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Oxygenation of acid sulfate soils stimulates CO2 emission: Roles of acidic dissolution and hydroxyl radical oxidation
Chemical Geology ( IF 3.9 ) Pub Date : 2020-02-01 , DOI: 10.1016/j.chemgeo.2019.119437
Peng Zhang , Songhu Yuan , Rong Chen , Xiaochuang Bu , Man Tong , Qiaoyi Huang

Abstract Emission of CO2 from acid sulfate soil regions has received great attention in recent years. Production of CO2 due to microbial respiration has been documented by previous studies, but the abiotic mechanisms are poorly understood. In this study, CO2 production was measured from oxygenation of 60 acid sulfate soil samples that were collected from a typical acid sulfate soil region. The soil samples were characterized by low pH (3.3–5.8) and high sulfate content (0.51–5.03 mg/g). The cumulative concentrations of CO2 were 0.76–54.54 μmol per g dry soil upon oxygenation for 24 h. When 0.1% HgCl2 was added into soil suspension to kill microbes, the yield of CO2 decreased by 8.7%–41.1%, which suggests that both microbial respiration and abiotic pathways contributed to CO2 production and abiotic pathway played a major role. Both acidic dissolution and hydroxyl radical ( OH) oxidation were identified to be the abiotic mechanisms for CO2 production. For acidic dissolution, CO2 was produced from the decomposition of carbonate by H+ generated. Production of CO2 from acidic dissolution was dependent on the content of carbonate and the generation of H+. A combination of Fe speciation sequential extraction and kinetic model shows that H+ was mainly generated from the oxidation of both Fe2+ and pyrite by O2. For OH oxidation, CO2 was produced from the oxidation of organic carbon by OH produced and its relative importance for CO2 production was estimated to be 14.6%–27.6%. OH was mainly produced from exchangeable Fe(II) oxidation in sulfuric horizon but from pyrite oxidation in potential acid sulfate soils. This study presents the overlooked abiotic mechanisms, acidic dissolution and OH oxidation, for CO2 emission in acid sulfate soils when perturbed by O2. Our findings implicate that contribution of microbial respiration for CO2 production is not as large as previously thought to be in acid sulfate soils, and instead abiotic mechanisms contribute largely, particularly for oxygenation of potential acid sulfate soils.

中文翻译:

酸性硫酸盐土壤的氧化刺激二氧化碳排放:酸性溶解和羟基自由基氧化的作用

摘要 近年来,酸性硫酸盐土壤区域的CO2排放受到了广泛关注。先前的研究已经记录了由于微生物呼吸而产生二氧化碳,但对非生物机制知之甚少。在本研究中,通过从典型酸性硫酸盐土壤区域收集的 60 个酸性硫酸盐土壤样品的氧化来测量 CO2 产量。土壤样品的特点是低 pH (3.3-5.8) 和高硫酸盐含量 (0.51-5.03 mg/g)。氧化 24 小时后,CO2 的累积浓度为 0.76–54.54 μmol/g 干土壤。当在土壤悬浮液中加入 0.1% HgCl2 杀死微生物时,CO2 的产量下降了 8.7%–41.1%,这表明微生物呼吸和非生物途径都有助于 CO2 的产生,非生物途径起主要作用。酸性溶解和羟基自由基 (OH) 氧化均被确定为 CO2 产生的非生物机制。对于酸性溶解,CO2 是由碳酸盐分解产生的 H+ 产生的。酸性溶解产生的 CO2 取决于碳酸盐的含量和 H+ 的产生。Fe 形态顺序提取和动力学模型的结合表明,H+ 主要由 O2 氧化 Fe2+ 和黄铁矿产生。对于 OH 氧化,CO2 是由产生的 OH 氧化有机碳产生的,其对 CO2 生产的相对重要性估计为 14.6%–27.6%。OH 主要来自硫酸层中的可交换 Fe(II) 氧化,但来自潜在酸性硫酸盐土壤中的黄铁矿氧化。这项研究提出了被忽视的非生物机制,酸性溶解和 OH 氧化,用于受 O2 扰动时酸性硫酸盐土壤中的 CO2 排放。我们的研究结果表明,微生物呼吸对 CO2 产生的贡献并不像以前认为的在酸性硫酸盐土壤中那么大,而是非生物机制的贡献很大,特别是对潜在酸性硫酸盐土壤的氧化作用。
更新日期:2020-02-01
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