Assessment On Water Environmental Capacity Of Plain Networked With Rivers

Networked rivers are widely distributed in the lower reaches of Yangtze River,Pearl River and Huaihe River.The ecosystems in these regions are in danger due to the flat terrain,weak hydrodynamics and low level of natural regulation that lead to easily accumulated pollutants.The pollution load is generally far beyond its water environmental capacity.Therefore,the research on water environmental capacity in the plain networked with rivers is of great significance to reduce the pollution and utilizing water resources rationally and reasonably.Through field investigation and data collection,this paper systematically evaluated the water environment in northern part of Jiaxing.The pollution sources are categorized as sewage outlet,farmland runoff,fishpond sewage,atmospheric deposition,village runoff,urban runoff and livestock excrement.The measurement results of water quality results in 62 sampling sites showed that the concentration of ammonia nitrogen,COD and TN decreased significantly during the study period,while the concentration of TP remained stable in dry,normal and flood periods.The concentration of COD and TP is relatively lower,and the concentration of ammonia nitrogen and TN is higher.The TN concentration in almost all the sampling sites is worse than Class Ⅴ.According to the investigation of the regional environment condition,the study area is divided into 10 control units,including 3 river control units and 7 lake control units,based on the main indicators including water function division,main water type,land use type,pollution source distribution and administrative area division.In this paper,after the generalization of the river network,a twodimensional model of hydrodynamics and water quality in the northern part of Jiaxing is built and simulated in SMS.The simulation results support the collected hydrological and water quality data,and provide scientific basis for the water quality warning and pollution control decision in the north part of Jiaxing.In this paper,the water environmental capacity is classified into ideal water environmental capacity,actual water environmental capacity and residual water environmental capacity.Different models were used to calculate the water environmental capacity according to the type of water in each control unit.Generally speaking,the study area is faced with severe TN and TP pollution situation,and it bears more pollution pressure during the flood period.The residual water environmental capacity of ammonia nitrogen and COD showed the tendency that flood period > dry period >normal period.It was found that the pollution loads of COD and TP didn’t exceed the water environmental capacity in the region,so there was no need to reduce.Finally,according to the characteristics of water environmental capacity in the normal,dry and flood periods,specific suggestions on pollution reduction were put forward for all key control units,and applicable measures for water environmental improvement were proposed for the study area.