Division Of Water Environment Control Units And Coping Strategy Of Non-point Source Pollution In Harbin

Songhua River flows through Heilongjiang,Jilin and Inner Mongolia provinces(autonomous regions).The river has spatial and temporal heterogeneity.Research on water environmental in Songhua River basin is mostly concentrated on the whole basin scale,which has made an important contribution to the analysis of water resources and non-point source pollution laws.However,it is necessary to carry out scientific research on hydrology and water pollution in specific region in order to solve the characteristic environmental problems in specific region,which can also carry out more detailed environmental planning and management.In this paper,Harbin municipal priority control unit(abbreviation as Harbin priority control unit)is used as the research area to analyze the changes of water resources and non-point source pollution in recent years.The future climate scenarios were generated basing on three GCMs(General Circulation Model).Future changes of water resources and non-point source pollution were then predicted.Water Environment Management and Control Unit were divided according to their distribution and variation characteristics,which provides a technical basis for the utilization of water resources and the prevention of non-point source pollution,and also provides a certain reference for the sectional management of river length system.Taking Harbin priority control unit as the research area,SWAT(Soil and Water Assessment Tool)model was established after collecting data and establishing databases.The study area was divided into 25 sub-basins.2008-2014 was set as a base year to analyze the variation of regional water resources and non-point source pollution.The results show that the precipitation of Harbin priority control unit was uneven in spatial and temporal distribution.The annual precipitation showed a nonsignificant upward trend.The annual mean precipitation is less in the north and more in the south.The areas with larger average precipitation are mainly concentrated in the upper reaches of Ashi River,which is above 700 mm.The annual average temperature of Harbin priority control unit was between 3.38? and 5.44? and the annual average flow was between 725 m3/s and 2872 m3/s.The sub-basins with large contribution to runoff are distributed in the upper reaches of Ashi River and the upper and lower reaches of Songhua River.Sub-basin with the largest and smallest contribution to runoff is 20 and 12.The distribution of non-point source total nitrogen(NPS-TN)and non-point source total phosphorus(NPS-TP)is uneven in spatial.Sub-basin 19 has the largest load of TN and TP.Based on the output results of three GCMs models in A1 B scenario,changes of water resources and non-point sources in future scenarios are analyzed.SDSM(Statistical downscaling model)is used to get the downscale meteorological data for SWAT model.The results show that temperature of all the three models were increased in the mid and late twenty-first Century.The increment in the end of the 21 st was higher than that in the mid.The maximum temperature increase in the mid 21 st century is GFDL,and the maximum temperature increase in the late 21 st century is HadCM3.The main increase periods of temperature for the three models occur in winter.The mean annual precipitation of GFDL decreased in the middle of the 21 st century and increased in the end of the 21 st century,while HadCM3 and MIROC increased in both the middle and end of the 21 st century.HadCM3 had a biggest change of precipitation and GFDL had a smallest one.Seasonal precipitation mainly increased in autumn and decreased in winter.In the mid-21 st century,precipitation is increased for only 7 of the 25 sub-basins of the GFDL model,while decreased for only 2 of the 25 sub-basins of the HadCM3 model and the MIROC model.At the end of the 21 st century,recipitation is increased fof 7 of the 25 sub-basins of the GFDL model.On the whole,precipitation increased more in the northwest than in the southeast.The downscaled meteorological data were used to get the water resources and non-point source pollution in the future scenario.Results show that GFDL had a decreased flow while HadCM3 and MIROC had a increased flow in the mid and late 21 st century.The areas with large contribution to the flow are concentrated in the upper reaches of Ash River and the upper and lower reaches of Songhua River.In the mid-21 st century,flow of all sub-basins in GFDL was declined.Whileat the end of the 21 st century,flow of 10 sub-basins was increased.Flow of HadCM3 and MIROC declined only in sub-basin 13 and 16.The loads of TN and TP in GFDL model decreased in the mid-21 st century and increased at the end 21 st century.The precipitation of HadCM3 and MIROC increased in both the mid the end of 21 st century.Among all the three models,the load increase in the end of the 21 st century was higher than that in the middle of the 21 st century.HadCM3 had the biggest load of TN and TP.The spatial distribution of NPS-TN and NPS-TP is similar.GFDLhad a lower load than HadCM3 and MIROC.The sub-basins with the largest output capacity in the three models are all sub-basins 19,while the smallest are sub-basins 12.Sub-basins with larger TN output were 19,2,17,14 and 22.Sub-basins with larger TP output were 19,2,17,8 and 22.Based on the three-level divisions of the National Water Resources Division and the National Ecological Function Division,nine water environment management and control units were further divided.Sub-basin was divided into priority control area,key control area,basic control area and general control area according to the NPS-TN and NPS-TP load.Due to the increasing trend of non-point source pollution load in the future scenarios,the levels of the control zones have also increased.The priority control zones have increased from three in the baseline period to five in the mid-21 st century,and then to nine in the late 21 st century.The basic control area and the general control area are gradually decreasing.Measures including constructed wetlands,vegetation buffer zones,conversion farmland to forests,fertilizer reductionand water conservation forests were taken to control the non-point source pollution.SWAT was used to simulate the load of non-point source pollution after three measures of converting farmland to forestry,reducing chemical fertilizer and vegetation buffer zone.The results showed that the vegetation buffer zone had the best effect on reducing non-point source pollution.It was suggested that the comprehensive control measures of over 25 degrees of cultivated land to forestry,10% of chemical fertilizer reduction and 5 m vegetation buffer zone should be adopted in Harbin priority control unit.The paper provided a reference for the management of Harbin priority control unit and the implementation of river chiefs system.