Abstract
Salt marsh ecosystems are critical to coastal communities, and understanding the biogeochemistry of these marshes is vital for restoration efforts in altered and degraded systems. Coastal marshes provide numerous ecosystem services such as water purification, flood protection, carbon storage, high biodiversity and productivity, and aesthetic value. Nonquitt Marsh in Dartmouth, MA was one of the largest tidally occluded salt marshes in Buzzards Bay, and was cut off from regular tidal exchange for around 70 years before restoration began in 2013. The two primary goals of this study were 1) to assess overall marsh vegetation recolonization; and 2) to investigate the effects of tidal regime, porewater chemistry, and sediment elevation and characteristics on the growth of transplanted Spartina alterniflora. Marsh recolonization was measured via marsh-wide vegetation surveys using a RTK GPS and a compact LiDAR mounted on a drone. Overall, area colonized by S. alterniflora experienced a 29-fold increase relative to pre-restoration values, mainly due to upland expansion, whereas low elevation areas remained largely unchanged. To determine the physical and biogeochemical factors affecting recolonization (or lack thereof) of S. alterniflora into the mudflat, a mesocosm experiment was conducted in the mudflat region to simulate 3 different wetting/drying regimes and 2 different sediment types. Plots were elevated by either 0 cm, 10 cm or 28 cm, and consisted of native mudflat sediment, with or without sand amendment from the marsh. Results showed high survival across all elevations and sediment types, higher belowground biomass in the 28 cm elevated plots and the sand addition plots, and higher aboveground biomass in sand addition plots. Results of the marsh-wide surveys suggest that further management actions may be required to facilitate recolonization of the mudflat region. Results of the mesocosm experiments suggest that further recolonization of the mudflat could be aided by direct transplant of S. alterniflora either with or without sediment addition.