Qinghai Lake Research Articles

Assessing site-safeguard effectiveness and habitat preferences of Bar-headed Geese (Anser indicus) at their stopover sites within the\xa0Qinghai-Tibet Plateau using GPS/GSM telemetry

BackgroundThe Bar-headed Goose (Anser indicus) breeds across the high plains and plateau of Central Asia and winters in the Qinghai-Tibet Plateau (QTP), the Yunnan-Guizhou Plateau and the Indian sub-continent. Of the two recognized discrete flyways of the Bar-headed Goose, the Eastern Tibetan Flyway (ETF) is the larger, comprising at least six migration routes. However, we remain ignorant about their migratory connectivity, habitat use and effectiveness of site-safeguard mechanisms set in place for the species.MethodsWe tracked 30 ETF Bar-headed Geese from Chinese and Mongolian breeding areas to their wintering grounds using GPS/GSM transmitters, to determine their migration routes and stopover staging patterns within the QTP, overlaying these upon GIS layers of protected area status and habitat type, to model their habitat selection.ResultsIn total, 14 tagged Bar-headed Geese provided information on their entire autumn migration and 4 geese on their entire spring migration. Qinghai Lake marked birds overwintered in the QTP (n = 2), geese tagged in Mongolia wintered either in the QTP (n = 3) or in India/Bangladesh (n = 9), representing three of the migration routes within the ETF. In total, tagged birds staged at 79 different stopover sites within QTP in autumn and 23 in spring, of which 65% (autumn) and 59% (spring) of all fixes fell within the boundaries of either National Nature Reserves (NNRs) or Important Birds Areas (IBAs) in the QTP. Bar-headed Geese predominantly occurred on four land-cover types: grassland (mostly by day), water bodies (at night), wetlands and bare substrates (salt flats, dry lake/river substrates and plough) with little change in proportion. Generalized linear mixed models comparing presence with pseudo-absence data suggested geese strongly selected for wetlands as staging habitat, avoiding bare substrates in spring.ConclusionsBased on our limited observations of these tagged geese, this study is the first to show that the current designated National Nature Reserves in place in the staging areas within the QTP appear adequate to protect this increasing population. In addition, Hala Lake in Qinghai Province and adjacent areas used as initial QTP staging during autumn migration (currently outside of designated as NNRs/IBAs) are recommended for protection, based on their use by tagged birds from this study. Habitat modelling confirmed the importance of natural wetlands as feeding areas and safe areas of open water as roosting places.

Water property in high-altitude Qinghai Lake in China

Qinghai Lake in China, which is located at an altitude of 3260 ​m, is the highest inland lake among the 50 largest lakes in the world. Therefore, satellite measurement of water quality is the most important and feasible tool for routinely assessing the water property and its variations in Qinghai Lake. We derive the normalized water-leaving radiance spectra nLw(λ) in Qinghai Lake from measurements of the Visible Infrared Imaging Radiometer Suite (VIIRS), after accurately computing the top-of-atmosphere Rayleigh radiances in the satellite Level-1 to Level-2 ocean color data processing. Satellite-derived nLw(λ) spectra, chlorophyll-a (Chl-a) concentration, and the water diffuse attenuation coefficient at 490 ​nm, Kd(490), in the period of 2012–2018 are used to evaluate and understand the dynamics of water properties in Qinghai Lake. Results show that VIIRS-measured nLw(λ) spectra match quite well with the in situ data, e.g., the mean and median ratios of the VIIRS-derived and in situ-measured nLw(λ) at 443 ​nm are 0.9741 and 0.9898, respectively. Enhanced nLw(λ) at 486 ​nm and 551 ​nm can be observed from satellite-derived nLw(λ) spectra for the entire lake. VIIRS-derived nLw(λ) spectra show significant seasonal cycles. High nLw(λ) values occur in July while low values occur in April. Results also show the seasonal and interannual changes of Chl-a and Kd(490) in Qinghai Lake. Low Chl-a and Kd(490) are normally observed in April, and they typically peak in the early summer. Peculiarly, however, anomaly high values in Chl-a and Kd(490) occurred in June 2016. The analysis of empirical orthogonal functions (EOFs) shows the dominant modes for Chl-a and Kd(490) are interannual modes that account for about 79.1% and 31.5% of the their total variances, respectively. The second EOF mode for Chl-a and Kd(490) shows the seasonal changes, and contributes to about 6.1% and 14.0% of their respective total variances.

