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A Lake Superior delta13C IsoScape
Citation:
Hoffman, J., M. Pawlowski, A. Cotter, AND P. Yurista. A Lake Superior delta13C IsoScape. State of Lake Superior Conference, Houghton, MI, October 09 - 12, 2018.
Impact/Purpose:
The stable isotope composition of fish tissue is an intrinsic marker that can be used to track animal movements or identify distinct zones of feeding. This information is fundamental to characterizing both environmental effects and contaminant exposure and bioaccumulation. Subtle but persistent isotopic differences in open waters through either depth or space may allow us to detect otherwise unobservable movements and feeding behaviors. In both 2011 and 2016, we had the opportunity to use a lake-wide sampling design to determine whether there are such isotopic differences in the surface waters of Lake Superior. Based on the results, we conclude that there is sufficient isotopic variability to provide the foundation for novel feeding and movement studies to examine depth- and spatial-based food web processes in Lake Superior.
Description:
he stable isotope composition of fish tissue is an intrinsic marker that can be used to track animal movements or identify distinct zones of feeding. Subtle but persistent isotopic differences in open waters through either depth or space may allow us to detect otherwise unobservable movements and feeding behaviors. In two years (2011, 2016) we used the Cooperative Science and Monitoring Initiative field program to measure the carbon stable “isoscape” across Lake Superior. In both years, we found surprising variability: carbon stable isotope ratios ranged from -23 to -29‰. By depth, the carbon stable isotope ratio of particulates in the deep chlorophyll layer was 13C-depleted compared to the epilimnion, and the epilimnion was more isotopically variable than the deep chlorophyll layer. Spatially, the most distinct feature was an eastern gyre represented by 13C-depleted values towards the center of the gyre. Principal component analysis revealed that the isotopic variability was related to both algal taxonomy and particle C:N. We conclude that there is sufficient isotopic variability to provide the foundation for feeding and movement studies to examine depth- and spatial-based differences in the Lake Superior food web.