Nutrient Variability and Sediment Contribution Along a Mixed Land-Use within Sturgeon Creek- Lake Erie Watershed

Considerable research has emerged over the past two decades investigating the resurgence of harmful algal blooms within Lake Erie. Improving the status of water quality resulting from nutrient pollution remains a top priority, particularly for areas prone to nutrient release within watersheds of the western Lake Erie basin. In this study, a nutrient impacted watershed in southwestern Ontario is chosen to investigate nutrient transport, sinks and sources along a river-lake continuum. To identify sources of nutrients in this mixed land use watershed, water samples were collected from upstream to nearshore of Lake Erie for nutrient (total phosphorus, soluble reactive phosphorus, nitrate) and dual nitrate isotopic analyses in 2019-2021. Riverbed sediment samples along the transect were taken for equilibrium phosphorus concentration (EPC0) determination to assess phosphorus retention capacity. Our results show values of δ18O-NO3- (with an average of +18.8‰) found in this watershed are appreciably higher than other rivers under urban and agricultural influence within the Great Lakes. It is further suggested that sources of nitrate within the watershed are likely influenced by at least two end members- inorganic nitrate fertiliser and organic/manure fertiliser. Additionally, large spatial variation in concentrations of nutrients and sediment EPC0 was observed along the transect. Segments where the concentrations of nutrients accumulated suggest limited phosphorus retention capacity, that may be due to legacy phosphorus from adjacent sources. Inorganic nitrate and/or nitrate from nitrification incorporated with rainwater isotopic signatures may also contribute to elevated concentrations of nitrate in the area. With additional land use information, our findings suggest a combination of potential influences from urban expansion and greenhouse operations, particularly for dissolved forms of nutrients, which warrants more studies for source delineation. The outcomes of this study, has identified critical points of nutrient load, provides foundation and future direction for devising effective watershed nutrient management plan