Andrew Fyson

Phytoplankton of the extremely acidic mining lakes of Lusatia (Germany) with pH ≤3

Most of the flooded, open-cast lignite mining lakes of Lusatia (Germany) impacted by the oxidation of iron sulphides (pyrite and marcasite) are extremely acidic. Of 32 lakes regularly studied from 1995 to 1998, 14 have a pH <3 (median pH 2.3–2.9). These lakes are typically buffered by high concentrations of Fe (III) and have high conductivity (1000–5000 μS cm−1). Concentrations of dissolved inorganic carbon (DIC) and phosphorus are typically extremely low. These factors result in a very different environment for algae than found in neutral and acid-rain impacted lakes. The planktonic algal flora is generally dominated by flagellates belonging to genera of Chlorophyta (Chlamydomonas), Heterokontophyta of the class Chrysophyceae (Ochromonas, Chromulina), Cryptophyta (Cyathomonas) and Euglenophyta (Lepocinclis, Euglena mutabilis). Near-spherical non-motile Chlorophyta (Nanochlorum sp.), Heterokontophyta of the class Bacillariophyceae (Eunotia exigua, Nitzschia), Dinophyta (Gymnodinium, Peridinium umbonatum), other Chlorophyta (Scourfieldia cordiformis) and Cryptophyta (Rhodomonas minuta) are also found.

Angiosperms in acidic waters at pH 3 and below.

Colonisation of extremely acidic waters (pH ≤3) by aquatic angiosperms occurs widely, but is poorly documented. Unlike acid rain affected and other naturally acidic aquatic ecosystems, waters with pH ≤3 usually have a high conductivity, with high concentrations of SO42- and often high concentrations of Fe3+, other heavy metal ions and Al3+. Where Fe3+ concentration is high, as in many mine waters, it provides a strong buffering system. In such waters, the biogeochemical Fe cycle exerts over water chemistry and the availability of nutrients and carbon for organisms. Biological activity is limited by low concentrations of phosphorus and inorganic carbon (DIC), which in this pH range is essentially all in the form of dissolved CO2. A number of angiosperms grow in such waters including Phragmites australis, Typha spp. and Juncus bulbosus, though the last is the only one reported to grow totally submerged in waters with pH ≤3 . J. bulbosus occurs in many lignite mining lakes in Lusatia (north eastern Germany) with pH ≤3. The characteristics and possible survival strategies for this and other species are discussed.

Microbially-Mediated Metal Removal from Acid Mine Drainage

Acid mine drainage (AMD) is generated through the microbially-mediated oxidation of pyrite-rich mining wastes and often contains high concentrations of heavy metals and acidity. AMD is traditionally treated with lime. However, such treatment is required indefinitely, representing a considerable economic burden to the mining industry and generates vast volumes of Fe(OH)3 sludges. The ARUM (Acid Reduction Using Microbiology) technology described in this paper provides a low-cost, low maintenance, environmentally acceptable alternative for the amelioration of AMD. ARUM exploits the ability of anaerobic microbial processes to generate alkalinity and ameliorate AMD through acidity reduction and precipitation of heavy metals, resulting from changes in pH and Eh. Anaerobic bacteria use a variety of electron donors and acceptors when molecular oxygen is depleted. In sediments, decomposition of organic matter provides electron donors such as volatile fatty acids and H2, and acid mine drainage (AMD) provides the electron acceptors, SO 4 2− and Fe3+. A test cell system was constructed near Sudbury, Ontario to test ARUM on an AMD seepage with high nickel concentrations. The system comprises two cells for iron precipitation in oxidising conditions and two cells for acidity and metal removal in reducing conditions through ARUM. The ARUM cells have a constructed sediment of organic materials and a floating cattail cover providing organic carbon for the anaerobic bacteria. In 1992, with flow rates of around 1 L/min, the test cell system removed > 88% of the Fe, 77% of the Ni, 39% of the S and 72% of the acidity in the seepage entering the system.

Characterization of acidic mining lakes by titration curves

Acidification of waters through mining activities is well known. During operation ofthe open-cast lignite mines of Lusatia, the groundwater level is lowered and a vast quantity of overburden as well as waste material exposed. The exposure o f these materials to oxygen results in the chemical and microbiological oxidation of meta! sulphide and consequent acidification. Following mine closures, water levels rise again and fill the mined holes. As a result of acidification, the new lakes are characterized by very low pH and high iron and sulphate content (FYSON et al. 1998). Although most lakes have a pH in the 2-3.5 range, they differ greatly in terms o f the acidity due to varying strength ofpH buffering systems (GELLER et al. 2000). The acidity va1ues are important to ecologica1 studies and to project the effects ofneutralization measures for acidic waters. Measuring acidity is routinely determined by endpoint titrations, using NaOH as a titrant, to a defined reference p H. Because of the neutralization reaction, acidity is also called base neutralizing capacity. Instead of endpoint titrations to a certain reference pH va1ue, comp1ete titration curves can be recorded, which hold additional information about the buffering systems o f the water. Recording and interpretation oftitration curves are wide1y used as ana1ytica1 methods employed in many fields to determine, for example, vitamin e in fruit juices or hydrogen sulphide and mercaptans in petroleum. In environmental science, acid-base titrations are used in soi! science (SCHACHTSCHABEL et al. 1984) and for the carboxy1 content of fu1vic acids (THURMAN 1985). The interpretation of acid-base titration curves could also be a useful too! to obtain a more sophisticated picture of the buffering systems of acidic mine waters; therefore, more detailed knowledge about the processes invo1ved is necessary.

Biogeochemische Stoffumsetzungen an der Sediment-Wasser-Grenzfläche in Tagebauseen (Teilprojekt 11)

Ziel der vorliegenden Untersuchungen war, die Auswirkung von Stoffeintragen auf biogeochemische Wechselwirkungen zwischen Grundwasser, Sediment und Freiwasser von extrem sauren Tagebauseen zu erfassen. Dabei wurde die Dynamik von pH-Wert, Phosphor und Kohlenstoff als wichtige Steuergrosen der biologischen Entwicklung besonders berucksichtigt. Artenzusammensetzung, Biomasse und Primarproduktion des Phytobenthos wurden als biologische Reaktionen auf die abiotischen Bedingungen an der Sediment-Wasser-Grenzflache untersucht.