Evaluation of the Radiometric Calibration of FY4A-AGRI Thermal Infrared Data Using Lake Qinghai

The absolute radiometric accuracy of thermal infrared channels of the Advanced Geosynchronous Radiation Imager (AGRI) onboard the FengYun-4A (FY4A) satellite was assessed with field experiment data in a vicarious calibration on 18, 2019, and August 20, 2019, in Lake Qinghai. Continuous water temperature records were collected by an unmanned surface vehicle equipped with a radiometer during the experimental period. We proposed a spectral matching method based on atmospheric transfer code to create consistent equivalent spectral radiance, and the results predicted by atmospheric transfer simulation were convolved with instrument response functions to obtain predicted brightness temperature for comparison with satellite-derived temperature. Our results indicated that AGRI had an average temperature bias of 0.12 K with an RMSE of 0.17 and 0.61 K with an RMSE of 0.22 K in band 12 and band 13 on August 18, while these biases decreased to -0.01 K with an RMSE of 0.13 and -0.48 K with an RMSE of 0.17 K on August 20, respectively. This radiometric accuracy indicated that AGRI TIR bands are well functional compared with their preflight requirement of less than 1 K. The uncertainty analysis also suggested that atmospheric conditions would alter the calibration accuracy by influencing the transmittance and path thermal radiance. Meanwhile, cloud cover also requires more attention to select the appropriate concurrent satellite pixels to reduce the possible cloud edge effects. It is important and necessary for FY4A AGRI to conduct more intense automatic observations and obtain more data to improve the accuracy of radiometric calibration and monitor the operational status of satellite instruments.

A Study on Heavy Metals in the Surface Soil of the Region around the Qinghai Lake in Tibet Plateau: Pollution Risk Evaluation and Pollution Source Analysis

In order to reveal the pollution characteristics and sources of heavy metals in surface soil of the region around the Qinghai Lake in Tibet Plateau, improve the prevention awareness and measures of local residents and urge the local government to implement necessary prevention and control measures, nine heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in the surface soil samples of the region around the Qinghai Lake have been collected and analyzed. The methods such as statistic method, geo-accumulation index method, Nemerow index method, potential ecological risk index method, human health risk evaluation method and positive matrix factor analysis model (PMF) have been used to evaluate pollution characteristics and potential risks and analyze the sources of heavy metals. The results are shown below. First, the average contents of heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in soil are 11.73 ± 3.78, 0.62 ± 1.40, 12.38 ± 3.68, 41.35 ± 13.01, 19.33 ± 8.92, 546.96 ± 159.28, 21.18 ± 7.04, 21.86 ± 6.61 and 63.51 ± 19.71 mg·kg−1, respectively. Compared with the background values of the soil environment in Qinghai Province, it can be seen that there is an accumulation of these heavy metals to varying degrees, which is the most serious in Cd, Co and Pb. Second, the analysis of the geo-accumulation index and Nemerow index indicates that the heavy metals in the surface soil of the region around the Qinghai Lake have reached the level of heavy pollution, mainly polluted by Cd, and the accumulation of heavy metal pollution in the north, south, southwest and southeast of the study area is more serious. Third, the results of potential ecological risk evaluation show that the study area as a whole is classified as an area with high ecological risk, and Cd contributes the most to the overall risk. In fact, the heavy metals in the soil of the study area produce no noncarcinogenic and carcinogenic health risks to human health, and children and adults may be exposed to these risks by the mouth. Finally, the PMF results reveal that the sources of heavy metals in the study area include the sources of agricultural production, the nature, coal burning and transportation, with a contribution rate of 43.10%, 25.34%, 19.67% and 11.89%, respectively.

