Macrofaunal Effects on Nitrification and its Coupling to Denitrification in Coastal Marine Sediments

本研究探讨了大型底栖动物与沿海海洋环境中沉积物硝化和反硝化作用的相互作用。Kemp博士和他的合作者Boynton博士将使用改进的15N同位素技术，对具有操纵动物密度的完整沿海海洋沉积物，直接测量大型动物对硝化作用和硝化-反硝化耦合作用的影响。大型动物丰度的三个级别将用于代表性物种(例如，双足类、双壳类、多毛类)。大型动物可能刺激硝化作用的替代机制(例如，氧气供应增加与铵的供应增加)将使用人造管子单独研究，并将使用微电极技术进行比较。三种可能的大型动物增强硝化-反硝化耦合的机制将通过同位素程序进行测试，包括：1)径向扩散几何形状的影响；2)缺氧-缺氧交替条件的影响；3)表面沉积粪便颗粒中缺氧微站点的作用。硝酸盐和铵等溶解的氮化合物是生物生产的重要营养物质。然而，氨氧化(硝化)与硝酸盐还原为氮气(反硝化)耦合导致生物活性水池中氮的减少，这可能是控制海水营养水平的重要机制之一。这项研究探讨了这些过程的耦合及其与生活在沿海沉积物中的较大生物体的关系，在沿海沉积物中，硝化/反硝化作用特别活跃。这项工作将定量地检验这样一种概念，即沉积物中的这些生物构造(以及这些动物的活动)促进了周围沉积物中的微生物硝化/反硝化活动。这项工作包括使用不同数量的生物的沉积物样本进行的新颖实验，以及使用人工洞穴进行的实验室实验。将利用同位素标记实验来测量硝化/反硝化的实际速率，并探讨较大的沉积物生物影响这些微生物过程的机制。

This study examines the interaction between benthic macrofauna and sediment nitrification and denitrification in the coastal marine environment. Dr. Kemp and his co-inves- tigator Dr. Boynton will make direct measurements of macrofaunal influence on nitrification and coupled nitrification - denitrification using a modified 15N isotope technique for intact coastal marine sediments with manipulated animal densities. Three levels of macrofaunal abundance will be used for representative species (e.g. amphipod, bivalve, polychaete). Alternative mechanisms by which macrofauna may stimulate nitrification (e.g. increased supplies of oxygen vs. ammonium) will be examined separately using artificial tubes will be compared using microelectrode techniques. Three possible mechanisms for macrofaunal enhancement of nitrification - denitrification coupling will be tested with the isotopic procedures including: 1) effects of radial diffusion geometry; 2) effects of alternating oxic- anoxic conditions; 3) role of anoxic microsites in surface deposited fecal pellets. Dissolved nitrogen compounds such as nitrate and ammonium are important nutrients for biological production. However, the oxidation of ammonium (nitrification) coupled to the reduction of nitrate to nitrogen gas (denitrification) results in the decrease of nitrogen in biologically active pools and may serve one of the important mechanisms controlling the nutrient levels in sea water. This study addresses the coupling of these processes and their relation to the larger organisms living in the coastal sediments, an environment in which nitrification/denitrication is particularly active. The work will test quantitatively the notion that the sediment burrows these organisms construct (along with the activities of these animals) facilitates the microbiological nitrification/denitrification activity in the surrounding sediment. The work include novel experiments using sediment samples with varying numbers of organisms and laboratory experiments using artificial burrows. Isotopic labelling experiments will be used to measure the actual rates of nitrification/denitrification and to address the mechanisms by which the larger sediment organisms influence these microbiological processess.