| The thermal disarged water from cooling system of coastal power plants directly causes the environmental change of receiving sea area and the low efficiency of cooling system. It may lead to obvious environmental variations, such as dynamics of receiving sea area and transportation of pollutants, which have inneglectable influences upon the physi-chemical characteristics of marine ecological system, as well as lives and reproduction of marine organisms.Thermal discharged water exerts great impact on marine ecological environment, in which temperature elevation and residual chlorine are the direct and main factors. To evaluate the influences of the thermal discharged water on receiving sea area and accumulate the basic data for the formulation of the relative standards, the impacts of temperature elevation and residual chlorine caused by the thermal discharged water from coastal power plants were investigated by the supports of Program on Research for Public Good of MOST, Provincial Natural Science Foundation of Zhejiang, the State Oceanic Administration Youth Science Fund, as well as the Special Fund from Science and Technology Bureau of Zhejiang Province.Subtropical bays, like the Xiangshan Harbour, the Yueqingwan Bay and the ShaCheng Harbour, were selected for the research on the representative communities of phytoplankton, the typical species of zooplankton, and the fish eggs and larvae of main nektons. The methods for in-situ survey, experimental ecology, ecological toxicology, chemical dynamics deduction, and 3-D hydrological numerical simulation were adopted and the impacts of temperature elevation and residual chlorine on marine ecological system were studied. The following conclusions were drawed.(1)Recovery of phytoplankton communities and the tolerances of typical zooplankton and main nektons were systematically compared in subtropical coastal areas with different temperature elevation.Appropriate increase of temperature can improve the productivity of Subtropical marine phytoplankton. The optimal increas of temperature was 2℃in summer at 28℃and 12℃in winter at 12℃, respectively. The tolerance of zooplankton is stronger than that of phytoplankton, which is different among species. Temperature elevation in receiving sea area generally has no impact on the survival of zooplankton because of the large span between semi-lethal temperature (LT50) and natural living temperature. The optimal living temperatures of different fishes are different. The appropriate increase of temperature can shorten the incubating time of fish eggs, but the temperature increase beyond certain value may lead to increase of incubating failure and egg malformation. The optimal incubating temperatures of four experimental fishes were 24.2℃of Miichthys miiuy >23.1℃of Pseudosciaena crocea > 22.2℃of Pagrosomus major > 21.0℃of Sparus macrocephalus, respectively. The 24 h LT50S of four experimental larvae fishes were: 33.4℃of Miichthys miiuy >30.3℃of Sparus macrocephalus >29.4℃of Pseudosciaena crocea >28.5℃of Pagrosomus major, respectively.(2) The recovery of phytoplankton communities and the tolerance of typical zooplankton species in subtropical coastal areas were studied under the short-time residual chlorine stress.Residual chlorine exerts influence on the biodiversity of phytoplankton communities. Because of different tolerances among different species, the species with smaller size are more tolerant to residual chlorine than those with larger size, and, the ratio of phytoplankton on r-selection increase. The higher the biodiversity index (H') of phytoplankton is, and the stronger the recovery of phytoplankton community is. The recoveries of phytoplankton communities on short-time chlorine stress were 4-6 day in spring, 3-4 day in autumn >3-9 day in winter, and 8 day-failure for recovering in summer, respectively. The results were basically in accordance with the natural rules of biodiversity change in Subtropical sea areas.The tolerances of zooplankton to residual chlorine are different among species, individual size and seasons. The differences occurred at the taxonomical level of kingdom and order. The toxicity of residual chlorine to zooplankton decreases with the increase of individual size, which indicates that the smaller ones are more sensitive to chlorine. Owing to the decrease of temperature, metabolisms of zooplankton weakened and the toxicity of residual chlorine reduced consequently with increase of the semi-lethal concentration. That is, the semi-lethal concentration of residual chlorine to the same species tends to be decrease with the increase of temperature.(3) The residual chlorine decay in the sea water was investigated through the chemical dynamics deduction. It was studied quantificationally at different salinities, temperatures and COD concentrations. The results showed that the residual chlorine decay in cooling system could be described as two-phase function, the first one being the rapid decay phase lasting 1 min only, and the second phase being the slow decay phase lasting 1min-30 min. The second phase of residual chlorine decay can be described with the first-order kinetic model at different salinities, temperatures and COD concentratons.Balance between the energy economy and environmental capacity should be considered, when standards for temperature elevation, chlorine dosage and emission inside the cooling system were constituted. From the viewpoint of ecological conservation, temperature elevation for Subtropical coastal power plants should be less than 8℃in summer and less than 12℃in other seasons, chlorine dosage should be no more than 1.8 mg·L-1.(4) Three-dimensional numerical experiments were conduced to evaluate the dispersion of thermal effluents, in which Wetting and Drying (WAD) approach was involved. Using Xiangshan bay as the typical location with large tidal flats, comparison of 15 kinds of scheme showed that the proposed model can be used to simulate the shapes of elevated temperature envelope with satisfactory results, and cooling tower method has less environmental effect than that of the direct emission mode. From the numerical experiments, it was recommended that the cooling tower method be adopted in the power plants, especially at the sea area with more than two power plants. The proposal based on the experimental results has been adopted by the local government and related enterprises.
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