Retention potential of a drained wetland in the Lusatian lignite mining district, Briesener Niedermoor, Germany, Europe

Abstract

Acid mine drainage (AMD) is one of the most important global causes for polluted water. It occurs in mining areas due to oxidation of sulfide minerals. Depending on hydrological conditions, wetlands are considered suitable for passive treatment of AMD. The aim of the study was to characterize the long-term retention performance of a drained wetland, Briesener Niedermoor, in an iron and sulfate contaminated catchment area. The site is located in the Lusatian lignite mining district, Germany. Hydrological and hydrochemical measurements as well as time series of groundwater and surface water were evaluated and saturation conditions of iron species were determined using Phreeqc Interactive and EH–pH diagrams for the Fe–S–K–O–H system. Progressing peat degradation due to drainage leads to a hydraulic behaviour of the wetland that is more comparable to a rain bog than a fen, and thus to more pronounced oxic conditions. Groundwater feeds the wetland with significant loads of iron and sulfate, which are temporally stored in the wetland. At low surface water discharge, iron is removed and weak acidic pH is buffered by the dominant phase of schwertmannite (Fe8O8(OH)6SO4), usually during summer months. In winter, greater water availability initializes a high source strength from the wetland, that cannot be retarded. Thus, only during summer, there is a retention potential; in winter, the retention potential is not strong enough to prevent an inflow of iron and sulfate. Only a significant rewetting of the wetland may result in a restoration of the retention potential of the wetland Briesener Niedermoor.