Collection, analysis, and age-dating of sediment cores from salt marshes on the south shore of Cape Cod, Massachusetts, from 2013 through 2014

The accretion history of fringing salt marshes located on the south shore of Cape Cod is reconstructed from sediment cores collected in low and high marsh vegetation zones. These marshes are micro-tidal, with a mean tidal range of 0.442 m. Their location within protected embayments and the absence of large rivers results in minimal sediment supply and a dominance of organic matter contributions to sediment peat. Age models based on 210-lead and 137-cesium are constructed to evaluate how vertical accretion and carbon burial rates have changed over the past century. The continuous rate of supply age model was used to age date 11 cores (10 low marsh and 1 high marsh) across four salt marshes. Both vertical accretion rates and carbon burial increase from 1900 to 2013/14, the years of collection. Elevation of the marsh surface was measured with RTK-GPS to evaluate where the marsh falls within the current tidal frame. The historic marsh surface elevation was then reconstructed using the calculated age of each depth interval and its elevation, assuming that elevations within this shallow zone (less than 30 cm) have been preserved for the past century.