DISAPPEARING SEDIMENTS: THE COST OF CLIMATE CHANGE TO MASSACHUSETTS' BEACHES

This project is a continuation of research that began in the summer of 2009, when the principal investigator began gathering data in an attempt determine the effects of climate change on the Massachusetts coastline. One factor contributing to increased erosion is frequent and severe storm activity, which is predicted to become more common as global temperatures rise. The erosional effects of these storms can be detected by collecting sand samples from beaches and sorting them to determine grain size distribution. Storms are associated with coarsening of beaches, as rapidly moving water tends to transport finer sediments from the shoreline area and deposit them offshore, leaving larger grains behind. A second indicator of erosion is a narrowing of beaches, as rising sea levels gradually submerge portions of gently sloping shorelines.

In 2009, 30 different sites were chosen North of Cape Cod, including barrier islands, mainland coasts exposed to open ocean, and beaches partially shielded by offshore islands, spits, or baymouth bars. Sites varied by degrees of coastal development, from beaches with mostly intact dune and lagoon systems, to those punctuated by seawalls, jetties, and roads and buildings. All locations were recorded using a GPS unit, which was then used to locate the sites on subsequent visits. Once per month from June through August 2009 and 2010, three sediment samples were taken from the foreshore of each site using a corer, and the distance from the high tide line to a sea wall or dunes was measured. Samples were then brought back to the university lab, where they were soaked in sodium hexametaphosphate, which is used as a dispersing agent to separate small particles. They were then dried and sorted by grain size in a graduated sieve. The data were then compiled to look for correlations between changing distribution of grain sizes over time, changes in beach width over time, and frequency of storms.

Our analysis of the data from this year indicated that many of the beaches had become narrower since last year, sometimes by several meters, due to erosion from sea level rise and/or increased storm activity. This observation was supported by additional coarsening of sediments at those beaches. More long-term trends will require the collection of additional data over the coming years.