RESEARCH
Nutrient Turnover in Lake Tahoe

Crystalline Lake Tahoe, located in the Sierra Nevada mountains of California is renown for its breathtaking vistas and clear waters. Since the 1960’s the Lake’s water clarity has steady decreased because of algae growth in the water column. This growth has be spurned by an increase in nutrients, particularly available N in the form of nitrate. Here does this nitrate come from and how fast is it removed from the Lake? We have been utilizing D17O to assess how much of the water column nitrate remains from the deposition of HNO3 , which is a product of air pollution. Our initial results show that deposition happens at a rate faster than biological cycling, suggesting air pollution is partially responsible for the build up of nitrate in the lake. Future work will look at the variations in nitrate concentrations and its isotopic composition to assess how quickly the lake might respond to remediation efforts.

Local concern about loss of lake clarity has spawned and environmental plan to “Keep Tahoe Blue”

Loss of water clarity has been monitored by UC Davis’s Tahoe Research Group (TRG) since the 1960’s. The steady decline is largely due to algal growth, spawned by nutrient additions from multiple sources in the basin.

Bob Richards of the Tahoe Research group setting up a 20 liter Niskin bottle during hydro-casting aboard the RV John Le Conte. Nutrient concentrations are determined and isotopic analysis is conducted on nitrate to assess how much lake N is derived from atmospheric deposition.