Collaborative Proposal: Probing the Reductive Potential of Wetland Sediments and Pore Waters

淡水湿地沉积物是一个复杂的生态地球化学系统，其中含有大量由微生物活动形成的天然还原剂。 这些天然还原剂如各种形式的Fe（II）和天然有机物（NOM）可能能够参与许多环境和地球化学反应。 此外，许多湿地能够通过沉积作用去除地表径流中的有机污染物。 迄今为止，许多这些污染物的命运被认为是可降解的或通过微生物过程进行转化。 由于沉积物及其孔隙水中天然还原剂的多样性和丰富性，许多污染物可能通过非生物途径发生反应。 我们假设，两组不同的环境“试剂”在湿地沉积环境中可能是特别有效的，在促进有机化合物的转化易受还原过程。 这些包括（1）Fe（II）物质，其最近被证明是硝基芳族和偶氮化合物的高反应性还原剂（特别是当吸附到Fe（III）氧化物上时），和（2）天然有机物质，其能够自身或与Fe（II）协同地充当还原剂。 我们建议探索湿地沉积物和孔隙水的还原潜力，通过多方面的调查，使用硝基芳香族和偶氮化合物，跨越一系列的物理化学性质（从极性到反应性）。 定义明确的吸附Fe（II）和NOM从孔隙水中分离的速率将与我们的探针的代表性基团反应，将在控制良好的批处理实验中确定。 相关参数将系统地变化，以帮助识别的反应物种，并促进了解动力学过程和反应途径。将仔细注意鉴别反应产物。 进一步的实验将在真实的系统中进行，其中孔隙水和沉积物从俄亥俄州（Old Woman Creek：NOAA站点）和格鲁吉亚（Bishop Pond：USDA站点）的一个站点缺氧分离。 我们将在天然孔隙水和沉积物泥浆中进行探针反应性研究。 为了阐明沉积物/表面驱动过程与溶液相中的反应之间的关系，我们将使用共价键合到琼脂糖凝胶珠的偶氮探针。 这些结合的探针将通过透析膜与颗粒相分离。 最后，我们将调查这些过程中原位在这两个网站使用偶氮探针。 为了区分孔隙水驱动的过程与沉积物催化的过程，将使用防止与任何固相直接接触的“窥视器”将偶氮探针埋在沉积物中。 将使用埋在地下的含有沉积物的“窥视器”进行平行实验，以确定总的减少率。 这些调查的结果将提供有用的信息，在评估湿地沉积物的还原潜力，以非生物转化那些有机化合物容易减少，是环境利益。 这些研究将提高我们对湿地沉积物中生物地球化学氧化还原过程的认识。 最后，我们还包括一个全面的推广计划，来自不同背景的中学生将积极参与拟议的研究项目。

Traina0337339 Freshwater wetland sediments are complex biogeochemical systems, which contain a host of natural reductants formed from microbial activity. These natural reductants such as Fe(II) in various forms and natural organic matter (NOM) may be capable of being involved in a number of environmental and biogeochemical reactions. Moreover, many wetlands are capable of removing organic pollutants from surface runoff by sedimentation. To date the fate of many of these contaminants are assumed to be recalcitrant or undergo transformation through microbial processes. Because of the variety and abundance of natural reductants present in sediments and their porewaters many of these pollutants may react through abiotic pathways. We hypothesize that two different groups of environmental "reagents" in wetland sedimentary environments may be particularly potent in promoting the transformation of organic compounds susceptible to reductive processes. These include (1) Fe(II) species that have recently been proven highly reactive reductants of nitroaromatic and azo compounds (particularly when adsorbed to Fe(III) oxides), and (2) natural organic matter that is capable of acting as reductants by themselves or synergistically with Fe(II). We propose to probe the reductive potential of wetland sediments and porewaters through a multifaceted investigation using nitroaromatic and azo compounds that span a range of physicochemical properties (from polarity to reactivity). The rates at which well-defined adsorbed Fe(II) and NOM isolated from porewaters will react with representative groups of our probes will be determined in well-controlled batch experiments. Relevant parameters will be systematically varied to aid in the identification of the reactive species and to facilitate understanding kinetic processes and reaction pathways. Careful attention will be paid to identifying reaction products. Further experiments will be conducted in real systems with porewaters and sediments isolated anoxically from a site in Ohio (Old Woman Creek: a NOAA site) and in Georgia (Bishop Pond: a USDA site). We will conduct probe reactivity studies in both native porewaters and sediment slurries. To elucidate between sediment/surface driven processes as oppose to reactions in the solution phase, we will use azo-probes covalently bonded to Sepharose beads. These bonded probes will be separated from particle phases by dialysis membranes. Finally, we will investigate these processes in situ at both sites using the azo probes. In order to differentiate between porewater driven processes to those catalyzed by the sediments, the azo probes will be buried in the sediments using a "peeper" that will prevent direct contact with any solid phases. Parallel experiments using buried "peepers" containing sediments will be conducted to determine the overall rate of reduction. The results of these investigations will provide information useful in assessing the reductive potential of wetland sediments to abiotically transform those organic compounds susceptible to reduction that are of environmental interest. These studies will improve our understanding of biogeochemical redox processes in wetland sediments. Finally, we have included a comprehensive outreach plan where middle school students from diverse backgrounds will be actively involved in the proposed research project.