Chow Alex T, Guo Fengmao, Gao Suduan, Breuer Richard S
Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA.
Chemosphere. 2006 Mar;62(10):1636-46. doi: 10.1016/j.chemosphere.2005.06.039. Epub 2005 Aug 10.
Soil organic matter is an important source of allochthonous dissolved organic matter inputs to the Sacramento-San Joaquin Delta waterways, which is a drinking water source for 22 million people in California, USA. Knowledge of trihalomethane (THM) formation potential of soil-derived organic carbon is important for developing effective strategies for organic carbon removal in drinking water treatment. In this study, soil organic carbon was extracted with electrolytes (deionized H2O and Na- or Ca-based electrolytes) of electrical conductivity bracketing those found in Delta leaching and runoff conditions. The extracts were physically and chemically separated into different fractions: colloidal organic carbon (0.45-0.1 microm), fine colloidal organic carbon (0.1-0.025 microm), and dissolved organic carbon (DOC) (<0.025 microm); hydrophobic acid (HPOA), transphilic acid, and hydrophilic acid. Two representative Delta soils, Rindge Muck (a peat soil) and Scribner Clay Loam (a mineral soil) were examined. Results showed that less than 2% of soil organic carbon was electrolyte-extractable and heterogeneous organic fractions with distinct THM reactivity existed. Regardless of soil and electrolytes, DOC and HPOA fractions were dominant in terms of total concentration and THMFP. The amounts of extractable organic carbon and THMFP were dependent on the cation and to a lesser extent on electrical conductivity of electrolytes. Along with our previous study on temperature and moisture effects on DOC production, we propose a conceptual model to describe the impacts of agricultural practices on DOC production in the Delta. DOC is mainly produced in the surface peat soils during the summer and is immobilized by accumulated salt in the soils. DOC is leached from soils to drainage ditches and finally to the Delta channels during winter salt leaching practices.
土壤有机质是萨克拉门托 - 圣华金河三角洲水道中异地溶解有机物质输入的重要来源，该三角洲是美国加利福尼亚州2200万人的饮用水源。了解土壤衍生有机碳的三卤甲烷（THM）生成潜力对于制定饮用水处理中有效去除有机碳的策略至关重要。在本研究中，使用电导率与三角洲淋溶和径流条件下的电导率相当的电解质（去离子水和钠基或钙基电解质）提取土壤有机碳。提取物在物理和化学上被分离成不同的部分：胶体有机碳（0.45 - 0.1微米）、细胶体有机碳（0.1 - 0.025微米）和溶解有机碳（DOC，<0.025微米）；疏水酸（HPOA）、亲脂酸和亲水酸。研究了两种具有代表性的三角洲土壤，林奇泥炭（一种泥炭土）和斯克里布纳粘壤土（一种矿质土）。结果表明，不到2%的土壤有机碳可被电解质提取，并且存在具有不同THM反应性的异质有机部分。无论土壤和电解质如何，就总浓度和THM生成潜力而言，DOC和HPOA部分占主导地位。可提取有机碳和THM生成潜力的量取决于阳离子，并且在较小程度上取决于电解质的电导率。结合我们之前关于温度和湿度对DOC产生影响的研究，我们提出了一个概念模型来描述农业实践对三角洲DOC产生的影响。DOC主要在夏季表层泥炭土中产生，并被土壤中积累的盐分固定化。在冬季盐分淋溶过程中，DOC从土壤中淋溶到排水沟中，最终进入三角洲河道。
