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Pore-scale controls on hydrological and geochemical processes in peat: Implications on interacting processes
Earth-Science Reviews ( IF 12.1 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.earscirev.2020.103227
C.P.R. McCarter , F. Rezanezhad , W.L. Quinton , B. Gharedaghloo , B. Lennartz , J. Price , R. Connon , P. Van Cappellen

Abstract Peatlands are wetlands that provide important ecosystem services including carbon sequestration and water storage that respond to hydrological, biological, and biogeochemical processes. These processes are strongly influenced by the complex pore structure of peat soils. We explore the literature on peat pore structure and the implications for hydrological, biogeochemical, and microbial processes in peat, highlighting the gaps in our current knowledge and a path to move forward. Peat is an elastic and multi-porous structured organic soil. Surficial (near-surface) peats are typically dominated by large interconnected macropores that rapidly transmit water and solutes when saturated, but these large pores drain rapidly with a reduction in pore-water pressure, and disproportionally decrease the bulk effective hydraulic conductivity, thus water fluxes that drive ecohydrological functions. The more advanced state of decomposition of older (deeper) peat, with a greater abundance of small pores, restricts the loss of moisture at similar soil water pressures and is associated with higher unsaturated hydraulic conductivities. As evaporation and precipitation occur, peat soils shrink and swell, respectively, changing the hydrological connectivity that maintain physiological processes at the peat surface. Due to the disproportionate change in pore structure and associated hydraulic properties with state of decomposition, transport processes are limited at depth, creating a zone of enhanced transport in the less decomposed peat near the surface. At the micro-scale, rapid equilibration of solutes and water occurs between the mobile and immobile pores due to diffusion, resulting in pore regions with similar chemical concentrations that are not affected by advective fluxes. These immobile regions may be the primary sites for microbial biogeochemical processes in peat. Mass transfer limitations may therefore largely regulate belowground microbial turnover and, hence, biogeochemical cycling. For peat, the development of a comprehensive theory that links the hydrological, biological, and biogeochemical processes will require a concerted interdisciplinary effort. To that end, we have highlighted four primary areas to focus our collective research: 1) understanding the combined and interrelated effects of parent material, decomposition, and nutrient status on peat pore connectivity, macropore development and collapse, and solute transport, 2) determining the influence of changing pore structure due to freeze-thaw or dewatering on the hydrology and biogeochemistry, 3) better elucidating the non-equilibrium transport processes in peat, and 4) exploring the implications of peat’s pore structure on microbiological and biogeochemical processes.

中文翻译:

泥炭中水文和地球化学过程的孔隙尺度控制:对相互作用过程的影响

摘要 泥炭地是提供重要生态系统服务的湿地,包括对水文、生物和生物地球化学过程做出响应的碳封存和水储存。这些过程受到泥炭土复杂孔隙结构的强烈影响。我们探索了有关泥炭孔隙结构的文献及其对泥炭中水文、生物地球化学和微生物过程的影响,突出了我们当前知识的差距和前进的道路。泥炭是一种具有弹性和多孔结构的有机土壤。地表(近地表)泥炭通常由相互连接的大孔所支配,这些大孔在饱和时会迅速传输水和溶质,但这些大孔会随着孔隙水压力的降低而迅速流失,并不成比例地降低整体有效水力传导率,因此,驱动生态水文功能的水通量。老(更深)泥炭的更高级分解状态,具有更丰富的小孔,在相似的土壤水压下限制了水分的流失,并与更高的不饱和水力传导率有关。随着蒸发和降水的发生,泥炭土分别收缩和膨胀,改变了维持泥炭表面生理过程的水文连通性。由于孔隙结构的不成比例变化以及与分解状态相关的水力特性,运输过程在深度受到限制,在靠近地表的较少分解的泥炭中形成了一个增强的运输区域。在微观尺度上,由于扩散,溶质和水在流动和固定孔隙之间发生快速平衡,导致孔隙区域具有相似的化学浓度,不受平流通量的影响。这些不动的区域可能是泥炭中微生物生物地球化学过程的主要场所。因此,传质限制可能在很大程度上调节地下微生物的更新,从而调节生物地球化学循环。对于泥炭,将水文、生物和生物地球化学过程联系起来的综合理论的发展需要跨学科的协同努力。为此,我们强调了四个主要领域来集中我们的集体研究:1) 了解母体材料、分解和营养状态对泥炭孔隙连通性、大孔隙发育和坍塌以及溶质运输的综合和相互关联的影响,
更新日期:2020-08-01
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