High-resolution modeling for development of nearshore ecosystem objectives in eastern Lake Erie

We develop a high-resolution (600 m) three-dimensional water quality model for Lake Erie capable of resolving predominant physical processes to study nutrient dynamics, with a particular emphasis on the northern nearshore region of Lake Erie's eastern basin. The lake model output in conjunction with the Cladophora growth model (CGM) is used to predict Cladophora growth. The models were validated using extensive nearshore water quality, Cladophora biomass and tissue phosphorus measurements collected during April-September of 2013. Together, the models were used to evaluate the response of nearshore phosphorus concentrations and Cladophora growth due to changes in external phosphorus loading. The water quality model described here was able to resolve the nearshore dominant physical processes that occur within the Cladophora habitat zone (0-8 m depth) and revealed that phosphorus concentrations in the nearshore are governed by a combination of local inputs from the Grand River and exchange with the hypolimnion. Frequent upwelling events driven by favorable winds of 5-10 days period dominated nearshore-offshore exchanges, and in some years (e.g., 2013) can potentially add significant phosphorus (as soluble reactive phosphorus; SRP) to the nearshore during the spring; however, in other years (e.g., 2008), their effects are less important. The model demonstrates that the offshore supply of phosphorus via upwelling is of ecological significance with respect to Cladophora and that both lake-wide and local action may be required to address nuisance blooms of Cladophora in Lake Erie.