淹水条件下三峡库区典型消落带土壤释放DOM的光谱特征：荧光光谱

Spectral Characteristics of Dissolved Organic Matter(DOM) Releases from Soils of Typical Water-Level Fluctuation Zones of Three Gorges Reservoir Areas: Fluorescence Spectra

作为水体DOM的重要来源,消落带土壤淹水释放过程十分重要.本文以三峡库区典型消落带土壤为例,通过模拟正常淹水和厌氧淹水的两种条件,利用荧光光谱,着重定性地分析并讨论了土壤向上覆水体释放DOM的动态特征.结果表明,消落带4个区域土壤淹水后产生的DOM荧光特性,呈现出和可见-紫外光谱相似特征,对上覆水体DOM荧光特征有重要贡献.淹水初期的快速释放及后期去除机制,是水体DOM荧光组分的动态'源-汇'平衡的关键;其中类腐殖峰(A和C)受无机矿物相的吸附-释放影响明显,而类蛋白峰(B和T)受微生物影响较为明显.另外,所有土壤淹水释放后水体DOM均呈现出'内源+外源'的复合特征.除忠县石宝寨(SB)外,整个淹水周期,其余区域土壤在厌氧和正常淹水条件下,水体DOM荧光特征的差异性不明显,这可能和土壤自身组成(例如无机矿物组成和有机组分)的复杂程度有关.结合可见-紫外光谱,两种技术相互补充,证明了土壤释放('源')和去除('汇')机制是控制DOM动态变化的重要因素;而淹水初期的较强芳香性和腐殖化程度,以及较强的陆源特征,无疑有利于进一步解释污染物在淹水过程中的环境行为,为进一步了解DOM的环境角色提供数据基础和实验支撑.

As an important sources of dissolved organic matter（ DOM） in aquatic system,DOM releases from flooding or submerged soils is a key process in water-level fluctuation zones. In this study,four typical sites in water-level fluctuation zones of Three Gorges Reservoir areas were selected to conduct simulated soil flooding experiments,under ambient（ open air） and anoxic conditions. By using fluorescence spectrum technique,the dynamic and geochemical characteristics of DOM releases from flooding soils were investigated. Results showed that the trend or model of DOM releases observed by fluorescence spectrum in all soils from four sampling sites was similar to the observation by UV-Vis spectrum. Fluorescence property of DOM releases showed an important contribution to DOM fluorescence in overlying waters. The rapid releases at initial stage and removal mechanism for later dynamic equilibrium were crucial to explain the dynamic＂source-sink＂equilibrium in whole flooding period. Effect of inorganic mineral adsorption-desorption on humic-like components（ A and C peaks） was significant. Also,impact of microbial utilization on protein-like components（ B and T peaks） was confirmative. Additionally,all DOM samples had＂autochthonousness plus allochthonousness＂property. Except Shibaozhai（ SB） site in Zhongxian county,during the whole flooding period,all three other sites didn＇t show any significant difference between ambient and anoxic conditions. They could be explained by the high heterogeneity of soil property including minerals and organic components. Meanwhile,both the UV-Vis and fluorescence spectra were complementary for each other,and they evidentially showed that the ＂source-sink＂（ release and removal） mechanism in DOM releases from submerged soils was the core to decide the dynamics of DOM in overlying waters. Importantly,DOM showed higher aromaticity and humification at the initial release stage when flooding occurred,as well as the greater terrestrial source characteristics,which further helped to explain the environmental fates of pollutants in these environmental sensitive areas. It would also be useful for unveiling the role of DOM in environmental system in future.