Study On Water Environmental Capacity Of Enclosed Water In Mountain City

With the developing of the social economic and the promoting of industrialization, urbanization and modern agricultural, the water scarcity and water pollution has be a assignable problem. Because of slow moving water, long residence time and poor water self-purification ability, Mountain lake have to face a huge challenges like the sharp deterioration of water quality and the water ecology function degradation and more. The traditional water environmental management technology based on concentration control has not to meet requirement, and the total amount based on water environment capacity must apply to development. It is different for large lakes and reservoirs in plain area, the mountain lakes and reservoirs by limited water area, deep water, more lake-bays, big lake terrain slope, the impact of natural topography point source pollution has obvious initial effect and other characteristics. So they could not be directly applied to their water environment capacity calculation methods. In this paper, we chose the typical mountain lakes and reservoirs — Longjing Lake as an example, based on a closed mountain city water hydrology and water quality characteristics, to study the establishment of mountain lake and reservoir water environment capacity calculation. to keep quality of water for the Longjing Lake and the water environment management programs provide a scientific basis. It can also provide a reference for the calculation of water environmental capacity of mountain lakes and reservoirs. The main research contents are as follows:Based on the investigation and analysis of pollution source and pollution load into Longjing lake, according to the result of water quality evaluation using FCWQA model, comprehensive nutrition state index and single factor evaluation method of different subzone, the results show that :The main pollution load of Longjing Lake is from upstream and the non-point source pollution in the park. The water quality is in the III ~ IV, basically is in a mild eutrophication, and part of the month is in moderate or severe eutrophication. Water quality showed changes in different season and subzone, while the main pollution indicators is COD, TN and TP.According to pollution source, water quality assessment and the feature of natural topography, static algorithm of water environmental capacity was calculated based on analytical formulas. On the condition that the water quality target is Ⅳ level water quality, the water environmental capacity of Longjing Lake should be: COD is 678.71 t/a, TN is 25.471 t/a, TP is 1.853 t/a.Dynamic algorithm of water environmental capacity of Longjing Lake was based on multi-dimensional dynamic water quality model, which had been established in this thesis, then compared with static water environmental capacity,the water environmental capacity of Longjing Lake should be: COD is 709.654 t/a, TN is 28.128 t/a, TP is 2.065 t/a. Influenced by rainfall runoff, water environmental capacity is a significant different in four seasons, summer is the largest, while inter is minimal. Water environmental capacity of each cell has large difference, the center part of lake is largest, the lake bays is smaller.Comparative analysis of water environmental capacity and pollution load into the lake,residual water environmental capacity and pollution reduction of each control unit was calculated. COD and TN have residual water environmental capacity in Longjing Lake, pollution reduction of TP is 1.767 t/a. In each control unit, water environmental capacity of COD was remaining, TN should be reduced in winter, TP should be reduced in each season, TP is is the key control index. Residual capacity of TN,TP is small in West garden bay and Jiangnan garden bay, need to focus on control.