Evaluation Of Ecological Treatment Of Two Typical Damaged Rivers In Changsha Area

At present,China is at the stage of high speed development.With the intense human activity,rivers are under high disturbance.The long-term accumulation will inevitably cause the destruction of ecosystem.Finally it will affect greatly to the human health and the social development This research mainly discuss the main factor to the pollution and degeneration of urban and the rural rivers of Changsha area.Through comparing the habitat condition between the treated section and the untreated section,to further understand the self-purification and the repair mechanism of rivers.Also accumulated some practice experience,which can provide reference to the future rivers ecological treatment.At present,the study on evaluating the effect of river ecological treatment in our country are positively launched among several rivers.This article can provide certain guiding significance to the similar or the same type of treatment to degenerated rivers.The main results of this research:(1)The main factors that cause the degeneration of rural rivers and the urban rivers habitat are different.To urban rivers,especially the small urban rivers located in rapid urbanization advancement area.The first pollutant origin are industrial sewage,sanitary sewage,solid waste ect.To the rural rivers,especially rivers that flow through the agriculture area,cultivation area and the communities of villages.The main stress factor originates from soil outflow runoff by cultivation activity.It may result in the serious degeneration of river physical habitat.River buffer zone vegetation massive vanishing often caused by the reclamation,which result in lacking of interception ability to rainfall,reducing of the ecology base current,even result in the zero flow during spring and winter.Also,surface source pollution from the agricultural employment of fertilizer and chemicals,and the cultivation waste water and the sanitary sewage emission,result in the degrading of water quality.But it is lightly compared to the urban rivers from same area.(2)The water quality improvement is the precondition of ecological treatment to the urban rivers,especially the seriously polluted urban rivers.After the completed ecological treatment,the rivers physical habitat condition can certainly improved,but the ecosystem can hardly recover to the near natural level.For some rivers the effect may not be remarkable.At present,the most prominent stress factor that the urban rivers received is still the water body pollution,including the heavy metal pollution and the water body eutrophication.The water quality index should be the first important matter in ecological treatment of urban rivers for a very long time.When carry on the ecological treatment to the urban rivers,separate repairment of the physical habitat of rivers is difficult to improve the biological habitat fundamentally.So under the complex condition,with limited invests.The foundation to the treatment which can improve the water quality,such as truncation dirt,the purification,should occupy as much as possible.For some seriously polluted rivers,since its main stress factor does not lie on the river bed degeneration.It will be less satisfied,even useless to improve physical habitat separately,especially on the section scale.(3)When working on the ecological treatment to the rural rivers,the soil and water keeping is the main target.First the exposed bank slope must be reinforced,as well as the interception to the farmland pollution and the soil erosion,to keep the silt intercepts away on the bank.The dredging to rural rivers,reinforcement of river bank and restoration of buffer zone can recover the partial habitat,and improve the biodiversity.Combination of other physical treatment(river step,rubble buffer,submerged bar ect.)River bank stability,buffer zone vegetation coverage,structure diversity,habitat complexity are fundamental factor When carry on the river biological treatment.Reasonable collocation of different treatment is the key to complete rural biological treatment successfully.(4)Based on the feature of Hunan rural river.Combination of recovery of buffer zone vegetation,reinforcement of fragile exposed river bank slope into biological rough slope,rubble buffer,submerged bar and near-river zone and ecological culture park can improve the damaged rural river in Hunan Changsha county.It is flexible to not only in Hunan province but other rural river in subtropical area in China.