Forty years of remote sensing mapping and monitoring of freshwater ecosystems in South Africa

Abstract

The first space-borne satellite was launched nearly fifty years ago in 1972, initiating global monitoring of freshwater ecosystems. Space-borne images have contributed to forty years of mapping and monitoring of wetlands in South Africa, and are important tools in our monitoring toolboxes. Changes in the areal extent and water quality of the lacustrine wetland biome have advanced much faster compared to studies on the palustrine wetland biome. Studies related to the palustrine wetland biome, making up 89% of the known wetland extent of South Africa, are rare and predominantly done at a fine scale. Most studies used land cover data to map and monitor changes in both the lacustrine and palustrine wetland biomes, however, a significant amount of work is required to improve our knowledge on the palustrine wetland biome in our country. Examples of how remote sensing was used to quantify Essential Biodiversity Variables of palustrine wetlands will be showcased, including the mapping of above-ground biomass, phenology, soil moisture, fire disturbances in peatlands, the hydrological regime and other health indices. The value of South Africa's land cover maps, derived from satellite remote sensed images, is also explored for use in the red listing of freshwater ecosystems. Four epochs of KZN's land cover data sets (2005, 2008, 2011 and 2017), derived from SPOT and Sentinel2 images, were used to quantify changes in the extent and fragmentation of subtropical-temperate forested wetlands on the Maputaland Coastal Plain. The limitations of these provincial data sets were compared to a finer-scale study, showing the challenges in using the coarser-scale data in estimating rates of decline. For example, the total extent lost over 11 years appeared to be underestimated using the provincial scale data.