Redox Potential and Seasonal Porewater Biogeochemistry of Three Mountain Wetlands in Southeastern Kentucky, USA

Abstract

Redox potentials (Eh) were monitored bimonthly and porewater chemistry was analyzed seasonally at three slightly-acidic, high-elevation Kentucky wetlands that differed in hydrology, parent materials, and vegetation. At all sites, Eh values were below 300 mV, which indicated that reducing conditions persisted within the upper 90 cm and fluctuated mainly within the range of iron and sulfate reduction. Significant relationships of Eh values with depth were observed only at the Martins Fork wetland, where precipitation was the primary water source. The strongest and most stable reducing conditions, observed at the Kentenia site, reflected consistently high water levels, which were sustained by ground water. The third wetland (Four Level) was distinguished by irregular Eh fluctuations coinciding with strong seasonal ground-water upwelling. Although Fe 3+ and SO 4 2-were the primary terminal electron acceptors in all wetlands, porewater chemistry also varied significantly by season and soil depth in response to piezometric water level fluctuations. Additional factors that influenced porewater chemistry included: (1) the presence of limestone parent materials that affected porewater pH, Ca 2+ , and Mg 2+ ; and (2) the prevalence of sphagnum moss or graminoid species that influenced dissolved organic carbon, CO 2 , and CH 4 . Results from this study indicated the diverse range and importance of multiple factors in controlling biogeochemical processes and properties in small, highelevation Appalachian wetlands.

Seasonal variability of tropical wetland CH<sub>4</sub> emissions: the role of the methanogen-available carbon pool

“…Conversely, seasonal macrophyte growth may result in increased methanotrophy due to increased O 2 transport to the subsurface. Seasonal variability in redox potential in wetland environments is controlled by microbial activity, and hence is indirectly controlled by temperature, nutrient availability, water table level and root biomass, amongst other factors (Seybold et al, 2002;Thompson et al, 2009;Schmidt et al, 2011). However, few long-term measurements of redox potential have been performed over seasonal timescales, and further research is required to determine the large-scale redox variability in wetland environments.…”

“…Singh, 2001;Seybold et al, 2002), although pH responses to redox potential and water table can vary widely (e.g. Singh et al, 2000;Thompson et al, 2009). Although seasonal variation in wetland pH as a significant control on CH 4 emissions is a viable hypothesis, to our knowledge there are currently no repeat measurements of pH in response to flooding in tropical wetlands.…”

Dynamics of oxidized and reduced iron in a northern hardwood forest

“…Yet we consistently found that a significant fraction of total Fe was in the reduced form, and this fraction was not related to the concentrations of DO. If microbial reduction of Fe was a significant process, concentrations of Fe(II) would be expected to be several orders of magnitude higher, as in wetland pore waters (Thompson et al 2009). Highly elevated Fe(II) concentrations, indicating reducing conditions (accompanied by odors of reduced sulfur compounds and lower sulfate concentrations) were observed only in a few isolated instances during our study (e.g., W1 high hardwood Oa horizon during summer and fall months).…”

Plant community composition as a function of geochemistry and hydrology in three Appalachian wetlands

“…The Martins Fork soils were characterized by pH of 5·0–5·2, base saturation < 26%, CEC < 11·0 cmol c /kg, and OC < 3·6% (Thompson et al , 2007). Martins Fork porewater was the most acidic of the three sites with pH of 4·5–5·5 and low Ca 2+ (<3·0 mg l −1 ) and Mg 2+ (<1·9 mg l −1 ) concentrations (Thompson et al , 2009).…”

“…The objectives of this study were to quantitatively assess the vegetation at three small southeastern Kentucky wetlands (Martins Fork, Kentenia, and Four Level) to determine plant species composition, including the identification of any uncommon or rare species, and to relate the vegetation characteristics to environmental attributes. Investigations indicated that these wetlands differed substantially in soil moisture conditions, soil properties, and porewater chemical composition (Thompson et al , 2007, 2009). Visually evident vegetation differences among the wetlands were expected to be related to differing abiotic factors.…”