河岸带地下水溶解性有机物输入对As迁移转化的影响

为了研究河岸带地下水DOM（dissolved organic matter，溶解性有机物）对As迁移转化的影响，选取了安徽省宿州市杨庄乡的奎河断面作为研究对象，通过三维荧光光谱技术、区域积分法、矿物E_h-pH稳定性图解，分析河岸带地下水荧光组分、As形态及其质量浓度在洪水前、后的变化特征，并探讨水文地质条件、ρ（Fe_T）（Fe_T表示总铁）、荧光有机物含量及其活性官能团对含As矿物溶解性和迁移性的影响.结果表明:①与洪水前相比，洪水后河岸带地下水ρ（DOC）升高，促进了微生物新陈代谢活动，导致潜水层出现明显的类酪氨酸、类色氨酸以及可溶性微生物降解产物荧光峰，弱承压层的类酪氨酸、类富里酸和类胡敏酸荧光强度也显著增加，各荧光物质含量Φ_i，n均表现为潜水层>弱承压层.②洪水后，潜水层与弱承压层呈现还原环境，导致As以电中性的亚砷酸盐形式存在，且河水入渗并未直接对各含水层贡献ρ（As_T）（As_T表示总砷），地下水ρ（As_T）升高可能主要受ρ（Fe_T）与荧光物质含量（Φ_i，n）升高的影响.③在空间上，由于弱承压层ρ（Fe_T）>潜水层ρ（Fe_T），铁氧化物通过桥接亚砷酸盐与荧光物质来增强As的迁移性和溶解性，导致洪水后弱承压层ρ（As_T）平均值接近于潜水层.④河岸带地下水ρ（As_T）升高途径主要是类蛋白和类腐殖质的羟基、羧基、氨基等官能团与亚砷酸盐形成DOM-As二元络合物，或铁离子充当DOM活性官能团与亚砷酸盐的"桥梁"，以共价键或氧桥形式形成多元络合物DOM-Fe-As、DOM-Fe-O-As.研究显示，由河水-地下水交互作用对含水层输入DOM导致的As溶解现象应纳入预防河岸带地下水As污染的前提考虑因素. 

Researching Effects of Dissolved Organic Matter Inputs on Migration and Transformation of Arsenic in Riparian Groundwater

In order to study the effects of dissolved organic matter (DOM) on arsenic migration and transformation in riparian groundwater, the Kuihe River in Yangzhuang Township, Suzhou City, Anhui Province, was selected as the research area. Based on excitation-emission matrix fluorescence, area integration method and diagram of mineral E_h-pH stability, the type and mass concentration of fluorescence component and arsenic in riparian groundwater before and after flood were analyzed, and the effects of hydrogeological conditions, ρ(Fe_T)(Fe_T means mass concentration of total iron), fluorescence organics content, and active functional groups on the solubility and migration of arsenic-containing minerals were investigated. The results showed that:(1) Compared with the period before the flood, ρ(DOC) in riparian groundwater increased after the flood, which promoted the microbial metabolism activities and caused obvious occurrence of tyrosine, tryptophan and soluble microbial degradation products fluorescence peak in phreatic layer. The fluorescence intensity of tyrosine, furic acid and humic acid in aquitard also increased significantly. Each fluorescent substance content (Φ_{i, n}) was characterized by phreatic aquifer>aquitard. (2) After the flood, phreatic layer and aquitard presented a reducing environment, resulting in the existence of As in the form of electrically neutral arsenite. River infiltration did not directly contribute ρ(As_T) (As_T means mass concentration of total arsenic) to each aquifer. Elevated ρ(As_T) in groundwater may mainly be affected by the increasing of ρ(Fe_T) and fluorescent substance content (Φ_{i, n}). (3) In spatial distribution, due to ρ(Fe_T) in aquitard was higher than that in phreatic aquifer, thus iron oxide bridged arsenite and fluorescent substances to enhance the migration and solubility of As, causing the average value of ρ(As_T) in aquitard close to that in phreatic aquifer. (4) The increasing of ρ(As_T) in riparian groundwater may be realized mainly through the following two ways. On one hand, the hydroxyl group, carboxyl group, amino group and other functional groups of similar proteins and humus formed DOM-As binary complexes with arsenite. On the other hand, iron ions acted as the 'bridge' between DOM active functional groups and arsenite, forming multi-complex DOM-Fe-As and DOM-Fe-O-As in the form of covalent bond or oxygen bridge. Therefore, the phenomenon of arsenic dissolution caused by inputting DOM into aquifer through river-groundwater interaction should be taken into account in the precondition of preventing groundwater arsenic pollution in riparian zone.