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.

Reconstruction of the Lacustrine Delta and Lake Level Change Analyzing Subsurface Geology and Geomorphology: Changes That Occurred during the Holocene in the Oguraike Reclaimed Land Area, Southern Kyoto, Japan

A paleo-lacustrine delta in Kyoto, Japan was reconstructed on the basis of subsurface geological and geomorphological analysis, and paleo-lake level changes were estimated from the structure of the delta. These analyses of the study region, i.e., the Oguraike reclaimed land area provided evidence that Lake Ogura existed until about 60 years ago in southern Kyoto, Japan. The Uji river delta was provided influents to this lake until ca. 400 years ago, as is indicated by an upward-coarsening delta succession of about 2 - 4 m thickness. The lake level could also have changed in the past as a result of a change in altitude of the delta-front (foreset) and delta-plain boundary, which probably reflects the lake surface elevation. About 400 years ago, the Paleo-Uji River was separated from Ogura Lake because a levee was constructed along the river for building a castle and for constructing a waterway for transportation. As a result of this construction, the lake level that was more than 13.0 m in elevation was reduced by 1.5 m. In a more ancient times, the lake level experienced two stages—one in which the elevation was more than 13.5 m, and one in which the elevation was reduced to less than 10 m. These changes in the lake level are represented by a flat surface with four steps and small cliff of height ca. 0.5 - 2 m (relative elevation) separating them, recognized at the southern lakeshore. The observation of strata along with the archaeological survey in the north of Ogura Lake reveals that the lake level was decreased ca. 800 - 680 years ago. The lake level was at its highest during two periods, the first from before the 8th century to the end of the 8th century and the second from the 14th century to 400 years ago.

THE STUDY ON CLIMATIC CHANGES AND LAKE LEVEL FLUCTUATIONS OF OINGHAIB LAKE IN HOLOCENE

According to loess and palaeosol climatic record, field observation, analysis data and 14C dating, we discuss the climatic changes and the water level fluctuations of Qinghai Lake. It is pointed out that there were four relatively warm and moist stages in Qinghai Lake basin during the Holocene. They formed in the periods from 10,300 yr.B.P. to 8,500 yr.B.P., 7,000 yr.B.P. to 3,500 yr.B.P., 2,800 yr.B.P. to 2,000 yr.B.P. and from 1,300 yr.B.P. up to now. The climate in the Holocene optimum period, from 7,000 yr.B.P. to 3,500 yr.B.P., was much warmer and moister than that today. Polypodium plant grew luxuriantly around Qinghai Lake. The annual temperature was 2.5℃ higher than that today, but there was no forest at Qinghai Lake shore. It is found that there was a good relationship between precipitation and water level fluctuation. In warm and moist period water level was high and in the cold and dry period it was low in the Holocene. There were four high water level periods for Qinghai Lake in the

Influencing mechanism and hydrogeological implications of water level fluctuation of lakes in the northern Qaidam Basin,Qinghai-Tibet Plateau

The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considerable scientific issues on the protection of salt lake resources and infrastructure,and monitoring of hydrological processes at the lake-basin scale.Although the spatial-temporal trends of lake changes on the Qinghai-Tibet Plateau(QTP)have been well documented,the underlying influencing mechanism and hydrogeological implications of rapid lake changes in the QB are not well understood.Three lakes in the northern QB were selected to investigate lake water level fluctuations on different time scales based on extensive in-situ monitoring and satellite observations.The influencing mechanism and hydrogeological implications of rapid changes of terminal lakes were discussed in combination with the reported increasing precipitation rate and mass balance of glaciers in the northern QTP.Results reveal the following:(1)the fluctuation pattern of Sugan Lake was asynchronous and out of phase with that of Xiao Qaidam and Toson lakes during the monitoring period;(2)Sugan Lake water rose gradually,and the rise interval was from late April to early July.In contrast,Xiao Qaidam and Toson lakes took on a rapid and steep rise,and the rise intervalwas from late July to September;(3)the influencing mechanisms for rapid lake fluctuations are controlled by different factors:glacier and snow melting with increasing temperature for Sugan Lake and increasing precipitation for Xiao Qaidam and Toson lakes;(4)in accordance with different intervals and influencing mechanisms of rapid lake expansions in the QB,hydrological risk precaution of lakes and corresponding river catchments was conducted in different parts of the basin.This study provided an important scientific basis for assessing the hydrological process and hydrological risk precaution,and protection of salt lake resources along with rapid lake expansions in the arid area.

