Subterranean ecosystems - Universidade de Évora

IAH 2007 XXXV Congress - Groundwater and Ecosystems Lisbon, Portugal
Microbial ecology and geochemistry of biodegradation in porous aquifers –
new concepts for limitations and stimulations
[1] Christian GRIEBLER, [1] Robert, BAUER, [1] Bettina ANNESER, [1] Christian WINDERL,
[1] Tillmann LUEDERS, [1] Piotr MALOSZEWSKI, [1] Florian EINSIEDL, [1] Willibald STICHLER,
[2] Massimo ROLLE, [2] Sebastian BAUER, [2] Christina EBERHARDT, [2] Peter GRATHWOHL,
[3] Lars RICHTERS, [1] Rainer U. MECKENSTOCK
[1] GSF – National Research Center for Environment and Health, Institute of Groundwater Ecology, Ingolstädter
Landstrasse 1, 85764 Neuherberg, Germany, e-mail: christian.griebler@gsf.de
[2] ZAG – Center of Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, 72076
Tuebingen, Germany.
[3] Stadtwerke Düsseldorf AG, Höherweg 200, 40233 Düsseldorf, Germany.
ABSTRACT
The biodegradation of organic pollutants in groundwater systems may be limited by the depletion of essential
nutrients, the low number of degraders and specific biokinetics. However, the main problem seems to be the
insufficient mixing of e-donors and e-acceptors. Main degradation activities in contaminant plumes should
therefore be located at their fringes. We call this working hypothesis the ‘plume fringe concept’. In order to
investigate if biodegradation in porous media is mixing-controlled and to elucidate the ecological role of
pollutant degrading microbes, lab and field investigations were performed. These comprised (1) experiments in
2-D aquifer model systems, (2) retrieving of intact sediment cores at a former gasworks site and (3) installation
of a novel high-resolution multi-level well.
1) To assess the importance of individual abiotic (e.g. mixing, toxicity, nutrients) and biotic (e.g. cell
distribution and activity, redox tolerance) parameters for biodegradation under well controlled lab
conditions, contaminant plumes were generated in 2-D aquifer model systems, and subsequently inoculated
with aerobic and/or anaerobic bacterial strains to investigate biodegradation at high spatial resolution. The
collection of empirical data was accompanied by state of the art reactive transport modelling.
2) For the linkage of processes involved in biodegradation and the respective microorganisms, fresh sediment
samples were collected repeatedly from a sandy tar oil-contaminated aquifer. The total microbial
community structure as well as the distribution of functional marker genes were correlated to prevailing
physical-chemical sediment characteristics.
3) To elucidate the importance of scale in relation to biodegradation activities in porous media, a highresolution
multilevel well was installed. This well allows the simultaneous withdrawal of groundwater
samples from the contaminated zone with a vertical spatial resolution of up to 3 centimetres.
The 2-D microcosms and the investigated aquifer biodegradation of contaminants was followed by vertically
resolved concentration measurements, compound-specific stable isotope ( 13
C/ 12
C, 34
S/ 32
S and 18
O/ 16
O) analysis, the
identification of signature metabolites, the spatial distribution of microbial biomass, and specific degraders via
marker genes indicating potential degradation activities.
Major outcomes so far may be summarized as follows:
▪ Dispersion in porous aquifers controls contaminant transformation to a high degree, but in anoxic
environments further processes (most probably coupled to biokinetics) limit anaerobic biodegradation.
▪ Sediment heterogeneity and transient hydraulic conditions exhibit a significant positive effect on the overall
biodegradation.
▪ The fringes of contaminant plumes display small scale and steep physical-chemical gradients in the range of
centimeters to decimeters. These gradients are the hot spots of biodegradation.
▪ At these hot spots the relative abundance of specific degraders was highest. Up to 50% of the cells present
in sediment samples from the fringe zone could be shown to carry degradation-specific functional genes.
Keywords: biodegradation ecology, plume fringe concept, small-scale gradients, high-resolution sampling,
mixing-controlled biodegradation, spatial and temporal dynamics
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