Abstract:

The main ions in lake and river water are an essential part of water chemical characteristics.Climate conditions control the changing trend of hydrochemical indexes in a large scale,while geological conditions determine the differences in its distribution.Thus,climate and environment have their important function to indicate the spatiotemporal variation of water chemistry.The Poyang Lake is the largest freshwater lake of China,and its hydrology is controlled by humid monsoon climate.The rainfall in the region and the volume of the lake are subject to large seasonal variation.With rapidly increasing urbanization and water contamination,a better understanding of the hydrochemical parameters of the region is necessary.Hydrochemical investigations were carried out in the Poyang Lake catchment.pH,TDS and major ions were determined from the Poyang Lake and its inflow river to analyze the spatial and temporal variation characteristics of the major ions in Feb.(dry season) and Jul.(wet season),2010.And the possible controlling factors were discussed.The results indicated that water in the Poyang Lake catchment was CaHCO-3 type,soft water with low mineralized degree.Ca2+ was the dominant cation in lake and river water,which were 5935% and 4989% of the total cations,respectively.On the other hand,HCO-3 was the dominant anion in lake and river water,which were 5337% and 5937% of the total antions,respectively.The annual mean values of the total dissolved solids (TDS) in lake and river water were 6381 mg/L and 587 mg/L,respectively,approaching to the midvalue of the whole world large rivers（65mg/L）.Besides,the composition of the major ions and TDS showed significant temporal and spatial variation,namely,higher concentrations in dry season and lower values in wet season except SO2-4.The concentration of the major ions in the river water increased gradually along the flow path.Different geological background played an important role in influencing the value of TDS.Hydrochemical type of surface water varied from HCO-3,HCO-3-SO2-4 to SO2-4,and from the upstream of the five rivers to the lake.The control mechanism of water chemistry in the Poyang Lake catchment were illustrated and it is indicated that the chemical composition of the major dissolved salts of the waters were mainly derived from chemical weathering of carbonate rocks in river basin,with the combinations of precipitation and the impact of human activities.In wet season,〖JP2〗the surface water was significantly controlled by the dilution effect of precipitation and geological condition; while in dry season,it is mainly influenced by rock weathering function,evaporationcrystallization effect and anthropogenic activities.In addition,the increasing of SO2-4type water were closely related to acidification of the Yangtze River and the backflow from the Yangtze River to the Poyang Lake