Study On Water Environment Carrying Capacity In Ecological And Clean Small-watersheds In Sheyuchuan, Beijing

Mountainous area is made natural ecological barrier of capital Beijing and the main sources for water conservation and supply. With suburban industrialization and urbanization, soil erosion and point & non-point pollution is a growing problem; and the contradiction of montane eco-environment is prominent especially in river basin. Water resource is the main bottleneck in watershed development, and human activities should be controlled within the scope of water environment carrying capacity to achieve ecological security and sustainable development of socio-economics. Therefore, under current condition of socio-economics and environmental development, the study on the water environmental carrying capacity of small watershed is of great significance.Sheyuchuan small watershed was selected as study area, which is the typical small watershed in Beijing mountainous area and is adjacent to Beijing Miyun reservoir. Combined investigation, monitor and hydrological simulation techniques, the water environmental carrying capacity was revealed based on assessing the eco-environmental condition comprehensively, and then small watershed carrying capacity was proposed. We have got the following conclusions by research:1) The runoff of Sheyuchuan small watershed is few in general, whose stream is mostly drying up and the groundwater is the main water resources for the residents. Water quantity of the small watershed represented by groundwater level changed with the season regularly which decreased in spring irrigation period and increased in summer because of the rainfall, and the increasing amount was more than the reduction.2) Surface water quality of this small watershed is in good condition and groundwater quality is impacted by agricultural non-point pollution significantly. With the nitrate as the main indicator, limit to 10mg/l, exceeding standard rate of groundwater quantity is 55.6%, which focus on agricultural planting and breeding areas and cultivation in middle and lower reaches of the watershed. Nitrate concentration increases with the rainfall increasing in rainy season which leads to more severe pollution.3) Water quantity of watershed is closely related to the precipitation, while in ordinary year, human production and living water can be fully supplied by rainfall, and the groundwater level rises to normal; and water level decreases significantly in dry years, which reduces the production scale. Comparing to precipitation, human impacts the groundwater level less:doubling population, developing the agricultural water-saving irrigation and banning poultry farm influences the water table dropped 0.9 m, increasing 0.2 m and 2.4 m respectively. In order to ensure the continued water supply of small watershed, banning or controlling the size of poultry farm should be considered first.4) Water quality of watershed is related to the agricultural scale and intensity closely. Current fertilization intensity equalling to 945 kg/hm2 (nitrogen fertilizer) is too high which exceeded the carrying capacity of the water and should be reduced by at least 50%. The large scale of poultry farm at the middle and lower reaches, high pollutant concentrations and large increase have exceeded the carrying capacity of water quality. In order to ensure water quality, poultry farm should be considered to ban or try to control its size by reducing to less than 3000 which is a secure environmental safeguard.This paper conducted a system research about water environmental carrying capacity, which will not only supply the Sheyuchuan watershed some management objectives and technical supports but also provide a reference for research and practice of building Beijing ecological and clean small-watersheds.