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.

Sedimentary Sulphur:Iron Ratio Indicates Vivianite Occurrence: A Study from Two Contrasting Freshwater Systems.

An increasing number of studies constrain the importance of iron for the long-term retention of phosphorus (P) under anoxic conditions, i.e. the formation of reduced iron phosphate minerals such as vivianite (Fe3(PO4)2⋅8H2O). Much remains unknown about vivianite formation, the factors controlling its occurrence, and its relevance for P burial during early sediment diagenesis. To study the occurrence of vivianite and to assess its relevance for P binding, surface sediments of two hydrologically contrasting waters were analysed by heavy-liquid separation and subsequent powder X-ray diffraction. In Lake Arendsee, vivianite was present in deeper sediment horizons and not in the uppermost layers with a sharp transition between vivianite and non-vivianite bearing layers. In contrast, in lowland river Lower Havel vivianite was present in the upper sediment layers and not in deeper horizons with a gradual transition between non-vivianite and vivianite bearing layers. In both waters, vivianite occurrence was accompanied by the presence of pyrite (FeS2). Vivianite formation was favoured by an elevated iron availability through a lower degree of sulphidisation and was present at a molar ratio of total sulphur to reactive iron smaller than 1.1, only. A longer lasting burden of sediments by organic matter, i.e. due to eutrophication, favours the release of sulphides, and the formation of insoluble iron sulphides leading to a lack of available iron and to less or no vivianite formation. This weakening in sedimentary P retention, representing a negative feedback mechanism (P release) in terms of water quality, could be partly compensated by harmless Fe amendments.