Impact of mining on geochemical signatures of riverine sediments in adjacent ecosystems

<p>As a result of the open-cast lignite mining in Lusatia (Eastern Germany), large quantities of iron (Fe) and sulphate (SO<sub>4</sub><sup>2-</sup>) are fed into small streams discharging into the Spree river system. The study examined whether the inputs of Fe and SO<sub>4</sub><sup>2-</sup> lead to longitu­dinal and depth-dependent gradients in the riverine sediments downstream the mining region in terms of element composition and mineral formations.</p><p>We sampled the surface (upper 0-3, 3-6 cm) sediment using a gravity corer at 18 sites from the heavily mining impacted Spreewald region downstream 200 km to the Bänke at Lake Müggelsee. We also included sampling sites at a pit water purification system in Vetschau, one neutral mining lake and a reference site without mining impact. Sedi­ments were analysed for total C, N using an element analyser, for various elements (incl. Fe, S, Mn, Al, P, heavy metals) by ICP-OES after digestion with hot aqua regia. A sequential Fe-extraction from fresh sediments and XRD was performed to differenti­ate solid iron forms and other minerals, respectively.  Characteristic sediment signatures are investigated with the help of a Principal Component Analysis (18 sites, 19 parameters).</p><p>We discovered a decreasing sedimentary Fe-content in flow direction from 300 mg g-1 in Vetschau, 130 mg g-1 close to the mining region in Lübbenau down to 30 mg g-1 at Bänke near Lake Müggelsee. In contrast, the S-content increased with decreasing mining impact from 3 mg g-1 in Vetschau up to 35 mg g-1. Minimum Fe- and S-contents are similar to Bautzen reservoir as a non-mining impacted reference location with Fe 28 mg g-1 and S 4 mg g-1. The statistical analysis with the PCA revealed the longitudinal influence of mining products within Spree river. Two major groups emerge from the score plot. First, there are those samples, which are clearly influenced by mining activities. Second, there are samples, which include the reference point and samples more distant from mining, where we expect no or only minor mining impact. This separation becomes even more apparent after taking heavy metals into account. Furthermore, the Fe binding shifts from more easily reducible Fe/amorphous minerals to less easily reducible Fe/more crystalline minerals in flow direction, which probably has consequences for the microbial degradability of organic matter and the strength of the ability of Fe to bind phosphorus.  </p><p>We were able to prove that the sedimentary ele­ment composition and especially the Fe mineral characteristics are influenced by mining activities at least 100 km downstream the Spree river system, probably affecting the phosphorus availability and carbon turnover.</p>

Mapping and quantifying groundwater inflow to the Spree River (Lusatia) and its role in Fe fluxes, precipitation and coating of the river bed.

<p><strong>The spatial distribution and temporal dynamics of groundwater inflow to rivers is often poorly defined but central to understanding water and matter fluxes. This is especially true for the Spree River which drains the Lusatia mining district, Brandenburg Germany. In the Spree catchment iron and sulphate fluxes to the river stem from the pyrite rich groundwater system, and the area’s history of open-pit lignite mining and re-flooding of many of these mines at the end of their lifetime. This iron flux threatens the river ecosystem, tourism in downstream communities (Spreewald) and the drinking water of Berlin. Iron is often observed as precipitates along the river bed, as well as colouring the river water yellow-brown, indicating the presence of iron (oxy)hydroxides such as ferrihydrite and goethite. In this work we have used radon as a natural groundwater tracer to delimited areas of active groundwater discharge to both the main Spree River and the Kleine Spree River to better understand the spatial destitution of groundwater input to the system. This was combined with mass-balance modelling to quantify the groundwater flux along the river using the FINIFLUX model. This was complemented by measurement of iron and sulphate concentrations in the steam and stream-near groundwater. During two measurement campaigns during 2018 the total groundwater inflow for a 20 km long reach of the Kleine Spree and a 34 km long reach of the Spree ranged between ~3,000 and ~7,000 m³ d<sup>-1</sup> (Kleine Spree) and ~20,000 and ~38,000 m³ d<sup>-1</sup> (Spree). Particularly high groundwater inflow was identified (up to 70% of total inflow) along the Spreewitzer Rinne, a local aquifer consisting of excavated mining materials. For the Kleine Spree the dominant groundwater and Fe flux occurred shortly before the confluence with the Spree. For these river reaches large amounts of dissolved iron and sulphate enters the rivers with inflowing groundwater as calculated from the radon data. Using the measured iron and sulphate loadings we calculated that up to 120 tons/day of iron (oxy)hydroxide was retained in the combined Spree and Klein Spree catchments, a large amount of which remains in the mining lakes. </strong></p>

