Effects of water temperature and water clarity on primary production in Lake Tahoe

Video: UC Davis staff sampling primary production in Lake Tahoe

Abstract

Primary production in freshwater is a vital link in the cycling of carbon between living and inorganic sources in aquatic systems. Anthropogenic activities in catchments of such freshwater lakes can significantly impact on their primary production. A typical example is Lake Tahoe in the Sierra Nevada Range, at the border of California and Nevada. Since the 1960’s a continuous increase of nutrient fluxes into Lake Tahoe has resulted in increased algae production and rapidly declining water clarity. While 30 yr ago primary production was nitrogen limited, today production is mainly phosphorous limited. The preservation of Lake Tahoe’s water quality is of major public concern as the Lake is an important water resource, recreational area and fishery resource. Numerical modeling of primary production in natural waters has proven to be a very effective tool in order to understand longterm anthropogenic impacts on natural lakes ecosystems and to predict current and future disturbances. Such models have been established and successfully applied to Lake Brienz (Switzerland) in order to quantify long-term impacts of oligotrophication and upstream hydropower operations. The present short term project aims to apply established numerical models to Lake Tahoe in order to better understand anthropogenic long-term effects on primary production. In particular, the effects of the supposed increase of surface turbidity and warming of the surface waters on algae production will be assessed by the means of numerical modeling. The model will be calibrated with in-situ light measurements and in-situ measured primary production. Long term production simulations allow a better interpretation of existing data. Furthermore predictions can be made for hypothetical scenarios allowing an assessment of the effects of increasing turbidity and global warming on productivity. Based on the model results the effects of decreasing water clarity and global warming on primary production in Lake Tahoe will be quantified.