再生水灌溉后农田土壤淋溶液DOM光谱学特征

再生水灌溉农业是实现再生水回用的有效途径，其天然优势和操作可行性已得到普遍认可。再生水灌溉农业能够取得良好的生态效益、社会效益和经济效益，但灌溉过程可能导致土壤有机质的性质异化和非定向流失，相关问题尚没有引起足够重视。选取溶解性有机质（DOM）为目标对象，对灌溉过程农业土壤淋溶液DOM谱学信息差异化机制这一科学问题展开研究。以污水源再生水和河水源地表水（参比对照）为灌溉水源，借助一维原状土柱分析灌溉过程对土壤和淋溶液的影响，对土壤表面形貌（SEM）、淋溶液DOM紫外可见光谱（UV-Vis）和三维荧光光谱（3D-EEMs）进行比对，初步掌握灌溉后土壤淋溶液DOM的基础信息。结果表明：灌溉后的土壤团聚体结构松散、表面粗糙，出现细粒组分聚集和粘结的现象。土壤有机质随土壤深度增加逐渐减少，土壤DOM在10～20 cm土层分布最多；灌溉过程能够增加0～30 cm土壤有机质和0～20 cm土壤DOM含量，证明土壤对灌溉水有机物具有截留作用。两种淋溶液DOM的UV-Vis谱图比较相近，均在240～270 nm区间出现吸收平台（源于DOM不饱和双键共轭结构）；相比之下，再生水源土壤淋溶液DOM的芳香化程度更低、结构更简单，两种淋溶液DOM中富里酸含量高于胡敏酸。淋溶液DOM三维荧光光谱仅出现一处荧光峰，位于E_x/E_m=260～270/420～430 nm区域，表明有类腐殖质组分的存在。经与前期研究结果比对，推测氨基酸类物质、类蛋白组分等可能被（灌溉过程）阻滞于土壤体系；自生源（内源）DOM对土壤淋溶液DOM的贡献更大，而外源DOM的影响程度有限。相关结果有助于深度评估再生水灌溉过程农业土壤DOM（或有机质）的流转归趋和生态效应。

Spectral Characteristics of Dissolved Organic Matter (DOM) in Leachate Released From Agricultural Soil Irrigated With Reclaimed Water

Agricultural irrigation is effective for the reutilization of reclaimed water, and the natural advantages and operational feasibility have been generally approved. Agricultural irrigation with reclaimed water can achieve acceptable ecological, social and economic benefits, while organic matters in the soil might lose or change during the irrigation process, and the related issue has received insufficient attention. Dissolved organic matter (DOM) was selected as the analysis target, and the scientific issue was to reveal the variation mechanism of DOM spectral information in leachate released from the irrigated agricultural soil. Samples of reclaimed water (from wastewater treatment plant) and surface water (from the river, for contrast) were used, and a one-dimensional undisturbed soil column was applied to study the irrigation effect on soil and soil leachate. The electronic scanning microscopy (SEM), ultraviolet-visible spectroscopy (UV-Vis) and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEMs) were involved in reveal the fundamental information of DOM released from soil irrigated with water samples. The results show: that soil aggregates appear lose structure and rough surface after irrigation, and small soil particles gather and stick together. The contents of organic matter decrease with the increased soil depth, and DOM content reaches maximal at 10~20 cm of the soil layer. The concentrations of organic matter (0~30 cm of soil layer) and DOM (0~20 cm of soil layer) increase after irrigation, suggesting the interception effect of water organic compounds by soil samples. The UV-Vis spectra of leachate are similar, and the unsaturated double-bond conjugate structures cause the absorption regions at 240~270 nm in DOM. The lower aromatization degree and more straightforward structure of DOM can be detected in soil leachate irrigated with reclaimed water, and the content of fulvic acid is higher than that of humic acid. The only fluorescence peak of DOM appears in theE_x/E_m=260～270/420～430 nm, regarded as a humus-like component. Compared to the previous results, it is deduced that amino acid-like and protein-like components might be adsorbed and retained in soil. Bio-source (endogenous) DOM plays a more important role than exogenous DOM in soil leachate. The achievements are significant to estimate further the circulation, transportation and ecological effect of DOM or organic matters in the reclaimed water-irrigated agricultural soil systems.