The Fate and Bioavailability of Resuspended Phosphorus in Lake Erie's Western Basin

Abstract

Lake Erie regularly experiences harmful algal blooms (HABs) that occur as a result of eutrophication from excess phosphorus (P) inputs. Due to this history of eutrophication, there is a large pool of P in the sediment of Lake Erie. Given the lake’s shallow western basin, and large fetch, this sediment P is regularly physically mixed into the water column. In other shallow lakes, this resuspended P is a source of bioavailable P (BAP) and contributes to primary production in the water column. However, the fate and bioavailability of this mechanically resuspended sediment P in Lake Erie has not previously been quantified. To investigate this, I took sediment cores harvested from Lake Erie’s western basin and increased the shear stress to resuspend sediment into the water column. I then took this resuspended water and diluted it with overlying lake water to simulate in-lake dilution of suspended sediment. The water was mixed for 48 hours in darkness while I took samples for nine functional fractions of P at regular intervals. Additionally, I investigated if small changes in pH affect the release of bioavailable P from the sediment by artificially lowering the pH of the overlying water prior to adding the resuspended water in duplicate units. I found that the majority of resuspended phosphorus is in particulate forms, and that a smaller percentage of these forms is bioavailable than in the Maumee River. Additionally, I found that total concentrations of P forms were stable over 48 hours regardless of the sediment resuspension, suggesting that sorption-desorption processes do not play a large role in changing the net bioavailability of P. I estimated that a mild resuspension event could result in a release of 2.782-8.381 mg/m2 of DRP, which would not be removed from the water column by sorption processes. This is larger than the daily release in the western basin from diffusive fluxes and represents an estimated 15.21% of DRP in the water column. These findings are important for determining how sediment resuspension may affect BAP in the water column, and their potential contributions to primary production in the western basin.