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TECHNICAL REPORT

Plant and Environment Interactions

Chemical Composition of Organic Matter in Extremely Acid, Lignite-Containing Lake Sediments Impacted by Fly Ash Contamination

^a Brandenburg Technical University, Faculty of Environmental Science, Department of Soil Protection and Recultivation, P.O. Box 10 13 44, D-03013 Cottbus, Germany
^b Lehrstuhl für Bodenkunde, Technische Universität München, D-85350 Freising-Weihenstephan, Germany
^c CNRS, Laboratoire de Biogéochimie des Milieux Continentaux, Centre INRA Versailles-Grignon, Bâtiment EGER, Aile B, F-78820 Thiverval-Grignon, France

^* Corresponding author (abad.chabbi{at}grignon.inra.fr).

Received for publication February 6, 2003. In the Lusatian lignite mining district of eastern Germany, extremely acid lakes developed during ground water rising after exploitation of lignite in open-cast mines. The reasons of plant colonization (Juncus bulbosus L.) of some lakes exhibiting moderate pH values while others remain extremely acid and unvegetated are unknown. Alkalinity gain may be achieved by addition of alkaline materials and/or decomposition of organic matter. Our objective was to examine fly ash deposition and the resulting changes in organic matter composition in the uppermost 0 to 5 cm of the sediment sampled from vegetated and unvegetated lakes. Bulk soil and particle size fractions were analyzed for elemental composition, magnetic susceptibility, and chemical structure of the organic matter by ¹³C solid-state nuclear magnetic resonance (NMR) spectroscopy. The lignite content of the samples was estimated by ¹⁴C activity measurements. The pH values decreased with increasing depth and the changes in pH were found to be correlated with changes in magnetic susceptibility. Carbon and nitrogen contents were found to decrease with increasing depth. The C to N ratios are consistent with the (i) the presence of decomposing plant residues and/or microbial material such as algae in the upper 0 to 5 cm of the sediment and (ii) the dominance of lignite in the layers below this depth as confirmed by ¹⁴C activity measurements. The structural analyses of the particle size separates from the 0- to 5-cm depth were consistent with the presence of organic matter derived from plant material. This study confirms that fly ash is an important source of alkalinity in the upper 0 to 5 cm of the sediment that enhanced plant growth and led to enrichment of the sediment with organic matter derived from plant material.

Abbreviations: CPMAS, cross polarization magic angle spinning • NMR, nuclear magnetic resonance • OC, organic carbon

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This Issue in Journal of Environmental Quality

JEQ 2004 33: 413-418. [Full Text]