CARBON DYNAMICS UPSTREAM AND DOWNSTREAM OF A TIDAL RESTRICTION, SPURWINK MARSH, CAPE ELIZABETH, MAINE

A salt marsh’s ability to sequester carbon may be inhibited by tidal restrictions. This study examines carbon dynamics and sedimentation upstream and downstream of a tidal restriction on Spurwink Marsh, Cape Elizabeth, Maine. Sediment core carbon and isotope analysis, monthly LICOR greenhouse gas flux data, sedimentation rates, and stream channel level hydrology data were used to identify restriction status and carbon dynamics over short and long timescales. The average carbon density in the upper 100 cm of sediment cores was 0.044 ± 0.009 gC/cm³ (n = 3) and 0.048 ± 0.008 gC/cm³ (n = 3) upstream and downstream of the restriction, respectively. CH₄ emissions were highest along marsh margins (ranging between 44 and 138 nmol CH₄/sec m²) where fresh groundwater inputs decrease pore water salinity and suppress methanogenesis within the sediments. The tidal range is ~ 1 m and 2 m on the upstream and downstream side of the restriction, respectively. Core isotope data indicate changes in vegetation and estuarine environment throughout the period of deposition. These data present important information to consider when thinking about the climate benefits of restoration.