Wetland Degradation Mapping and Evaluating Its Impacts on the Surrounding Environment, Using Geospatial Technique, A Case Study in Geba Watershed, Southwest Ethiopia
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Date
2019-05-03
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Addis Ababa University
Abstract
Wetland is one of the world’s most significant ecosystems, threatened from both natural and human-induced activities. As a result, the overall objective of this study is to map, monitor, and evaluate the impacts of wetland degradation on the environment, the case of Geba watershed southwest, Ethiopia. Remote Sensing and Geographic Information System approach integrated with ground data calibration were used to evaluate and quantify wetland resources. To conduct this study Landsat Thematic Mapper (TM) images was acquired for 1985, 2000 and Landsat 8 Operational Land Imager (OLI) imagery for 2018. In addition, SRTM DEM was acquired from the archives of the United States Geological Survey (USGS) for the analysis. Three different approaches have been used for mapping and monitoring of wetlands. Pixel-based classification (Supervised classification), index-based classification (NDVI & MNDWI), SRTM Slope and (TWI)wetness index and image enhancement methods were used. The use of multi-spectral Landsat imagery, including SRTM DEM, combined with ground truth data and GIS produced acceptable results for the delineation and mapping of wetland degradation in the study area. The overall accuracy of the 3 aggregated wetland (1985, 2000 and 2018) in the study area was 86.66 percent with reasonable errors of omissions (7.54 percent) and low errors of commissions (13.33 percent). TWI and slope map enhance the detection of forested wetland in the study area. Based on the results, wetland areas of 31.115km2 (14.53%), was converted to agricultural land in the period of 1985 to 2000. Similarly, in the same fashion from 2000 to 2018, 17.515km2 (10.9%) of wetland converted to agricultural land. Hydro-chemical parameters indicate a significant difference in water quality of degraded and undegraded wetlands and there is a change in ground water table based deep-well data between drained and undrained wetland types. A considerable driving force for wetland degradation within the watershed was directly related to agricultural expansion and population increment. Climate variability has also its own impacts on the degradation of wetlands in the study area.
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Keywords
Wetland Mapping, Wetland Degradation, Geba Watershed, Geospatial, Twi, Water Quality