Lake Level Changes Recorded by Tree Rings of Lakeshore Shrubs： A Case Study at the Lake West-Juyan, Inner Mongolia, China

Variation in water resources is a main factor influencing ecohydrological processes and sustainable development in arid regions. Lake level changes are a useful indicator of the variability in water resources. However, observational records of changes in lake levels are usually too short to give an understanding of the long-term variability. In the present study, we investigated the tree rings of shrubs growing on the lakeshore of Lake West-Juyan, the terminus of the Heihe River in western China, and found that Lake West-Juyan had undergone degradation three times over the past 200 years. The lake level decreased from 904.3 to 896.8 m above sea level （a.s.1.） during the period 1800-1900, to 892.0 m a.s.1, from around 1900 to the late 1950s, and the lake dried out in 1963. The trend for changes in lake levels, which was represented by the composite chronology of three beach bars, showed that the phases of increasing lake levels over the past 150 years were during the periods 1852-1871, 1932-1952, 1973-1982, and 1995-1999. Comparison with the history of regional economic development showed that human activity has played an important role in regulating the water resources of the lower reaches of the Heihe watershed over the past 200 years.

A note on the lake level variations of Nam Co,south-central Tibetan Plateau from 2005 to 2019

Tibetan lake levels are sensitive to global change,and their variations have a large impact on the environment,local agriculture and animal husbandry practices.While many remote sensing data of Tibetan lake level changes have been reported,few are from in-situ measurements.This note presents the first in-situ lake level time series of the central Tibetan Plateau.Since 2005,daily lake level observations have been performed at Lake Nam Co,one of the largest on the Tibetan Plateau.The interannual lake level variations show an overall increasing trend from 2006 to 2014,a rapid decrease from 2014 to 2017,and a surge from 2017 to 2018.The annual average lake level of the hydrological year(May−April)rose 66 cm from 2006 to 2014,dropped 59 cm from 2014 to 2017,and increased 20 cm from 2017 to 2018,resulting in a net rise of 27 cm or an average rate of about 2 cm per year.Compared to the annual average lake level based on the calendar year,it is better to use the annual average lake level based on the hydrological year to determine the interannual lake level changes.As the lake level was stable in May,it is appropriate to compare May lake levels when examining interannual lake level changes with fewer data.Overall,remote sensing results agree well with the in-situ lake level observations;however,some significant deviations exist.In the comparable 2006−2009 period,the calendar-year average lake level observed insitu rose by 10−11 cm per year,which is lower than the ICESat result of 18 cm per year.

Hydro-Chemical Processes in Lake Qinghai throughout Climate Warming: In Situ Investigations of the Largest Lake in China

In the wake of climate warming, the water level of Lake Qinghai has been continuously and rapidly declining during the past decades, causing the regional government and citizens to worry about its future as a water resource. To understand the lake evolution process, the hydro-chemical characteristics of Lake Qinghai were investigated in August of 2008. The results show that Na+ and Cl- are the dominant cations and anions in the lake water, respectively, and hydrochemistry type is Cl-- Na+ with an obvious characteristic of a saline lake. The Gibbs plot illuminates that evaporation/crystallization is responsible for the chemical composition of the lake water. The variation in hydro-chemical regime might be attributed to the reduced lake levels between 1960s and 2000s. The lake level significantly correlated with the precipitation and evaporation in the Lake Qinghai catchment. In addition, changes of the lake level in the future are simulated according to climate warming scenarios from the IPCC report. The simulated results suggest that the lake level could rise again in the following decades due to the increased precipitation under the climate warming conditions, which is already a trend in the lake level observation data.

Groundwater contributions in water-salt balances of the lakes in the Badain Jaran Desert,China

Groundwater-fed lakes are essential for the ecology in arid and semiarid regions.As a typical arid region,the Badain Jaran Desert （BJD） is famous in the world for the presence of a large number of groundwater-fed saline lakes among the mega dunes.Based on the up to date geological surveys and observations,this study analyzed the groundwater contributions in water-salt balances of the lakes in the desert.We found different types of springs,including the sublacustrine springs that indicate an upward flow of groundwater under the lakebed.A simplified water balance model was developed to analyze the seasonal variations of water level in the Sumu Barun Jaran Lake,which revealed an approximately steady groundwater discharge in the lake and explained why the amplitude of seasonal changes in lake level is less than 0.5 m.In addition,a salt balance model was developed to evaluate the salt accumulations in the groundwater-fed lakes.The relative salt accumulation time is 800–7,000 years in typical saline lakes,which were estimated from the concentration of Cl-,indicating a long history evolution for the lakes in the BJD.Further researches are recommended to provide comprehensive investigations on the interactions between the lakes and groundwater in the BJD.