Study On Water Environmental Capacity Of Yiyang Section Of The Zishui Main Stream

The study of river water environmental capacity is an important link to coordinate the development of regional water environment and social economy.In this paper,the Yiyang section of the Zishui main stream was taken as the research object.The water environment quality was evaluated by Nemero index method,the pollution load was estimated by using the pollution coefficient method and the output coefficient model,and the amount of pollutants into the river was determined.On this basis,with COD,NH₃-N and TP as the calculation factors of the water environmental capacity,Calculating the water environmental capacity and discharge reduction of the Yiyang section of the main stream of Zishui in the rich period,the flat period and the dry period by using one-dimensional steady-state model,and finally some suggestions are put forward to improve the water environmental quality of the Yiyang section of the Zishui main stream.The main research conclusions are as follows:（1）The water quality evaluation results of the nemero comprehensive index in the Yiyang section of the Zishui main stream showed that:The water quality of each monitoring section reached or exceededⅢclass water quality standards in 2017;There were certain fluctuations in the annual water environmental quality.,From 2008to 2015,the water environmental quality category of Yiyang section of the main stream of Zishui from 2008Ⅱinto 2015Ⅲclass,The water environmental quality changed from cleaner to slight pollution;From 2015 to 2017,the water quality in the monitored sections of Yiyang section of the main stream of Zishui showed a trend of improvement,and the water environment quality changed from light pollution to cleaner;From the perspective of spatial scale,the water quality in the upper reaches of the Yiyang section of the Zishui main stream was obviously better than that in the lower reaches;From the point of view of water quality in each hydrological period,the nemero comprehensive index in the dry year larger and the water quality was the worst,followed by the flat year,the water quality in the rich year was the best.（2）The calculation results of water environmental pollution load show that:In2017,the average amount of COD into the river in theYiyang section of the Zishui main stream was the largest,the amount of NH₃-N into the river was the second,and the amount of TP into the river was the smallest,which was 37,951.41 tons/year,3588.47 tons/year and 344.16 tons/year respectively.（3）According to the calculation results of water environmental capacity:The total COD water environmental capacity in Yiyang section of Zishui main stream was165,447.19 tons/year,the total NH₃-N water environmental capacity was 55746.13tons/year,and the total TP water environmental capacity was 15645.70 tons/year.;The water environmental capacity of COD,NH₃-N and TP in different hydrological periods was different.The water environmental capacity of COD,NH₃-N and TP was the largest in the rich period,followed by the flat period,and the smallest in the dry period;Influenced by river length and water quality objectives,the water environmental capacity of COD and NH₃-N in reach 5（Jinghuacun-Taojiang county water works）was the largest,followed by reach 8（Xinqiao river-Longshan port）,and reach 2（Zhexi reservoir-Chengbei water works）was the smallest;The TP water environmental capacity of reach 7（Taogushan-Xinqiao river）was the largest,followed by reach 9（Longshan gang-Wanwanzui）,and reach 2（Zhexi reservoir-Chengbei water plant）was the smallest.（4）The remaining total environmental capacity of COD,NH₃-N and TP in Yiyang section of the Zishui main stream was 50983.83 tons/year,46843.96 tons/year and 14808.34 tons/year,respectively.The environmental capacity or reduction amount of each section of the river varies greatly,most river sections have remaining water environmental capacity,The river reach 2（Zhexi reservoir-Chengbei water plant）in the rich period,the river reach 1（Pingkou-Zhexi reservoir）in the dry period,and the river reach 1（Pingkou-Zhexi reservoir）in the flat period has no remaining water environmental capacity.The reduction of sewage discharge was 95.36 tons/year,26.46tons/year and 59.05 tons/year,respectively.（5）On the basis of the water environmental capacity,the pollutant reduction targets in river reach are determined.Some suggestions are put forward,such as strengthening the unified management of the Yiyang section of the Zishui main stream,preventing and controlling the pollution caused by livestock and poultry breeding and the black and smelly water,reducing the flow in the rich period,restricting the discharge in the dry period,speeding up the construction of the municipal sewage treatment plant and the utilization of pollutants.