ATMOSPHERIC DEPOSITION OF NITROGEN AND PHOSPHORUS IN THE ANNUAL NUTRIENT LOAD OF LAKE TAHOE (CALIFORNIA NEVADA)

Atmospheric deposition provides most of the dissolved inorganic nitrogen (DIN) and total nitrogen in the annual nutrient load of Lake Tahoe. Deposition also contributes significant amounts of soluble reactive phosphorus (SRP) and total phosphorus loading but plays less of a role than in the case of nitrogen. Most of the DIN probably originates outside of the drainage basin in urban and agricultural areas to the south and west. Spatial patterns of SRP deposition differ from those of DIN and suggest a within-basin terrestrial source, such as leachate from windblown dust or other particles. Because of atmospheric N deposition, the N:P (molar) ratio in combined loading is well above the Redfield ratio of 16 and consistent with an observed shift from colimitation by N and P to persistent P limitation in the lake phytoplankton.