The significance of microbial processes in hydrogeology and geochemistry

Abstract

Microbial processes affect the chemical composition of groundwater and the hydraulic properties of aquifers in both contaminated and pristine groundwater systems. The patterns of water-chemistry changes that occur depend upon the relative abundance of electron donors and electron acceptors. In many pristine aquifers, where microbial metabolism is limited by the availability of electron donors (usually organic matter), dissolved inorganic carbon (DIC) accumulates slowly along aquifer flow paths and available electron acceptors are consumed sequentially in the order dissolved oxygen > nitrate > Fe(III) > sulfate > CO 2 (methanogenesis). In aquifers contaminated by anthropogenic contaminants, an excess of available organic carbon often exists, and microbial metabolism is limited by the availability of electron acceptors. In addition to changes in groundwater chemistry, the solid matrix of the aquifer is affected by microbial processes. The production of carbon dioxide and organic acids can lead to increased mineral solubility, which can lead to the development of secondary porosity and permeability. Conversely, microbial production of carbonate, ferrous iron, and sulfide can result in the precipitation of secondary calcite or pyrite cements that reduce primary porosity and permeability in groundwater systems.

Large Fractions of CO 2 -Fixing Microorganisms in Pristine Limestone Aquifers Appear To Be Involved in the Oxidation of Reduced Sulfur and Nitrogen Compounds

“…Factors that affect microbial diversity and abundance in groundwater ecosystems were previously linked to the interplay between organic contaminants, nutrients, and hydrogeology (8,(51)(52)(53). In addition, seasonal hydrological dynamics, e.g., resulting from snowmelt, may have strong effects on groundwater microbial community composition (54).…”

Diffuse hydrological mass transport through catchments: scenario analysis of coupled physical and biogeochemical uncertainty effects

“…Regarding bacterial degradation of organic contaminants, for instance, the subsurface permeability affects the availability of ratelimiting electron acceptors and donors, as well as the bacterial transport and community structure. Microbial processes can in turn also influence the permeability (Chapell, 2000). However, although there may clearly be a relation between attenuation and permeability, it is highly uncertain how and how strongly attenuation rates are correlated with K. Not even the sign of correlation can be determined a priori.…”

Denitrifying Bacteria from the Genus Rhodanobacter Dominate Bacterial Communities in the Highly Contaminated Subsurface of a Nuclear Legacy Waste Site

“…Microorganisms in the terrestrial subsurface provide critical ecosystem services that include the mitigation of contaminants (33). Research on subsurface ecosystems has intensified over the past two decades, leading to important discoveries on the ecology, physiology, and phylogeny of subsurface microorganisms (14,24). However, despite this excellent progress, the structure-function relationships of subsurface microorganisms remain largely uncharacterized.…”