Using Constructed Wetland-Pond Systems to Treat Agricultural Runoff: A Watershed Perspective

ABSTRACT

Long and Cross Lakes in the St. John Valley watershed of northern Maine have exhibited chronic algae blooms in past years. Survey data and modeling determined agricultural runoff to be die main source of phosphorus and sediments in both watersheds. “Nutrient/Sediment Control Systems” (NSCS) are being used to treat runoff from target subwatersheds. The systems consist of a sedimentation basin, grass filter strip, wetland, and detention pond in series. Annual removal efficiencies for one system were 85–88% for total phosphorus and 96–97% for total suspended solids. Seasonal removals varied considerably, with spring flows exporting more phosphorus and sediment from the system than was imported. Phosphorus loadings to Long Lake will be reduced between 10–33% with 20 NSCS and diversion of municipal wastewater effluent to a nearby river.

Key Words:

• phosphorus
• agriculture
• export coefficients
• constructed wetlands
• non-point source
• watershed management