Internal phosphorus loading in Lake of the Woods

Session: Nutrient Sources, Transport, and Internal Cycling (2)

Md Samrat Alam, University of Toronto, samrat.alam@utoronto.ca
Barthhod Blandine, University of Toronto, blandinebarthod@gmail.com
Jiying Li, University of Minnesota Duluth, lixx0590@d.umn.edu
Arthur Zastepa, Environment and Climate Change Canada, arthur.zastepa@canada.ca
Maria Dittrich, University of Toronto Scarborough, mdittrich@utsc.utoronto.ca

Abstract

Lake of the Woods (LOW), an important source of freshwater, has suffered from excessive cyanobacterial and harmful algal blooms (cHABs). One possible driving force for cHABs is release of limiting nutrient phosphorus (P) from sediments (internal loading). With the large LOW basins and its strong spatial variability, it is critical to understand the dynamics of internal P loading in order to improve P management strategies. Our goal is to quantify P internal loading, its contribution to P budget of LOW, and investigate the mechanistic controls. We quantified sediment geochemistry and sediment-water exchanges of P at four locations in LOW. Our results showed that the diffusive fluxes of P ranged between -54 and 49 µmol m^-2 d^-1, and was greater under anaerobic conditions. Long-term net P release rates were between 0.21 and 9.96 mg m^-2d^-1, with higher values in anaerobic sediments. Control of P release by oxygen is likely due to the redox-sensitive Fe-P coupling. Iron-oxides bound-P represented the largest portion of solid-P, and the P mobilization was associated with reductive dissolution of redox-sensitive compounds such as iron hydroxides.