Water depth variation and its impact on carbonate content and oxygen isotopes: A study from a satellite lake near Lake Qinghai over the past 7.6 kyr

The oxygen isotopic composition of sedimentary carbonate (δ18Ocarb) provides information on the regional water balance between precipitation and evaporation in a lacustrine system. A volume effect was proposed to explain the abnormally low δ18Ocarb values in Lake Qinghai on the northern Tibetan Plateau, under the conditions of high evaporation and low water levels, as observed during the early Holocene. Volume effect theory states that the small volume of the lake and its sensitivity to isotopic signals from freshwater discharge control the δ18Ocarb values. In this study, we present 7.6-kyr records of carbonate content and oxygen isotopes from Lake Gahai, a small and saline satellite lake near Lake Qinghai. The records demonstrate that the water level and lake size of Lake Gahai considerably changed over the past 7.6 kyr, and the volume effect was responsible for the δ18Ocarb variations. The records also suggest contrasting responses of carbonate precipitation to water depth across different timescales. For example, over the past 7.6 kyr, the carbonate content decreased with increasing lake water levels. This can be explained by gradual water freshening under low evaporation conditions and enhanced connection between Lake Qinghai and Lake Gahai. On the centennial scale, however, the carbonate content varied significantly and was positively correlated with Lake Gahai's water level. Such a variation is probably due to the periodically lower lake water levels and a stronger influence of terrestrial clastic material, which contributed to the dilution of the carbonate content under centennial cool and dry periods. Therefore, in order to advance our understanding of past hydroclimatic variations in the climatically sensitive region, information across different timescales should be separated.

Exploring the potential factors on the striking water level variation of the two largest semi-arid-region lakes in northeastern Asia

Global warming and drying have caused desiccation of lakes in arid and semi-arid regions worldwide, and the mechanisms underlying sharp decreases in water level of great lakes in arid and semi-arid regions in recent decades require elucidation. Using a combination of multiple statistical and modeling methods, we extracted multi-decadal trends from water level time series (~1960–2017) of the two largest lakes in northern China, and explored the influences of hydro-meteorological factors on the multi-decadal and inter-annual variation in lake water level. The hydrology components of the Hulun Lake basin varied with greater amplitude than those of the Qinghai Lake basin, with water level decreases of 5.3 (1991–2011) and 3.1 (1961–2004) m in Hulun Lake and Qinghai Lake, respectively. River runoff influenced multi-decadal changes in water level of the two great lakes most, followed by lake surface evaporation and precipitation at the lake surface. Lake surface evaporation, driven by potential evaporation and lake area dynamics, was the largest hydrology component of the two great lakes. Lake surface evaporation mitigated the decline of Hulun Lake over 1995–2011, while it aggravated the decline of Qinghai Lake over 1990–2005. Although El Niño–Southern Oscillation significantly affected various hydro-meteorological factors, it contributed less than 6% of inter-annual variation in Hulun Lake, and no significant effect on the variation in Qinghai Lake was found. Pan evaporation was negatively correlated with precipitation and land evapotranspiration in both great lake basins.

Mineralogical Record for Stepwise Hydroclimatic Changes in Lake Qinghai Sediments Since the Last Glacial Period

Lake Qinghai is sensitive to climatic changes because of its pivotal location between mid-latitude Westerlies and the low-latitude East Asian monsoon. An 18.6 m long drilling core (1Fs) from Lake Qinghai provides new information on the hydroclimatic dynamics since the last glacial period. Here, we present the results of bulk mineral assemblages of this core. X-ray diffraction (XRD) results showed that the bulk minerals of the core sediments consist of major clastic minerals (e.g., quartz, feldspar, muscovite), carbonates (e.g., calcite, aragonite, dolomite), and minor clay minerals (e.g., chlorite). Quartz as an exogenous detrital mineral in lake sediments, its abundance is related to lake level changes resulting from regional climate changes via fluvial/aeolian transportation. Aragonite was precipitated from water solutions or chemical alteration of pre-existing minerals or biogenic mediation, closely related to lake hydroclimate change. Mineral assemblages revealed remarkable stepwise hydroclimatic changes. High quartz content and low calcite without aragonite suggested a cold-wet climate condition under predominant westerlies during the last glacial period from 35 to 25.3 ka. Afterward, quartz decreased and aragonite occasionally appeared, indicating an unstable hydroclimatic condition during the last deglaciation. Since the Early Holocene (11.9–8.2 ka), predominant minerals shifted from terrigenous quartz to authigenic carbonates, suggesting an increasing lake level, possibly due to intensified Asian summer monsoon with increased effective moisture. Aragonite became the primary carbonate mineral, implying a warming and humid hydroclimate environment with a relatively higher lake-level. During the Middle Holocene (8.2–4.2 ka), aragonite showed a decreasing trend indicating a higher lake level with weak evaporation. During the Late Holocene since 4.2 ka, there were lower quartz and aragonite, suggesting a deep lake with a weak summer monsoon. Our quartz and carbonate minerals record provided essential clues to reconstruct hydroclimate change in Lake Qinghai since the last glacial period.

