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Nitrate removal and denitrification in headwater agricultural streams of the Pacific Northwest
Citation:
Sobota, D., J. E. COMPTON, AND K. Goodwin. Nitrate removal and denitrification in headwater agricultural streams of the Pacific Northwest. Presented at Society for Freshwater Science Annual Meeting, Louisville, KY, May 20 - 24, 2012.
Impact/Purpose:
Headwater streams can serve as important sites for nitrogen (N) removal in watersheds. Here we examine the influence of agricultural streams on watershed N export in the Willamette River Basin of western Oregon, USA, a region with mixed agricultural, urban and forestry land uses.
Description:
Headwater streams can serve as important sites for nitrogen (N) removal in watersheds. Here we examine the influence of agricultural streams on watershed N export in the Willamette River Basin of western Oregon, USA, a region with mixed agricultural, urban and forestry land uses. In August 2011, we measured nitrate removal on five streams surrounded by different types of agricultural activity with whole-stream nitrate additions and laboratory assays of sediment denitrification potential. Nitrate concentrations were low in all streams (4 – 231 µg NO3-NL-1). Ambient uptake lengths, rates, and velocities ranged from 60 – 740 m, 7.6 – 271.2 µg m-2 min-1, and 0.18 – 2.96 mm min-1, respectively. This translates to 75 – 99% of nitrate loaded at one location removed with 1 km downstream. Sediment assays suggested nitrate availability limited denitrification, with half-saturation coefficients ranging from 499 to >10,000 µg NO3-N L-1. Our results suggest that in-stream nitrate removal contributes to the low summer nitrate concentrations observed in these agricultural streams