Researches On The Water Environmental Carrying Capacity In Tianjin City

In China, water resources shortage because of water pollution has become the vital problem to economical development and it was the key influential factor of the water environmental carrying capacity. Water environmental protection has become the current first-class job of environmental protection. How to evaluate water environmental carrying capacity exactly has become a hot topic in watershed water-quality management. It is necessary for healthy development of important regions to study their water environmental carrying capacity as fully as possible and to establish the pointed plans for water pollution control and for water environmental protection. Taking the water environment in Tianjin as an example, this dissertation assessed the current status of its water environment and analyzed the pollutants into rivers in 2008 and in 2020, separately. From the narrowed meaning of carrying capacity of water environment, the watercourse module analogous to reservoirs was developed to calculate the capacities to assimilative chemical oxygen demand (CODCr) and ammonia nitrogen (NH4+-N) of the 81 water functional zones in 2010 and 2020. According to the results of the assimilative capacity, the limiting emissions and the pollutant reductions of every water functional zone were identified. From the broad meaning of carrying capacity of water environment, the water environmental carrying capacity of Tianjin was evaluated based on index system under different social-economic development scenarios. The management strategy was put forward to improve the water environment of Tianjin basing on the researching results of the assimilative capacity and the assessment of carrying capacity. The main results were summarized as follows.1. Simple factor assessment and comprehensive identification index were used to assess the current status of water environment in Tianjin.14.2 percent sections were satisfied with the demand of the water functional zones for 2010 by the method of simple factor assessment. The water pollution in Tianjin was very serious and the indexes that exceeded the water criterion were CODCr, potassium permanganate index (CODMn) and NH4+-N. The condition of water environment in Tianjin became worse and worse year by year during the period of 2001-2008. The water quality in flood season was better than that in dry season. The comprehensive identification index not only considered the general condition of water quality, but also avoided the limitation of the simple factor assessment method. The ratios of the sections belonging to class V and worse than class V were 31.7% and 48.3%, respectively. Multivariate statistical techniques were used to analyze the condition of water environment in Tianjin. Hierarchical cluster analysis was used to group 81 water functional zones into 5 clusters and discriminant analysis provided the reliability for the result of hierarchical cluster analysis.2. The pollutant loads of the wastewater and the pollutants into river in 2008 and in 2020 were analyzed. There was 8.08×108 ton wastewater into river in 2008. The quantities of CODCr and NH4+-N into river were 17.11×104 ton and 1.34×104 ton, respectively.74.6% inlets into river exceeded the limitation demanded. These inlets centered on the Haihe mainstream water system and the Daqing River water system. Four water functional zones mainly accepting the pollutant and their primary inlets were chosen by the method of equal standard pollution load. According to the results of forecast, there will be 15.80×108 ton wastewater,8.56××104 ton CODCr and 1.31×104 ton ammonia nitrogen into rivers in 2020. Nine water functional zones were chosen as the main zones accepting the pollutant.3. The watercourse module analogous to reservoirs was developed to calculate the assimilative capacities of CODCr and ammonia nitrogen in Tianjin. The results indicated that the total CODCr and ammonia nitrogen assimilative capacity calculated based on 75% confidence instream flow condition were 48009t.a-1 and 4335t.a-1, respectively. The total CODCr and ammonia nitrogen assimilative capacity of water system in Tianjin decreases in the following order:Haihe mainstream water system> Beisan River water system>Daqing River water system>Yongding River water system>Ziya River water system>Zhangwei South Chanel. Xiqing has the most amount of assimilative capacity of CODCr and ammonia nitrogen among the 13 districts. The limiting emissions of CODCr and ammonia nitrogen based on 75% confidence instream flow condition were 46913t.a-1 and 4275t.a-1, respectively. The reduced loads of CODCr and ammonia nitrogen were 138431 t.a-1 and 9810t.a-1, respectively.4. In 2020, the total CODCr and ammonia nitrogen assimilative capacity calculated based on 75% confidence instream flow condition were 78088t.a-1 and 10681 t.a-1, respectively. The Haihe mainstream water system had the most amount of assimilative capacity of CODcr and ammonia nitrogen. The centre of Tianjin had the most assimilative capacity among the 13 districts. The limiting emissions of CODCr and ammonia nitrogen basing on 75% confidence instream flow condiction were 77468t.a-1 and 10641t.a-1, respectively. The reduced loads of CODCr and ammonia nitrogen were 22860t.a-1 and 6173t.a-1. It was the improvement of the drainage system that led to the increasement of assimilative capacity of Tianjin in 2020.5. The evaluation method of water environmental carrying capacity under different social-economic development scenarios was constructed. According to the socioeconomic development planning demand and water pollution state in Tianjin, The index system to evaluate the carrying capacity of water environment was designed from the aspects of economy, society, resources, environment and technology, and a three-layer hierarchy-structured water environmental carrying capacity evaluation model was proposed. The current situation of water environmental carrying capacity was evaluated and different scenarios of medium or long period were analyzed using the evaluation model of the water environmental carrying capacity. The result of current situation evaluation showed that the carrying capacity of water environment increased in Tianjin from 2000 to 2007. The assimilative capacity of water environment had the most influence on the water environmental carrying capacity. The supporting ability of water resource decreased and the water environmental carrying capacity and the ability of the social optimized configuration increased during the assessed period from 2000 to 2007. The scenarios analysis indicated that all of the following measurement, such as saving water, increasing investment on environmental protection to reduce the amount of COD per unit discharge, comprehensive measurement, could improve the water environmental carrying capacity of Tianjin.6. Basing on the research of the assimilative capacity and the carrying capacity of water environment in Tianjin, the managing measurement of water quality basing on the assimilative capacity and the limiting emission and the comprehensive managing measurement on how to improve water environment carrying capacity were put forward.