Study of biogeochemical factors affecting organic matter (lipid biomarkers) degradation
MetadataShow full item record
Major portion of this dissertation focused on comprehensively examining the degradation processes of three classes of lipid biomarkers derived from alga Emiliania huxleyi in three simulated microcosms (oxic/anoxic seawater systems, oxic/anoxic sediment-water interface, and sediment cores with and without presence of macrofauna). The results obtained from these studies demonstrated that both internal factors, which arise from the structural associations of different molecules within cellular components, and external factors, which result from different environmental conditions, affect the fates of various algal biomarkers in marine systems significantly. This dissertation includes five chapters. Chapter 1 described the research background. Chapter 5 summarized the major new results and conclusions. Chapter 2 focused on how the intracellular structural associations affect degradation of Chl-a. By calculating degradation rate constants of Chl-a based on a 90-day incubation of E. huxleyi cells in natural oxic and anoxic seawaters, the effects of the structural complexes on Chl- a degradation were evaluated. By following the variations of Chl-a derivatives, a concept model was established to describe the degradation pathways of Chl-a from various pigment complexes. Chapter 3 described a 56-day incubation experiment of E.huxleyi in simulated oxic/anoxic sediment-seawater interface microcosms. The structural effects on the degradation of algal fatty acids bound in intracellular and membrane components under various redox conditions were discussed based on the experimental results. The complicated relationships among enzymes, microbial community and fatty acid degradation were discribed by following time-dependent variation of lipase activities and bacterial abundance. Chapter 4 was concentrated on how crustacean (P. pugio) affect the fates of algal lipids by incubating E. huxleyi cell in simulated sediment-seawater microcosms with or without presence of crustacean for six weeks. Experimental results indicated that crustacean’s activities caused differential degradation of algal fatty acids and alkenones and minimized the structural effects of intracellular and membrane components on fatty acid degradation, but had little k’influence on U37. Moreover, a conceptual model was proposed to assess the fates of various algal lipids in surface sediments. Overall, this study added new knowledge on the degradation of organic biomarkers, which is helpful in understanding global carbon cycling and in paleoceanographic research.