The Respone Mechanism Of Land Use/Cover Change To Water Environment In The Typical Oasis Of Arid Region

Researches on dynamic change process of arid oasis land use/coverage and its downstream ecological environment evolution is a component of global change research.It also constitutes the research foundation.Yanqi Basin Oasis,as the typical representative of inland arid land,enjoys a special geological position and natural conditions,which.causes the instability and fragility of its ecosystem.The oasis and its downstream Bosten Lake form a united whole;in terms of environmental changes,they interact on each other.Since 1950s and 1960s,the unreasonable land development in the research area led to deterioration of oasis ecological environment.That's because oasis systems are connected by water.The paper collects remote sensing images,water quality monitoring data and hydrological data over the past 50 years as well as Landsat TM/ETM remote sensing images of 1993,2000 and 2013.The research employs multi-source data integration and multidiscipline and utilizes.tools including ArcGIS spatial analysis,ENVI software platform,LUCC quantitative analysis model,multivariate statistical analysis and hydrothermal equilibrium model to study land use/coverage evolution of Yanqi Basin Oasis and changes of Bosten Lake's ecosystem from multiple perspectives,scales and levels.It expounds the dynamic process of Yanqi Basin Oasis's land use,driving mechanism and appropriate size and discusses the impact of land use/coverage changes on Bosten Lake's water environment.Through objectively analyzing the current situation and historic evolution rules of Bosten Lake's water environment,the paper puts forward the total pollutant control plan based on the water quality objective of water functional areas.Finally,pollution control and treatment countermeasures are proposed with the constraints of water environment.Main achievements include:(1)Significant changes have taken place in the land use of the research area over the past two decades:rapid expansion of arable area and gradual reduction of natural vegetation.The research of land use index reflects that the land use;of the;research area has maintained a rising trend.The driving mechanism of land use/coverage changes consists of natural factors and human activities.Of the two,human activities have a more significant than that of natural factors.(2)The correlation between land use type&area and water quality concentration is constructed.On this basis,the response relationship of water quality evaluation factor and land use structure is concluded.The arable land and habitat area at Bosten Lake Basin presents a positive correlation with salinity degree,COD,TN and TP.Water bodies and grassland shows a negative correlation with the above-mentioned water quality indexes.Different correlations are reflected by woodlands and water quality indexes.Besides,it is justified basically.(3)In the perspective of hydrothermal and soil-water balance,the paper proposes a mathematical model for an appropriate oasis area.The appropriate oasis irrigation area of Yanqi Basin is 725.5km2,including 652.05km2 area of arable land;in Yanqi Basin Oasis,the current irrigation area is about 1047km2,322.5km2 more than the capacity of water resources.Therefore,the oasis has been in an unstable state.(4)It is reached through multivariate statistical analysis that the dominant factors of Bosten Lake's water pollution are salinity degree,BOD5,sulfate,CODMn,CODCr,NH4-N,TP and TN.Currently,the lake's water quality meets the Class IV Water Standard,i.e.,light pollution.Of the four functional areas,the water quality of Area III is the worst while that of Area I is the best.The nutritious state is moderate.The main factor affecting its nutritious state is total nitrogen.(6)The allowable salt amount of rive pollutants is figured out in line with the specific water quality objective.Besides,the excessive pollutants are cut and distributed.When the design hydrological frequency stays at 90%,the kk-1?kk-2 of the research area and salt acceptance capacity of the Bosten Lake control unit are 67373.51 t/a?306630.17 t/a?186318.48 t/a.Of them,only kk-3 control unit and its main drainages have to reduce their salinity.The reduction amount is 76847.42 t/a.Finally,according to the total amount control plan,the paper proposes the partitioned,classified and phased pollution strategy.