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SFS Annual Meeting

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DENTRIFICATION AND NITROGEN FIXATION – DO THEY OCCUR IN LAKE SUPERIOR TRIBUTARIES?

Lake Superior receives inputs from approximately 2800 tributaries whose periphyton are limited by both nitrogen and phosphorus. Nitrogen can be rapidly taken up in these tributaries during all seasons of the year, yet we know little about the specific processes that contribute to this instream uptake. We measured denitrification, nitrogen fixation and N2 flux at 7 locations in 6 Lake Superior tributaries in the Keweenaw Peninsula region of the Upper Peninsula of Michigan in June to August 2016. Total nitrogen (TN) concentrations across all sites averaged 0.65 mg/L and nitrate-N concentrations averaged 0.37 mg/L. We found that rates of nitrogen fixation measured using acetylene reduction were low at all sites. Rates of denitrification measured using acetylene block ranged from zero in two streams, up to 0.5-10 mg N/m2/hr on rock and/or sediment substrates in four streams. Together, our results suggest that denitrification may be an important mechanism that removes N from Lake Superior tributaries as they transport nutrients from watersheds to Lake Superior.

Andrea Norton (Primary Presenter/Author), Michigan Technological University, annorton@mtu.edu;


Kevin Nevorski (Co-Presenter/Co-Author), Michigan Technological University, kcnevors@mtu.edu;


Amy Marcarelli (Co-Presenter/Co-Author), Michigan Technological University, ammarcar@mtu.edu;