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

Traina0337339淡水湿地沉积物是一个复杂的生物地球化学系统，其中含有大量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)，可能参与许多环境和生物地球化学反应。此外，许多湿地能够通过沉淀去除地表径流中的有机污染物。到目前为止，许多这些污染物的命运被认为是顽固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种类和丰富程度，这些污染物中的许多可能通过非生物途径进行反应。我们推测，湿地沉积环境中的两组不同的环境“试剂”在促进易受还原过程影响的有机化合物转化方面可能特别有效。这些物种包括(1)Fe(II)物种，这些物种最近被证明是硝基芳香化合物和偶氮化合物的高活性还原剂(特别是在吸附到Fe(III)氧化物上时)，以及(2)能够单独作为还原剂或与Fe(II)协同作用的天然有机物。我们建议通过使用硝基、芳香和偶氮化合物的多方面研究来探索湿地沉积物和孔隙水的还原潜力，这些化合物涵盖了一系列物理化学性质(从极性到反应性)。从孔隙水中分离出来的明确吸附的Fe(II)和NOM与我们的探针的代表性基团反应的速率将在受控良好的批处理实验中确定。将系统地改变相关参数，以帮助识别活性物种，并有助于了解动力学过程和反应路径。将仔细注意识别反应产物。进一步的实验将在真实系统中进行，从俄亥俄州(老妇人溪：NOAA地点)和佐治亚州(毕晓普池塘：美国农业部地点)的一个地点分离出缺氧的孔隙水和沉积物。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。为了阐明沉淀物/表面驱动过程之间的区别，而不是溶液相中的反应，我们将使用偶氮探针共价键合到琼脂糖珠上。这些结合的探针将通过透析膜与颗粒相分离。最后，我们将使用偶氮探针在两个地点原位研究这些过程。为了区分由孔隙水驱动的过程和由沉积物催化的过程，偶氮探针将被埋入沉积物中，以防止与任何固相直接接触。将利用埋藏的含有沉淀物的“窥视者”进行平行实验，以确定总体减少的速度。这些调查的结果将为评估湿地沉积物的还原潜力提供有用的信息，以非生物方式转化那些对环境有影响的易还原的有机化合物。这些研究将加深我们对湿地沉积物中生物地球化学氧化还原过程的理解。最后，我们纳入了一个全面的外展计划，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.