| Water resource is one of the basic living conditions of human beings.It is the controlling factor for the ecosystem.The total amount of water resource of China is 2.8 trillion cubic meters,which is the sixth largest in the world.However,the per capita share of it is only 2400 cubic meters per year,only a quarter of the world’s averages.China is one of the thirteen poorest countries of this resource in the world.Recently,with the increase of the popul ation and the development of the economy,the environmental pressure of the water resource has increased dramatically.Excessive consumption,disorderly exploiting,and water pollution have caused ecological damage and water resource degeneration,which ca n restrict the development of the economy and even endanger the safety of the country.The length of Xiangjiang River in Chang-Zhu-Tan economic zone is about 132 kilometers,with a total population of 11,000,000 people.It passes through the central part of the construction of the two-oriented society and plays a strategic role in the social and economic development of the whole province.Since the early 1970 s,over 570 industrial and mining enterprises were built successively along the river in Chang-Zhu-Tan economic zone.Every year,plenty of heavy metals-polluted waters were directly discharged into the Xiangjiang River.This brings tremendous ecological risks and disasters to the ecological environment,animal and plant,as well as the residents along the river.Technical quantitative assessment analysis of water environment management and ecologic risk were conducted according to catastrophe theory,experim ent method,assessment of ecological risks and multi-grey system theory.In the meantime,it is significant to implement an assessment of this area for exploring the heavy metal pollution and the exposure level of water ecology risk.These studies may cont ribute to the correctly selection of restoring strategy and ensuring the construction of the two-oriented society.Theoretically,they can also enrich the research of the water resource environmental remediation and ecological risk assessment.This research mainly includes the following several aspects:(1)To objectively and accurately evaluate the pollution level of Cr(Ⅵ)in Xiangjiang River and the ecological disasters caused by Cr(Ⅵ),this study showed that the contribution rate of Cr(Ⅵ)to the tota l heavy metal pollution of Xiangjiang River in Chang-Zhu-Tan economic zone was 13.21%,and the average pollution index was 2.33.This was far beyond the clean water standard.Due to the Cr(Ⅵ)pollution,hydrophilic waterfront and aquatic animals decreased more than ten kinds per year on average,the composition of microorganism community became simplified and deactivated,fish production have declined dramatically,and some rare fish species were endangered.The ecological risk had exposed obviously.(2)In order to analyze the sustainable development potential of water resources in the Chang-zhu-tan regions of Xiangjiang River,this study used the catastrophe theory to evaluate ecological risk caused by the migration of Cr(Ⅵ)-polluted wastewater.The result showed that,the evaluation value of the ecological risk of the 8 monitoring sites in Chang-zhu-tan regions of Xiangjiang River was very high.The average value was 0.958,which belongs to the high level.Therefore,the treatment of water polluted by Cr(Ⅵ)is urgently needed.(3)To further control the harm of Cr(Ⅵ)-polluted waste water to the ecological environment of Xiangjiang River,and seek a methods to deal with Cr(Ⅵ)-polluted waste water on a theoretical level,modified –chitosan was used to reduce the concentration of Cr(Ⅵ)in the water and to restore water ecological environment.According to the experiment,the maximum adsorption capacity of modified-chitosan was 90.651 mg/g.The equilibrium time of adsorption was 2 hours,and the best extract p H value was 2-6.The experimental data could be fitted well with the Pseudo-first-order adsorption kinetics and Langmuir isotherm.The modified-chitosan also showed an excellent ability to remove Cr(Ⅵ)from the actual water of sampling points of the Xiangjiang River.Only 0.05 g modified-chitosan can remove more than 90% of Cr(Ⅵ)out of 200 m L actual water from the sampling points.(4)The addition of EDDS significantly increased the migration of Cr from the underground part to the overground part of Leersia Hexandra Swartz.With the addition of 5,10 mmol/kg EDDS,the Cr in the overground part of L.Hexandra were all more than 1000 mg/kg.And,the translocation factor s of these treatments were above 1,which suggested that Leersia Hexandra Swartz had reached the level of hyperaccumulator under these conditions.When treated with 5 mmol/kg EDDS,the plants grow well and have shown excellent phyto extraction capacity.The results suggested that the application of Leersia Hexandra Swartz accompanied with the addition of 5 mmol/kg EDDS has shown high potential to adsorb Cr in the contaminated soil of Xiangjiang river shore.(5)Multi-grey system was used to evaluate the exploiting potential of the heavy metals polluted water resource of Xiangjiang River.The third class indicators were established according to the effect degree of social productive activity,urban and rural life,industrial and agricultural production as well as ecological environment in Chang-zhu-tan region of Xiangjiang River,via optimizin g of Analytic Hierarchy Process by correlation coefficient.Through building grey determining matrix,it extrapolated that the developing potential coefficient was approximately 2.983,within the evaluation range of [2.5,3.25].This result illustrates tha t the developing potential of the water resource in this area is high,which ensures that the sustainable development and strategic exploit and use of the Chang-Zhu-Tan water ecological environment in the future. |
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