Biogeochemistry of coastal marine sediments

对金属环境化学的兴趣源于金属对生物体的根本重要性，以及人们认识到人类活动改变了金属的自然循环。金属通过不同途径进入环境，并通过沉积在海底和埋藏而被清除。在金属被埋得很深，以至于它们被永久移除并成为地质记录的一部分之前，它们参与了化学和生物化学反应，由居住在沉积环境中的生物体介导。这项建议将研究沉积物中的生物-沉积物相互作用，其中主要的大型生物是无脊椎动物或植物。重点将是由生物体产生的金属结合有机化合物，以及它们与金属离子形成的络合物。这些配合物具有不同的溶解度，流动性，可用性和毒性比未络合的金属。无脊椎生物建造洞穴和廊道，延长沉积物和上覆水之间的接触，并刺激沉积物和水之间的络合和未络合金属的交换。潮间带维管植物不影响金属与水柱的交换，但它们的空心根运输氧气，氧化还原沉积物。根也释放金属结合有机酸。根的生长和腐烂产生了深刻的变化，在金属形态，并导致沉积物，孔隙水和植物组织之间的金属强烈的循环。拟议的研究将使用电化学技术与固态伏安微电极相结合，以确定金属和金属络合物的浓度，性质和通量。事实上，无脊椎动物和根是隐藏的观点是一个主要的障碍，了解生物沉积物的相互作用。我们将通过对完整岩心的CAT扫描分析，可视化根系和无脊椎动物的分布。三维图像将指导微电极的定位，让我们测量洞穴和根系表面附近的氧气，硫化物，铁和锰。根系分布的三维图像将使我们能够估计在生长季节根系生物量和氧通量的演变。

The interest in the environmental chemistry of metals stems from the fundamental importance of metals to living organisms and the realization that man's activities have altered the natural cycle of metals. Metals enter the environment via different pathways and are removed by deposition on the sea floor and burial. Before metals are buried so deep that they are removed permanently and become part of the geological record, they participate in chemical and biochemical reactions, mediated by the organisms that inhabit the sedimentary environment. This proposal will examine organism-sediment interactions in sediment where the dominant macro-organisms are either invertebrates or plants. The focus will be on metal-binding organic compounds produced by organisms, and the complexes they form with metal ions. These complexes have different solubility, mobility, availability, and toxicity than uncomplexed metals. Invertebrate organisms construct burrows and galleries, extending the contact between sediment and overlying water, and stimulating the exchange of complexed and uncomplexed metals between sediment and water. Intertidal vascular plants do not influence exchange of metals with the water column, but their hollow roots transport oxygen, which oxidizes reduced sediment. Root also release metal-binding organic acids. The growth and decay of roots produce profound changes in metal speciation and cause intense cycling of metals between sediment, pore water, and plant tissue. The proposed research will use electrochemical techniques in combination with a solid-state voltammetric microelectrode to determine concentrations, properties, and fluxes of metals and metal-complexes. The fact that invertebrates and roots are hidden from view is a major impediment to understanding organism-sediment interactions. We will visualize the distributions of roots and invertebrates with CAT-scan analysis of intact cores. The 3-D images will guide the positioning of microelectrodes and let us measure oxygen, sulfide, iron, and manganese near surfaces of burrow and roots. 3-D images of root distributions will let us estimate how root biomass and oxygen flux evolve during the growth season.