5-2 Efficacy of Novel Restoration Methods in Enhancing Salt Marsh Resilience

Session: Nearshore and Estuarine Research: Dynamics and Future Resiliency in the Coastal Zone (Posters)

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Salt marshes are vegetated coastal wetlands which protect and sustain coastal regions through essential ecosystem functions. They provide storm protection, blue carbon storage, and marine fishery habitat, yet their existence is threatened by human degradation and sea level rise. Humans historically dug linear drainage ditches in salt marshes for agricultural and mosquito control purposes, and they are still etched in marshes across the Northeastern US today. Excessive drainage of salt marshes lowers the water table, causing organic material in the soil to decompose and release carbon dioxide (CO₂), leading to soil compaction and marsh elevation loss. Ditch remediation is a novel restoration technique designed to combat marsh loss in the face of accelerating sea level rise. In this practice, ditches are progressively filled in with thatch to effectively “turn off” excess drainage channels created by humans, thereby restoring water tables to reduce soil decomposition and enhance marsh resilience. However, the efficacy and impacts of this emerging restoration strategy have not yet been researched. 

This study offers a preliminary analysis of ditch remediation efficacy at two recently treated sites in the Great Marsh, Ipswich, MA through comparing how remediated and non-remediated ditches differ in impacts to marsh hydrology and net CO₂ exchange. We installed groundwater monitoring wells to record multi-seasonal water level fluctuations along transects running perpendicular to remediated and non-remediated ditches, capturing the hydraulic gradient across the marsh platform. Along the same transects, we deployed gas flux chambers to measure CO₂ respiration and uptake during fall senescence when photosynthesis impacts are minimal. Preliminary data suggests that the magnitude of water level fluctuations, the thickness of the unsaturated zone (the distance from the marsh surface to the water table), and CO₂ respiration are higher proximal to ditches, without a distinct difference between remediated and non-remediated ditches. Future work will investigate mature ditch remediation sites to assess how success metrics become more prevalent as time post-restoration increases. We apply these findings to recommend where and how ditch remediation projects should be implemented to maximize success and improve health in marshes with a high density of ditches.

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