Studies On The Impacts And Mechanism Of The Large-Scale Engineering On The Coastal Marine Ecosystem In The Yangtze River Estuary

Human activities, whose main carrier is large-scale engineering, make comprehensive impacts on ecosystem servies by altering habitat, ecosystem structionand biogeochemical cycles. Large-scale basin engineering influences directly material fluxes and their compositions from river discharge into the sea by changing esturine habitat and biogeochemical cycle. However, large-scale estuarine engineering affects directly estuarine ecosystem mainly by altering local estuarine habitat.The Three Goreges Project didn't affect significantly the annual water runoff into sea of the Yangtze River, but its impounding and sluice did notably mensal water runoff and annual sediment flux into sea. Among of material into sea, the annual average concentrations of NO3-N, NO2-N, NH4-N and SiO3-Si from 2002 to 2004 are lower than those of many years except PO4-P, and the ratios of N/P, Si/P and Si/N behaved the reducing trend. The salinity in the estuary responded distinctly to the impounding of the Three Gorges Project with difference in different sea areas. In contrast to that of 2000, the zenith location of front salinity isoline 5 from 2002 to 2004 moved gradually to estuary by 28.9km, 45.6km and 58.9km respectively. The aggravation of seawater intrusion in the South Branch was mainly induces by the alteration of water runoff into sea of the Yangtze River, while movement of the estuarine plume, inner shift of Frequently-Occurring Sea Areas of HABs, and increase and change of HABs species wrer influenced comprehensively by the change of water runoff and the reduction of sediment into sea of the Yangtze River and coastal oceanic circumfluences. In addition, the impacts of the correspondence of salinity, the concentrations and ratios between nutrients in the estuary on the structure and function of entire estuarine ecosystem were still proved by more tests.The first stage project of the Deep-Waterway Regulation in the Yangtze River Estaury had affected obviously local estuarine water body and benthic habitat fragmentation with maximum fragmentation impacts of small-scale oceanic water masses, benthic habitat and fishery resource habitat and significant differences of seascape index (H), seascape dominance (D), and seascape fragmentation (C). The number of patches of DO and COD and the values of H, D and C in May 2002 were higher than that in pre- first stage project (May 1997). The composition and biomass of estuarine benthos species were also affected by local alteration of ecosystem structure. It resulted in directly habitat fragmentation of partial fishery grounds, breeding migration channels, spawning grounds, growing-up grounds and fishery grounds.The indicator system of the estuarine ecosystem heatlh assessment may be constructed by structural and functional indicator assessement method under selecting three kinds of 30 indicators of physiochemical, ecological and scioeconoic indicators. By hierarchial analysis method, the relative importance, remark and power values of different indicators in each hierarchial assessment may be determined. The Integrated Health Index (IHIYRE) of the Yangtze River Estuary in 2002～2004 were 3.09, 3.17 and 4.36 respecitvely, which was located between healthiness and unhealthiness (3≤IHIYRE≤5). It showed that it had distantces from the condition of health, but it had been gotten better in recent years.