Methodology And Application Of Total Discharge Control Of Pollutants In Leqing Bay

Leqing Bay is located at coastal area of southern Zhejiang Province. Leqing Bay covers 463.6 km2 in area and the coastal line is 184.7 km in length. With the rapid economic and social development of regions along Leqing Bay, more and more different pollutants have been discharged into the bay. The amount of these pollutants exceeds the marine environmental capacity of Leqing Bay, therefore the current water quality of the bay is worth worrying. According to the monitoring data in 2006, there was no first-type water quality of sea water in the bay, and water quality had deteriorated to the fourth-type water quality or less. Worse more, most sea zones are under eutrophication due to excessive discharge of total nitrogen(TN) and total phosphorus(TP), which has greatly destroyed the ecological environment of the ocean and even affected the further healthy development of economy and society in the coastal regions.In order to deal with the stiff situation of water quality deterioration and improve the environmental quality, it's urgent to set up the scheme of total discharge control of pollutants, which includes the estimation about flux of pollutants entering to the sea, the calculation of marine environmental capacity, optimization of capacity allocation among water zones and towns, industrial capacity allocation, establishment and improvement of discharge trading system and the relevant trading rules. According to the practical situation of Leqing Bay, the capacity allocation technology, the discharge trading system and the related trading institutions were studied in this paper based on the fruits of the estimation about flux of pollutants entering to the sea and the calculation of marine environmental capacity. The main research contents and results are shown as follows:(1) The water quality analysis and comprehensive evaluation on Leqing BayThe quality of the surface water environment, the sedimentary environment and the ecological environment were analyzed, and the overall environmental quality of the bay is evaluated. The results show that Leqing Bay is under severe eutrophication, and the sedimentary environmental quality of the sediment is generally in good condition. Diversity and homogeneity of zooplankton and zoobenthos are both decreasing in most sea zones of the bay except phytoplankton. The overall environmental quality of the open bay is the best, while that of the inner bay is the worst.(2) The establishment of the total discharge control technologyThe theory study was conducted mainly on the allocation technology and the discharge trading system in the scheme of total discharge control of main pollutants entering into sea. The regional pollutant allocation was made by the method of mathematical programming and equal right functions, respectively. The eventual regional allocation scheme was determined by the evaluation of fairness and economy. The pollutant allocation among towns was made by the group decision game model based on the analytical hierarchy process (AHP). The industrial pollutant allocation was made according to the proportional principle. To ensure the practical operability, the pollutant allocation results were adjusted by building the adjustable model which took the realistic reduction ability in different areas into consideration. As for the discharge trading system, the trading rules, operational steps and measures were described in the paper.(3) The application of the total discharge allocation technology in Leqing BayThe established total discharge allocation technology was applied in Leqing Bay for the short-term and middle-term planning. Different scenarios of economic and social development in the future were simulated to make the middle-term planning more advisable. Results show that for the CODCr allocation in the short term, the amount of allowable discharge in Wugen Town is the largest in 2010, which is 7031.99 tons, and that in Zhiren Town is the smallest in 2010, which is 176.30 tons. Lupu Town, Dajin Town, Lecheng Town and Wenqiao Town have the largest amount of allowable discharge from fish farming, industry, domestic usage and agriculture in 2010, respectively. In 2010, the allowable industrial CODCr for these tows are 7246.78 tons,601.32 tons,778.54 tons,432.87 tons, respectively. For the CODCr allocation in the middle term under two simulated scenarios in 2015, the amounts of allowable discharge of Wugen Town are both the largest, which is 7931.99 tons, and those of Fuxi Town are both the smallest, which is 82.11 tons. Lupu Town, Dajin Town and Lecheng Town all have the largest amount of allowable discharge from fish farming, industry and domestic usage under different simulated scenarios in 2015, respectively.For the TN allocation in the short term, the amount of allowable discharge in Wugen Town is the largest in 2010, which is 334.27 tons, and that in Fuxi Town is the smallest in 2010, which is 17.22 tons. Lupu Town has the largest amount of allowable discharge from fish farming in 2010, which is 271.56 tons. And Lecheng Town has the largest amount of allowable discharge from domestic usage and agriculture in 2010, which are 93.06 tons and 167.56 tons, respectively. For the TN allocation in the middle term under three simulated scenarios in 2015, the amounts of allowable discharge of Wugen Town are all the largest, which is 270-320 tons, and those of Fuxi Town are all the smallest, which is 11.19 tons. Lupu Town, Lecheng Town and Wenqiao Town all have the largest amount of allowable discharge from fish farming, domestic usage and agriculture under different simulated scenarios in 2015, respectively.For the TP allocation in the short term, the amount of allowable discharge in Wugen Town is the largest in 2010, which is 49.89 tons, and that in Fuxi Town is the smallest in 2010, which is 1.93 tons. Lupu Town has the largest amount of allowable discharge from fish farming in 2010, which is 42.47 tons. And Lecheng Town has the largest amount of allowable discharge from domestic usage and agriculture in 2010, which are 18.95 tons and 15.71 tons, respectively. For the TP allocation in the middle term under three simulated scenarios in 2015, the amounts of allowable discharge of Wugen Town are all the largest, which is 38-48 tons, and those of Fuxi Town are all the smallest, which is from 1.7 tons to 2.2 tons. Lupu Town, Lecheng Town and Wenqiao Town all have the largest amount of allowable discharge from fish farming, domestic usage and agriculture under different simulated scenarios in 2015, respectively.