Assessment of the environmental impacts of gold mining activities at Gankombol (Adamawa-Cameroon) using Leopold matrix, Fecteau grid and remote sensing approach

Abstract

In the present study, the environmental impacts of gold mining activities at Gankombol (Adamawa Cameroon) are assessed over four-year period. The Leopold matrix and the Fecteau grid are used to identify the environmental impacts and to determine their absolute importance. The spatio-temporal variation of spectral indices and land degradation are assessed using remote sensing analysis. The approach adopted is based on the calculation of spectral indices and spatio-temporal analysis. For this purpose, from Sentinel-2 satellite images, spectral indices such as the normalized difference vegetation index (NDVI), the brightness index (BRI), the normalized difference water index (NDWI), the bare soil index (BSI) and the dry bare soil index (DBSI) are computed during four years (2016, 2019, 2020 and 2021). The environmental degradation maps are generated by using supervised Random Forests (RF) algorithm and field observations. Finally, the confusion matrix and the kappa coefficient are used to check the performance and the accuracy of the classification maps. The environmental impact assessment by the Leopold matrix and the Fecteau grid reveal that the environmental impacts of mining activities are mainly negative and manifested by deforestation, degradation of water and soil quality, and high risks to human health. These impacts have a major absolute importance. The analysis of the spectral indices suggest a clear difference between the values obtained for each year due to the evolution of the mining activity over time. The environmental degradation maps which made it possible to discriminate water bodies, exploited area, vegetation and barren soils show that the values of water bodies decrease from 16.33 to 11.69 km2 between 2016 and 2020, then increase to 13.46 km2 in 2021. The exploited area increases from 0.00 to 13.75 km2 between 2016 and 2021. Vegetation cover decreases from 24.49 to 15.25 km2 between 2016 and 2021, while barren soils increase from 19.65 to 21.53 km2 between 2019 and 2021. These results reveal significant environmental degradation in the study area due to mining activities.