Speciation of trace elements in the sediment of a meromictic Piaseczno Lake (inundated opencast sulphur mine, southern Poland) with permanently anoxic monimolimnion was studied. A 6-step sequential extraction procedure was applied to determine operationally defined phases: exchangeable (FI), carbonate (F2). easily reducible (F3), moderately reducible (F4), organic/sulphides (FS). and residual (F6) in the sediment. The differences in trace elements (except Mn) speciation in the littoral sediment with the respect of lake depths were not found Considerable difference in the trace elements speciation between the littoral sediment and permanently anoxic profundal one was found.

Exploitation of lignite within the area of Muskau Arch, carried out from the mid-nineteenth century, contributed to the transformation of the natural environment and changes in water regime. In the post-mining subsidences pit lakes were formed. The chemical composition of waters is a consequence of the intensive weathering of pyrite (FeS2), which is present in Miocene lignite-bearing rock forming the embankments of the lakes. This process leads to the formation of Acid Mine Drainage (AMD) and finally acidification of lake waters.

This paper presents results of the identification of hydrogeochemical processes affecting the chemistry of waters from these reservoirs carried out using the speciation and statistical (cluster and factor) analyses. Cluster analysis allowed to separate from the analyzed group of anthropogenic reservoirs 7 subgroups characterized by a similar chemical composition of waters. The major processes affecting the chemistry of waters were identified and interpreted with help of factor and speciation analysis of two major parameters (iron and sulfur).