Mesocosm studies to assess acidity removal from acidic mine lakes through controlled eutrophication

Flooded lignite pits (Tagebaurestseen) in Lusatia, Germany, are acidic (pH 2.5-4) with high concentrations of iron. Mesocosms (total volume 20 l) were set up with water and sediment from a Tagebaurestsee (Koschen, pH 3.1, Fe 20 mg l(-1), acidity (KB,,) 2.45 mM) to assess the effects of phosphate and organic amendments under natural light and low temperature. Chemical and biological parameters were observed over a 9-month period. Phosphate rock addition (300 mg l(-1)) resulted in sustained reduction in acidity (H+ and Fe3+) in the water column and induced the growth of Chlamydomonas spp. (Chlorophyceae) near the water surface and Lepocinclis teres (Euglenophyceae) in a band above the sediment. Addition of potatoes to mesocosms resulted in the generation of near-anoxic conditions above the sediment, and phosphorus, ammonium and carbon (organic and inorganic) were released as the potatoes decomposed. A pH > 6 was attained with 5.1 g (dry weight) of potatoes and pH > 8 with 34 g (dry weight). In both mesocosms, more than 90% of total acidity was removed. Algal growth, mainly of small, coccoid Chlorophyceae, Ulothrix sp. (Chlorophyceae) and Eunotia exigua (Bacillariophyceae), was observed throughout the water column. (C) 1998 Elsevier Science B.V. All rights reserved.