灞河流域溶解性有机质分子量分级表征及其与水质的相关性

Molecular weight fractionated characterization of dissolved organic matter and its correlation with water quality in the Bahe River Basin,Northwest China

溶解性有机质是水体中有机质分解与营养盐再生的核心载体之一,是碳、氮等生源要素生物地球化学循环的重要环节,也是水环境科学研究的重点内容.本研究应用液相-有机碳-有机氮检测(LC-OCD-OND)技术研究了西安市灞河流域水体中溶解性有机质(DOM)不同分子量组分特征,分析其与河水水质的相关性.结果表明:河水DOM按照分子量分布,主要由生物大分子、腐殖质类物质、腐殖质降解产物、低分子中性物质和低分子酸组成,各组分平均浓度分别为0.15、1.75、0.48、0.36和0.002 mg·L^(-1),河水中DOM总体含量水平由高到低的顺序为城市河段>城镇河段>源区河段.组分中分子量介于1000～20000 Da的腐殖质类物质占DOM总量的49.0%,含量及丰度从高到低依次为中游城镇段>污水厂出口段>污水厂下游河口段>上游源头段;分子量>20000 Da的生物大分子约占DOM总量的5.1%,丰度由高到低依次为污水厂出口>污水厂下游河口>上游源头>中游城镇段,污水处理厂出水所产生的外生源有机质对河流DOM的贡献最大.DOM不同分子量组分与水质的相关性明显,表明基于LC-OCD-OND分级表征的DOM各分子量组分和丰度不仅可以作为水质监测的一个综合性指标,也可以用来表征河流水质的空间异质性,并能对污染物各组分进行定量化判别和来源解析.

Abstract： Dissolved organic matter （DOM） is one of the core carriers of organic matter decomposi- tion and nutrient regeneration in water. It is an important link of biogeoehemical cycle of carbon and nitrogen, and the key content of water environmental science research. We used liquid chromatogra- phy-organic carbon detection-organic nitrogen detection （LC-OCD-OND） to investigate the molecu- lar weight distribution of riverine DOM in the Babe River of Xi＇ an City and further analyzed its cor- relation with water quality. The results showed that riverine DOM was composed of biopolymers, humic substances, humus degradation products, and low molecular-weight neutrals, with the ave- rage concentration of 0.15, 1.75, 0.48, 0.36 and 0.002 mg · L-l , respectively. The DOM along the river was in order of urban 〉 town 〉 river source. The humic substances with molecular weight of 1000-20000 Da accounted for 49.0% of total DOM which followed the order of town〉 waste water treatment plants （WWTPs） effluents〉river estuary〉 river source. The biopolymers with the molecu- lar weight of 〉20000Da accounted for 5.1% of total DOM, with the sequence of WWTPs effluents〉 river estuary〉river source〉town. The allochthonous （terrigenous） DOM produced by WWTPs efflu- ents had the greatest contribution to the riverine DOM. The fractions of DOM with different molecu- lar weights had significant correlations with water quality parameters. The results showed that the molecular weight fractions and abundance of DOM based on LC-OCD-OND could be used as acom-prehensive index for water quality monitoring, to characterize the spatial heterogeneity of river water quality, and used for quantitative identification and source apportionment of pollutant components.