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Workreport 2020-2

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Name:

Microbial Metabolism Resulting from the Mixing of Sulfate-Rich and Methane-Rich Deep Olkiluoto Groudwaters in Drillholes OL-KR11, OL-KR13 and OL-KR46

Writer:

Bell, E., Lamminmäki, T., Pitkänen, P., Bernier-Latmani, R.

Language:

English

Page count:

130

Summary:

Olkiluoto, an island in south-west Finland, has been selected as the site for a deep geological repository for the final storage of spent nuclear fuel. It is therefore important to understand the geomicrobial processes underway at this site to ensure long-term, safe storage of the fuel. Of particular concern is the generation of sulfide, as it can induce corrosion of the waste-bearing copper canisters. Groundwater at Olkiluoto is hydrogeochemically stratified with depth, and sulfide production is observed when shallower sulfate-rich groundwater mixes with deeper more saline methane-rich groundwater.

To constrain the electron donor(s) driving the production of sulfide (sulfidogenesis), three groundwaters from different depths with high, intermediate and low concentrations of sulfide were investigated. The three groundwaters vary in their bicarbonate, sulfate, methane, and chloride concentration.

Detailed metaproteogenomic characterisation coupled to hydrogeochemical and isotopic analyses uncovered distinct communities involved in sulfur, carbon, nitrogen and iron cycling. The data shows that, in the deepest of the three groundwaters investigated (OL-KR46_570), sulfate reduction is fuelled by hydrogen as well as organic carbon from primary production and fermentation. At the transition between sulfate-rich and methane-rich groundwaters (OL-KR13_405), sulfate-reducing bacteria oxidise hydrogen and small organic compounds. Methane oxidising archaea are also detected, but it was not possible to clearly constrain the electron acceptor coupled to this process. In the third groundwater (OL-KR11_411), also a mixture of sulfate-rich and methane-rich waters, sulfide is often below detection limit, but evidence points towards the reduction of sulfate and subsequent oxidation of sulfide in a cryptic sulfur cycle. The results contribute towards our understanding of microorganisms in deep terrestrial subsurface ecosystems and their role in hydrogeochemical cycling.

Keywords:

bedrock, deep groundwater, sulfate-reducing bacteria, sulfide, metagenomics, metaproteomics

File(s):

WR 2020-02_web (pdf) (7.8 MB)


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