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

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，如各种形式的铁（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降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顽固性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，许多这些污染物可能通过非生物途径发生反应。我们假设，在湿地沉积环境中，两组不同的环境“试剂”可能特别有效地促进易受还原过程影响的有机化合物的转化。这些包括(1)最近被证明是硝基芳香族和偶氮化合物的高活性还原剂的铁（II）物种（特别是当被铁（III）氧化物吸附时），以及(2)能够本身作为还原剂或与铁（II）协同作用的天然有机物质。我们建议通过使用硝基芳香族和偶氮化合物进行多方面的调查来探索湿地沉积物和孔隙水的还原潜力，这些化合物跨越了一系列物理化学性质（从极性到反应性）。从孔隙水中分离的明确吸附的Fe（II）和NOM将与我们的探针的代表性基团反应的速率将在控制良好的批量实验中确定。相关参数将被系统地改变，以帮助识别反应物种，并促进理解动力学过程和反应途径。将仔细注意识别反应产物。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将从俄亥俄州（老妇溪：NOAA站点）和佐治亚州（毕晓普池塘：USDA站点）的一个站点缺氧隔离。我们将在原生孔隙水和沉积物浆液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反应之间的关系，我们将使用偶氮探针与Sepharose beads共价结合。这些结合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。为了区分孔隙水驱动的过程和沉积物催化的过程，偶氮探针将使用“窥视器”埋在沉积物中，以防止与任何固相直接接触。将使用埋藏的含有沉积物的“窥眼”进行平行实验，以确定总体减少率。br /一些

Chin0337434Freshwater 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. br/&g