Study On Water Environmental Carrying Capacity In The First Grade Water Source Protection Area Of Miyun Reservoir

As an important part of the Miyun reservoir ecosystem,the first grade water source protection area plays a significant role to the protection of water source. However, industrial structure with agriculture to dominate in recent years causes the non-point source pollution in this region more and more serious. Aslo, climate drought and water amount of flowing into Miyun reservoir reducing lead to a serious shortage of water resources. So that water environmental pollution and the shortage of water resources has become the“bottleneck”to restrict the social and economic sustainable development in the first grade water source protection area of Miyun reservoir. Study for water environmental carrying capacity (WECC) of in this area has important significance to the coordinated development of social economy activity and the water environment, also to guarantee the safety of water supply to capital. This study combines WECC with ecological environment water demand and water environment capacity, and uses the method of system dynamics to evaluate and analysis the WECC in the first grade water source protection area of Miyun reservoir. The main achievements obtained are as follows:(1) The sources of non-point source pollution in the researched area were discussed, then estimated its pollution load by export coefficient modeling approach. The calculation results show that livestock and poultry manure would discharge chemical oxygen demand (COD) 199.00 t/a, ammonia nitrogen (NH3-N) 16.46 t/a, total phosphorus (TP) 20.48 t/a; Life and tourism wastewater would discharge COD 93.10 t/a, NH3-N 6.21 t/a, TP 1.24 t/a; Water and soil loss would discharge NH3-N 3.64 t/a, TP 1.49 t/a. Livestock and poultry manure was considered to be the main pollution source. Life and tourism wastewater discharges a higher quantity of COD, water and soil loss discharges a higher quantity of NH3-N.(2) Based on the theoretical research on river water environment capacity, the river system in studied area was simplified, and the calculation model that consistent with the water environment situation in this region was established. After calculation according to the model, water environmental capacity of COD, NH3-N and TP are respectively 3170.36, 128.20 and 25.27 t/a,so there are a certain amount of residual capacity exist.(3) After analyzing the characteristic of water environmental system in this protection area, and the relationship between it and society or economy, the evaluation indicator system of WECC was constructed. This indicator system includes five subsystems of tourism, agriculture, population, water resources and water pollution altogether twelve indicators. It decides the weight of each indicator and subsystem by the method of analytic hierarchy process.(4) System dynamics (SD) was used in this study. According to the cause-effect analysis of the complicated system as well as subsystems, SD model of WECC in the first grade water source protection area in Miyun reservoir was established. After the test of effectiveness the model was simulated to evaluate the WECC of research area from 2008 to 2020 under the present condition. On the basis of this evaluation, ten optimization schemes were supposed separately from the perspective of water source developing, water saving and pollution treatment, and then got the corresponding result of WECC through simulation. The results showed that: under the condition of maintaining present development scheme, WECC of the studied area would be decreased year after year; Any single optimization scheme could enhance the WECC, the effect was different, however, comprehensively shows that water saving measure > pollution-preventing measure > water source developing measure. The best measure to improve the WECC is the comprehensive scheme that focuses the job mainly on water saving, and exploits the local water resources and control the water pollution at the same time.(5) According to the optimum scheme, operable and specific measures to improve the WECC in studied erea werw put forward.