Morpho- and hydrogenesis of water bodies in subsidence basins as exemplified by water bodies in Zabrze, Upper Silesia (Southern Poland)

One of the more spectacular subsidence basins in the Silesian Upland is situated in the western part of the Katowice Upland, in a southern district of the Zabrze city. Subsidence basins form in places where minerals are mined below the ground surface. The purpose of the study was to assess the rate of change in subsiding land surfaces and conditions for the formation of water bodies as well as to conduct a qualitative examination of the water and sediments deposited within the subsidence zone that forms a new sedimentary basin. Within the framework of the study conducted in the catchment of the subsidence basin, its geological structure was identified, and detailed geomorphological mapping was conducted. Land use within the area examined was identified. Land profiles were drawn based on the cartographic material collected. The mechanical composition of sediments was determined using the sieving and areometric methods. Basic composition and content of elements were determined using inductively coupled plasma (ICP) atomic emission spectrometry and instrumental neutron activation analysis (INAA). Chemical analyses of water in the water bodies were conducted for three years; nitrate and chloride concentrations were determined using potentiometric methods, phosphate (PO43-) concentrations were determined using the spectrophotometric method, and those of sulfates (SO42) using the turbidimetric method. Studies have demonstrated that these water bodies were subject to transformations at each stage of the development of the subsidence zone. Currently, their areas range from just over 1.0 ha to more than 2.5 ha, maximum depths reach approximately 2 m and capacities range from a few to around a dozen thousand m(3). During the period analysed (from 1939 to 2000), the bottom of the basin subsided by around a dozen metres. It was found that the water bodies in question set a new erosion base level and act as local sedimentary basins. In the depressions thus formed, the material deposited from the atmosphere sedimentates and sediments supplied as a result of damage to the banks as well as of erosion processes in the catchment area accumulate. The bottom sediments accumulated in water bodies are significantly contaminated, particularly with heavy metals such as lead, zinc and cadmium.