LAUSR

Abstract Continued re-eutrophication of Lake Erie has led to the updated 2012 Great Lakes Water Quality Agreement (fully enacted in 2016) that established new binational phosphorus load reduction of 40% from 2008 baseline loading rates. Nonpoint source pollution is the leading cause of water impairment in agricultural watersheds; however, the water quality can be improved by implementing various BMPs for control of erosion and nutrient loss from watersheds. The Grand River watershed (GRW) occupies about 6800 km2 and is an important agricultural area in Southern Ontario. Changes in land use over the past century in the GRW have led to altered hydrology and greater export of sediment and nutrient loads into Lake Erie. The objective of this study was to investigate the impact of various BMPs in reducing sediment and phosphorus loading rates on various spatial and temporal scales in the watershed using SWAT for the years 2001–2010. The baseline sediment and P loading at Dunnville, prior to the Grand River’s discharge to Lake Erie, were predicted to be 2 × 105 tonnes y−1 and 2 × 105 kg y−1, respectively. Different source, transport and water body treatment BMPs were simulated. With respect to reducing sediment and P loading into Lake Erie, implementing wide buffer strips resulted in a decrease of 23% and 50%, respectively. Stabilizing channel banks resulted in reduced sediment and P loading of 38% and 36%, while grassed waterways resulted in reductions of 15% and 17%, respectively.