Trend of Salt Lake Changes in the Background of Global Warming and Tactics for Adaptation to the Changes

Salt lakes are a mirror of climatic changes and provide holographic records of environmental changes of lakes. According to a study of geological hazards in typical salt lake areas in China and other regions, the authors explain how geological hazards in salt lake areas are caused by natural agents and how humans can seek benefits, avoid hazards and reduce losses on the premise that they have monitored and mastered the trend of salt lake changes in advance and even can store flood and recharge water in lakes and extract saline resources. The climate in western China is probably turning from warm-dry to warm-moist. The authors analyze the change trend of salt lakes sensu lato (with salinity≥0.3 wt% (NaCl)eq) and salt lakes sensu stricto (with salinity ≥3.5 wt% (NaCl)eq) in China in such climatic conditions and distinguish three types of salt lake areas (i.e. lake water rising type, lake water falling type and lake water rising and unstable type) according to the characteristics of lake water rising and shrinking. In order to conform to the climatic and lake changes in China's salt lake areas, the authors propose to add and improve hydrological and meteorological observation stations and integrate observations with remote sensing monitoring in important salt lake areas and set up multidisciplinary and interdepartmental basic projects to monitor and study recent climatic and environmental changes in salt lake areas of western China. Moreover, it is necessary to build additional flood-control and drought-preventing water conservancy facilities in key salt lake areas and work out measures for ecological protection in salt lake areas. Full consideration should be given to the influence of flooding when building saltfields and implementing capital projects.

Change of lake area in the southeastern part of China's Badain Jaran Sand Sea and its implications for recharge sources

Understanding the relationship between the changes in lake water volume and climate change can provide valuable information to the recharge sources of lake water. This is particularly true in arid areas such as the Badain Jaran Sand Sea, an ecologically sensitive area, where the recharge sources of lakes are heatedly debated. In this study, we determined the areas of 50 lakes （representing 70% of the total permanent lakes in this sand sea） in 1967, 1975, 1990, 2000 and 2010 by analyzing remote-sensing images using image processing and ArGIS software. In general, the total lake area decreased from 1967 to 1990, remained almost unchanged from 1990 to 2000, and increased from 2000 to 2010. Analysis of the relationship between these changes and the contemporaneous changes in annual mean temperature and annual precipitation in the surrounding areas suggests that temperature has significantly affected the lake area, but that the influence of precipitation was minor. These results tend to su- pport the palaeo-water recharge hypothesis for lakes of the Badain Jaran Sand Sea, considering the fact that the distribution and area of lakes are closely related to precipitation and the size of mega-dunes, but the contemporaneous precipitation can hardly balance the lake water.

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.

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.

Effect of hydrological variability on diatom distribution in Poyang Lake, China

Poyang Lake is the largest freshwater lake in China, and it has a seasonal flooding cycle that significantly changes the water level every year. The aim of this paper was to explain how these hydrological changes influence diatom populations in Poyang Lake. The yearly hydrological cycle can be divided into 4 phases: low water-level phase, increasing water-level phase, high water-level phase and decreasing waterlevel phase. Variations in the abundance of planktonic diatoms were studied using quarterly monitoring data collected from January 2009 to October 2013. Generally, diatoms were dominant in Poyang Lake and accounted for more than 50% of the total phytoplankton biomass except in July 2009(26%) and January 2012(35%). Aulacoseira granulata and Surirella robusta were the predominant species in all four phases, and they accounted for 25.02% to 56.89% and 5.07% to 14.78% of the total phytoplankton biomass, respectively. A redundancy analysis(RDA) showed that changes in physico-chemical parameter were related to the water level, and changes in diatom biomass were related to nitrite levels and p H. These results indicate that changes in environmental parameters related to both seasonal variations and water-level fluctuations caused variations in diatom biomass and community composition in Poyang Lake. Furthermore, extreme hydrological events can have different influences on the diatom community composition in the main channel and lentic regions. This research provides data on the diatom variations in Poyang Lake and will be useful for establishing biological indicators of environmental change and protecting Poyang Lake in the future.

Water storage changes in North America retrieved from GRACE gravity and GPS data

As global warming continues,the monitoring of changes in terrestrial water storage becomes increasingly important since it plays a critical role in understanding global change and water resource management.In North America as elsewhere in the world,changes in water resources strongly impact agriculture and animal husbandry.From a combination of Gravity Recovery and Climate Experiment（GRACE） gravity and Global Positioning System（GPS） data,it is recently found that water storage from August,2002 to March,2011 recovered after the extreme Canadian Prairies drought between 1999 and 2005.In this paper,we use GRACE monthly gravity data of Release 5 to track the water storage change from August,2002 to June,2014.In Canadian Prairies and the Great Lakes areas,the total water storage is found to have increased during the last decade by a rate of 73.8 ± 14.5 Gt/a,which is larger than that found in the previous study due to the longer time span of GRACE observations used and the reduction of the leakage error.We also find a long term decrease of water storage at a rate of-12.0 ± 4.2 Gt/a in Ungava Peninsula,possibly due to permafrost degradation and less snow accumulation during the winter in the region.In addition,the effect of total mass gain in the surveyed area,on present-day sea level,amounts to-0.18 mm/a,and thus should be taken into account in studies of global sea level change.

Preface:Value and dynamics of salt lakes in a changing world

The statement that the world’s ecosystems are rapidly deteriorating due to human intervention and global warming is nowadays commonplace.Some of the ecosystems most heavily impacted are inland salt lakes.The salt lakes are among the most valuable and fascinating ecosystems on Earth,and their study has both basic scientifi c interest as well as applied aspects.

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.

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.

Causes of Lake Area Changes in Poland

The northern part of Poland is occupied by numerous lakes formed during the last glaciation as a result of the Scandinavian ice sheet. Studies carried out in the lake district areas show progressive reduction of the surface area of the lakes, which leads to their eventual disappearance. The paper discusses the degree of the observed changes and points out main natural and anthropogenic factors influencing changes of lake area in Poland, including climate change, depth of lake basins, biomass growth, deforestation, hydrotechnical works, use of fertilizers and discharge of wastewater.

Spatiotemporal change patterns of urban lakes in China’s major cities between 1990 and 2015

China has experienced unprecedented urbanization in the past decades,resulting in dramatic changes in the physical,limnological,and hydrological characteristics of lakes in urban landscapes.However,the spatiotemporal dynamics in distribution and abundance of urban lakes in China remain poorly understood.Here,we characterized the spatiotemporal change patterns of urban lakes in China’s major cities between 1990 and 2015 using remote-sensing data and landscape metrics.The results showed that the urban lake landscape patterns have experienced drastic changes over the past 25 years.The total surface area of the urban lakes has decreased by 17,620.02 ha,a decrease of 24.22%,with a significant increase in the landscape fragmentation and a reduction in shape complexity.We defined three lake-shrinkage types and found that vanishment was the most common lake-shrinkage pattern,followed by edge-shrinkage and tunneling in terms of lake area.Moreover,we also found that urban sprawl was the dominant driver of the lake shrinkage,accounting for 67.89%of the total area loss,and the transition from lakes to cropland was also an important factor(19.86%).This study has potential for providing critical baseline information for government decision-making in lake resources management and urban landscape design.