Based on studies of high-elevation, Sierra Nevada catchments during the period from 1983 through 1996, we describe temporal variations in the concentrations of NO3- and SO42- in surface waters. During snowmelt, some catchments had a pattern of NO3- increase to a plateau between the start of snowmelt and some weeks before runoff peaked, and a decline as runoff increased to its maximum. In other catchments, NO3- concentrations peaked during the autumn and winter. Long-term trends in surface water chemistry were evident in only two catchments: an increase in SO42- concentrations in surface waters of the Ruby Lake basin, and a lowering of annual maxima and minima of NO3- concentrations at Emerald Lake. From October 1987 through April 1994, SO42- concentrations increased from about 6 mu eq L-1 to about 12 mu eq L-1 in Ruby Lake, and in Emerald Lake, NO3- maxima declined by 25-50 . References: 21
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