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

淡水溶解有机物(DOM)强烈影响着许多重要的过程，特别是在富含有机物的系统中。最近的报道表明，(1)高色萨蒂拉河质子平衡中的主要术语是“有机碱度”，以及(2)该水中的光反应，部分由铁催化，消耗O2，漂白颜色，形成CO，CO2(主要产物)和Fe(II)。我们假设二氧化碳是由铁催化的“光脱羧化”反应产生的：DOM-COO-H+O2+Hv_FEDOM-H+CO_2。主要有机可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：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(如氯化)中的行为。然而，一项初步研究测定并模拟了Satilla水在光解前和光解后的整个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降低(形成的酸比消耗的更强)。此外，铁参与了观察到的变化。目标：因此，我们建议(1)更好地描述二氧化碳的释放、质子结合位置(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流水域来评估这些影响的一般性和环境变异性；(3)检查这些变化对HV-DOM的一个重要物理化学性质：其铜结合强度和容量的影响；以及(4)制定比上述假设更好的启发式方案，以使结果在化学上合理化。显然，在某种程度上，光生二氧化碳并不是简单地来自COO-基团。工作计划和方法：这是一位博士后助理和两位在有机/无机碱度-pH-CO2性质和DOM光化学方面有经验的PI共同努力的成果。我们正在使用应用于这个问题的方法的优化，以及众所周知的铜结合研究方法。阿尔塔马哈河是一条更典型的第二条河流，也是DOM丰富的河流。它的DOM被认为既来自异地来源，也来自原地来源，与Satilla主要来自异地的、色彩鲜艳的DOM形成对比。Suwannee河水及其著名的腐殖酸和黄腐酸分离物(SRFA、SRHA)也在研究中，因为在有机含量丰富的有色水域中，这些污染物构成了DOM、有机碱度和光吸收材料的主要部分。教育：这个项目通过让一名独立工作的博士后助理和UGA和WHO的研究生参与进来，为环境科学的培训做出贡献。社会影响：这项研究增加了我们对潜在影响水透明度、肥力和处理(例如氯化)、水生生物以及农用化学品和污染物(特别是铜)的结合、传输和转化的过程的了解。

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).