Using satellite imagery and GIS for land-use and land-cover change mapping in an estuarine watershed

The degradation of world-wide estuarine ecosystems as a result of accelerated human population growth accompanied by agricultural, industrial and urban development justifies a strong need to find efficient ways to manage and protect these sensitive environments. Starting from 2001, the authors have been involved in an interdisciplinary research project aiming to develop environmental indicators for integrated estuarine ecosystem assessment in the Gulf of Mexico. As part of this project, a study was conducted to characterize land-use and land-cover changes with the Pensacola estuarine drainage area as a case. The Pensacola bay was targeted because it is one of few exemplary large river-driven estuarine systems across the northern Gulf of Mexico. The study had two major sections. The first part was dedicated to the development of an improved method for coastal land-use and land-cover mapping, which was built upon hierarchical classification and spatial reclassification. An image scene was separated into urban and rural regions early in the classification, with a 'mask' defined by road intersection density slices combined with road buffers. Each part was classified independently in its most effective context and, later, both were merged to form a complete map. In spatial reclassification, image interpretation procedures, auxiliary vector data and a variety of Geographical Information System (GIS) functions were synthesized to resolve spectral confusion and improve mapping accuracy. This method was used to map land use and land cover from Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM +) imagery for 1989, 1996 and 2002, respectively. The accuracy assessment shows that the overall classification errors were less than 10%. The second part focused on the analysis of the spatio-temporal dynamics of estuarine land-use and land-cover changes by using post-classification comparison and GIS overlay techniques. The project has revealed that a substantial growth of low-density urban land occurred in the lower drainage basin in connection with population and housing growth, as well as a significant increase of mixed forest land in the upper watershed as a result of active logging and harvesting operations. These growths were achieved at the cost of evergreen forest and wetlands, thus compromising safeguards for water quality, biodiversity of aquatic systems, habitat structure and watershed health in the Pensacola estuarine drainage area.