MICROBIAL EUKARYOTIC ECOLOGY AND PRESERVATION IN AN ACID MINE DRAINAGE SYSTEM

Acid mine drainage (AMD) at the abandoned Green Valley coal mine site, western Indiana, is host to a number of eukaryotes, including Euglena mutabilis, Chlamydomonas, fungal hyphae, filamentous algae, and diatoms. Four main ecologic associations are tentatively identified (list in descending abundance): 1) E. mutabilis + fungal hyphae + Chlamydomonas ± diatoms; 2) diatoms + fungal hyphae + filamentous algae ± E. mutabilis; 3) Chlamydomonas + fungal hyphae + E. mutabilis ± diatoms; and 4) E. mutabilis + Chlamydomonas + diatoms + fungal hyphae. Preliminary field investigations show patchy eukaryote distribution. All four communities have been observed within 1 m², yet within a week, one or two of the communities will displace the others. From observations over the last three years, eukaryote distribution periodically changes from full channel coverage to <1% coverage of the channel bottom. During periods of <1% coverage, the highly patchy communities occur in limited areas that are suitable for survival. These restricted areas serve as refugia from where the communities expand across the stream when conditions are favorable. The variation in community distribution is likely influenced by a combination of changes in weather conditions, water chemistry, pH, temperature, and/or stream roughness. Benthic communities dominated by diatoms expand their distribution immediately following major and/or extended rainfall events, which temporarily increase effluent pH. These communities become patchier as pH returns to pre-existing levels (pH 3.0-3.5). Under normal AMD pH conditions, E. mutabilis proliferates in benthic communities, for the most part, displacing diatoms and Chlamydomonas. The E. mutabilis dominated communities are most extensive during the spring and fall, and sparsely distributed during the winter and summer when average temperatures are at their extreme.

The succession of eukaryotic communities are preserved as layered iron-rich biolaminates or stromatolites. These organosedimentary structures consist of layers that reflect local variations in the microbial communities, and thus, preserve the spatial and temporal ecological relationships in the AMD system.