Effect of temperature on phosphorus flux from anoxic western Lake Erie sediments

The western basin of Lake Erie experiences annual Harmful Algal Blooms (HABs), which degrade water quality, threaten drinking water supplies, and deter recreation. The size of HABs in Lake Erie is highly correlated with the external loading of phosphorus (P) from a major tributary, the Maumee River, during spring and summer months. Because HAB size is largely explained by external loading, the contribution of P from lake sediments (internal loading) is considered to be minimal. However, if lake sediments become warmer and more hypoxic or anoxic in response to climate change, the relative contribution of internal P loading from sediments may become greater. In this study, we examined the potential effect of elevated lake temperatures on internal loading of P under anoxic conditions. Sediment cores were collected during Summer 2014 from 4 locations in the western basin of Lake Erie ranging from highly productive areas near Maumee Bay to less productive offshore areas. Cores were incubated for 4 days under anoxic conditions under different temperatures (10 °C, 20 °C, and 30 °C). P flux varied greatly between temperature treatments and sites. Average P flux at 20 °C and 30 °C were 2 and 14 times higher respectively, than for cores incubated at 10 °C. The site closest to the mouth of the Maumee River had the highest P flux, 10 times higher than the furthest site, and highest total P concentration in the surface sediment, 2 times higher than the furthest site, suggesting a gradient of sediment P characteristics associated with the Maumee River plume. Extrapolating these fluxes across the western basin suggests that with four days of anoxia at 30 °C, lake sediments could contribute ∼415 metric tons of dissolved P, which is equivalent to the springtime dissolved P loading from the Maumee River for 2011, the second-largest HAB on record.