Environmental Challenges (Jan 2021)
Landscape-based analysis of wetlands patterns in the Ogou River basin in Togo (West Africa)
Abstract
Climate change and anthropogenic pressures are increasingly affecting land resources, especially wetlands. This work is a contribution to the sustainable management of wetlands in Togo, particularly in the Ogou basin, which are still not been the focus of scientific investigations. The objectives of this study are to (i) map the diversity of wetlands in the Ogou River basin, and (ii) analyze the wetland habitat fragmentation at the landscape level in the study area. First, three images from Landsat 8 of 2017 and 2018 were used for wetland mapping in ENVI 4.7 software. The unsupervised classification ISODATA were used after a color composition based on neochannels (Brighness, Greeness of the Tasseled Cap and the Modified Water Detection Index (MNDWI)). Next, the Normalized Difference Vegetation Index (NDVI) was used to map land cover for wetland categorization. Field surveys and very high resolution Google Earth images were used to evaluate the land use and wetland mapping, using Pontius matrix which showed total discrepancies of 20% and 21% for land use and wetlands, respectively. Finally, the ''LECOS'' extension of the QGIS software was used to calculate landscape fragmentation based on landscape metrics. Two wetland types were identified according to Ramsar categorization. The “inland wetlands” (90.66%) consists of forested peatlands (33%), tree-dominated freshwater wetlands (26.68%), bush-dominated wetlands (22.14%), and non-forested peatlands (8.84%). The “artificial wetlands” (09.34%) consists of seasonally flooded agricultural land (09.32%) and water storage areas (0.03%). These wetlands make up 34.98% of the land use in the study area. The landscape metrics revealed that these wetlands are differently affected by the fragmentation process. Thus, at the global scale inland wetlands are less fragmented than artificial wetlands. However, at a more detailed scale of categorization, bush-dominated wetlands are the most fragmented on the landscape. Study results indicate that knowledge on landscape configuration will be important to monitor wetland dynamics in multifunctional areas. This study can assist in efforts towards the biological conservation and ecological restoration planning addressing wetland resources in the study area.
