(523c) Electrochemical Sensors for Microbial Activities in Benthic Sediments: A Sentry for Lacustrine P Biogeochemistry

Internal loading (i.e. release from benthic sediments) of PO₄^3- to the lacustrine water column could induce harmful algal blooms (HABs). The extents of internal PO₄^3- loading are difficult to constrain and detect in situ and in real time because fluxes are measured in laboratory incubations, monitoring approaches are difficult to deploy in the field, and the scales of microbially-induced redox gradients can occur on sub-centimeter scales. Release or entrained of PO₄^3- from benthic sediments is controlled by the activities of microorganisms in those sediments. In this work, we develop an electrochemical approach to detect, identify, and monitor benthic sediment-associated microbiological activities that could be deployed in situ and in real-time.

A series of laboratory and field experiments was conducted to identify electrochemical signatures associated with a variety of microbiological activities occurring in Lake Erie sediments. Our technique makes use of zero-resistance ammetry (ZRA) measurements, which we have previously used to diagnose microbiological activities. The approach uses inexpensive materials, demands little power, and can interrogate microbial activities at small spatial scales. The ZRA approach detects internal PO₄^3- loading (the release of PO₄^3-, as “dissolved reactive phosphorous” from sediments), which can contribute to harmful algal blooms (HABs). Microbial degradation of algal biomass and microbially-induced mineralogical transformations can profoundly influence the PO₄^3- concentration in the water column, and therefore, the potential for HABs despite adequate management of external PO₄^3- loading. Thus, microbial metabolism in PO₄^3--loaded benthic sediments represents a remnant threat to induce or contribute to HABs well into the future. Microbiological activities induce redox gradients in sediments, depending on the predominant terminal electron accepting process. Most notable from the standpoint of PO₄^3- flux is the anaerobic reductive solubilization of Fe(III) (hydr)oxide phases by Fe(III) reducing bacteria (FeRB), which releases PO₄^3- that was previously adsorbed to those phases. However, microbial activity can induce a variety of other chemical conditions that enhance or limit PO₄^3- solubility (e.g. Fe(II) oxidation, organic carbon mineralization, acid production, primary productivity). ZRA-based monitoring can determine extents and types of microbial metabolism in the sediments, be exploited for long-term stewardship of Lake Erie sediments, and serve as an “early-warning system” for internal PO₄^3- loading events.

This presentation describes our newly-developed, ZRA-based technique for monitoring sediment activity and internal PO₄^3- loads. We believe that this will eventually be an “early warning system” for internal PO₄^3--supported HABs.