The Choptank Coastal SEES project: creating sustainable agricultural watersheds with good water quality
The Choptank Basin in the Chesapeake drainage is experiencing symptoms of eutrophication. N and P concentrations in streams are rising, phytoplankton and turbidity in estuarine surface waters are increasing, and summer dissolved oxygen in estuarine bottom waters is decreasing. The approach of the EPA Chesapeake Bay Program to improve water quality in streams is applications of Best Management Practices (BMPs) on land to reduce transport of N, P, and sediment to estuarine waters. However, few BMPs have been adequately tested at the watershed scale. To address this issue, we are working with stakeholders to install BMPs in four small (8-14 km2) watersheds dominated by agriculture (60-80%) and characterized by high TN concentrations in baseflow (3-6 mg N L-1) and high TP in stormflow (0.1-1 mg P L-1). One watershed is a monitored control, whereas in the other three watersheds we are working with stakeholders to install additional BMPs in three classes (water, soil, and fertilizer management). The goals of the project are to improve the attitudes of stakeholders towards BMPs and water quality, to monitor BMP effects at three spatial scales (watershed, meso-scale, field scale), and to understand the mechanisms of observed N, P, and sediment reductions.
After 1.5 years, we have completed the initial baseline sampling, recruited stakeholders (farmers and residents), and are working with cooperative stakeholders to implement additional BMPs. The agricultural community has responded positively (62% cooperation), whereas the residential community has shown little interest in working with us to date (3% cooperation). In the first year baseline sampling, we showed that much of the N exported from the watershed originates as nitrate in groundwater, primarily from fertilizer applications to corn in the 2-year corn-wheat-soy rotation of agricultural fields, with smaller contributions from septic nitrate. We found that much of the P originates from overland flows over cropland soils with high P concentrations due to manure applications based on N content. Over the next 3.5 years, we will continue to recruit the more reluctant stakeholders, monitor for effects of BMPs from the field to watershed scale, and seek the most cost-effective BMPs to reduce export of N and P from our experimental watersheds relative to the control. The results of this project can be used to inform the current TMDL planning process underway in the Chesapeake Basin.