Phylogeny and genetic diversity reveal the influence of Qinghai-Tibet Plateau uplift on the divergence and distribution of Gymnocypris species

The complex environments and climatic conditions of the Qinghai-Tibet Plateau (QTP) create unique patterns of species diversity. However, the effect of uplift of the QTP on the distribution of Gymnocypris species (Gymnocypris) remain unclear. We found that the Qilian Mountain (QL) population has the highest genetic diversity by mitochondrial DNA hypervariable region of Gymnocypris species, the Tibetan (T) population has the lowest genetic diversity. The T population differs significantly from the Qinghai Lake (QH) and QL populations based on single nucleotide polymorphisms. A phylogeny and network distribution of this species on the QTP reveal differences in its genetic structure and support its taxonomic status. Neutrality tests reveal that Gymnocypris species has experienced different degrees of expansion, even secondary expansion. A divergence timetree estimates that the time of separation of different populations is possible related to uplift of the QTP and is consistent with the time of corresponding geological events. The QL population was separated from the other populations during the third uplift of the QTP (approximately 0.14 million years ago), and the QH and T populations were separated in the late Pleistocene to the Holocene (approximately 0.03 million years ago). In conclusion, this study provides different insights into the distribution of Gymnocypris species due to uplift of the QTP. Gymnocypris species was separated into different populations by this uplift, and each population exhibits unique characteristics, especially in terms of genetic structure and the degree of expansion. Moreover, the divergence time is consistent with the time of uplift of the QTP.

Using ESI FT-ICR MS to Characterize Dissolved Organic Matter in Salt Lakes with Different Salinity.

Dissolved organic matter (DOM) composition in salt lakes is critical for water quality and aquatic ecology, and the salinization of salt lakes affects the DOM composition. To the best of our knowledge, no study has explored the effects of salinity on salt lake DOM composition at the molecular level. In this work, we selected Qinghai Lake (QHL) and Daihai Lake (DHL) as typical saline lakes. The two lakes have similar geographical and climatic conditions, and the salinity of QHL is higher than that of DHL. Fourier transform ion cyclotron resonance mass spectrometry coupled with electrospray ionization was applied to compare the DOM molecular composition in the two lakes. At higher salinity, the DOM showed larger average molecular weight, higher oxidation degree, and lower aromaticity. Moreover, the proportion of DOM that is vulnerable to microbial degradation (e.g., lipids), photo-degradation (e.g., aromatic structures), or both processes (e.g., carbohydrates and unsaturated hydrocarbons) reduced at higher salinity. On the contrary, compounds that are refractory to microbial degradation (e.g., lignins/CRAM-like structures and tannins) or photo-degradation (e.g., aliphatic compounds) accumulated. Our study provides a useful and unique method to study DOM molecular composition in salt lakes with different salinity and is helpful to understand DOM transformation during the salinization of salt lakes.

Response of water level fluctuation to climate warming and wetting scenarios and its mechanism on Qinghai Lake

Response of water level fluctuation to climate warming and wetting scenarios and its mechanism on Qinghai Lake

<p><strong><em>Ctenophora sinensis</em>: a new diatom species (Bacillariophyta) from China with comments on its structure, nomenclature and relationships</strong></p>

Lake Qinghai is an ancient brackish water lake in the Qinghai province of China. A number of endemic diatom species have already been discovered and described from the lake. This study describes another new endemic diatom species: Ctenophora sinensis sp. nov. Ctenophora sinensis has the following features: (1) frustule and valve are lanceolate; (2) the central area is slightly buttressed internally; (3) its areolae have both outside sieve-like closing plates and inside hymenate occlusions; (4) an apical hyaline field exists near each rimoportula; (5) a pseudoseptum is always presents at each pole; and (6) the cingulum has a 4:2 configuration of girdle bands in normal vegetative cells. Some remarks are provided on the nomenclature of Ctenophora and a few comments on the relationships of the genus.

