Serghei Bocaniov,Philippe Van Cappellen (2022). Long-term (2003-2016) phosphorus net mass-balance analysis: Can in-lake processes explain the re-eutrophication of Lake Erie?. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

While the trophic states of lakes are tightly coupled to the external nutrient loadings from their watersheds, in-lake processes can play an important role, not only by modulating the efficiency of nutrient recycling but also by supplying additional amounts of nutrients through coastal erosion and sediment resuspension. These in-lake processes can relax the watershed-lake coupling, especially in situations when the external nutrient loadings decline. Water quality management of lakes therefore requires a more integrated lake-watershed approach that builds on an improved understanding of in-lake processes that can potentially attenuate or even reverse the water quality improvements expected from watershed nutrient abatement measures. An exemplar are the significant efforts over many decades to reduce the external phosphorus (P) loads to Lake Erie (Canada-USA), one of the lower Laurentian Great Lakes. Despite these reductions in external loading, the lake has been showing symptoms of accelerated re-eutrophication, especially the increasing frequency, severity, and spatial extent of cyanobacterial harmful algal blooms, hypolimnetic hypoxia, and outbreaks of nuisance benthic algae. To help unravel the possible drivers of Lake Erie’s re-eutrophication, we conducted a detailed analysis of the long-term water and P mass balances for the entire lake, as well as for each of its three distinct basins. We show that the known external inputs (from upstream Lake Huron, the lake’s watershed, and atmospheric deposition) and losses (sediment burial and lake outflow) are not in balance: the losses significantly exceed the external inputs. To maintain the balance between external inputs and losses there must be large additional, but currently unidentified, fluxes of P generated within the lake. In our presentation, we will present the first quantitative characterization of these additional supply fluxes and propose the in-lake processes responsible for the fluxes.

AOSM2022 First Author: Serghei Bocaniov, University of Waterloo, Ontario Additional Authors: Philippe Van Cappellen, University of Waterloo, Ontario