Mapping high marsh and salt pannes/flats along the northern Gulf of Mexico coast

Abstract Coastal wetlands are predicted to undergo extensive transformation due to climate and land use change. Baseline maps of coastal wetlands can be used to help assess changes. Found in the upper portion of the estuarine zone, high marsh and salt pannes/flats provide ecosystem goods and services and are particularly important to fish and wildlife. We developed the first map of high marsh and salt pannes/flats along the northern Gulf of Mexico using regional models that included spectral indices related to greenness and wetness from optical satellite imagery, elevation data, irregularly flooded wetland probability information, and synthetic aperture radar backscatter. We found the greatest relative coverage of high marsh along the Texas coast (30% to 65%) and the Florida Panhandle (40%), whereas the greatest relative coverage of salt pannes/flats was along the lower Texas coast (74%) and the middle Texas coast (15%). As part of this effort, we also developed a map that highlighted irregularly flooded wetlands dominated by Juncus roemerianus (black needlerush) for part of the study area. Both maps had an overall accuracy of around 80%. Our results advance the understanding of estuarine marsh zonation and provide a baseline for assessing future transformations. HIGHLIGHTS This is the first map of high marsh and salt pannes/flats along the northern Gulf of Mexico and provides a baseline for understanding transformations predicted to occur with climate change. Due to high elevation uncertainty in wetlands, we used a map of irregularly flooded wetland probability that was created using elevation error assumptions. Irregularly flooded wetland probability, synthetic aperture radar backscatter, and spectral indices related to greenness and wetness were important predictor variables. Differences in wetland zonation and species composition along the study area led to variation in models by region. The framework presented here could be adapted to other areas.

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