Changes detected in the extent of surface mining and reclamation using multitemporal Landsat imagery: a case study of Jiu Valley, Romania

摘要

Surface mining represents the dominant driver of land coverage changes in the Jiu Valley mining area in Romania. Detecting and quantifying active mines and reclaimed areas are very important tasks given the effects of surface mining on the environment. In this paper, Landsat imagery for the years 1988, 1998, 2008, and 2017 was used to map the extent of surface mining and reclamation in the Jiu Valley mining area. The satellite images were classified using the Support Vector Machine (SVM) algorithm to map land cover classes, including mined areas, and post-classification comparison (PCC) technique to track changes through time. In order to identify and quantify active mines and reclaimed areas of mined areas, we used indices such as Normalized Difference Vegetation Index (NDVI), Soil-Adjusted Vegetation Index (SAVI), and Modified Soil-Adjusted Vegetation Index-2 (MSAVI-2). For the entire area studied, during the period 1988-2017, the extent of surface mining was 6.5%, with peaks in the periods 1988-1998 and 1998-2008, namely, 205.2% and 4.0%, respectively, as a result of the extension of surface exploitation as distinct from that underground. Land cover conversion to mined areas was almost exclusively from agricultural, forest, and pasture. The results show that NDVI estimated the largest surfaces with active mines, reclaimed grassland, and reclaimed woodland, within the mined areas. SAVI and MSAVI-2 estimated larger surfaces classified as reclaimed forest. As a result of the expansion of surface mining areas, the landscape was considerably degraded through mining scars, landscape fragmentation, degradation, and pollution. However, during the past few years, reclamation activity has intensified in the affected areas through the occurrence of spontaneous vegetation, but also through forestation.