Geochemical signatures of lignite mining products in sediments downstream a fluvial-lacustrine system.

As a result of the open-cast lignite mining in the Lusatian region of north-eastern Germany, large amounts of iron, sulphate, trace metals, and aluminium are fed into the groundwater and small streams that discharge into the River Spree, which ultimately flows through urban Berlin. In this study, we examined whether the input of these mining products leads to longitudinal gradients in element compositions and mineral formations in the riverine sediments. The signatures of fluvial and interconnected lacustrine sediments along a 190-km flow section were evaluated via principal component analysis to define the impact range of the open-cast products. These products clearly showed a sediment impact range of at least ~90 km downstream of the mining area. In particular, nickel and cobalt readily co-precipitate with iron, while sedimentary sulphur initially increases and therefore shows a longer impact range than amorphous iron oxy-hydroxides. These findings further demonstrate that sulphur and iron have different transport mechanisms. Although sulphate concentrations in the river waters of Berlin are still high, sedimentary iron and sulphur contents at the city border are only slightly higher than at the reference point close to the source of River Spree. The strongly diminished but still present mining signature in urban Berlin is replaced by an urban signature characterised by high levels of zinc, chromium, lead, and copper.