| According to the ecological and environmental survey data in the Yangtse River estuary and its adjacent waters from 1998 to 2009. the environmental variation characteristics of the Yangtze River Estuary were analyzed during ten years, environment variations before and after the Three Gorges Reservoir impoundment were studied in the Yangtze River Estuary. The research results will provide scientific basis for further analysis of human activitiy influences on the Yangtze River Estuary ecosystem. The main results are as following:During spring, average salinity of the whole investigated waters tended to increase after 2004, but declined in 2009; the water temperature was highest in 2004, DO, pH values had significant annual fluctuation; COD showed a gradual downward trend, but rebounded in 2009; After 2007, total nitrogen content in water body significantly increased, while total phosphorus content significantly reduced; suspended particulate matter content in water body significantly decreased after 2004.In autumn, the salinity variations showed state annual fluctuation.The average temperature in 2009 was minimal. DO, pH, total nitrogen, total phosphorus had significant annual changes. COD was decreased from 1998 to 2009. From 2004, the suspended particulate matter content was significantly reduced. The environmental factors in different waters of the Yangtze River Estuary (mouth, offshore and shelf waters) had different variation trend.Before and after impoundement of Three Gorges Reservoir, the environment in Yangtzi River Estuary significantly changed, especially the content of total phosphorus and suspended particulate matter had significant variations. After the reservoir impoundement, the total phosphorus and suspended particulate matter had significantly decreased in the Yangtzi River Estuary and its adjacent waters. The environmental elements in estuary mouth, offshore waters and shelf waters had different variation trends before and after impoundement of the reservoir. In the present thesis, we analysed the data obtained from the surveys which was carried out in the Changjiang River Estuary and its adjacent sea areas in February, May, August, and November of 2007, and 40 stations were designed. This research systematically discussed the temporal and spatial distribution features of the total organic carbon (TOC) of the Yangtze Estuary surface sediments, and analyzed the main influence factors of the Yangtze Estuary surface sediments TOC by analyzing the Yangtze River's physics, chemistry and sedimentary features.The results showed that the surface sediment of the Yangtze River Estuary and its adjacent waters were mainly comprised of fine sand and silt, fine sediment was mainly distributed in the southern of the investigated waters, the advantaged component of the north sea sediment was sand. Besides, the sediment compositions and distributions had significant seasonal variations; The surface sediment TOC content of Yangtze River estuary and adjacent waters was between 0.012% and 1.589%, with an average of 0.524%, its spatial distribution characteristics showed season variances; the surface sediment TOC contents in maximum turbidity zone and southeast offshore area (122°30′E, west,31°31′N, north of) were significantly higher than in northern waters. Sediment grain size was an important factor that affects the surface sediment TOC, hydrodynamic conditions influenced spatial and temporal distribution of TOC by afecting on the sediment composition, the high distribution area of TOC was at Yangtze River diluted water front, the mixing area with the Taiwan Warm Current, the Yellow Sea coastal current. The distribution area changed with hydrodynamic conditions in different seasons. In different areas, surface sediment TOC had varied factors during different seasonsThe total nitrogen (TN) content of surface sediment in the Changjiang River Estuary and its adjacent was between 0.017%～0.119%, averaging 0.065%. In different regions, TN showed varied distribution characteritics:TN content of the northern waters was lower than the southeast areas of investigated waters and the maximum turbidity zone area. TN content was lowest in May, and highest in August; TN content in the maximum turbidity zone was significantly lower than in the southeast areas of investigated waters in May. TN content in the maximum turbidity zone during May was lower than durting February, August, and November.TN content was significantly negatively correlated with fine sand proportions and significantly positively correlated with silt and clay proportions. As fine grain size had an increasing surface area, and the elements adsorption increased, sediments could absorb more nutrients. In February, sediment TN negatively correlated with salinity in a certain degree in the Changjiang diluted water and the offshore area. In May, sediment TN positively correlated with salinity, and sediment TN in the off shore area had a weak negative correlation with salinity during August. In November, sediment TN in the Changjiang diluted water area positively correlated with salinity, and sediment TN in the off shore areas significantly negatively correlated with salinity. In addition, the surface water TN and chlorophyll content also affected sediment TN in August, which reflected the nutrient retention between water body and sediment.Surface sediment TOC significantly associated with TN in Changjiang River Estuary and its adjacent waters, which indicated a close relationship between nitrogen and organic carbon in marine sediments. But, sediment TN distribution had weak correlation with TOC during August, flood season, due to effects of other factors.Using the organic index and the organic nitrogen index, the nutrition health status of surface sediments were evaluated in the Changjiang River Estuary and its adjacent waters. The results showed that the health status was poor in August and November in this area during a year.
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