Study On Degradation Features And Restoration Approaches Of Downstream Riparian Wetland From The Xiaolangdi Dam Of The Yellow River

Riparian areas are important zones of matter and energy transfer across the boundary between terrestrial and aquatic ecosystems and are increasingly recognized as having a rich biodiversity and unique ecosystem structure,processes and functions.However,in recent years,due to the increasing human impacts on rivers,the cumulative effects of increasing wetland loss,as well as intensified adjacent land use continue to threaten the structure and function of wetlands.Taking the typical riparian wetlands along the Yellow River downstream from Xiaolangdi Dam to Huayuankou as example,this paper focuses on the impacts of dam establishment on riparian wetland degradation features by field survey,remote sensing image interpretation and field site observation methods.First,the current degeneration situation of downstream riparian wetlands from the Dam will be discovered by remote sensing image interpretation and field survey.Second,the changes of land use patterns of riparian wetlands after impoundment of the Dam will be illustrated through multiperiod remote sensing image interpretation,and their driving forces will be found out.Third,the recharge-discharge relationship and response features of river water and riparian groundwater will be illuminated.Furthermore,the typical hydrological transitional zone and the key restoration riparian zone will be determined.Finally,based on the above researches,the feasible measures of riparian wetland restoration will be put forward.The main research contents as follows:(1)The results showed that the rivers and river flood plains wetlands have been found distributed widely.Much of the original wetland has been developed into drylands and agricultural wetlands such as lotus ponds,fishponds and paddy fields.The shrinking trend of the natural wetlands is significant.Only small fragments of riverine wetland remain,a total of 76 plant species were recorded belonging to 65 genera and 25 families.The species of Compositae,Gramineae and Crperaceae were dominant occupying 46.24 % of the total.Herbs have the numerical advantage.Soil nutrition content is low in the riparian wetlands.Plant communities significantly influenced the contents of organic matter and total nitrogen.(2)To reveal the dynamic changes of floodplains along the Yellow Riverdownstream from Xiaolangdi Dam to Huayuankou,the land use change since 1988 was investigated based on the Landsat remote sensing data in 1988,1993,1999,2002,2007 and 2014.The results showed that the area of cultivated land,artificial wetland and construction land has increased,and the area of river,bare land and forestland has greatly decreased.Cultivated land was the main forms of land use type in the study area,especially increased areas significantly after the successful dam in 1999.The synthesis land use dynamic degree of the study area for the period 1988 to 2014 was 0.9%.Among single land use types,the annual conversion rates of construction land and bare land were most severe during study periods,where the former gained 7.1 % and the latter lost 2.7 %.Four major conversion forms were bare land?cultivated land?construction land,bare land?river?cultivated land,bare land?forest land?cultivated land and bare land?wetland?cultivated land in the study area.Changes of hydrological condition on river and riparian wetlands along the Yellow River because of dam establishment,development of local economy,lack of wetland management and fund from local government were t the main driving forces of the land use change in study areas.(3)Due to the river stage change and effect of nearby groundwater pumping,the groundwater levels in the Wuzhi wetland were obvious fluctuation.The results showed that the river stage was higher than the groundwater level in the study area.Large quantity of groundwater pumping in the riparian wetlands formed regional groundwater depression cone.The range of influence of pumping water was relatively small and groundwater level persistent decline is not truth for life irrigation along the Wuzhi wetlands.(4)After reserving water,the hydrological process of the riparian area in this study had changed greatly.Interactions between river flow and riparian groundwater had changed that the groundwater was recharged by vertical infiltration before the Xiaolangdi Dam was impounded,while it was recharged by lateral inflow after reserving water.Agricultural irrigation was an important factor affecting the hydrological process in the study areas.Interactions between groundwater and river flow were groundwater charged river flow and river flow lateral recharged groundwater temporarily during the short period of water and sediment regulation in south bank ofYellow River.However,in north bank of Yellow River,interactions showed that river flow lateral recharged groundwater,and the recharge increased obviously during the short period of water and sediment regulation.Water quality analysis results indicated that the quality of the riparian wetlands groundwater had been negatively affected by agricultural development,which is,in turn,a response to flood control by the Xiaolangdi Dam.(5)In north bank of Yellow River,the interaction between groundwater and river flow linked relatively closer within 2000 m of the river,the riparian zone should be treated as the typical hydrological transitional zone,while the riparian zone within 1000 m of the river should be treated as the key restoration riparian zone.Meanwhile,in south bank of Yellow River,the riparian zone within 400 m of the river should be treated as the typical hydrological transitional zone,while the riparian zone within 100 m of the river should be treated as the key restoration riparian zone.(6)Distribution along the river,the pattern of “riverbed natural wetland-close to natural shelter belt and riparian buffer-close to natural wetland-artificial wetland-farmland area” in both bank of Yellow River,and “moderate development of eco-tourism” on both sides of Yellow River are the best patterns of protection and utilization of wetland.This pattern not only protects the nature reserve but also gives consideration to the willingness and vested interest of local community residents.