Mass balance of saline lakes considering inflow loads of rivers and groundwater: the case of Lake Issyk-Kul, Central Asia

摘要

This study aimed to elucidate the influence of inflow water on the salinity concentration process of a saline lake and the mass balance of Lake Issyk-Kul,a tectonic saltwater lake in Kyrgyzstan.Based on the survey results and meteorological data from 2012 to 2015,we analyzed the dissolved chemical composition loads due to water inflow.Then,we discussed the relationship between the increase in salinity and water inflow into the lake.Through the water quality analysis data,we used the tank model to estimate the river inflow and analyze the loads by the L-Q curve.The groundwater loads were then estimated from the average annual increase in salinity of the lake over a period of 30 a.The results suggest that Lake Issyk-Kul was temporarily freshened between about AD 1500 and 1800 when an outflowing river existed,and thereafter,it became a closed lake in AD 1800 and continued to remain a saline lake until present.The chemical components that cause salinization are supplied from the rivers and groundwater in the catchment area,and when they flow into the lake,Ca^(2+),HCO_(3)−and Mg^(2+)precipitate as CaCO_(3) and MgCO_(3).These compounds were confirmed to have been left on the lakeshore as evaporite.The model analysis showed that 1.67 mg/L of Ca^(2+)and Mg^(2+)supplied from rivers and groundwater are precipitated as evaporite and in other forms per year.On the other hand,salinity continues to remain in the lake water at a rate of 27.5 mg/L per year.These are the main causes of increased salinity in Lake Issyk-Kul.Since Na^(+)and Cl^(-)are considered to be derived from geothermal water,they will continue to flow in regardless of the effects of human activities.Therefore,as long as these components are accumulated in Lake Issyk-Kul as a closed lake,the salinity will continue to increase in the future.