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

本研究探讨了沿海海洋环境中底栖大型动物与沉积物硝化和反硝化的相互作用。Kemp博士和他的合作者Boynton博士将直接测量大型动物对硝化作用和耦合硝化-反硝化作用的影响，使用改良的15N同位素技术对完整的沿海海洋沉积物进行测量，并控制动物密度。代表性物种（如片足类、双壳类、多毛类）的大型动物丰度将分为三个等级。大型动物可能刺激硝化作用的替代机制（例如，增加氧气与铵的供应）将分别使用人工管进行检查，并使用微电极技术进行比较。将用同位素程序测试大型动物增强硝化-反硝化耦合的三种可能机制，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)缺氧微位点在粪便微球表面沉积中的作用。溶解的氮化合物如硝酸盐和铵是生物生产的重要营养物。然而，氨氧化（硝化作用）和硝态氮还原为氮气（反硝化作用）导致生物活性池中氮的减少，可能是控制海水营养水平的重要机制之一。这项研究解决了这些过程的耦合及其与生活在海岸沉积物中的大型生物的关系，在海岸沉积物中，硝化/反硝化特别活跃。这项工作将定量地检验这些生物建造的沉积物洞穴（以及这些动物的活动）促进周围沉积物中的微生物硝化/反硝化活动的概念。这项工作包括使用不同数量生物的沉积物样本和使用人工洞穴的实验室实验。同位素标记实验将用于测量硝化/反硝化的实际速率，并解决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.