灞河溶解性有机质三维荧光光谱特征及相对分子质量分布研究

3D fluorescence spectroscopic characteristics and relative molecular mass distribution of riverine dissolved organic matter in Bahe River,Xi ’an,Shaanxi

为了研究溶解有机质(DOM)与水质的相关性,联合应用三维荧光光谱(3D-EEMs)和液相-有机碳-有机氮检测(LC-OCD-OND)技术,在河流上游源区、中游城镇与下游城市河段设置16个采样点,结合人类活动及河流地貌特征对灞河流域的影响,研究了西安市灞河水体DOM。结果表明,河水DOM主要由生物大分子、腐殖质类物质、腐殖质降解产物和低分子中性物质组成,平均质量浓度分别为0.157 mg/L、1.746 mg/L、0.478 mg/L、0.361 mg/L。类腐殖荧光物质(紫外光区富里酸和类腐殖酸)主要集中在相对分子质量为1000~20000的腐殖质类物质中,占DOM总量的46.5%;类蛋白荧光物质(可见光区色氨酸和酪氨酸)主要分布在相对分子质量大于20000的生物大分子和相对分子质量小于350的低分子中性物质中,约占DOM总量的15.1%。从源头到入灞河口,河水DOM含量水平由高到低的顺序为城市河段、城镇河段、源区河段。灞河水体总体腐殖化程度较弱,陆生源DOM贡献较小,下游城市河段DOM中自生源指数(BIX)相对较高,微生物及藻类代谢活动旺盛,新生自生源较多。下游污水处理厂出水对灞河下游水体中DOM组成及水质的变化具有关键作用,影响河水营养状态的潜在因子包括TN、EC、DO、生物大分子、腐殖质类物质和低分子中性物质。因此,3D-EEMs及LC-OCD-OND联用技术可以用来表征河流水质的空间异质性,并对污染物组分进行定量化判别和来源解析。

The present paper is aimed to identify and determine the fluorescent component features and the molecular weight variation of DOM(Dissolved Organic Matter)in the longitudinal gradient of the Bahe River.The chief aim of the paper is to analyze and determine the mutual relation between the DOM and the water quality,so as to make clear the status-in-situ of the river source,the dynamic process and main control factors of DOM in the river.And,for the research purpose,we have managed to analyze the DOM of the river in terms of the 3-D fluorescence spectroscopy(3 D-EEMs)and liquid-phase-organic carbon-organic nitrogen detection(LC-OCD-OND)joined with the water’s physical and chemical componential factors.The results of our analysis show that the DOM of its water is mainly made up of biopolymers,humic substances,building blocks and low molecular neutrals,in correspondence with their relative molecular mass.The average concentration content rates of DOM are equal to 0.157,1.746,0.478 and 0.361 mg/L,respectively.More specifically speaking,humic-like fluorescence peaks up A and C of the same terrestrial origin,though the sources of the proteinlike and humic-like components are obviously different.For example,humic fluorescent contents(fulvic acid and humic acid in the ultraviolet region)have mainly been clustered on the humic substances with their relative molecular mass ranging from1000 to 20000,accounting for 46.5%of the total DOM.But,the protein-like fluorescent substances(in the visible region abundant with tryptophan and tyrosine)are mainly distributed among the biologically macromolecules with Mr>20000 and Mr<350,in a percentage of 15.1%of the total DOM.From the top source of the river,the order for DOM content from high to low can be classified in a descending order of urban reach to the upper suburban source reach.And,in terms of the biological index(BIX)of DOM,the downstream urban reach proves to be higher,with the metabolism of microorganisms and algae being vigorous,and the neonatal autochthonous(authigenic)being much more active.The potential factors affecting the nutritional status of the river water include TN,EC,DO,biological macromolecules,humic substances,and low molecular neutral substances.Thus,it can be concluded that the overall humification degree of the Bahe River is relatively weak,and the contribution to the terrestrial DOM tends to be bigger.The effluent of the downstream sewage treatment plant plays a key role in the DOM composition and water quality change in the lower reaches of the river.The combination of 3 D-EEMs and LC-OCD-OND can be used to identify and determine the spatial heterogeneity of the river water quality by quantitatively discriminating the pollutant components and analyzing the source of DOM.