Modeling attenuation of nitrogen loads delivered to coastal bays from ecological restoration of cultivated wetlands

Authors: Wiegman, Adrian; Kennedy, Casey; NEILL, CHRIS - Woodwell Climate Research Center; JAKUBA, RACHEL - Consultant; Welsh, Molly; Millar, David; Buda, Anthony

Submitted to: Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: A watershed is defined as the contributing area that drains through a specific point on the landscape. Studying watersheds is key to water resource management. The contributing area of watersheds in many regions can be delineated using land surface elevation, following the principle that water flows downhill. This is not necessarily the case in the sandy glacial outwash plains that make up much of the cranberry producing region of southeastern Massachusetts. Leveraging existing USGS groundwater models, we created a tool that can be used to quickly estimate the contributing area of cranberry farms in Southeastern Massachusetts. We used this tool to estimate which cranberry farms intercepted the greatest amount of nitrogen from sources within their farm’s watershed. Farms that can document that they receive high watershed nitrate loads may have the opportunity for financial assistance to enroll certain cranberry beds into wetland restoration programs that enhance the capture and removal of N from watersheds. Potential future applications of this study for farmers include enhanced water use efficiency, soil moisture and soil fertility management, awareness and mitigation of waterborne pollutants, and solutions for cranberry farm renovation and or retirement.

Technical Abstract: Water quality is deteriorating in estuaries of Southeastern Massachusetts, USA, primarily due to nitrogen (N) overloading from residential septic systems. Ecological restoration of wetlands on retired cranberry farms represents an opportunity to attenuate N pollution and enhance conservation goals. However, because the region’s hydrology is dominated by groundwater processes, the magnitude and spatial distribution of watershed N loads passing through cranberry farms are poorly understood. We adapted a U.S. Geological Survey (USGS) groundwater model to delineate watershed contributing areas and model potential N load reductions resulting from retirement and restoration of 942 cranberry farms representing two-thirds of the production area in Massachusetts. Variability in contributing areas produced a 10,000-fold range N loads delivered from watersheds to cranberry farms. We estimated the watershed N load reductions for farm retirement and restoration scenarios in 24 bays. For a scenario where all cranberry farms were restored, median N load reductions amounted to =3% in 9 bays, from >3% to <10% in 7 bays, and from =10% to =30% in 8 bays. Potential N reductions were limited primarily by the contributing area that cranberry farms intercepted, which ranged from <1% to 75% across the 24 embayments. Our work demonstrates that across portions of the coast there is substantial potential to reduce nutrient loading through wetland restoration Our model can be used as a screening tool identify retired cranberry farms that have high potential attenuate watershed N loads. More research is needed to estimate nutrient removal efficiencies before and after wetland restoration.