| As the world’s rapid development of economic and, large amounts of pollutants have been discharged into surface water, especially the reservoirs and its watersheds which are the most important places and water sources of human social and economic development. The function of aquatic ecosystem was damaged by water pollution seriously and caused water shortage. Yuqiao Reservoir is a unique drinking water source for Tianjin, this paper analyzed its water quality status, spatio-temporal variations in water quality and eutrophication, identified its potential pollution sources, and analyzed the threshold of eutrophication management of Yuqiao reservoir. This paper takes Yuqiao reservior basin for study, and uses fives methods to have a deep study to determine the standard of the ecological compensation.Fuzzy comprehensive assessment and multivariate statistical techniques including cluster analysis, discriminant analysis, principal component analysis, factor analysis and PMF model were applied to analyze the water quality status of Yuqiao Reservoir Basin, North China, for assessing its spatio-temporal variations and identifying potential pollution sources. The results demonstrated that, at temporal scale, the characteristics of water quality can be divided into two periods, flood season (7-9) and non-flood season (4～6,10,11), and there was a delay for the response of water quality to precipitation. Moreover, the concentrations of SS, CODMn, CODcr, BOD5and TP were much higher in flood season, and DO, TN and NO3-N were much higher in non-flood season, while the concentrations of NH3-N were similar between the two periods. These findings indicated the influence of point source pollution on eutrophication was higher than that of non-point source pollution. Because there was a delay for the response of water quality to precipitation, measures should be taked to control the agricultural nonpoint source pollution to reduce the pressure of phosphorus pollution controlling in the rainfalty in the Yuqiao reservoir is significantly better than the water quality outside the reservoir. According to the GB3838-2002standards, the water quality in Yuqiao reservoir from 1990～2012was belong to Class Ⅱ～lass Ⅲ, higher than the water quality of outside reservoir from1to2levels. The results further revealed that water quality of Yuqiao Reservoir Basin showed a downtrend from1990to2001with fluctuation, and a steady fluctuation from2001to2008, the water quality of Yuqiao reservoir basin has been changed better from2008.Three different methods of GIS spatial interpolation and Carlson eutrophication index were applied to analyze the status and spatial distribution characteristics of eutrophication and environmental factors in YuQiao Reservoir. The results revealed that the key exceeded standard factor of eutrophication in Yuqiao Reservoir was N, and the limit factor was P. The trophic state index of TN in the reservoir gradually decreased with the direction of flow of water body, the TN pollutants mainly come from upstream rivers and agricultural nonpoint source pollution. The distribution of total phosphorus trophic state index was relatively steady, and its pollutants mainly come from animal husbandry and aquaculture in the Baxia area. Spatial differences of the nutrient status during the flood season were significantly higher than that during non-flood season. The eutrophication level of Yuqiao reservoir was mainly effect by the economic activities around the reservoir. So it is necessary to encourage resident green living guide behavior to protect the water quality of reservoir.The CMB model was used in this paper to estimate the threshold of eutrophication management at a specific water quality goal by the application of Bayesian method. The results revealed that Yuqiao Reservoir is a P-controlled water ecosystem, and the inner concentration of TP in the reservoir is significantly correlated with TP loading concentration, hydraulic retention coefficient and bottom water dissolved oxygen concentration. In the case of the goal of water quality for the total phosphorus of reservoir has been set (0.05mg/1, the third level of national surface water standard for reservoirs according to GB3838-2002), management measures could be took to improve water quality standard of TP in reservoir through controlling the highest inflow phosphorus concentration (0.153～0.211mg/1) and the lowest DO concentration (3.756～5.589mg/1) to the threshold. Inverse method was applied to estimate the joint manage measures, and the results revealed that controlling lowest dissolved oxygen concentration and adjusting the inflow and outflow of reservoir to modify the hydraulic retention coefficient to the maximum value is also a valuable measure to avoid eutrophication.Through the comparing the results among the ecological compensation calculation of Yuqiao reservoir Basin, we found that the standard based on the value of ecosystem services is too high and it can be used as the upper limit of compensation standard. The compensation standard based on the development opportunities is too low and it can be used as the lower limit of compensation. The method which considered the impact of water quantity and quality, economic, social and other factors is relatively more comprehensive. The method based on water environment capacity calculation is a good method for management of objectives, but it ignores other factors outside of the water quality and quantity. |
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