Impacts on Spartina alterniflora: Factors Affecting Salt Marsh Edge Loss.
Browne, James Paul
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Spartina marshes are found on shores along the Atlantic coast of North America. A number of natural and anthropogenic impacts are thought to affect the rate of salt marsh loss. However, few long term assessments of changes in salt marshes are available. This dissertation project characterized and ranked factors that influence the recession of the edge of Spartina alterniflora salt marshes, focusing on Hempstead Bay, the westernmost bay of Long Island's South Shore Estuary reserve. I used 12 sets of aerial photographs of these marshes taken from 1926 to 2007 Using a randomization process, I chose 500 points along the edge of the marsh and determined the gain or loss of marsh by the change in the location of the edge of marsh for each time period for which aerial photographs were available. For the time interval 1966-2007, I examined a number of different potential predictor variables, each associated with factors hypothesized to cause marsh loss, and assessed which variables were most correlated with salt marsh loss or gain. I then compared change in the marsh from 1966-2007 with that seen from 1926-1966 to test for the effects of different factors pre and post heavy urban development. The loss of salt marsh area from the edge was not attributable to any single influence. Edges formed artificially by dredging continued to lose marsh at a high rate long after the initial damage. The distance of the marsh to borrow pits was also a significant factor correlated with marsh loss. Urbanization and increased boat use after 1966 were also correlated with greater marsh loss. Several natural factors were also correlated with marsh loss, including having a large fetch and storm impacts and tidal flow rate. Surprisingly, increased nutrient load was not correlated with marsh loss or gain. In general, the edges of smaller channels that were most distant from both natural and anthropogenic disturbance have changed relatively little over this 81 year time frame