CS35 Trophic Dynamics
Date: Friday, June 14, 2002
Time: 11:15:00 AM
Location: Carson A
 
RussME, Michigan State University, East Lansing, USA, russmary@msu.edu
Ostrom, N, E, Michigan State University, East Lansing, USA, ostromn@msu.edu
Ostrom, P, H, Michigan State University, East Lansing, USA, ostrom@msu.edu
Field, A, L, Michigan State University, East Lansing, USA, fieldama@msu.edu
Gandhi, H, , Michigan State University, East Lansing, USA, gandhiha@msu.edu
 
AN IN SITU DEPTH INTEGRATED STUDY OF TEMPORAL AND SPATIAL VARIATIONS IN NET HETEROTROPHY IN LAKE SUPERIOR: IMPLICATIONS FOR THE CARBON CYCLE
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The magnitude and frequency of net heterotrophy in oligotrophic freshwater lakes is not well known. This study was designed to quantify temporal and spatial variations in net heterotrophy in Lake Superior. Sampling was conducted monthly along a three station transect extending north from Houghton, Michigan, and biannually along an eight station transect from Whitefish Bay to Duluth, Minnesota. Trophic state was quantified by calculating R/P from the isotopic composition and concentration of dissolved oxygen. The entire water column, for coastal and pelagic stations, was net heterotrophic during the spring (R/P ~ 1.16) and fall (R/P ~ 1.11). Summer was a period of net autotrophy across Lake Superior (R/P ~ 0.91 to ~ 0.71), within the epilimnion at pelagic stations, and throughout the epilimnion and metalimnion at coastal stations. Net heterotrophy required an external organic carbon source. Consistent R/P between coastal and pelagic stations during lake turnover indicated a carbon source other than nearshore inputs. Resuspension of organic rich sediments is one potential lake-wide source. Net autotrophy across Lake Superior during summer resulted from a resuspension barrier due to thermal stratification.