| Summary: | 碩士 === 國立中山大學 === 海洋地質及化學研究所 === 94 === Chromophoric dissolved organic matter (CDOM) is a part of total dissolved organic matter (DOM), playing an important role in marine carbon cycling. Thus, a better description of the fates of DOM may increase our understanding of DOM sources and sinks in the coastal zone. This study aims to explore the distributions, transformation and transport of CDOM in the Kaoping Estuary-Canyon system.
The water exchange time (τ) of Kaoping estuarine water ranged from 0.1 to 2.2 day, being much shorter in the wet season than in the dry season. The riverine materials may be flushed out of the estuary without significant transformation in the estuary during the wet season, thus, distributions of nutrients and dissolved organic carbon(DOC) were largely determined by the mixing process. However, distributions of materials may be controlled by biogeochemical processes during the dry season, due to longer water residence time. In early spring, higher temperature and longer water residence time may be responsible for the effective decay of organic matter and nitrate reduction and/or denitrification in the estuary. Nonconcervative distribution (addition) of protein-like CDOM in early spring appeared to be derived from biological and/or sewage sources.
In the wet season, the distribution of terrestrial humic-like CDOM was not only controlled by the conservative mixing between river water and coastal water, but also influenced by a release from total suspended matter (TSM). In the dry season, the CDOM was slightly removed from the photobleaching process occurring around the river mouth, which may be regarded as the major sink process of CDOM.
In the Kaoping Canyon, the addition of terrestrial humic-like CDOM from TSM resuspension is significant only in the deep water. The photobleaching reaction occurred only in the limited area during the dry season, and gave little impact on CDOM concentration. There were no significant in-situ addition and removal in the coastal surface waters suggesting that the terrestrial humic-like CDOM could be a conservative tracer of terrestrial DOM in the coastal zone.
The terrestrial inputs of DOM may play a minor role in determining distributions of protein-like CDOM in the Kaoping Canyon. On the contrary, distributions were primarily controlled by biological sources. Nutrient inputs from the Kaoping River may be responsible for increasing the primary production in the surface water of coastal zone, linking to a potential source of protein-like CDOM. Significant correlations were found between DOC and tryptophan for those surface waters with higher fluorescence intensity. The results suggested that tryptophan may be derived from biological origins. DOC released from phytoplanktons generally contains lower Tyrosine/Tryptophan ratio than that released from microbes. The Tyrosine/Tryptophan ratio may be used as an indicator for the condition of microbial community.
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