The impacts of climate variability and anthropogenic activities on salt marsh accretion and loss on Long Island

This thesis examines how Long Island salt marshes responded to the environmental changes that occurred on Long Island during the past century. Five sites were studied: the Nissequogue River, Hubbard County Park, Carmans River, Hempstead Bay and Jamaica Bay. Each salt marsh exists in a different physiographic environment, which critically affects the history of natural and anthropogenic inputs. The physiography influences the manner in which these marshes are influenced climate variability and human impacts. Accretion in the Nissequogue River, a high tidal range environment, responds mostly to the long-term change in annual mean sea level sea level. In sites with decreased tidal ranges and increased fetches (Hubbard County Park, Hempstead Bay and Jamaica Bay) short-term changes in the rate of sea level change are more important for marsh accretion. These short term changes are most likely forced by meteorological processes such as winds, storms and floods. The North Atlantic Oscillation also appears to be coupled to salt marsh accretion, and it may be responsible for some of the short-term changes in sea level. While climate is an important driver of salt marsh accretion, accretion rates do not appear to be related to salt marsh loss. Across a wide range of environments, salt marsh loss patterns are not correlated with accretion rates; instead they are coupled to anthropogenic impacts. In particular, it appears that eutrophication and organic matter loading drive salt marsh loss in Jamaica Bay by affecting the salt marsh sulfur cycle. These changes leads to high concentrations of the phytoxic molecule, H2S, which causes plant die-offs and lead to salt marsh loss in Jamaica Bay, and perhaps elsewhere on Long Island.