COMPARING URBAN AND AGRICULTURAL NUTRIENT MASS FLUX INTO THE LOWER GREAT LAKES

Harmful algal blooms have historically been a significant problem in the Lower Great Lakes, and are currently an issue in Lake Erie, due to excessive nutrient loading from streams. Sources of two major nutrients, nitrogen and phosphorous, occur in both agricultural and urban-dominated watersheds from fertilizers, wastewater treatment plants, and sewage overflow. This study compares nutrient efflux from two streams with contrasting land uses that discharge to the Lower Great Lakes near Buffalo, NY; one is predominantly agricultural land and the other originates in the City of Buffalo. The streams were sampled on a weekly basis during the summer, 2015 for nutrients, major anions, and field parameters. Continuous water discharge data was obtained from stage measurements by creating a rating curve for one stream and by adopting continuous flow measurements from the USGS for the other stream. Additionally, diurnal sampling was conducted at each site under baseflow conditions to evaluate daily nutrient processing patterns in each stream. The nitrate mass flux was consistently greater in the agricultural-dominated watershed than in the urban-dominated watershed by a factor of ten or more. The phosphate mass flux showed this same pattern, but the nitrate concentrations and mass fluxes were at least ten times greater than those of phosphate. Finally, analysis was done to determine the relationship between nutrient concentrations and discharge in order to calculate total mass flux for nitrate and phosphate in each stream for the summer months. Although only two stream segments were tested, this research suggests that agricultural-dominated watersheds contribute more to nutrient contamination in the Lower Great Lakes than urban-dominated watersheds in the summer.