Hydrochemical characteristics of the Hurleg Lake

The Hurleg Lake is located at Delingha sub-basin,NE Qaidam Basin,in an arid areas(37°14′-37°20′N,96°51′-96°57′E)with 11.3 km-length,10.5 km-width and an average depth of 2.94 m. Its catchments area is about12 360.0 km2 with two inflow rivers of Bayin River and Baluogen River and one outflow into Tuosu brackish lake. In the area,annual precipitation is only 176.1 mm but the evaporation ranges from 2 000 to 2 500 mm. It is currently the only freshwater lake in the Qaidam Basin. Fluvial and lacustrine sediments were widespread in the area. This study aims to discuss the main reason of keeping fresh water,hydrochemical characteristics,material sources and effect factors of lake water. Total 30 water sample were collected from the Hurleg Lake in October 2012. All of them were filtrated by 0.22 μm membrane in the field. Water samples were analyzed for TDS,p H by a p H meter of STARTER 3C and a TDSTester 11+,respectively. The anion concentrations of Cl-,SO42-and NO3-were analyzed with Dionex ICS-900 and K+,Ca2+,Na+and Mg2+with ICP-OES. The contents of Na ranges from 115.8 to 189.7 mg·L-1with an average of 131 mg·L-1,while Ca from 55.1 to 64.9 mg·L-1with an average of 59.8 mg·L-1,Mg from 47.6 to 71.39 mg·L-1with an average of 52.1 mg·L-1,K from 6.5 to 8.8 mg·L-1with an average of 7.1 mg·L-1,Cl-from 200.3 to 406.3 mg·L-1with an average of 300.8 mg·L-1,and SO42-from 0.08 to 211.5 mg·L-1with average of 178 mg·L-1. Thus,the lake water belongs to Cl-·SO42-- Na+·Ca2 +type or [Cl]NaⅢ type with high hardness. The p H value ranges from 8.03 to8.42 with an average of 8.26. It is almost invariable. The TDS ranges from 785 to 1 150 mg·L-1with an average of848.33 mg·L-1. The hardness has a range of 322.448 to 392.917 mg·L-1with an average of 332.870 mg·L-1. The values of p H,TDS and hardness increase gradually from west to east and have obvious correlation. The possible reason is the presence and increasing distribution of hydrophytes from east to west. Ternary plots show that the major ion compositions of the lake water and Bayin River are significantly different. The Bayin River is the main river flowing into the lake with HCO3--Ca2+type. The contents of SO42-,Mg2+and Na+in the Hurleg Lake are much higher with relative low contents of Ca2+and HCO3-than those in Bayin river water. The possible reason is that the Ca2+and HCO3-of lake water were precipitated as carbonate minerals during the process of strong evaporation. According to the distribution of all of data in Gibbs Figure,the chemical compositions of the Hurleg Lake water are mainly controlled by rock weathering and evaporation in the whole basin. Because of little rainfall and less human activity,weathering products is the main source of lake components with groundwater input. The Hurleg Lake can keep fresh water may lie in recharge of glacier melt water,groundwater,and the lake itself is an outflow lake