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

0003680 Cai淡水溶解有机物（DOM）强烈影响许多重要过程，特别是在有机物丰富的系统中。最近的报告表明：（1）在高度着色的萨提亚河的质子平衡中，主要的术语是“有机碱度”;（2）在这种水中的光反应，部分由Fe催化，消耗O2，漂白颜色，并形成CO，CO2（主要产物）和Fe（II）。我们假设CO2是由Fe催化的“光脱羧反应”产生的：DOM-COO-H + O2 + hv_ FeDOM-H + CO2是简单分子的一个众所周知的反应。主要有机可电离基团的大量丢失将深刻影响光蚀变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/凝结、生物利用度、光学性质以及可能的水净化行为然而，确定和模拟Satilla水在光解之前与之后的整个pH滴定曲线的初步研究（太阳模拟器）证伪了上述假设：每形成一个CO2，只有约0.1个酸性基团丢失; pH值下降（形成的酸比消耗的酸更强）。目的：因此，我们建议（1）更好地表征CO2释放，质子结合位点之间的关系，（2）通过研究不同季节的其他河水样品，评估这些影响的一般性和环境变异性;（3）考察这些变化对hv-DOM的一个重要物理化学性质：铜结合强度和容量的影响;（4）提出一个比上述假设更好的启发式方案，使结果在化学上合理化。显然，在某种程度上，光生CO2并不简单地来源于-COO-基团。酸性基团，如果丢失，似乎被替换为类似的，但不完全相同的新的酸DOM photo-oxidation.Work计划和方法：这是一个合作的努力之间的博士后助理和两个PI withexperience在有机/无机碱-pH-CO2性质，DOM光化学。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。Altamaha，一个更典型的第二条河流选择的研究，也是DOM丰富。它的DOM被认为是来自外来和本地的来源，与萨提亚的主要是外来的，高度着色的DOM相反。萨旺尼河水及其著名的腐殖酸和富里酸分离物（SRFA，SRHA）也正在研究中，因为在有机物丰富的有色沃茨中，这些组分构成了DOM、有机碱度和吸光材料的主要部分。教育：该项目通过涉及一名独立工作的博士后助理和UGA和WHOI的研究生，为环境科学培训做出贡献。这项研究增加了我们对可能影响水透明度，饮用性和处理（例如氯化），水生生物区系的过程的理解，以及农业化学品和污染物（特别是Cu）的结合，运输和转化。

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).