Saginaw Bay is a eutrophic embayment of Lake Huron with excess nutrient loading from a largely agricultural watershed. Despite ongoing efforts to reduce nutrient loads, phosphorus levels remain elevated. We assessed the potential importance of internal phosphorus loading; focusing on influences of sediment type, oxygen levels and dreissenid mussels on sediment phosphorus fluxes. Sediment cores were collected from three regions of the bay, and assessed for carbon, nutrients, porosity and bulk density. These cores were utilized in two separate incubation experiments evaluating: 1) sediment P flux under aerobic and anaerobic conditions, and 2) nutrient remineralization from mussel biodeposits when added to the surface of the cores.
Results/Conclusions Anaerobic treatments exhibited significantly higher P release back to overlying waters (p < 0.05) when compared to aerobic treatments. This release was greatest in sediments collected from the depositional zone. These results may indicate that contributions of P from sediments in Saginaw Bay are controlled by episodic anoxic events in this region. Results from the second experiment found no P release from dreissenid biodeposits in the timeframe of the study. This may raise further questions of remineralization rates of biodeposits when assessing loading effects.
