MICROBIAL ECOLOGY OF ACID STRIP MINE LAKES IN SOUTHERN INDIANA (SURFACE-REDUCTION)

RUTH ANN GYURE, Purdue University

Abstract

In this study, we examined the limnology and microbial ecology of two acid strip mine lakes in the Greene-Sullivan State Forest near Dugger, Indiana. Reservoir 29 is a larger lake (225 ha) with water column pH of 2.7 and sediment pH of 3.8. Lake B, a smaller (20 ha) lake to the south of Reservoir 29, also has an acidic water column (pH 3.4) but more neutral sediments (pH 6.2). Both have very high sulfate concentrations: 20-30 mM in the water column and as high as 100 mM in the hypolimnion of Lake B. Low allochthonous carbon and nutrient input characterize these lakes as oligotrophic, although algal biomass is higher than would be expected for this trophic status. In both lakes, algal populations are not diverse, with a few species of single-celled Chlorophyta and euglenoids dominating. Algal biomass is concentrated in a thin 10 cm layer at the hypolimnion/metalimnion interface, although light intensity at this depth is low and severely limits productivity. Bacterial activity based on ('14)C-glucose incorporation is highest in the hypolimnion of both lakes, and sulfate-reduction is a dominant process in the sediments. Rates of sulfate-reduction compare with those in other freshwater environments, but are not as high as rates measured in high sulfate systems like saltmarsh and marine sediments. When samples from either lake were pH-adjusted and allowed to equilibrate for 12-24 h, rates were highest at pH 7. However, because we showed energy limitation even at higher pH, the direct effect of low pH may not be solely responsible for relatively low in situ rates. In both lakes, sulfate-reduction was stimulated by a variety of added organic compounds and H(,2), although organic acids were toxic at low pH and concentrations >0.1 mM. Pyrite was formed in the sediments of both lakes, and was formed during relatively short-term incubation of samples in the laboratory. Its formation in acid sediments allows a sink for consumption of iron, sulfur, and excess acidity. Pure cultures were not obtained at low pH, although active sulfate-reduction, H(,2)S evolution, and pH increase were demonstrated in pH 3.8 enrichment cultures of Reservoir 29 sediment bubbled with H(,2). A number of Desulfovibrio strains were isolated at pH 7. These isolates showed uptake of ('35)SO(,4) at pH 6 or 7, but not at pH 4 or 5.

Degree

Ph.D.

Subject Area

Microbiology

COinS