Distributions Of Dissolved Organic Carbon And Particulate Organic Carbon In The Changjiang Estuary And Its Adjacent Area

Organic carbon cycle in the ocean represents an important part in the global carbon cycle. It is of great significance to make aware of the distributions, transportations and transformations of dissolved organic carbon and particulate organic carbon in the ocean. In the present thesis, particulate organic carbon (POC) and dissolved organic carbon (DOC) in water were determined using a Shimadzu TOC-Vcph 和 Vario EL III CHONS The samples were collected from the sampling locations in the Changjiang drainage basin, Xuliujing, Changjiang estuary, and the East China Sea. The main purposes of this current study are to elucidate the distributions, the dominant factors of dissolved organic carbon and particulate organic carbon in the study areas. Moreover, a dissolved organic carbon budget for East China Sea Shelf is evaluated by box-model in this work.DOC and POC samples collected in the Changjiang drain basin in 2003 and 2006 were analyzed. It suggested that the concentration of POC and DOC in the main steam increased downstream towards the Changjiang Estuary, and the concentrations of samples in 2003 were higher than those in 2006. The POC content in suspended particles (POC%) are particularly high in the middle and lower reaches of the Changjiang drain basin, which may be derived from the primary production of the phytoplankton in river. Since greatly influenced by the human activities, the tributaries of Changjiang River showed higher concentrations of DOC and POC than the main stream. The annual TDC fluxes were estimated to be 4.01×10~6t, 2.83×10~6t, 3.68×10~6t and 2.07×10~6t from 2003 to 2006 in Xuliujing, respectively. It suggested that the annual fluxes of TOC in the wet season are higher than those in dry, while the POC fluxes occupies the predominance. A dramatic drop of the POC fluxes as well as a sharp increase in the ratios of DOC fluxes to POC fluxes was showed during the observed period after the completing of Three-Gorges Dam, which could have significant effects on the trapping and degradation of POC.DOC and POC samples collected in the Changjiang estuary from four cruises in2005 and 2006 were analyzed. Near bottom water collected from the Turbidity Maximum Zone in the Changjiang Estuary showed the highest DOC and POC among all the near bottom samples in August 2005, while a decreasing tendency for both DOC and POC were found in the surface water. The results of the three cruises in2006 indicated similar temporal variations of DOC and POC (June>Aug>Oct). A good correlation ship was expected between paniculate organic carbon and Chl a in the surface water, and lower POC was found in the middle and near-bottom water. Organic carbon derived from phytoplankton make a comparable contribution to POC in August and October, relative to a lower one in June. Oxygen consummation caused by particulate organic carbon degradation may be one of the reasons for the seasonal hypoxia in the near-bottom water of Changjiang estuary.The distribution characteristic of DOC and POC in the continental shelf of the East China Sea revealed that the distribution of DOC was controlled by the geography and hydrology factors, while the distribution of POC being greatly impact by biochemical factor such as Chl a. A DOC budget was estimated for the shelf of East China Sea and the result suggested the shelf to be a net source of DOC offshore. Four types of water derived from the Taiwan Warm Current, Changjiang river, the Kurosio water and productive area were sampled for incubation to examine the bioavailability of the DOC in each water type. The DOC concentration decreased fastest in the water deriving from the productive area followed by the Taiwan Warm water sample. However, the DOC concentration remained stable till to the end of the incubation.