Analyses and monitoring of lignite mining lakes in Eastern Germany with spectral signatures of Landsat TM satellite data

Coal mining activities cause an increased acidity and an associated decrease of the pH-value in mine waters. This process is also known as acid mine drainage (AMD). Due to AMD, lakes that were formed in the post mining landscapes in the lignite mining area of Central Germany are characterized by specific limnological development changes. Remote sensing is a time and cost saving technique that enables the observation of the hydrological and limnological development of the lakes ranging from a small to a mid size scale.The current research was based on Landsat TM5/ETM+7 satellite data collected between 1999 and 2004. In combination of satellite data, surface waters of the post mining lakes in Central Germany were sampled and analyzed for their physicochemical properties. The objective of this approach was to evaluate the environmental conditions and to develop a monitoring system. On the other hand, the research was conducted to assess the potential of the use of satellite data and to calibrate its content for monitoring the geochemistry of mining lakes.Correlation of hydrochemical parameters of lake water to spectral signatures detected by satellites was performed with multivariate statistical analysis methods. The five determined clusters of spectral partitions described the actual data (ground truth data) within the visible range. The statistically identified clusters were combined with expert knowledge in limnology, geology and water chemistry of large scale lakes in open cast mining areas, in order to analyze the spectral information of the satellite images scientifically. The utilization of spectral signatures revealed an acceptable classification of hydrological and hydrochemical properties of mining lakes and established the basis for further investigation of open cast lignite mining concerning the environmental impact, particularly in areas where lignite mining lakes usually form.

Research Highlights
► Spectral signatures of Landsat satellite data are employed as appliances for investigation of mining lakes regarding their geochemistry of abandoned open pit mines.
► These almost acidic mine residual lakes are characterized by a highly dynamic development.
► Welfare results strongly depend on spectral and spatial resolution of satellite data.
► These analyses proved that the mining lakes could be classified based on available data for their water properties.
► For the first time, water quality assessment and monitoring with satellite data characterized by a medium resolution were investigated.