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SEASONAL VARIATIONS IN NUTRIENT CONCENTRATIONS AND RIVER FLOW IN A NORTHWESTERN USA WATERSHED
Citation:
Sigleo, A C. AND W. E. Frick. SEASONAL VARIATIONS IN NUTRIENT CONCENTRATIONS AND RIVER FLOW IN A NORTHWESTERN USA WATERSHED.
Impact/Purpose:
To determine nutrient loading from theYaquina River watershed
Description:
Dissolved nutrient concentrations were measured in the Yaquina River, Oregon from 1998 through 2001 to determine nutrient loading from the watershed as part of a larger agency program for evaluating nutrient sources. The effects of storms on dissolved nutrient transport were investigated relative to stream discharge for three storm events, including one in a high rainfall-discharge year, and two in average years, one of which followed a drought year. During the drought year (no flows >25 m3s-1), total dissolved nitrate input was considerably less than in wetter years. However, dissolved nitrate concentrations were unusually high in the first winter storm runoff after the drought. In the November 2001 storm, dissolved nitrate increased rapidly (to nearly 200 M) but decreased by 20 to 30 percent as the storm progressed. The dissolved nitrate nitrogen loads varied from 8,480 kg day-1 during high-flow storm events to less than 74.6 kg day-1 during late summer, low flow conditions. Dissolved silica dynamics were quite different and during storm events silica concentrations in the Yaquina River decreased to near zero at the storm height, probably due to dilution by rapid, shallow flow, and then recovered after 48 hours. During the time interval studied, over 94% of the dissolved nitrate and silica were transported during the winter months of greater rainfall indicating that seasonality and river flow are important determinants when considering nutrient loadings.