Influence of pH on the balance between methanogenesis and iron reduction

Abstract

Methanogenesis and iron reduction play major roles in determining global fluxes of greenhouse gases. Despite their importance, environmental factors that influence their interactions are poorly known. Here, we present evidence that pH significantly influences the balance between each reaction in anoxic environments that contain ferric (oxyhydr)oxide minerals. In sediment bioreactors that contained goethite as a source of ferric iron, both iron reduction and methanogenesis occurred but the balance between them varied significantly with pH. Compared to bioreactors receiving acidic media (pH 6), electron donor oxidation was 85% lower for iron reduction and 61% higher for methanogenesis in bioreactors receiving alkaline media (pH 7.5). Thus, methanogenesis displaced iron reduction considerably at alkaline pH. Geochemistry data collected from U.S. aquifers demonstrate that a similar pattern also exists on a broad spatial scale in natural settings. In contrast, in bioreactors that were not augmented with goethite, clay minerals served as the source of ferric iron and the balance between each reaction did not vary significantly with pH. We therefore conclude that pH can regulate the relative contributions of microbial iron reduction and methanogenesis to carbon fluxes from terrestrial environments. We further propose that the availability of ferric (oxyhydr)oxide minerals influences the extent to which the balance between each reaction is sensitive to pH. The results of this study advance our understanding of environmental controls on microbial methane generation and provide a basis for using pH and the occurrence of ferric minerals to refine predictions of greenhouse gas fluxes.

Influences of pH and substrate supply on the ratio of iron to sulfate reduction

“…We characterized the pH, elemental composition, organic matter content, particle size distribution, mineralogy, and microbial community composition of the sediment. Results of the analyses are presented in Marquart et al (2019). To briefly summarize, those analyses showed that the sediment was primarily composed of clay minerals with 0.7 mmol Fe and 7.5 mmol organic carbon per gram.…”

“…We analyzed the samples as described previously (Marquart et al, 2019). A detailed description of the analysis is available in the Supporting Information.…”

Biogeochemical dynamics and microbial community development under sulfate- and iron-reducing conditions based on electron shuttle amendment

“…Geobacter in particular has been shown to predominate in sedimentary environments where Fe III reduction is occurring [86][87][88][89][90][91], typically in response to acetate biostimulation [56,[92][93][94][95][96][97]. This pattern is well-established, as Geobacter blooms have been observed in Fe III -and acetate-amended bioreactors using material from rice paddies [98], marshes [99], and aquifer sediment [100,101]. Geobacter has also been enriched in acetate-amended experimental systems where AQDS (not Fe III ) was added as the sole electron acceptor [102].…”

Analisis Molekular dan Karakteristik Hidrogen Sianida (HCN)

“…143,1 kj/mol Tabel 3. Sifat Termodinamika Hidrogen Sianida pembuatan asam sianida (HCN) yang paling sering dilakukan menggunakan metode, yang diciptakan oleh Leonid Andrussow, dimana metana (155)(156)(157)(158)(159)(160)(161)(162)(163)(164)(165)(166)(167)(168)(169)(170)(171)(172)(173)(174) , dan amonia bereaksi pada suhu [206] sekitar 1200 o C menggunakan katalis platina (175)(176)(177)(178)(179)(180)(181)(182)(183)(184)(185)(186)(187)(188)(189)(190)(191)(192)(193)(194) , dengan reaksi sebagai berikut :…”