Synthesis of the ICESat/ICESat-2 and CryoSat-2 observations to reconstruct time series of lake level

Synthesis of multi-satellite altimetry facilitates the acquisition of long-term changes in lake level but may induce biases due to inconsistent data sources,and thus remains largely unexplored.This study investigates the integrated application of Ice,Cloud,and land Elevation Satellite(ICESat),ICESat-2,and CryoSat-2 missions to provide consecutive lake level series in 2003–2020.The sample comprises 48 lakes in the world with gauge-based or Hydroweb water level data.The CryoSat-2 data arefirst adjusted to the ICESat-2 height reference based on the mean values of their monthly water level difference during their overlapping period(2018–2020).Then,the corrected CryoSat-2 data are used to link the ICESat and ICESat-2 data.Results show that in the sample lakes,the deviations between CryoSat-2 and ICESat-2 data vary and range from-0.78 m to 0.13 m.The data quality of the synthesized time series is evaluated by comparing against the validation data,with an average R^(2) of 0.84.This study shows that CryoSat-2 has the potential offilling the gap between ICESat and ICESat-2.The three altimeters can be expected to integrate effectively for monitoring lake water level changes in the past two decades.

A continuous simulation of Holocene effective moisture change represented by variability of virtual lake level in East and Central Asia

The fluctuation of a single lake level is a comprehensive reflection of water balance within the basin, while the regional consistent fluctuations of lake level can indicate the change of regional effective moisture. Previous researches were mainly focused on reconstructing effective moisture by multiproxy analyses of lake sediments. We carried out a series of experiments, including a transient climate evolution model, a lake energy balance model and a lake water balance model to simulate continuous Holocene effective moisture change represented by variability of virtual lake level in East and Central Asia.The virtual lake level, area, water depth and salinity are not equivalent to actual values, but we estimated relative changes of the regional effective moisture. We also explored the driving mechanisms of effective moisture change in different geographical regions. Our results indicated that gradually falling effective moisture during the Holocene in northern China was due to the combined effects of high lake evaporation caused by longwave and shortwave radiation, and low precipitation caused by reductions of summer solar insolation. A decline in effective moisture through the Holocene in the Tibetan Plateau and southern Central Asia resulted from decreased precipitation because of the weakening of the Asian summer monsoon. Increased precipitation induced by the strengthening of the westerly circulation contributed to the effective moisture rise during the Holocene in northern Central Asia.

Paleosalinity and lake level fluctuations of the 3rd Member of Paleogene Shahejie Formation,Chezhen Sag,Bohai Bay Basin

The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environment of the sag in the 3rd Member of Paleogene Shahejie Formation(Es3)is not clear.Recovering the paleosalinity and lake level fluctuations is helpful for understanding organic matter rich rocks sedimentation.Therefore,a detailed geochemical,mineralogical and paleontological analysis of the Es3 in the Chezhen Sag was conducted.Index like Sr/Ba ratios,B/Ga ratios,equivalent boron content and methods concluding Adams'formula and Couch's method were adopted to reveal the paleo-salinity and lake level variations.The results indicate that the lower submember(Lower Es3)was deposited in a salt water with high salinity,accompanied by dry climate and transgression event.The middle submember(Middle Es3)and upper submember(Upper Es3)record a freshwater to brackish environment.The paleosalinity and paleoclimate changes are consistent with the global sea level variations.The type and content of sporopollen indicate a dry climate in Lower Es3,which further confirms the reliability of the reconstruction results of paleosalinity.Combined with the paleoclimate and previous marine paleontological evidence,we proposed that the high salinity period is associated with a high lake level and a large-scale transgression event in Lower Es3.According to salinities and corresponding Lake depths,we established a sedimentary environment variation model of the Es3 Member in Chezhen Sag.

