Page 57 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Natural CPLs are therefore a mixture of mineral and biological matrices and are a promising sustainable alternative to current, harsher corrosion inhibition methods. The layer stability is, however, highly pH dependent, and the pH in turn is dependent on microbial processes. The hydrogen (H2) produced through corrosion can be an energy source for many microorganisms, including hydrogenotrophic methanogenic archaea that convert this substrate to methane (CH4), a potent greenhouse gas (Dean et al. 2018). However, the composition of microbial communities within natural CPLs is largely unknown. Associating chemical processes with microbial communities is essential in determining the formation and dynamics of corrosion- protective layers.
We studied 4-m-deep iron sheet piles at a pumping station in Gouderak, Zuid-Holland, the Netherlands. The Gouderak pump station was constructed in 1866 and pushes excess water out of the Stolwijksche Boezem into the river Hollandse IJssel. The iron sheet piles protect the dikes and banks from erosion. The average life span of these sheet piles ranges between 50 and 100 years. Their replacement is both a risky and expensive endeavor. At Gouderak, sheet piles were replaced preemptively 50 years after installment. Previous studies of iron sheet piles from similar environments in the Netherlands showed that a CPL often formed on the interface of the sheet pile and the surrounding sediment (Kip et al. 2017). This layer was also found on the Gouderak sheet piles. We investigated the geochemical composition and the microbial communities of the CPLs, the surrounding sediment, and the bulk sediment. The metabolic potential of the microorganisms was investigated using Illumina MiSeq sequencing and metagenome analysis of the same samples, providing a unique insight into the full functional potential of natural CPL communities. This data set was also interrogated to study the microbial community structure using rRNA gene-based phylogeny. The combination of microbial composition data, metabolic potential, and physicochemical parameters enabled us to reconstruct a microbial food web that is likely involved in CPL formation. This study provides insights into the microbiology of corrosion protection processes in freshwater ecosystems and is a follow-up on the microbial-diversity screening study of Kip et al. (2017). Our findings could support the development of screening protocols to investigate the current status of iron sheet piles and to decide whether replacement is required.
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