A watershed model predicts the effects of cover crops on river flows, sediment transport, and nutrient loss to Lake Michigan

Abstract

Recent investigations highlight the imperative of diminishing nonpoint nutrient loading to mitigate the prevalence of harmful algal blooms and hypoxic conditions in the Great Lakes region. This study employs the Soil and Water Assessment Tool (SWAT) to conduct a comprehensive assessment of the model’s performance in simulating hydrology, sediment, and nutrient dynamics at the St. Joseph River Basin (SJRB). We used the SWAT model to evaluate the effectiveness of the planting of winter cover crops (WCC) on the magnitude and dynamics of dissolved nutrient and sediment export within the basin. We modeled different WCC scenarios by varying the fraction of the row-crop land to which WCC were planted during the fallow period. We show that although WCC have a minimal effect on streamflow, they substantially reduce total suspended solids (TSS) losses by up to 30 %, demonstrating their efficacy in soil erosion control. In contrast, there were variable effects of WCC on reducing dissolved reactive phosphorus (DRP) and nitrate-N (NO₃-N) losses, with a higher effect on NO₃-N losses than on DRP, resulting in up to a 4 % reduction in DRP and 12 % reduction in NO₃-N losses. This study underscores the versatility of the SWAT model in assessing watershed flow and nutrient and sediment dynamics, offering valuable insights into the quantification and intercomparison of conservation and management interventions that improve water quality in agricultural watersheds in the Great Lakes region.