IMPACT OF A TIDAL RESTRICTION ON CARBON DYNAMICS AND SEDIMENTATION IN THE JONES CREEK SALT MARSH, SCARBOROUGH, MAINE, USA

Healthy salt marshes are among the most productive ecosystems on the planet. However, tidal restrictions can degrade a salt marsh, resulting in subsidence, decreased CO₂ sequestration, and carbon outwelling, compromising the system’s efficacy as a carbon sink. This study examines carbon stocks and sequestration, greenhouse gas emissions, pore water salinity, and sedimentation upstream and downstream of a tidal restriction in the Jones Creek Marsh, Scarborough, Maine, USA. Carbon stocks were assessed by measuring loss on ignition in sediment cores. The average carbon density in the upper 100 cm was 0.025 ∓ 0.015 g¹cm^-3 and 0.035 ∓ 0.008 g¹cm^-3 upstream and downstream of the restrictions, respectively, indicating significantly lower carbon stocks upstream of the restriction (t(59) = -4.24). Greenhouse gas fluxes at the marsh surface were measured with a LI-COR-7810 Trace Gas Analyzer in June and in July. Methane emissions varied significantly across the study area, with a high of 24.5 μmol¹m^-2hr^-1 downstream of the restriction in late June, 2023, and a high of 88.2 μmol¹m^-2hr^-1 upstream of the restriction in July, 2023, seemingly independent of pore water salinity. Sedimentation rates were estimated by analyzing lead concentration at depth and were found to be comparable on either side of the restriction, and sedimentation traps showed inconsistent mass with distance from the stream channel. A multidimensional analysis of marsh biogeochemistry and hydrological history such as that presented in this paper is necessary to assess carbon dynamics in a highly complex system.