Treating acid mine drainage with decomposed organic soil: Implications for peatland rewetting

Cement pastes containing air entraining agent release the biocide octylisothiazolinone posing ecotoxicological effects

We investigated whether cement pastes are a possible source of ecotoxicologically potent substances. For this purpose, leaching according to DIN EN 16637-2 was performed on portland cement pastes as well as blast furnace slag cement with and without an air entraining agent (AEA). The AEA, consisting of wood rosin and resin, contained the stabiliser drometrizole and the biocide octylisothiazolinone (OIT), which was confirmed by our non-target screening (NTS). Our ecotoxicological studies (Daphnia magna, Aliivibrio fischeri and Desmodesmus subspicatus) of the pure cement eluates showed no effects at all. In these samples, it was possible to attribute up to 85 % of the dissolved organic carbon (DOC) to acetate, formate and diethylene glycol (DiEG). Eluates from cement pastes with AEA contained up to 70 μg/L octylisothiazolinone (OIT), and no drometrizole was found. Around 90 % of the total OIT release happened within the first 6 h. It was possible to attribute the observed ecotoxicological effects mainly to the OIT concentrations. Additional leaching with elevated sulphate concentrations (800 mg/L) did not influence the release of DOC and OIT or increase the ecotoxicological effects. As a consequence, we advise curing the cement paste for 24 h prior to use, as this largely avoids the release of OIT and the observed ecotoxicological effects.

Reduced greenhouse gas emissions from particulate organic matter degradation in iron-enriched sediments

Iron (Fe) plays an important role in the biogeochemical cycling of carbon and nutrients in aquatic systems. Reactive Fe phases can interact with organic carbon and facilitate the removal of carbon from the biogeochemical cycle; however, this important ecosystem function is often strongly controlled by Fe availability. Due to pollution from lignite mining in the Lusatian province in Northeast Germany, large amounts of iron and sulfate are released into the fluvial-lacustrine system of the Spree River. It was hypothesized that the input of freshly precipitated iron oxyhydroxides from mining areas (e.g., ferrihydrite) alter the biodegradation of particulate organic matter (POM) in downstream lacustrine sediments. To investigate the Fe-dependent degradation of POM, slurries mimicking iron-polluted sediments (85 mg Fe per g, 116 mg Fe per g, and 149 mg Fe per g dry weight) were incubated with plankton or leaf POM under anoxic and oxic headspace conditions, and CO2 and CH4 emissions, water chemistry, and stable isotopes of dissolved inorganic carbon were measured. The experiments revealed that (i) with an increasing Fe content, the CO2 and CH4 emissions were gradually reduced, (ii) CO2 and CH4 production was higher during plankton degradation than during leaf decomposition, and (iii) under oxic conditions, CO2 production was higher and CH4 production was lower when compared to the treatments under anoxic conditions. These findings demonstrate that while benthic mineralization of fresh POM typically releases greenhouse gases into the water column, the availability of iron oxyhydroxides can contribute to reduced greenhouse gas emissions from sediments. This is of considerable relevance for future carbon budgets of similar mining-affected, iron-polluted fluvial-lacustrine river systems.

Unravelling the role of sulphate in reed development in urban freshwater lakes

Many European lakes have suffered from reed die-back since the 1950s. Previous studies have concluded that this is due to a combination of several interacting factors, but possibly also a single threat with high impact might be responsible for the phenomenon. In this study, we investigated 14 lakes in the Berlin area differing in reed development and sulphate concentration from 2000 to 2020. To unravel the decline of reed beds in some of the lakes with coal mining activities in the upper watershed, we compiled a comprehensive data set. Thus, the littoral zone of the lakes was divided into 1302 segments considering the reed ratio relative to segment area, water quality parameters, littoral characteristics and bank usage of the lakes which all have been monitored for 20 years. We ran two-way panel regressions with a within estimator to consider the spatial variation between and within the segments over time. The regression results revealed a strong negative relationship between reed ratio and sulphate concentrations (p<0.001) as well as tree shading (p<0.001) and a strong positive relationship with brushwood fascines (p<0.001). Taking only sulphate into account, reeds would have covered an additional area of 5.5 ha or 22.6% in 2020 (total reed area: 24.3 ha) in the absence of increased sulphate concentrations. In conclusion, changes in water quality upstream the catchment cannot be ignored in the development of management plans for downstream lakes.