Science Inventory

A modeling study to determine the contribution of interbasin versus intrabasin phosphorus loads on the southwestern nearshore of Lake Ontario

Citation:

Pauer, J., W. Melendez, T. Hollenhorst, D. Woodruff, AND T. Brown. A modeling study to determine the contribution of interbasin versus intrabasin phosphorus loads on the southwestern nearshore of Lake Ontario. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 48(2):343-358, (2022). https://doi.org/10.1016/j.jglr.2021.09.014

Impact/Purpose:

Elevated phosphorus and nuisance algae such as Cladophora have been persistent environmental concerns in the coastal areas of Lake Ontario. Phosphorus is regarded as one of the drivers of nearshore Cladophora although the link has not been completely established. The Niagara River, which includes most of the Lake Erie interbasin load, is the major contributor of phosphorus to Lake Ontario. Due to the circulation patterns of the lake, this contribution is especially significant in the southwestern (US) nearshore areas west of the Niagara River where Cladophora blooms often occur including Hamlin and Ontario beaches. Here we applied a mathematical model to determine to what extent the Niagara, Genesee and smaller local rivers (intrabasin) impact the nearshore phosphorus concentrations. Our model results suggested that the Niagara River dominates the nearshore region (~20 meter) between its outflow and the Genesee River, which includes Hamlin Beach, while the Genesee River strongly impacts the very nearshore (less than 5 meters) Ontario beach region west of the Genesee River. Smaller rivers have some impact on the very nearshore close to their discharge locations. However, the accuracy of the Niagara River phosphorus load is the limiting factor in making any credible nearshore phosphorus concentration predictions. This is further complicated by insufficient daily phosphorus loads for all the rivers, and the dynamic nature of the lake circulation which can have significant short-term implications. Accurate short temporal scales of phosphorus loads for the Niagara River and other major rivers, credible nearshore lake circulation and frequent nearshore phosphorus measurements will be necessary to better understand existing and future nearshore phosphorus concentrations.

Description:

Elevated phosphorus and nuisance algae such as Cladophora have been persistent environmental concerns in the coastal areas of Lake Ontario. Phosphorus is regarded as one of the drivers of nearshore Cladophora and the most likely mitigation that can be used to control levels of this nuisance algae in the lakes. The Niagara River, carrying the Lake Erie interbasin load, is the major contributor of the overall phosphorus load to Lake Ontario. Due to circulation patterns in the lake, this contribution is especially significant in the southwestern nearshore areas. Here we apply a mathematical model to provide insight into the relative contribution of the Niagara River versus loadings from local rivers (intrabasin loads) on the nearshore phosphorus concentrations in this region. We performed numerical experiments to determine to what extent the Niagara, Genesee and smaller local rivers impact the nearshore (<20 m depth) phosphorus concentrations. Our model results show that the Niagara River dominates the nearshore region between its discharge location and the Genesee River’s mouth, but the Genesee River strongly impacts the nearby Ontario Beach region in the very nearshore (<5 m depth). Smaller rivers have some impact close to their discharge locations. However, uncertainty with the Niagara River phosphorus load is the limiting factor in making any credible nearshore phosphorus predictions. Model accuracy is also impacted by insufficient short time scale phosphorus loads for all of the rivers, the dynamic nature of the lake circulation n shallow nearshore areas, and the simplified assumptions of the model.