Diffusive phosphorus fluxes in relation to the sediment phosphorus profile in Big Traverse Bay, Lake of the Woods

Abstract

ABSTRACT James WF. 2017. Diffusive phosphorus fluxes in relation to the sediment phosphorus profile in Big Traverse Bay, Lake of the Woods. Lake Reserv Manage. 33: 360–368. The role of sediment diffusive phosphorus (P) flux in the P economy and cyanobacteria blooms in Lake of the Woods (LOW) is needed to establish total maximum daily load requirements. I quantified aerobic and anaerobic diffusive P fluxes as a function of temperature to estimate annual internal P loading in Big Traverse Bay of LOW. Replicate cores were collected seasonally and incubated at 5, 11, 18, and 25 C for rate determination. In addition, a sediment core collected in February 2015 was sectioned to analyze sediment P fractions and characterize P burial. Aerobic and anaerobic diffusive P fluxes varied nonlinearly with temperature. Rates were lowest under aerobic conditions, ranging between 0.05 and 0.36 mg/m2/d, and much higher under anaerobic conditions, ranging between 0.77 and 16.78 mg/m2/d, at 5 and 25 C, respectively. The annual diffusive P flux contribution to Big Traverse was 38 and 1172 mg/m2/yr under aerobic and anaerobic conditions, respectively, based on mean monthly bottom temperatures in 2015. The sediment vertical P profile exhibited a distinct surface maximum, suggesting an imbalance between gross deposition and burial. Assuming a constant sedimentation rate, potential annual internal P loading was higher at 246 mg/m2/yr compared to the annual aerobic diffusive P flux, suggesting anaerobic diffusive P flux and other unmeasured internal P loading processes contributed to the P budget. Low P burial efficiency and maintenance of a surface P bulge may be due to cyanobacteria-mediated biological uptake of sediment P, recycling, and redeposition to the sediment surface.