Authors’ responses to the letter to the Editor regarding Hu et al. (2020): 3-D soil macropore networks derived from X-ray tomography in an alpine meadow disturbed by plateau pikas in the Qinghai Lake watershed, north-eastern Qinghai-Tibetan Plateau

Authors’ responses to the letter to the Editor regarding Hu et al. (2020): 3-D soil macropore networks derived from X-ray tomography in an alpine meadow disturbed by plateau pikas in the Qinghai Lake watershed, north-eastern Qinghai-Tibetan Plateau

Letter for Hu et al. (2020) “3-D soil macropore networks derived from X-ray tomography in an alpine meadow disturbed by plateau pikas in the Qinghai Lake watershed, north-eastern Qinghai-Tibetan Plateau”

Letter for Hu et al. (2020) “3-D soil macropore networks derived from X-ray tomography in an alpine meadow disturbed by plateau pikas in the Qinghai Lake watershed, north-eastern Qinghai-Tibetan Plateau”

Evidence for Solar Modulation on the Millennial-Scale Climate Change of Earth

In this study, we use available reconstructed data to investigate periodicities of solar activity (i.e., sunspot number) and the Earth’s climate change (temperatures of Lake Qinghai in China and Vostok in Antarctica, the GISP δ18O climate record of Greenland, and the stalagmite δ18O monsoon records of Dongge Cave in China) as well as their cross-wavelet coherences on millennial scale. We find that the variations of the Earth’s climate indices exhibited the 1000-year cyclicity, which was recently discovered in solar activity (called Eddy cycle). The cross-wavelet correlations between the millennium-cycle components of sunspot number and the Earth’s climate change remains both strong and stable during the past 8640 years (BC 6755–AD 1885). The millennial variation of sunspot number keeps in-phase with variations of Lake Qinghai temperature, Greenland temperature, and East Asian Monsoon, but anti-phase with the variation of Antarctica temperature. The strong and stable resonant relationships between sunspot numbers and these climate indices indicate that solar variability may have played a role in modulation on this millennial seesaw pattern of the Earth’s climate change before the modern industrial era.

Source and Quality of Groundwater Surrounding the Qinghai Lake, NE Qinghai‐Tibet Plateau

Comprehensive studies on the spatial distribution, water quality, recharge source, and hydrochemical evolution of regional groundwater form the foundation of rational utilization of groundwater resources. In this study, we investigated the water levels, hydrochemistry, and stable isotope composition of groundwater in the vicinity of the Qinghai Lake in China to reveal its recharge sources, hydrochemical evolution, and water quality. The level of groundwater relative to the level of water in the Qinghai Lake ranged from -1.27 to 122.91 m, indicating most of the groundwater to be flowing into the lake. The local evaporation line (LEL) of groundwater was simulated as δ2 H=6.08 δ18 O-3.01. The groundwater surrounding the Qinghai Lake was primarily recharged through local precipitation at different altitudes. The hydrochemical type of most of the groundwater samples was Ca-Mg-HCO3 ; the hydrochemistry was primarily controlled by carbonate dissolution during runoff. At several locations, the ionic concentrations in groundwater exceeded the current drinking water standards making it unsuitable for drinking. The main source of nitrate in groundwater surrounding the Qinghai Lake was animal feces and sewage, suggesting that groundwater pollution should be mitigated in areas practicing animal husbandry in the Qinghai-Tibet Plateau, regardless of industrial and urbanization rates being relatively low in the region. The scientific planning, engineering, and management of livestock manure and wastewater discharge from animal husbandry practices is a crucial and is urgently required in the Tibetan Plateau.

