Coastal marshes fringing the Long Island Sound (Connecticut, USA) are dynamic ecosystems positioned at the interface between land and sea, and provide an array of essential ecosystem services to society associated with improved water quality, carbon sequestration, and disturbance regulation. However, these wetlands are increasingly altered by rising seas and invasive species, and have been affected by historical management such as tidal manipulation. We conducted a survey of 20 Connecticut salt marshes (10 tidally restored, 10 unrestricted references) in 2017 to quantify carbon mineralization, denitrification potential, microbial community composition, above and belowground biomass and a suite of sediment characteristics. Carbon density was our only paramenter that differed between unrestricted and tidally restored marshes, but we observed strong differences across vegetation zones, with vegetation being a top predictor of microbial respiration and potential denitrification rates. Based on sea-level rise model projections, the replacement of S. patens by short-form S. alterniflora is expected to be widespread across the Connecticut coastline, decreasing statewide potential denitrification from the low-to-high marsh transitional zone. Our results suggest that changes in vegetation zones can serve as landscape-scale predictors of the rapid changes occurring in salt marshes.

We sampled 20 polyhaline salt marshes (10 reference marshes with no history of restriction or restoration (i.e., "reference sites"), 10 tidally restored) along the north shore of the Long Island Sound in Connecticut (CT), USA. Sites were selected based on their restoration history and presence of target vegetation: Spartina alterniflora (short-form, < 30 cm tall), S. patens, and Phagmites australis. Within each vegetation zone at each site, we sampled three 1-m² plots in mid-August 2017. We visually estimated percent cover of all plants in each plot. From each plot we collected aboveground biomass (from a randomly selected 25 x 25 cm subplot) and three surface soil cores (5-cm diameter to 10-cm depth; 196-cm³ volume); samples were composited by zone and used to estimate above and belowground biomass (C and N content), bulk density, microbial process rates (denitrification potential, carbon mineralization, substrate induced respiration) and a suite of soil chemistry parameters using standarized methods (soil pH and specific electrical conductivity, soil moisture, total C and N, soil organic matter, carbon density, and soil SO4^2-, Cl^-, NH₄⁺  concentrations). 

Please see associated manuscripts (Barry et al. 2021, Ooi et al in revision) for details on data collection and analysis:

Barry, A., Ooi, S.K., Helton, A.M. et al. Vegetation Zonation Predicts Soil Carbon Mineralization and Microbial Communities in Southern New England Salt Marshes. Estuaries and Coasts (2021). https://doi.org/10.1007/s12237-021-00943-0

Plant, microbial process rates, and sediment chemistry are in associated CSV file titled "LISS_2017survey"  Responses with "NA" indicate that no data are available, either due to sample processing error or concentrations below the instuments detection limit. A brief description of the response metric headers and their associated units can be found in the CSV file titled "LISS_2017survey_metadata." Geographic locations of sample points are in associated CSV file titled "LISS_2017survey_locations".  Soil bacterial sequences generated in this study are available in the NCBI sequence read archive under the accession number PRJNA555079. Please see associated manuscripts (Barry et al. 2021, Ooi et al in revision) for details on data collection and analysis:

Barry, A., Ooi, S.K., Helton, A.M. et al. Vegetation Zonation Predicts Soil Carbon Mineralization and Microbial Communities in Southern New England Salt Marshes. Estuaries and Coasts (2021). https://doi.org/10.1007/s12237-021-00943-0