ASSESSMENT OF THE OCNELE MARI SALT MINE EXPLOITATION IMPACTS ON THE VEGETATION COVERAGE USING MULTISPECTRAL REMOTE SENSING DATA

In Romania there are several inactive or abandoned mine sites which can create a significant impact on the environment, affecting the use of local surface and groundwater. The environmental impacts that can occur at an abandoned mine site can be divided into several categories, amongst which: metal contamination of ground surface water and sediments, air emission and deposition, erosion, physical impacts (slope failure, structural stability of tailings impoundments, ground subsidence, unsafe structure, mine openings and vegetation contamination). The Ocnele Mari salt mine is one of disused mines affected by subsidence phenomena as a result of pillars dissolution by uncontrolled leaching processes that led to the formation of a huge cavern of up 10.5 ha on horizontal direction and its volume of 2.5 million m(3) of brine. The land deformation (subsidence and landslide) phenomenon influences vegetation coverage changes. The object of the present study is to investigate the temporal changes of vegetation caused by salt exploitation using multispectral remote sensing data (Landsat 5, Landsat 7, ASTER and MODIS). We elaborated maps for the vegetation indices: normalized difference vegetation index - NDVI, leaf area specific index - SLAVI, normalized difference water index - NDWI - and thermal index. The change detection technique in vectorial format is applied on NDVI data in order to determine the areas affected by land degradation, with direct effects on vegetation coverage. Thus, an analysis of vegetation index NDVI proves the vegetation degradation in Field II of probes of the mining area, especially in the area of the 360-366 probes, with an area of 146700 m(2). For the Field I of probes, sample 472, a decrease of 19 800 m(2) of vegetation was noticed, while the third field, samples 431-433, decrease was determined to 30 600 m(2). The results confirmed feasibility of using remote sensing technique to assess the vegetation growth status in the salt mining area.