A Sediment and Blue Carbon Budget for Boston Harbor, MA - Melissa Rymaszewski Senior Thesis defense

Abstract: Recent concerns suggest that human activities are starving coastal habitats of the sediment inputs they need to build elevation against sea level rise, which could cause loss of recreational beaches and coastal wetlands. In order to assess the resilience of Boston, MA’s beaches and marshes to the impacts of climate change, we compiled reports and geospatial calculations to create a sediment budget for Boston Harbor. We considered bluff erosion and rivers as the main imports, and dredging as the main export. Some dredged material is re-imported to the system via beach nourishment. We found that exports exceed imports by 340%, resulting in a net sediment deficit of ~5.6E+5 Mg/yr. We also quantified blue carbon storage for salt marshes and marine muds using carbon density concentrations and areal calculations. Boston Harbor’s subtidal muds store 1.4E+6 MgC, which is 7x the amount of carbon stored in adjacent salt marshes, and 20% of that stored in salt marshes across the entire state. These findings have implications for how marine sediment is managed after dredging and assessed for carbon stocks.