We study peat deposits that overlie a mineral bed of Lockport Dolomite extending from eastern New York State to Guelph (Canada). These peat soils contain elevated concentrations of some metals (Zn and Cd) and sulfur (Figure 1). In this work, we report the variability in bacterial microbial community, enzymes involved in sulfate respiration, rate of sulfate reduction, and sulfur redox species as a function of soil depth and moisture content. Intact soil cores were colleted in Western New York in July 2002 (dry season) and March 2004 (wet season). The soil columns were collected along a gradient (visual inspection) starting in an area where there was no plant (onion) growth (78°6.146'W, 43°9.470'N) and moving eastwards for about 10 meters (second core), and for about 15 additional meters (third core). A total of three soil columns were pulled from the soil each season and brought to the laboratory where they were kept at 4°C. The undisturbed soil columns were then cut open and sectioned (5 cm intervals) for analyses. DNA was extracted from the sub-samples and Ribosomal Intergenic Spacer Analysis (RISA) was used to study bacterial communities. The dissimilatory sulfite reductase gene (dsrAB), a key enzyme in sulfate respiration (reduction of sulfite to sulfide), was amplified by PCR to assess the presence of sulfate reducers. The activity of sulfate reducers was determined by a sulfate reduction test. Bacterial communities differed along the profile and between seasons. The dsrAB genes were detected in sub-samples deeper than 45 cm. The rate of sulfate reduction was correlated to the presence of dsrAB genes. Furthermore, S-XANES analyses show that 40-60 % of the total sulfur in these soils exists in reduced forms (e.g., sulfides and/or thiol groups) while 20-30 % exists in oxidized forms (e.g., sulfate). Our results suggest that bacteria that specialize in sulfate reduction show distribution and activity patterns that may be relevant to understanding biogeochemical processes occurring in these metal- and sulfur- rich organic soils.

Figure 1. Total sulfur concentration (mg kg^-1) as a function of depth (cm) in soil cores collected during the dry season.