Modeling Attenuation of Nitrogen Loads Delivered to Coastal Bays From Ecological Restoration of Cultivated Wetlands

Abstract

Nitrogen (N) pollution is a major threat to coastal ecosystems, worsened by the loss or degradation of natural wetlands, which historically acted as N sinks. In the glacial outwash plain of Southeastern Massachusetts, N pollution primarily from human waste and turf fertilizer has caused coastal eutrophication. Social and economic factors have driven ecological restoration efforts on wetlands previously modified for cranberry farming. These restoration projects offer a chance to enhance ecosystem N attenuation, but the extent and spatial distribution of watershed N loads through these farms remain poorly understood. To address this gap, we adapted a U.S. Geological Survey (USGS) groundwater model to identify wetland contributing areas and model potential N load reduction from the retirement and restoration of 984 cranberry farms. Using modeled contributing areas and data and assumptions about attenuation rates, we estimated N load reductions for farm retirement and restoration scenarios in 24 embayments. For restoration of all farms, median N load reductions were less than 3% in nine embayments, 3%–10% in seven embayments, and 10%–30% in eight embayments. Attenuation was limited by the contributing area intercepted by cranberry farms, ranging from 1% to 75% of watershed areas. Our model serves as a screening tool to identify farms with high potential to reduce watershed N loads, but more field monitoring is needed to refine N attenuation estimates in former cranberry wetlands. This work highlights the critical linkage between wetlands, development patterns, and ecosystem health, emphasizing the need for sustainable resource management approaches.