BIOGEOCHEMISTRY AND MOLECULAR MICROBIAL ECOLOGY OF GREAT SULPHUR SPRING, WESTERN LAKE ERIE, MICHIGAN

The Great Sulphur Spring is located along the western Lake Erie coastline, in southeastern Monroe County, MI.  First described by William H. Sherzer in 1900, the spring delivers a relatively constant 0.14 m³/s of water to Erie Marsh, a remnant of once much more extensive wetlands.  Spring waters (10 m depth, spring origin) were analyzed for major ions, trace metals, nutrients, tritium, ¹⁴C, ¹³C/¹²C, ²H/¹H, ¹⁸O/¹⁶O, and dissolved H₂, CO₂, CH₄, and N₂.  Geochemical data from the spring, and data from 32 USGS wells installed in Monroe County for a previous study, indicate the spring water most likely derives from the Salina Group of the Silurian/Devonian aquifer of southeastern Michigan.  Spring water is rich in Ca (627 mg/L), Sr (15.9 mg/L), SO₄ (1417 mg/L), and sulfide (1 mg/L), and is in striking contrast to the composition of Lake Erie water.  Over 350 Bacteria and 90 Archaea 16S rDNA sequences were obtained from the spring origin, and from microbial mats along shallow pond margins.  Based on sequence similarities to known Bacteria, chemolithotrophy and sulfur metabolism are dominant metabolic pathways at Great Sulfur Spring.  The Epsilonproteobacteria accounted for 15% of the sequences from the spring origin, and were related to several recently-cultured organisms that oxidize H₂, and reduced sulfur in inorganic and organic (e.g., petroleum) compounds.  If present in the Silurian/Devonian aquifer, Epsilonproteobacteria may contribute to the heterogeneous distribution pattern of calcium-magnesium-sulfate waters along regional ground water flow paths, and might indicate sulfuric-acid speleogenesis as an important factor in karst development in the region.  With only one exception, Archaea sequences fell into phylogenetic groups for which there are no cultured representatives, and hence, no inference of function can be made for these ubiquitous organisms.  Several spring Archaea sequences were related to sequences that dominate cold, oxic ocean waters, or to those detected in sediments at depth in the Great Lakes.   Molecular analysis of the microbial community of Great Sulphur Spring provides insight into the biogeochemistry of the Silurian/Devonian carbonate aquifers that compose large portions of the basins of the Laurentian Great Lakes.