Ilg/g 0.509 0.003 Yes Iron % 0.345 0.042 Yes Lead Ilg/g -0.053 0.780 No Lithium Ilg/g 0.439 0.010 Yes Magnesium % -0.018 0.944 No Manganese Ilg/g 0.228 0.184 No Mercury Ilg/ g -0.380 0.025 Yes Nickel Ilg/g 0.544 0.001 Yes Potassium % 0.170 0.327 No Scandium Ilg/g 0.357 0.036 Yes Silicon % 0.135 0.442 No Sodium % 0.123 0.484 No Strontium Ilg/g 0.006 1.000 No Titanium % 0.673 0.000 Yes Vanadium Ilg/ g 0.626 0.000 Yes Zinc Ilg/g 0.298 0.080 No Direction Upward over time Downward over time Downward over time Downward over time Upward over time Downward over time Downward over time Downward over time Downward over time IDENTIFICATION OF WATER-QUALITY TRENDS 15