T89 Applications for DNA Sequencing and Microbial Analysis in Hydrogeology and Environmental Geosciences

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

THE ROLE OF BACTERIAL COMMUNITIES ON IN-SITU ARSENIC AND IRON CYCLING IN RIVERBANKS ALONG THE MEGHNA RIVER, BANGLADESH

Paper number: T89-8
Program: Technical Sessions
Time: 3:15 PM – 3:30 PM

Authors

Abstract

Along the Meghna River in Bangladesh, season and tidal river stage fluctuations cycles drive oxygen-rich river water into permeable banks, oxidizing dissolved iron (Fe(II)) and precipitating Fe(III)-oxyhydroxides (FeOOH). These Permeable Natural Reactive Barriers (PNRB) sorb arsenic (As) oxyanions arriving from groundwater discharge, but the role of bacteria in a PNRB has not previously been examined. We report a detailed analysis of microbial community structure, function, and biogeochemical transformations occurring within a previously characterized PNRB on the Meghna River during the early dry season (January), when gaining river conditions predominate. The PNRB is located up to 3 m depth along the river’s edge, located along the final 10 m of a well-studied 90 m groundwater flow path that is rich in dissolved Fe(II) and As. This zone undergoes robust mixing with the river and contains high solid-phase concentrations of Fe(III) and sorbed As within a zone of fine sand and silt at the low-tide river edge. The reducing aquifer up-gradient of the PNRB contains concentrations of As and Fe that are relatively constant year-round and even a microbial community populated by anaerobic bacteria that prefer strongly reducing conditions and employ the use of siderophores to dissolve Fe(III) in complex organo-mineral matrices, contributing to a steady release of As to groundwater. This contrast with the biogeochemical signals within the PNRB, wherein the community contains high relative abundances and increased diversity of bacteria with a range of chemoautotrophic and facultative, dissimilatory metabolisms capable of catalyzing the oxidation of Fe(II)/As(III), or reduction of Fe(III)/As(V) using labile dissolved organic carbon (DOC), respectively. At the time of sampling, we observed a simultaneous removal of Fe, As, and DOC within the PNRB. However, the metabolic flexibility of metabolisms, and range of aero-tolerances in these communities indicate they also possess the functional potential to switch between microbially-mediated oxidation and reduction, during high and low river stages, respectively. This study sheds new insights into how fine-scale aquifer structure interacts with local hydrodynamics and microorganisms to dynamically shift the sequestration and release of Fe and As to drinking water.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357913

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