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SFS Annual Meeting

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RESPONSES OF SILICA STOICHIOMETRY TO HYDROLOGIC AND VEGETATION CHANGES

Silica (Si) is an essential nutrient in aquatic ecosystems, yet the understanding of Si transport and cycling is lacking compared to nitrogen (N) and phosphorus (P). The stoichiometry of these nutrients is critical for the dynamics of algal communities, including the formation of harmful algal blooms (HABs) by cyanobacteria. Understanding how N:P:Si stoichiometry responds to agricultural conservation (winter cover crops) and hydrology (storm versus baseflow conditions) is a first step in predicting the occurrence of HABs. We collected water samples from tile drains and stream sites in two agricultural watersheds in northern Indiana, including locations with and without cover crops. We combined these analyses with data from similar agricultural streams in central Indiana and east-central Illinois. We found that molar ratios deviate highly from the Redfield ratio for both N:Si and P:Si, and N:Si ratios were consistently enriched in N relative to Si. In contrast, P:Si ratios vary above and below the Redfield ratio for a relatively narrow range of discharge values. These results suggest that N:P:Si stoichiometry can vary significantly over short time periods as hydrological conditions change, and that conservation practices could impact N:P:Si ratios in unexpected ways.

Lienne Sethna (Primary Presenter/Author), Indiana University, lsethna@iu.edu;


Todd V. Royer (Co-Presenter/Co-Author), Indiana University Bloomington, troyer@indiana.edu;


Matt T. Trentman (Co-Presenter/Co-Author), University of Notre Dame, mtrentma@nd.edu;


Shannon Speir (Co-Presenter/Co-Author), University of Notre Dame, sspeir@nd.edu;


Jennifer L. Tank (Co-Presenter/Co-Author), University of Notre Dame, tank.1@nd.edu;