Temporal and Spatial Variation of PM2.5 in Xining, Northeast of the Qinghai–Xizang (Tibet) Plateau

PM2.5 was sampled from January 2017 to May 2018 at an urban, suburban, industrial, and rural sites in Xining. The annual mean of PM2.5 was highest at the urban site and lowest at the rural site, with an average of 51.5 ± 48.9 and 26.4 ± 17.8 μg·m−3, respectively. The average PM2.5 concentration of the industrial and suburban sites was 42.8 ± 27.4 and 37.2 ± 23.7 μg·m−3, respectively. All sites except for the rural had concentrations above the ambient air quality standards of China (GB3095-2012). The highest concentration of PM2.5 at all sites was observed in winter, followed by spring, autumn, and summer. The concentration of major constituents showed statistically significant seasonal and spatial variation. The highest concentrations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and water-soluble inorganic ions (WSIIs) were found at the urban site in winter. The average concentration of F− was higher than that in many studies, especially at the industrial site where the annual average concentration of F− was 1.5 ± 1.7 μg·m−3. The range of sulfur oxidation ratio (SOR) was 0.1–0.18 and nitrogen oxidation ratio (NOR) was 0.02–0.1 in Xining. The higher SO42−/NO3− indicates that coal combustion has greater impact than vehicle emissions. The results of the potential source contribution function (PSCF) suggest that air mass from middle- and large-scale transport from the western areas of Xining have contributed to the higher level of PM2.5. On the basis of the positive matrix factorization (PMF) model, it was found that aerosols from salt lakes and dust were the main sources of PM2.5 in Xining, accounting for 26.3% of aerosol total mass. During the sandstorms, the concentration of PM2.5 increased sharply, and the concentrations of Na+, Ca2+ and Mg2+ were 1.13–2.70, 1.68–4.41, and 1.15–5.12 times higher, respectively, than annual average concentration, implying that aerosols were mainly from dust and the largest saltwater lake, Qinghai Lake, and many other salt lakes in the province of Qinghai. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was utilized to study the surface components of PM2.5 and F− was found to be increasingly distributed from the surface to inside the particles. We determined that the extremely high PM2.5 concentration appears to be due to an episode of heavy pollution resulting from the combination of sandstorms and the burning of fireworks.

Lake level changes determined by Cryosat-2 altimetry data and water-induced loading deformation around Lake Qinghai

Lake Qinghai mass variation can cause local crustal deformation and lake level is sensitive to the change of regional climate. Hence, in order to explore the possibility of the Global Positioning System (GPS) technology to monitor the water-induced crustal deformation, we use the Cryosat-2/SIRAL altimeter data to investigate the variations of Lake Qinghai level and its impacts on local crustal deformation from July 1, 2010 to December 31, 2018. We apply the load Green's function method to model the loading deformation field around the Lake Qinghai region and compared it with GPS measurements. The results show that the Cryosat-2/SIRAL altimeter can effectively monitor the water level changes of Lake Qinghai, and the lake water level rises at a rate of 0.19 m/yr and exhibits obvious seasonality. The vertical deformation is more sensitive to changes in water level than the horizontal deformation. The apparent loading displacements induced by lake level change are mainly distributed within 25 km of the boundary of Lake Qinghai, with the horizontal and vertical displacements exceeding 1 and −3 mm, respectively. Furthermore, the accumulative vertical and horizontal displacements of −7 and 2 mm are found at the boundary of Lake Qinghai during the period from July 1, 2010 to December 31, 2018 and the detected linear trend of displacements are about −0.70 mm/yr and 0.15 mm/yr, respectively. The modeled loading displacements and GPS measurements at QHGC station have good trend consistency in the vertical component, but the amplitude consistency and correlation coefficient are not satisfactory, which may be caused by the resolution of GPS data, the uncertainty of modeled loading displacement and the remote geographical location of QHGC station. The feasibility to monitor the local crustal deformation caused by Lake Qinghai level change with geodetic techniques such as Global Navigation Satellite System (GNSS) still needs further study.

