Detecting Coastal Marsh Change from Aerial Imagery using Spectral and Textural Methods: Pascagoula River Estuary, Mississippi, 1955-2014

As sea level rise accelerates, coastal marsh ecosystems are increasingly vulnerable. Vertical accretion rates must exceed or keep pace with rates of sea level rise to prevent transition to open water or inland migration of marsh vegetation. While some marsh systems along the northern Gulf of Mexico coast have remained stable, others, e.g., the marshes of the Louisiana Gulf Coast, have experienced high rates of conversion to open water. This study examined the historical extent of intertidal marsh at the mouth of the Pascagoula River in Jackson County, Mississippi to determine whether marsh extent changed during the period 1955-2014 and to ascertain rates of change. Marsh extent was mapped at 3 meters GSD using spectral and textural aerial image data for image dates of February 13, 1955 (black and white), February 12, 1996 (color-infrared), and October 5-16, 2014 (color-infrared). Waterways represented in the imagery were classified using a near-infrared band threshold for 1996 and 2014 and a CV-band threshold for 1955. Land cover was classified into three groups–marsh, woodland/shrubs, and unvegetated–using a Maximum Likelihood Classifier. Change detection analysis revealed a net marsh loss of 1314.4 ha (19.9%) between 1955 and 2014. Classified marsh extent decreased by 1068.3 ha (16.1%) between 1955 and 1996, and 246.1 ha (4.4%) between 1996 and 2014. Linear regression of marsh extent with year yielded a slope of -22.9 ha/year with a coefficient of determination of r2 = 0.98. The results indicate that marsh extent will continue to decrease in the Pascagoula River Estuary