Spatial Elevation Dynamics and Carbon Sequestration Variability Within Sprague Marsh, Phippsburg, Maine

The purpose of this study was to assess the elevation dynamics and carbon sequestration rates in Sprague Marsh in Phippsburg, Maine. Sediment Elevation Tables (SETs) were used to obtain vertical sediment accretion, subsidence, and surface elevation change at four locations on the marsh over a 6-year monitoring period (2014-2020). Lead-based horizons were identified on sediment cores obtained at each SET in order to calculate sedimentation rates over approximately 50 years. Loss on Ignition (%LOI) and Dry Bulk Density (DBD) values were measured on each core and used to calculate carbon density values and carbon sequestration rates. Data analysis from the SETs indicates that the highest subsidence rate values occur at the southernmost (SET 1: -1.9 mm/yr) and northernmost (SET 4: -1.3 mm/yr) locations on the marsh. The vertical accretion rates increase consistently from southernmost to northernmost points on the marsh likely due to increased organic matter deposition (%LOI). The average lead-based sedimentation rate ranges from 1.7 to 3.7 mm/yr. Carbon sequestration rates increase progressively from south to north, ranging between 70 and 170 gC/ m2*yr. The compilation of the data sets suggests that the southern end of Sprague Marsh is experiencing lower rates of vertical sediment accretion, higher rates of subsidence, and diminished ecosystem functioning (carbon sequestration). Comparison of elevation dynamics with projected sea level rise rates in Maine suggest that the southern end of Sprague Marsh is more vulnerable to inundation due to sea level rise than other examined areas in the marsh