Application of voltammetric microelectrodes for studying redox biogeochemistry in prairie pothole wetland sediments

Redox-active species play a regulatory role in lacustrine sediments, controlling a myriad of biogeochemical processes such as element cycling, greenhouse gas emissions, and contaminant fate. The deployment of microelectrodes combined with voltammetric techniques offers a convenient yet uncompromised way of quantifying the in situ concentration of major redox-active species, including O₂, Fe²⁺, Mn²⁺, Fe³⁺-complexes, and free reduced sulfur (H₂S, HS^-, S^2-), in the sediment porewater at the sub-cm vertical scale. Here, we applied voltammetric microelectrodes to quantify the vertical distribution of redox-active species from mesotrophic wetlands in the Prairie Pothole region that have distinct hydrogeology, carbon inputs, and terminal electron acceptor composition. A bismuth film electrode was used to measure reduced sulfur species at high concentrations (> 100 µM) while a mercury/gold amalgam electrode was employed to measure all other redox-active species. Dissolved organic carbon and the identity of microbial communities based on 16S rRNA gene sequencing were also determined to assess the relationship between redox and microbial gradients in the sediment cores as a function of space. This combination of geochemical and microbial characterizations of lacustrine benthic environments is a powerful approach that enables us to better understand processes that drive carbon degradation and greenhouse production in these systems.