Sulfur cycling in an acid mining lake and its vicinity in Lusatia, Germany

Abstract

The sulfur cycle plays a key role in the hydrochemical development of lignite and coal mining districts, which are often characterized by acid mine drainage. Identification of sulfur sources and transformations is essential if we are to understand the current status of acid lakes and propose successful remediation strategies. We utilized stable isotope (δ34Ssulfate, δ18Osulfate, δ34Sdissolved sulfide, δ18Owater) and hydrochemical data of lake and groundwater samples as well as the concentrations and isotope ratios of various sedimentary sulfur compounds (acid-soluble sulfate [ASS], acid-volatile sulfur [AVS], chromium-reducible sulfur [CRS]) in aquifer and lake sediments for assessing the biogeochemical sulfur cycle in a Lusatian acidic mining lake (ML111) and the surrounding area.Pyrite oxidation is the dominant source of sulfate and iron in the two aquifers west and east of mining lake ML111. Concentration and isotope data for dissolved sulfate suggest that bacterial (dissimilatory) sulfate reduction became an increasingly important process in the flow direction of the western aquifer, thereby improving water quality. In contrast, bacterial sulfate reduction was only of local importance in the dump aquifer on the eastern side of the lake. Oxygen isotope ratios of the lake water sulfate, and mass and isotope balances demonstrate that ∼80% of the sulfate in mining lake ML111 is derived via groundwater influx from the dump aquifer, with the remainder contributed by the western aquifer. In-lake pyrite oxidation or bacterial sulfate reduction in the water column are insignificant. The latter process is restricted to the monimolimnion, which represents less than 1% of the lake volume. Hence, the potential for natural generation of alkalinity by bacterial (dissimilatory) sulfate reduction is presently low. For successful remediation of ML111, it is essential to reduce significantly the continuous input of sulfate and acidity from inflowing dump groundwater.