The Influence of Landscape Position on Coastal Marsh Loss

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Rogers, Andrew Stephen
Kearney, Michael S.
Coastal marshes are considered as important features of the landscape that are at risk of loss. Accurately assessing their prospects for survival is difficult in view of the wide possible causes of loss, the large areas involved and that most research is done on relatively small parcels. This project examined the probability of conversion of marsh surface parcels to open water as a function of distance from roadways across marshes, tidal creeks, and upland areas, and the distance upstream, and the size of a marsh parcel. These are understood to be stand-ins for hydrology, elevation and other factors that are more difficult to measure. The study area was divided into a MidAtlantic coastal region and a large bays region comprising the Chesapeake and Delaware Bays. A semi-automated system was developed for measuring the extent and severity of coastal marsh loss using Thematic Mapper (TM) data. The data derived from the TM analysis were used to develop algorithms to examine the impacts of the five factors listed above. The factors were examined individually using ordinary least squares (OLS) regression, and collectively using logistic regression. The OLS regression revealed that distance from uplands and distance from the nearest tidal creek were highly correlated with marsh loss in both areas. For the Atlantic Coast, however, the loss was negatively related to distance from tidal creeks, the opposite of what was expected. Distance upstream was negatively correlated with marsh loss as predicted. The relationship between distance from roads and marsh loss indicated that marshes are healthier near roads than farther away. The relationship between parcel size and marsh loss was non-linear, with small and large marshes having a lower probability of degradation than mid-sized marshes. The logistic regression model is useful for identifying areas with higher probabilities of conversion to open water. Sea level rise (SLR), tidal range, easting and northing were examined for use with the logistic models. SLR and tidal range added no information to the bay areas, but sea level rise was weakly negatively correlated with marsh loss on the Atlantic Coast and tidal range was weakly positively related.