Long‐distance atmospheric moisture dominates water budget in permafrost regions of the Central Qinghai‐Tibet plateau

AbstractPrecipitation plays an important role in permafrost hydrology; it can alter the hydrothermal condition of the active layer and even influence the permafrost aggradation or degradation. Moisture recycling from evaporation and transpiration can greatly contribute to local precipitation in some regions. This study selected four monitoring sites and used an isotope mixing model to investigate local moisture recycling in permafrost regions of the central Qinghai‐Tibet Plateau (QTP). The results showed that the local water vapour flux in the summer and autumn were dominantly influenced by westerlies and the Indian monsoon. Moistures for precipitation in Wudaoliang (WDL) and Fenghuoshan (FHS) mainly came from the western QTP, eastern Tianshan Mountains, western Qilian Mountains, and the surrounding regions. In comparsion, more than half of precipitation at Tanggula (TGL) was mostly sourced from the Indian monsoon. Local moisture recycling ratios at the four sites ranged from 14% ± 3.8% to 31.6% ± 4.8%, and depended on the soil moisture and relative humidity. In particular, the higher soil moisture and relative humidity promoted local moisture recycling, but frozen ground might be a potential influencing factor as well. The moisture recycling ratios of the study area were consistent with the results from both the Qinghai Lake Basin and the Nam Co Basin, but differed from those of the northwestern QTP. This difference may indirectly confirm the great spatial variability in precipitation on the QTP. Moreover, the rising air temperature and ground temperature, increasing precipitation, higher soil moisture, higher vegetation cover, and expanding lakes in the study area may be conductive to enhancing future local moisture recycling by altering ground surface conditions and facilitating the land surface evaporation and plant transpiration.

Cladophora reblooming after half a century: effect of climate change-induced increases in the water level of the largest lake in Tibetan Plateau.

Massive Cladophora growth was reported half a century ago around Birds Island in Qinghai Lake, and in 2015, Cladophora populations have rebloomed and have formed green "meadows," with areas up to thousands of hectares. The present study investigated the distribution and biomass of Cladophora in Qinghai Lake and found that two key factors contribute to Cladophora blooming. First, recent climate change, especially increased precipitation, has induced the expansion of the lake's area, and the submerged grassland around Birds Island has provided a plethora of grass stems on which Cladophora can attach and twine. In addition, the submerged grasslands are covered with less than 1m of water, which allows enough sunlight to support the growth of Cladophora on available substrates. Second, the submerged grassland may function as a key source of nutrients, especially phosphate. A large number of migratory birds live in these area for very long times, which lead to higher phosphorus content due to the accumulated birds dropping. Thus, the high phosphate level further exacerbates the massive growth. Future studies should investigate the functions of Cladophora in the nutrient cycling of submerged areas, and the improvement of methods for removing Cladophora biomass.

Effects of freeze-thaw cycles on soil macropores and its implications on formation of hummocks in alpine meadows in the Qinghai Lake watershed, northeastern Qinghai-Tibet Plateau

The alpine regions are characterized by frequent freeze-thaw cycles, which influence the soil structure remarkably. However, the effects of freeze-thaw cycles on the soil macropore structure and its implications on the formation of hummocks are not well understood. This study aims to quantify the soil macropores of hummocks and the effects of freeze-thaw cycles on soil macropores to reveal its implications on the formation of hummocks in alpine meadows. A total of nine intact soil columns (0–50 cm deep) were excavated from the alpine meadows. Three replicates were collected from the hummocks and three were collected from the interhummocks, and they were scanned by X-ray computed tomography (CT). Another three replicates were excavated from the adjacent non-hummock alpine meadows, which were subjected to successive freeze-thaw cycles (0, 1, 3, and 6) and then scanned using X-ray CT. Soil macropore network of hummocks was more extensive and continuous than that of the interhummocks. The volumetric distribution of soil macropores in hummocks was multiple, while soil macropores of the interhummocks intensively fell in the volume range of 0–400 mm3. The soil macroporosity, macropore number density, surface area density, length density, node density, branch density, and mean macropore size of the hummocks were several times higher than those of the interhummocks. These soil macropore parameters showed a decrease after the first and third freeze-thaw cycle and later increased through the next three cycles. Soil macropores with volume > 1000 mm3 transformed into smaller ones (600–1000 mm3) during the freeze-thaw process. The soil macropore patterns of hummocks and interhummocks differed distinctly. Soil macropores responded significantly to freeze-thaw cycles. The effects of freeze-thaw cycles on the macropore number and size were more significant than on the morphology in alpine meadows. Hummock formation is closely related to the soil macropores during the freeze-thaw cycles, and the soil moisture played a crucial role in the hummock formation process.