Chronic nutrient loading from Lake Erie affecting water quality and nuisance algae on the St. Catharines shores of Lake Ontario

Water quality and lake circulation in the nearshore of Lake Ontario bordering the city of St. Catharines were examined from May to October 2013 to interpret factors impacting water resources and contributing to nuisance algae. Our findings suggest that loadings from eastern Lake Erie via Twelve Mile Creek and the Welland Canal are a primary driver of variability in nearshore water quality, creating mixing areas enriched in particulate and dissolved phosphorus and turbidity. Impingement of the Niagara River plume and regional lake circulation also impact water quality conditions. Quantitative benthic sampling revealed that Cladophora was abundant to lake depths of about six meters, which is shallower than other nearshore areas of Lake Ontario. Estimates of PAR intensity at the lakebed interpolated over the study area suggest that light limitation counteracts the stimulation of Cladophora growth attributable to elevated dissolved phosphorus over the discharge mixing areas. No evidence was found that the chronic loading of phosphorus in the area resulted in a higher prevalence of Cladophora compared with other areas of the lake. The abundance of dreissenid mussels, reaching 4760 individuals/m2, was not correlated with water chemistry features or biomass of Cladophora. Interactions between dreissenids and Cladophora may be muted in the area due to overriding physical factors which appear to limit Cladophora to shallow depths and mussels to deeper waters.