Long-term monitoring of biophysical characteristics of tidal wetlands in the northern Gulf of Mexico - A methodological approach using MODIS

Accurate and efficient monitoring is critically important for the effective restoration and conservation of threatened tidal wetlands in the Gulf Coast. The high carbon sequestration potential, habitat for important wildlife and fish, and numerous ecosystem services make these tidal wetlands highly valuable both ecologically and economically to Gulf Coast communities. Our study developed a new methodological approach for mapping biophysical health of coastal tidal wetland habitats in terms of green leaf area index (GLAI), canopy level chlorophyll content (CHL), vegetation fraction (VF), and above ground green biomass (GBM). We measured these biophysical characteristics in tidal wetlands of the northern Gulf of Mexico using a combination of ground data collected from field surveys during the growing seasons of 2010 and 2011 and NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m and 500 m images. Additionally, we compared and evaluated the performances of both in situ proximal and satellite remote sensing measurements in terms of their potential for mapping the wetland biophysical characteristics. MODIS-based models proved superior at the landscape level compared to models developed from in situ proximal sensing, as species level signals seemed to be diluted at coarser spatial scales. We selected Wide Dynamic Range Vegetation Index (WDRVI) for MODIS 250 m and Visible Atmospheric Resistant Index (VARI) for MODIS 500 m to map biophysical characteristics of tidal wetlands. Time-series composites and phenological information derived using the MODIS based models captured the impact of the selected disturbances in the last decade on the ecological and physiological status of the tidal wetland habitats in the Gulf Coast. This is the first study to employ MODIS data to analyze the biophysical characteristics of tidal wetlands in the Gulf Coast, which, in turn, has the potential to improve our ability to predict their productivity and carbon sequestration potential. These techniques could also be used to assess the success of previous and ongoing tidal wetland restoration projects, and evaluate the productivity of marshes under threat from developmental activity, sea level rise, and industrial pollution. (C) 2015 Elsevier Inc. All rights reserved.