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Adaptive Management Essential to Long-Term Nitrogen Removal Success in an Urban Tidal Wetland
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Alldred, Mary, Zarnoch, Chester, Fuss, Colin
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Spring 2025
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Surface waters in New York City (NYC) are polluted by billions of gallons of untreated wastewater annually from combined sewage overflows (CSOs), contributing to nutrient pollution and poor water quality. Coastal wetlands have the ability to improve water quality and reduce the risk of flooding, but NYC has lost over 85% of its wetlands to urban development. The loss of coastal wetlands in NYC has led to an increase in vulnerability to flooding from coastal storms, sea level rise, and pollution of local waterways. New nature-based infrastructure for restoring ecosystem services and stabilizing NYC’s shorelines uses natural materials such as marsh plants, shell bags, and rocks to attenuate wave energy, provide buffers, and remove pollutants from the water. Here we synthesize the results of a multi-year study of the Sherman Creek Living Shoreline in New York, NY. We conducted studies of shoreline habitat types pre- (2019) and post- restoration (2020), following a mussel-addition experiment (2021), and following the implementation of enhanced goose-exclusion techniques (2023). In each year, we collected sediment cores from shoreline habitat types (mudflat, rip-rap, existing marsh, new marsh) and performed continuous-flow incubations to quantify dissolved gas and nutrient fluxes, with the goal of comparing rates of nitrogen removal among habitat types. We also assessed above- and belowground biomass and sediment characteristics of each habitat. We found greater sediment organic content in the existing marsh, but similar rates of nitrogen removal via denitrification in the existing and newly restored marsh. Adding mussels to the marsh plants increased nitrogen removal. Post goose-exclusion, we saw plant growth similar to that of the existing marsh, showing that managing species interactions can have a positive effect on the benefits provided by living shorelines.