Manipulation of the sediment-water interface of extremely acidic mining lakes with potatoes: Laboratory studies with intact sediment cores

The water of flooded, abandoned, open-cast pits (Tagebauseen) in the Lusatia region of eastern Germany is characterised by a high acidity (Fe3+/H+), low pH (2.5-3.5) and low concentrations of dissolved phosphorus (SRP) and carbon (DIC). Investigations are investigating the use of amendments to assist in removal of acidity from Tagebauseen through controlled eutrophication. A simple system has been developed to investigate the effects of amendments on water chemistry around the sediment-water interface. Intact, little-disturbed sediment cores (diameter 5.5 cm) with overlying water (total volume 1.5 1) from one Tagebausee (Koschen: pH 3.1, Fe 15-20 mg/l) have been incubated at low temperature (6-10 degrees C) to investigate the effects of organic amendments (potato) on the concentrations of some major ions in the system. In particular, the dynamics of Fe, P, N and C over time in the presence or absence of organic amendment (potato) have been investigated. Addition of potatoes results in the rising of a sharp pH gradient from near the sediment surface, and an overall increase in dissolved Fe, P and C in the system. The Fe eventually precipitated as black particulates but the SRP remained in solution. Intact sediment cores provide a useful tool for studying changes in water column and sediment pore water chemistry and the potential effects of amendments on the sediments of Tagehauseen.