CAREER: Generation of Sediment Heterogeneity by Macrophytes and Macrofauna and Consequences for Redox Chemistry and Trace Metal Speciation

知识价值：沿海和内陆湿地地区受到快速增长的人口的巨大影响。这通常会导致金属和营养负荷的增加，以及湿地水文、动植物的显著变化。可持续的沿海和内陆湿地开发(和补救)战略依赖于开发准确的预测模型，预测金属和营养物质的形态、生物有效性和移动性，以及它们对湿地动植物种群的依赖。在盐沼和沿海海洋之间或内陆湿地和淡水含水层之间的敏感界面上尤其如此。生活在富含有机物质的盐沼和淡水湿地中的大型植物和大型动物在周围沉积物中产生了显著的三维、时间变化的地球化学异质性。这对底栖氧、金属和营养物质的通量、氧化还原敏感化学物质的内部循环和有机物的降解动力学都有巨大的影响。将利用以下实验室和现场调查来评估这些影响，并推进沉积物氧化还原化学和痕量金属形态、生物有效性和流动性的复杂3D数学模型的开发。(1)利用混合模型矿物组合的金属吸附实验，求出热力学表面络合稳定常数，并评价其对天然沉积物的适用性。(2)作为WMU创新的野外课程的一部分，将测量邻近植被和非植被沉积物中的大部分沉积物特性(矿物学、孔隙水化学、微量金属形态)。(3)利用微电极、扫描电子显微镜和激光烧蚀电感耦合等离子体质谱对根部和洞穴周围沉积物中的矿物学和痕量金属形态进行微尺度分析。(4)微量金属掺杂铁氧化物的化学还原溶解与微生物还原溶解对痕量金属形态的影响将被量化。(5)通过室内人工根中隔实验，研究植物根部渗漏氧气和活性有机化合物引起的矿物学和微量金属形态的微尺度三维变化。更广泛的影响：这项研究包括一个完全整合的研究和教育计划。一项为期6周的创新暑期课程被提出，学生将有机会参加佐治亚州萨佩洛岛(NSF-LTER的一个地点)和密歇根州的实地研究。这门课程的学生将从威斯康星大学及其周边机构招收，特别是那些没有研究生研究项目的机构，以及招收大量传统上代表性不足的群体的大学。此外，为期一周的课程将与中学教育教师讲习班同时进行。教师们将有机会亲身参与一项积极的科学研究计划，并将被鼓励在密歇根科学教师年会上传播这一经验产生的课程。与这项研究的实验室部分相关的项目将被纳入本科生的一门地球化学课程。除了传统的研究生辅导外，来自卡拉马祖地区数学和科学学院的本科生和积极性很高的高中生将参与研究的各个方面，在国内或国际科学会议上展示个别项目的成果。通过这项研究资助的设备将是对WMU研究生和本科生可用的研究基础设施的宝贵补充，WMU是一家快速发展的博士研究机构。

AbstractIntellectual Merit: Coastal and inland wetland areas are enormously impacted by rapidly growing human populations. This typically leads to increased metal and nutrient loading together with significant changes in wetland hydrology, fauna and flora. Sustainable coastal and inland wetland development (and remediation) strategies depend on the development of accurate, predictive models of metal and nutrient speciation, bioavailability and mobility and their dependence on wetland flora and fauna populations. This is particularly true at the sensitive interface between saltmarshes and the coastal ocean or between inland wetlands and freshwater aquifers. Macrophytes and macrofauna inhabiting organic-rich saltmarsh and freshwater wetlands produce significant three-dimensional, temporally varying, geochemical heterogeneity in the surrounding sediments. This has a tremendous influence on benthic fluxes of oxygen, metals and nutrients, internal cycling of redox sensitive chemical species, and organic matter degradation kinetics. The following laboratory and field investigations will be used to assess these influences and to advance the development of sophisticated 3D mathematical models of sediment redox chemistry and trace metal speciation, bioavailability and mobility. (1) Metal adsorption experiments on mixed model mineral assemblages will be used to derive thermodynamic surface complexation stability constants and to assess their applicability to natural sediments. (2) Bulk sediment properties (mineralogy, pore water chemistry, trace metal speciation) in adjacent vegetated and unvegetated sediments will be measured as part of an innovative new field course at WMU. (3) Microscale analyses of mineralogy and trace metal speciation in sediments surrounding roots and burrows will be completed using microelectrodes, SEM/TEM, and laser ablation ICP-MS. (4) Changes in trace metal speciation resulting from chemically versus microbially mediated reductive dissolution of trace-metal doped iron oxides will be quantified. (5) Controlled laboratory mesocosm experiments with artificial roots will be used to assess microscale 3D changes in mineralogy and trace metal speciation resulting from root leakage of oxygen and labile organic compounds. Broader Impacts: This study includes a fully integrated plan of research and education. An innovative 6-week summer course is proposed in which students will have the opportunity to participate in field research at Sapelo Island, Georgia (an NSF-LTER site) and at field sites in Michigan. Students will be recruited for this course from WMU and surrounding institutions, especially those without graduate research programs and from colleges with significant enrollments of traditionally underrepresented groups. In addition, a full week of the course will coincide with a secondary education teacher workshop. The teachers will have a hands-on opportunity to participate in an active scientific research program and will be encouraged to disseminate curricula resulting from this experience at the Michigan Science Teachers Annual Meeting. Projects related to the laboratory portions of the study will be incorporated into an undergraduate geochemistry course. In addition to traditional graduate student mentoring, undergraduate students and highly motivated high school students from the Kalamazoo Area Math and Science Academy will participate in all aspects of the research, presenting results of individual projects at national or international scientific conferences. Equipment funded though this study will be a valuable addition to the research infrastructure available to graduate and undergraduate students at WMU, a rapidly growing doctoral research institution.