Characteristic Relationships between Phosphorous Accrual, Ecosystem Aspects and Water Level Fluctuations in Tropical Lakes: Naivasha Ramsar Site, Kenya

Hydrological dynamics affect water levels and thus affecting ecosystem structure and functions. Lake levels in tropical ecosystems affect phosphorous input through runoff from adjacent watersheds. The resultant biological community, water and sediment quality of the lakes due to water level changes is a reflection of the geology of the area and the anthropogenic activities in the watershed. The study conducted between January 2018 and December 2019 was to explore relationships between the phosphorous input and Water Level Fluctuations (WLF) recorded by Water Resource Authority (WRA). Lake water samples were analyzed in the laboratory for phosphorous using molybdenum blue-ascorbic method and recorded using spectrophotometer. Chlorophyll-a was determined by extracting a filtered sample with 15 ml acetone and incubating overnight and thereafter read using a double beam spectrophotometer. Total Suspended Solids (TSS) was determined by filtering 200 ml of a water sample and dried overnight at 105°C. The lowest and highest phosphorous concentrations recorded were 0.2 mg/l and 0.42 mg/l at NST7 and NST2, respectively. Measurements of Chlorophyll-a were 0.32 mg/l and 0.42 mg/l at NST9 and NST2, respectively. Secchi transparency measurements were 32.9 cm at NST3 and 84 cm at NST1. The highest and lowest TSS concentrations were 0.14 mg/l and 0.13 mg/l at NTS1 and NST8, respectively. The hydrodynamic regime in most tropical lakes plays a significant role in the re-reaction of phosphorous that consequently influences productivity. Tropical lakes have extreme lake level fluctuations which accelerate the production process. The influence of water level changes on aquatic productivity is crucial in most tropical lakes and should be taken into consideration when assessing the environmental impacts.

High lake levels on Alxa Plateau during the Late Quaternary

Field investigations including lake shoreline measurement and 14 C chronology have been carried out on the Alxa Plateau to better understand the formation and evolution of the high lake levels in northwest China during the late Pleistocene.Comprehensive field investigations show that there are at least ten shorelines at different elevations at Juyan Lake,at least four on the northwest side of the Jilantai Salt Lake,and nine shorelines and one terrace on the northeast margin of Zhuye Lake.Stratigraphic correlations and chronological evidence indicate that the paleo-lakes have the highest lake levels in Marine Isotope Stage (MIS) 3.Though the optically stimulated luminescence (OSL) results which have been reported by some scholars do not support this view,the fact that the paleo-lakes have the highest lake levels in MIS 3 can not be denied.Differences between OSL and 14 C results from this work might indicate that high lake levels existed on the Alxa Plateau during two different periods.It also suggests that the high lake levels may exist in both MIS 5 and early MIS 3.This paper also provides the basic hydrological information for further water resources research in this arid region.

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.l.) during the period 1800-1900, to 892.0 m a.s.l. 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.

Relationship Between Changes of River-lake Networks and Water Levels in Typical Regions of Taihu Lake Basin,China

The typical regions of the Taihu Lake Basin,China,were selected to analyze the variation characteristics of river-lake networks under intensive human activities.The characteristics of the fractal dimension of river networks and lakes for different periods were investigated and the influences of river system evolution on water level changes were further explored through the comparison of their fractal characters.The results are as follows:1) River network development of the study area is becoming more monotonous and more simple;the number of lakes is reducing significantly,and the water surface ratio has dropped significantly since the 1980s.2) The box dimension of the river networks in all the cities of the study area decreased slowly from the 1960s to the 1980s,while the decrease was significant from the 1980s to the 2000s.The variations of lake correlation dimension are similar to those of the river network box dimensions.This is unfavorable for the storage capacity of the river networks and lakes.3) The Hurst exponents of water levels were all between 0.5 and 1.0 from the 1960s to the 1980s,while decreased in the 2000s,indicating the decline in persistence and increase in the complexity of water level series.The paper draws a conclusion that the relationship between the fractal dimension of river-lake networks and the Hurst exponents of the water level series can reveal the impacts of river system changes on flood disasters to some extent:the disappearance of river networks and lakes will increase the possibility of flood occurrence.

