Collaborative Research: The Effects of Aquatic Photochemistry on the Proton and Metal Binding Properties of Dissolved Organic Matter in Freshwater Systems

0003680淡水溶解有机物（DOM）强烈影响许多重要的过程，特别是在富有机质系统中。最近的报告显示：(1)高颜色的萨提拉河的质子平衡的主要术语是“有机碱度”，(2)在这种水中的光反应，部分由铁催化，消耗O2，漂白颜色，形成CO， CO2（主要产物）和铁（II）。我们假设二氧化碳是由铁催化的“光脱羧”产生的：DOM-COO-H + O2 + hv_______ FeDOM-H + CO2a是一个众所周知的简单分子反应。主要有机电离基团的大量损失将深刻影响光修饰DOM （hv-DOM）的许多重要性质：例如金属结合能力、酸碱性质、疏水结合、吸附/混凝、生物利用度、光学性质，以及可能在水净化中的行为（例如氯化）。然而，一项初步研究测定和模拟了satila水光解前后的整个pH滴定曲线（太阳模拟器），证实了上述假设：每形成一个CO2，只损失约0.1个酸基；pH值降低（形成的酸比消耗的酸更强）。此外，铁也参与了观察到的变化。因此，我们提出(1)更好地表征CO2演化、质子结合位点（浓度和亲和力）以及其他变量（[Fe]、pH、[O2]、光剂量和波长）之间的关系；(2)通过研究不同季节采样的其他河水，评估这些影响的普遍性和环境变异性；(3)考察这些变化对hv-DOM的重要理化性质：铜结合强度和容量的影响；(4)制定比上述假设更好的启发式方案，从化学上合理化结果。显然，在某种程度上，光产生的二氧化碳并不仅仅来源于- co -基团。酸性基团如果丢失，似乎会被DOM光氧化产生的类似但不完全相同的新酸所取代。工作计划和方法：本课题由一名博士后和两名具有有机/无机碱- ph - co2性质和DOM光化学经验的pi共同完成。我们正在使用优化的方法证明适用于这个问题，以及众所周知的铜结合研究方法。研究中选择的另一条更典型的河流阿尔塔马哈也富含dom。它的DOM被认为是来自异域和本地的来源，与萨蒂拉的主要是异域的，高度着色的DOM形成对比。苏旺尼河水及其著名的腐殖酸和黄腐酸分离物（SRFA， SRHA）也正在研究中，因为在富含有机物的有色水中，这些组分构成了DOM、有机碱度和吸光物质的主要部分。教育：该项目通过独立工作的博士后助理和UGA和WHOI的研究生参与环境科学培训。社会影响：这项研究增加了我们对潜在影响水透明度、可饮用性和处理（如氯化）、水生生物群以及农用化学品和污染物（特别是铜）的结合、运输和转化过程的理解。

0003680CaiFreshwater dissolved organic matter (DOM) strongly affects many important processes, particularlyin organic-rich systems. Recent reports show that (1) the major term in the proton balance of the highlycolored Satilla River is "organic alkalinity," and (2) that photoreactions in this water, catalyzed in part byFe, consume O2, bleach color, and form CO, CO2 (the major product), and Fe(II). We hypothesized thatCO2 arises by Fe-catalyzed "photodecarboxylation":DOM-COO-H + O2 + hv_______ FeDOM-H + CO2a well-known reaction for simple molecules. The implied massive loss of the principal organic ionizablegroups should profoundly influence many important properties of photo-altered DOM (hv-DOM): e.g.metal-binding capacity, acid-base properties, hydrophobic binding, adsorption/coagulation,bioavailability, optical properties, and perhaps behavior in water purification (e.g. chlorination).However, an initial study determining and modeling Satilla water's whole pH titration curves before vs.after photolysis (solar simulator) falsified the hypothesis above: for every CO2 formed only ~ 0.1 acidicgroup was lost; pH decreased (stronger acids formed than were consumed). Furthermore, Fe was involvedin the changes observed.Objectives: Hence we are proposing (1) better characterizing the relationships among CO2 evolution,proton binding sites (concentrations and affinities), and other variables: [Fe], pH, [O2], light dose, andwavelength; (2) assessing the generality and environmental variability of these effects by studying otherriverwaters, sampled in different seasons; (3) examining the effect of these changes on an importantphysico-chemical property of hv-DOM: its copper binding strength and capacity, and (4) formulating abetter heuristic scheme than the hypothesis above to rationalize the results chemically. Clearly to someextent photo-generated CO2 does not originate simply from -COO-groups. Acidic groups, if lost, seem tobe replaced by similar but not identical new acids from DOM photo-oxidation.Work Plan and Methods: This is a collaborative effort among a postdoctoral associate and two PIs withexperience in organic/inorganic alkalinity-pH-CO2 properties, and DOM photochemistry. We are usingoptimizations of methods demonstrated to apply to this problem, and well-known Cu-binding studymethods. The Altamaha, a more typical second river chosen for study, is also DOM-rich. Its DOM isthought to be derived from both allochthonous and autochthonous sources, in contrast to the Satilla'smainly allochthonous, highly colored DOM. Suwannee River water and well-known isolates of its humicand fulvic acids (SRFA, SRHA) are also being studied, since in organic-rich colored waters thesefractions comprise a major portion of the DOM, organic alkalinity, and light-absorbing material.Education: This project contributes to training in environmental science by involving an independent-workingpostdoctoral associate and graduate students at UGA and WHOI.Societal Impacts: This study increases our understanding of processes potentially affecting watertransparency, potability and treatment (e.g. chlorination), aquatic biota, and also the binding, transport,and transformations of agrichemicals and pollutants (especially Cu).