Isotope insights into sulfate loads and sulfur cycling in a heavily polluted river network

<p>Sulfate isotopes in a heavily polluted river network</p><p>Tobias Goldhammer<sup>1</sup>, Juliane Lenz<sup>2</sup></p><p><sup>1</sup>Leibniz-Institute for Freshwater Ecology and Inland Fisheries, Department of Chemical Analytics and Biogeochemistry, Berlin, Germany</p><p><sup>2</sup>University of Bremen, Department of Geosciences, Germany</p><p>The Spree is the major river system in NE Germany, with about 380km in length and a catchment of more than 10,000 km<sup>2</sup>. While intensive open pit lignite mining in the upper catchment has significantly altered the hydrology and hydrochemistry over the last century, River Spree is at the same time a critical supplier of drinking water to the city of Berlin. Acid mine drainage is the major contributor to the river water sulfate load, which frequently exceeds the drinking water limit of 250mg L<sup>-1</sup>. Increasing summer drought and low-flow regimes are projected to intensify this situation in the future. The sulfate pollution in River Spree has induced a significant shift in biogeochemical regimes, in particular in those compartments of the river network where low flow velocity is supportive to sediment accumulation and bacterial sulfate reduction. Secondary effects include the mobility of iron and phosphorus, and entail critical consequences for the aquatic ecosystem.</p><p>In this contribution, we discuss the results of an integrated study of hydrochemistry and sulfate and water isotopes in the Spree river network. We put particular emphasis on</p><p>(1) Differentiating major geographic and functional sulfate sources and sinks in the Spree river network based on sulfur and oxygen isotopes in river sulfate</p><p>(2) Quantifying these sources and sinks by simple endmember models, and identifying limitations of this approach</p><p>(3) The role of biogeochemical sulfur cycling (reduction/reoxidation cycles and intermediates) in retention spaces of the river network and the consequence for prevailing isotope signatures.</p>

Flussbad Berlin Re-Naturalization Project for the Spree River in the Museum Island

This article considers the issues of the re-naturalization of riverbanks and the urban regeneration of historic centres while focussing on the Flussbad Berlin, a project of sustainable redevelopment of the Spree River, around the Museum Island, which today is the focus of major city debate. Spree River is considered as a public space, an important resource that concerns the whole city. For the project, the historic centre is the main place to combine hot topics pertaining to the contemporary society such as ecology, environmental sustainability, concertation, and public-private collaboration. Berlin is conceived as a «dialogic city» where diverse sites and activities can express themselves and interact productively.

Morphodynamic effects of stone and wooden groynes in a restored river reach

Restoration works on an 11 km long reach of the Spree River near Cottbus in Germany were accomplished in 2014. The overall objective was to improve the biodiversity, changing the morphological structure from a straight single-thread river to a braiding one with reshaped thalweg, and creating zones with varying flow velocities required for fish spawning. Several interventions were made, among which also two types of groynes were constructed along the reach: impermeable stone groynes, with an inclined crest so that only the tip is typically submerged during normal flow conditions, and wooden groynes made of several large trunks, which are mainly submerged at normal flow conditions. To compare local morphodynamic effects caused by the different types, flow velocities and bed topography were measured at distances of 12 m upstream and 16 m downstream of two selected groynes. The vertical profile was captured by measuring at five levels above the bed. Bed material was sampled at several locations around the groynes. The analysis of the measurements showed the effect of each groyne type on the flow velocity, bed topography and bed material. Furthermore, the differences in the effects of each groyne type on the flow, bed topography and bed material were highlighted.