Patterns of nitrogen transport in streams of the Lake Tahoe basin, California-Nevada

In an effort to characterize the spatial and temporal patterns of nitrogen concentration and load in streams of the Lake Tahoe basin, we analyzed 10 years of data from 10 streams, developing discharge-concentration relationships and total load estimates for nitrate-N, ammonium-N, and organic N. The results indicate that (1) most of the nitrate transport occurs early in the snowmelt season or during large winter rainstorms; (2) dissolved organic nitrogen concentrations peak early in the runoff season, decline during snowmelt, and in some streams peak again during the summer low-flow period; (3) organic nitrogen accounts for over 90% of the total nitrogen load in basin streams; (4) averaged over 10 years and the area of 10 watersheds, the nitrogen fluw rates in kg ha(-1) yr(-1) are 0.081 for nitrate-N, 0.017 For ammonium-N, 0.58 for dissolved organic N, and 0.47 for particulate organic N; (5) the variation in annual runoff explains most of the interannual and interwatershed variability in total nitrogen load; and (6) the dominance of organic nitrogen relative to nitrate-nitrogen in Tahoe basin streams contrasts with sites in eastern North America.