| Summary: | 博士 === 國立臺灣大學 === 海洋研究所 === 95 === To understand the integrated effects of organic matter loading on the benthic chemical properties, microbial communities, and benthos in an estuarine system, two field studies and a set of laboratory experiments were conducted. In the Tanshui River, the horizontal characteristics of the estuarine sediments were revealed in three spatial settings from the river mouth to a mid-reach section: a nitrate-abundance type, a phosphate-release type, and a sulfide-generation type; the vertical characteristics in four layers of Guandu sediment were also elucidated. With the exception of the mixed layer, a variety of metabolic processes by denitrifier strains occur in different vertical layers including nitrification-denitrification coupling processes in the nitrate-concentrated layer, denitrification or dissimilatory nitrate reduction to ammonium in the denitrifier-aggregation layer, and fermentation or spore formation in the ammonium-enriched layer. In addition, two laboratory experiments indicated that environmental condition gradually became worse, which leads to decreasing of dissolved oxygen, increasing of ammonium, nitrate and sulfide concentrate. However, high levels of treatment with the photosynthetic bacterium (PSB, Ectothiorhodospira sp.) decreased sulfide and nitrogenous nutrients in both aerated and hypoxic conditions, and then significantly improved the survival rate of the hard clam (Meretrix lusoria). In summary, the degree of organic matter degradation could be defined by the chemical properties in both the horizontal and vertical sediment profiles. A variety of metabolic processes by denitrifiers, which occur in the comparative sediment profile, indirectly correspond to these different stages. The use of the PSB, Ectothiorhodospira sp., actively removed some chemicals and mediated the sediment properties (from polluted to a transitory stage). Benthic hard clams can serve as a good indicator of the shift in benthic chemical processes toxic to the benthos, which are incapable of being detected by environmental measurements.
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