SS3.06 Large Scale Change in Prominent Ecosystems
Date: Wednesday, June 12, 2002
Time: 2:45:00 PM
Location: Lecture Theatre
 
SickmanJO, University of California, Santa Barbara, Santa Barbara, USA, jsickman@sprintmail.com
Melack, J, M, University of California, Santa Barbara, Santa Barbara, USA, melack@lifesci.ucsb.edu
Clow, D, W, United States Geological Survey, Denver, USA, dwclow@usgs.gov
 
LONG-TERM CHANGES IN LAKE NUTRIENT AND TROPHIC STATUS IN THE SIERRA NEVADA: RESULTS FROM SYNOPTIC SURVEYS AND INTENSIVE MONITORING OF EMERALD LAKE, CALIFORNIA
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Two decades of monitoring subalpine Emerald Lake (Sierra Nevada, California) has revealed several significant trends. Nitrate, both during spring runoff and during growing seasons declined by half from 1988 through 1998. Declining snowmelt nitrate peaks were associated with changes in snow regime induced by the 1987-1992 drought. Our evidence suggests that growing season trends were primarily the result of increased atmospheric P-supply to the lake and the release of phytoplankton from P-limitation. Contemporaneous with these nutrient supply changes was an increase in phytoplankton biomass and a shift towards more frequent N-limitation of phytoplankton growth. Particulate carbon levels in the late 1990s were three-fold greater than in the early 1980s. These site specific trends in nitrogen and phosphorus were also reflected in a larger set of Sierra Nevada lakes (n=38) sampled during synoptic surveys in 1985 and 1999, suggesting that lakes throughout the Sierra Nevada are becoming more productive in response to increased nutrient loading. Our data indicate that critical loads for nutrient deposition in the Sierra Nevada appear to be <5 kg/ha/yr for N and <0.1 kg/ha/yr for P.