Monitoring Acid Mine Drainage’s Effects on Surface Water in the Kizel Coal Basin with Sentinel-2 Satellite Images

Abstract

Mining in the Kizel coal basin (Perm Region, Russia) ceased 20 years ago; however, AMD with high levels of total iron (Fetotal) and trace elements still affects the rivers. In this study, we attempted to estimate inter-annual and seasonal variability of AMD-related surface water contamination using Sentinel-2 images from 2016 to 2019. The acid mine water index (AMWI), which is a normalized difference of spectral reflectance in the red and blue bands, was calculated from Sentinel-2 images. We compared the AMWI values with measured Fetotal concentrations in the surface water. A statistically significant (at a 0.05 significance level) Spearman’s rank correlation between AMWI and Fetotal concentration was found for 5 out of 7 surface water sampling points. We found that surface water contamination reaches a seasonal maximum in July, 1–1.5 months after the end of the snowmelt high water period. Excessive summer rainfalls also contributes to increased contamination, causing contamination to possibly spread more than 200 km from the AMD sources. In contrast, arid summer conditions were associated with a substantially decreased AMD discharge and Fetotal concentrations in the surface water. The main uncertainties in our results are associated with the effect of contaminated bottom and bank sediments and suspended sediments on the spectral characteristics of the water surface, and the relatively coarse (10 m) spatial resolution of Sentinel-2 images. However, despite the data and method limitations, our results show that Sentinel-2 images have substantial potential for monitoring AMD-related contamination of surface water.