Rapid assessment of biogeochemical ecosystem services in restored salt marshes in New York City

Salt marsh restoration can deliver multiple socio‐economic and ecological benefits; however, there is a strong need for standardized monitoring and assessment methodologies to assess the effectiveness of these restorations. This study aimed to (1) gather baseline data and evaluate the ecosystem services related to nitrogen removal by denitrification provided by restored salt marshes in New York City, and (2) evaluate the ability of a statewide assessment protocol to encompass this biogeochemical function. We made measurements of denitrification potential in sediment samples from three restored and one reference salt marsh sites. The restored sites supported denitrification potential equivalent to the reference wetland, and the oldest restored sites had the highest and the youngest sites had the lowest potential. However, none of the variables included in the statewide assessment protocol (elevation, substrate, algae, and plant cover) encompassed or predicted this potential. Denitrification potential was significantly positively correlated with carbon cycle variables (soil organic matter [SOM] content, microbial respiration) and significantly negatively correlated with nitrogen cycle variables (potential net nitrogen mineralization and potential net nitrification). The negative correlations with nitrogen cycle processes suggest that denitrification is an important “sink” for reactive nitrogen in these wetlands, and the positive correlations with carbon cycle variables suggest that restoration should focus on facilitating plant growth and organic matter accumulation. If assessments are to include biogeochemical processes such as denitrification, they may need to incorporate indicators of belowground variables such as SOM content.