Evaporative enrichment of stable isotopes(δ^(18)O and δD) in lake water and the relation to lake-level change of Lake Qinghai, Northeast Tibetan Plateau of China

Stable isotopic compositions(δ18O and δD) have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship between the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions(δ18O, δD and d-excess) in lake water and precipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and δD in lake water were higher than those in precipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and δD in lake water and precipitation showed that the local evaporative line(LEL) in lake water(δD=5.88δ18O–2.41) deviated significantly from the local meteoric water line(LMWL) in precipitation(δD=8.26δ18O+16.91), indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quantified the E/I ratio(evaporation-to-input ratio) in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios(ranging from 0.29 to 0.36 between 2009 and 2012) clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleolake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.

Lake evaporation： A possible factor affecting lake level changes tested by mod- ern observational data in arid and semi-arid China

金海·莱克和宰埃·莱克， 400 km 分开，位于亚洲夏天季风的西北边缘。这二个湖的水主要来自 Qilian 山的中间、东方的部分。以前的研究证明从湖记录暗示的二个湖的 Holocene 气候变化是不同的。湖蒸发是否在异步的 Holocene 气候变化起一个作用，是重要的理解湖记录。在这份报纸，我们在金海·莱克和宰埃·莱克旁边使用了现代观察为湖蒸发测试影响因素。二个湖附近的平底锅蒸发主要与相对湿度，温度，蒸汽压力和阳光持续时间有关。但是温度有不同影响到二个湖的湖蒸发，它能影响 Holocene 千年规模的湖水平变化。另外，在相对湿度在上的差别千年规模将更重要，它能也贡献异步的湖记录。

Impact assessment of climate change and human activities on annual highest water level of Taihu Lake

The annual highest water level of Taihu Lake (Zm) is very significant for flood management in the Taihu Basin. This paper first describes the inter-annual and intra-annual traits of Zm from 1956 to 2000. Then, using the Mann-Kenall (MK) and Spearman (SP) nonparametric tests, the long-term change trends of area precipitation and pan evaporation in the Taihu Basin are determined. Meanwhile, using the Morlet wavelet transformation, the fluctuation patterns and change points of precipitation and pan evaporation are analyzed. Also, human activities in the Taihu Basin are described, including land use change and hydraulic project construction. Finally, the relationship between Zm, the water level of Taihu Lake 30 days prior to the day of Zm (Z0), and the 30-day total precipitation and pan evaporation prior to the day of Zm (P and E0, respectively) is described based on multi-linear regression equations. The relative influence of climate change and human activities on the change of Zm is quantitatively ascertained.The results demonstrate that: (1) Zm was distinctly higher during the 1980-2000 period than during the 1956-1979 period, and the 30 days prior to the day of Zm are the key phase influencing Zm every year; (2) P increased significantly at a confidence level of 95% during the 1956-2000 period, while the reverse was true for E0; (3) The relationship between Zm, P and E0 distinctly changed after 1980; (4) Climate change and human activities together caused frequent occurrences of high Zm after 1980; (5) Climate change caused a substantially greater Zm difference between the 1956-1979 and 1980-2000 periods than human activities. Climate change, as represented by P and E0, was the dominant factor raising Zm, with a relative influence ratio of 83.6%, while human activities had a smaller influence ratio of 16.4%.

Residual Levels and New Inputs of Chlorinated POPs in Agricultural Soils from Taihu Lake Region

Selected persistent organochlorine pesticides (OCPs), including 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its principal metabolites 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) and 1,1-dichloro-2,2-bis(p-chlorophenyl)e- thane (DDD), hexachlorocyclohexane (HCH) and its isomers (α-,β-, γ-, and δ-HCH), hexachlorobenzene (HCB), endo- sulfan, dieldrin, and endrin were quantified to determine current levels of organochlorine pesticides, to assess the eco- toxicological potential, and to distinguish previous and current inputs in agricultural soils from the Taihu Lake region. Gas chromatography equipped with a 63Ni electron-capture detector (GC-ECD) system was employed. Thirteen OCPs were detectable in all soil samples, with DDTs being the main residues, and HCHs had the second highest level of OCP residues. Although OCP residual levels were lower than those in 1990s, the residual levels for most of the DDTs and some of HCHs were still higher than the national environmental standards for agricultural soils. The ratios of DDT/DDE and γ-/α-HCH in twelve soils indicated that new inputs could be present in the soils. Thus, efforts should be made to completely ban the production of OCPs and their use in agriculture so as to reduce the threat of OCPs to food quality and human health.

