The Respone Mechanism Of Water Environment Change To Climate Variations In The Tipical Inland Lake Of Arid Area

Lake is the sensitive area of global environmental change,and also typical research area of climate change research.In arid regions,inland lake,as sensitive indicator of climate change,has direct and significant impact on ecological and environmental change.Bosten Lake is located in the arid region,which once was the largest inland freshwater lake in China.However,in the past decades,the impacts of climate change and human activities lead to lake surface shrink,water reduction,water pollution and water salinization,which consequently deteriorate the ecological environment of the Bosten Lake.In the perspective of hydrological and ecological point,nearly 50 years of hydrological and meteorological observations and the recent water quality monitoring data were used to analyze the variation of the hydro-climatic factors,changes of water environment as well as impacts of climatic variability on the lake by utilizing hydro-meteorological,environmental and other related theories.The means of GIS spatial analysis,wavelet analysis,water balance model,climate resilient models and other tools were used in this paper to analyze these variations.The results showed that:(1)Bosten Lake,was original a freshwater lake,has evolved into oligosaline lake.Before 1958 the lake salinity was only 0.39 g/L and it increased to 1.44 g/L by 1975.In 1987 the value peaked at 1.87g/L and the current salinity is 1.55 g/L.There are significant differences in the spatial distribution of the lake.The highest value of salinity appeared in northwestern lake,while the lowest value in the southwest.(2)The water balance of the Bosten Lake is determined by the Kaidu River inflow,Kongque River outflow and evaporation loss.Approximately 93%of the total water input to the lake comes via the Kaidu River,with a small fraction of water input coming from precipitation(3%).The lake outflow via the Kongque River and evaporation from the lake accounted for 57%and 43%of the total water output from Bosten Lake,respectively.(3)These factors have caused three dramatic fluctuations of the lake level over the past 50 years.To be specific,the lake level decreased by 3.61m in the period of 1958-1987.Thereafter,it increased by 4.6m from 1988 to 2002,and then dropped by nearly 4.0m by 2012.Overall,the lake level shows a downward trend,while the Mann-Kendall test results showed that the lake level declined significantly.(4)From 1958 to 1987,the lake level declined mainly due to excessive evaporation loss,while the artificial way to increase the lake outflow just exacerbated the declining rate.In the period of 1988-2002,the rising of lake level was mainly due to the increased lake inflow and the reduction of evaporation loss.From 2003 to 2012,the decrease of lake level was mainly caused by the inflow reduction and evaporation which were the result of climate change.In addition,the ecological transfering water from the Kongque River to the downstream of Tarim River intensified the lake level decrease.(5)Currently,the water quality of Bosten Lake belongs to the class IV water quality standard,indicated that the water is polluted slightly.The water body of the lake could be regarded as mesotrophic.The mainly impact factors of eutrophication is total nitrogen that the average concentration is 0.91 mg/L.(6)Anthropogenic activities and climatic variations resulted in the salinization of Bosten Lake.Due to large-scale agricultural development in Yanqi Basin,salt washing and alkaline soil improvement increased high salt water that flow into the Bosten Lake from farmland after 1960s.Reduction of freshwater into the lake and artificially increasing of the lake outflow resulted in the lake salinity increase from 1958 to 1987.The decrease of salinity in 1988-2003 was mainly due to global warming.The rising temperatures made precipitation and glacial meltwater increase,and large quantities of inflow freshwater diluted Bosten Lake leading to reduction of water salinity.After the early glacial ablation,the total glacier has reduced which directly lad to the decrease of inflow.Additionally,the lake salinity rose again in the period of 2004-2012 due to the ecological water transport.(7)The ecosystem health condition in Bosten Lake maintains in the middle level.From 1993 to 2012,the water ecological health conditions show a downward trend.The results of this paper can provide scientific basis for water pollution control and countermeasures in Bosten Lake,and also provide references for the water resources management.This paper is of great significance to protect the ecological environment of the Bosten Lake.