Microbiology Department, The Ohio State University, Columbus, OH, 43210, USA.
Environmental Molecular Sciences Laboratory, Richland, WA, 99350, USA.
Glob Chang Biol. 2017 Aug;23(8):3107-3120. doi: 10.1111/gcb.13633. Epub 2017 Feb 23.
Inland waters are increasingly recognized as critical sites of methane emissions to the atmosphere, but the biogeochemical reactions driving such fluxes are less well understood. The Prairie Pothole Region (PPR) of North America is one of the largest wetland complexes in the world, containing millions of small, shallow wetlands. The sediment pore waters of PPR wetlands contain some of the highest concentrations of dissolved organic carbon (DOC) and sulfur species ever recorded in terrestrial aquatic environments. Using a suite of geochemical and microbiological analyses, we measured the impact of sedimentary carbon and sulfur transformations in these wetlands on methane fluxes to the atmosphere. This research represents the first study of coupled geochemistry and microbiology within the PPR and demonstrates how the conversion of abundant labile DOC pools into methane results in some of the highest fluxes of this greenhouse gas to the atmosphere ever reported. Abundant DOC and sulfate additionally supported some of the highest sulfate reduction rates ever measured in terrestrial aquatic environments, which we infer to account for a large fraction of carbon mineralization in this system. Methane accumulations in zones of active sulfate reduction may be due to either the transport of free methane gas from deeper locations or the co-occurrence of methanogenesis and sulfate reduction. If both respiratory processes are concurrent, any competitive inhibition of methanogenesis by sulfate-reducing bacteria may be lessened by the presence of large labile DOC pools that yield noncompetitive substrates such as methanol. Our results reveal some of the underlying mechanisms that make PPR wetlands biogeochemical hotspots, which ultimately leads to their critical, but poorly recognized role in regional greenhouse gas emissions.
内陆水域正日益被视为向大气排放甲烷的重要地点，但推动这些通量的生物地球化学反应却知之甚少。北美洲的草原洼地（PPR）是世界上最大的湿地复合体之一，拥有数百万个小而浅的湿地。PPR 湿地的沉积物孔隙水中含有一些在陆地水生环境中从未记录过的最高浓度的溶解有机碳（DOC）和硫物种。本研究采用一系列地球化学和微生物学分析方法，测量了这些湿地中沉积物碳和硫转化对甲烷向大气通量的影响。该研究代表了 PPR 内首次进行的地球化学和微生物学耦合研究，表明丰富的易生物降解 DOC 池如何转化为甲烷，导致该温室气体向大气中的通量达到前所未有的高度。丰富的 DOC 和硫酸盐还支持了在陆地水生环境中测量到的最高硫酸盐还原速率之一，我们推断这在很大程度上解释了该系统中碳矿化的情况。在活跃的硫酸盐还原区积累的甲烷可能是由于自由甲烷气体从较深位置的运输，或者是产甲烷作用和硫酸盐还原同时发生的结果。如果这两种呼吸过程同时发生，那么硫酸盐还原菌对产甲烷作用的任何竞争抑制作用，可能会因大量易生物降解的 DOC 池而减弱，这些池提供非竞争基质，如甲醇。我们的研究结果揭示了使 PPR 湿地成为生物地球化学热点的一些潜在机制，这最终导致它们在区域温室气体排放中发挥关键但尚未得到充分认识的作用。