Simulation of the water level influence on the difference within the water-tube tiltmeter in Shuangyang Lake

This article analyzes the relationship between the water level and the water-tube tilting in Shuangyang lake,based on the differential deformation features reflected by the NS and EW components of the water-tube tiltmeter.The results show a good spatiotemporal consistency between the variation of water level and the NS tilt component,which is considered to be affected by the magnitude and duration of the water level variation in Shuangyang Lake.The article uses Landsat remote sensing image data to extract the water boundary of Shuan-gyang Lake,and takes advantage of the finite element numerical simulation method to build three-dimensional models for different geological structural conditions of the Shuangyang seismostation.The simulation results show that when the underground medium is granite,the effect of water level variation on the vertical displacement of the surface is non-directional.With a 50-m soil layer in Model 2,the simulated NS tilt variation is equivalent to the actual observed water-tube tiltmeter NS component when the water level variation is 0.44 m and 0.8m.When the variation of water level reaches 2.0m,the simulation result of the NS component is 79.6 ms,which is slightly larger than the observed result of 60.32 ms.However,the simulation results show that the variation of the EW component is significantly smaller than that of the NS one.Due to the fact that the Shuan-gyang lake is long in the NS direction and short in the EW direction,the existence of the soil layer tends to generate ground deformation along the NS direction in the vicinity of the lake after the increase of water level,thereby resulting in the difference of the ground deformation in the two directions.

Water Security-based Hydrological Regime Assessment Method for Lakes with Extreme Seasonal Water Level Fluctuations：A Case Study of Poyang Lake,China

Extreme seasonal water level fluctuations characterize natural floodplain lakes in monsoon regions, which are crucial for ensuring lake water security, including flood prevention water supply and health of aquatic ecosystem. In order to achieve this goal, we established a hydrological regime assessment method based on a set of hydrological indicators for lakes with heavy seasonal water level fluctuations. The results suggest that time-sensitive hydrological indicators and specific time scales for various water security aspects must be considered. We discovered that it is more practical and meaningful to combine the water level classification derived from statistical analyses with characteristic hydrological values linked to water security. The case study of Poyang Lake results show that there are no discernable trends of Poyang Lake water regime status over the last 35 years, and the two periods of poor status are in accordance with climate variation in the lake basin area. Scholars and policy makers should focus on both floods and droughts, which are the main water security problems for Poyang Lake. It is hoped that this multi-scale and multi-element hydrological regime assessment method will provide new guidelines and methods for other international scholars of river and lake water assessment.

INTERANNUAL CHANGE OF QINGHAI LAKE LEVEL IN RECENT 30 YEARS

The Qinghai Lake level (QLL) dropped at a rote of 10 cm/a according to formal records since 1958. Hydrometerological and earthquake information has been used on the Qinghai Lake and its environs in recent decades to study the variation of QLL and discuss its possible reasons.

A TECHNOLOGY OF PALEOPRECIPITATION RESTORATION BASED ON CHANGES OF INLAND LAKE LEVEL——WITH REFERENCE TO THE DAIHAI LAKE IN INNER MONGOLIA

The Daihai Lake,situated in the south of the Inner Mongolia Plateau, is a rift inland lake with a drainage area of 2621.6 km^2 and an annual average precipitation (AAP) of 436.8mm. Remarkable changes of the Daihai Lake have taken place since the Holocene.

RELATIONSHIP BETWEEN QINGHAI LAKE LEVEL DESCENDING AND ARTIFICIAL WATER－CONSUMPTION

Qinghai Lake is the largest inland lake in China. It is a closed-drainage saline lake located at 3194m above sea level in the northeastern Qinghai-Xizang (Tibet) Plateau. Qinghai Lake region, about 36°15' -38°20' N and 97°50, - 101°20' E,is a closed basin