In 2006 and 2008, extensive field surveys, with submeter georeferencing, were conducted at the Sapelo Island and Mission-Aransas Bay National Estuarine Research Reserves in Georgia and Texas in coordination with the acquisition of 1 m, high spectral resolution AISA imagery collected with a University of Nebraska research aircraft. We addressed the following: what is the spatial extent of different habitats within coastal wetland complexes, how effective is our high resolution imagery for mapping at species level, what are the within class spatial variability and patterns, and how well do geomorphic and hydrologic settings explain observed patterns? We developed procedures to delineate habitats using masking techniques and the unique spectral characteristics of micro and macro vegetation in order to map salt marsh and mangrove wetlands, tidal mudflats, and surface water and we applied our own algorithms to estimate and map primary producer biomass. ENVI software was extensively used in our image processing, classifications, and summary statistics.
Results/Conclusions
Two vegetation indices had strong correlations with clip plot marsh biomass (r2 = 0.74 for NDVI and 0.64 for VARI-green) at Sapelo Island. In the Duplin River watershed at Sapelo, aboveground biomass averaged 1250 g dry wt/m2 and total watershed biomass was 12,850 MT. In the Duplin, Spartina alterniflora covered 84.6% of the marsh, with mudflats and Juncus roemerianus covering 6.2% and 5.3%. The Duplin River and tributaries covered 223.5 ha. Estimated phytoplankton chlorophyll ranged from 7 to 30 ug/L. Upper tributary arms had highest chlorophyll, probably due to sloughing of marsh benthic diatoms. The middle Duplin River tidal prism contained lowest chlorophyll, perhaps related to longer hydrological residence times in this reach and less mixing with Doboy Sound water. At Mission-Aransas, our mapping efforts focused on invasive Avicennia in Redfish Bay. A robust correlation (r2 = 0.67) was found between measured mangrove height and VARI-green index. Initial results from our training area found Avicennia <60 cm covered 7.6% of the stand, while trees in the 60-75, 75-90, and >90 cm classes covered 62.4%, 26.5%, and 3.5% respectively. Tallest trees were generally closest to tidal channels, perhaps reflecting more protection from freezes or better nutrient availability.
