Modeling phosphorus loss reduction strategies from the international St. Clair-Detroit River system watershed

Increased nutrient inputs have increased globally and have led to enhanced algal production, eutrophication, and increases in the number and sizes of harmful algal blooms and low oxygen zones. Lake Erie, the southernmost, shallowest, and most productive of the Great Lakes, has undergone recent re-eutrophication resulting in increases in toxic algal blooms and hypoxic extent due to excessive phosphorus loads, mainly from the Maumee and the St. Clair-Detroit River System (SCDRS) watersheds. Here, SCRDS watershed was assessed to identify potential pathways for phosphorus load reduction strategies such as nutrient management (rate reduction, subsurface application, and change in application timing of fertilizers), filter strips, wetlands, cover crops, and other urban management practices. Combinations of these individual management strategies were used to develop five bundle scenarios. These bundles were then assessed for their phosphorus load reduction efficiencies using the Soil and Water Assessment Tool (SWAT) model. Results show that, though no single management practices can effectively reduce the required phosphorus reduction, there are multiple bundle scenario pathways which could achieve the reduction goal set by the agreement between US and Canada. In this watershed, bundles that involve wetlands or subsurface placement of fertilizers were found to be more effective. The approach used in this analysis can also be used in any coastal watershed nutrient load reduction assessment.