Multitemporal Estimation of Environmental Degradation from Alluvial Gold Mining in Nechí river, Using Normalized Difference Turbidity Index and Dynamic World
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Abstract
A multitemporal assessment was conducted to quantify the environmental degradation caused by alluvial gold mining in the Nechí River basin, Colombia, using Sentinel-2 imagery and the Dynamic World product within Google Earth Engine. The analysis focused on bare soil areas to minimize interference from vegetation and water bodies in the calculation of the Normalized Difference Turbidity Index (NDTI). Change metrics, including Euclidean Distance and Spectral Angle Mapper, were applied to annual NDTI composites to evaluate the magnitude and structural changes of surface transformation between 2016 and 2024. Results revealed a sustained increase in the extent of bare soil, particularly along the eastern river margin, accompanied by a relative decrease in average NDTI values, reflecting greater sediment exposure. The combined use of spectral metrics and global classifiers proved effective for identifying and monitoring mining-related land cover changes in areas with limited accessibility and complex social dynamics. This methodology demonstrates a robust integration of remote sensing indices and spectral analysis for spatially and temporally explicit environmental monitoring in regions affected by uncontrolled artisanal gold mining.
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