Namco Lake Research Articles

ENSO-driven hydroclimate changes in central Tibetan Plateau since middle Holocene: Evidence from Zhari Namco’s lake sediments

The Tibetan Plateau, often referred to as the “Asian Water Tower”, holds immense significance as a critical water source for billions of people in surrounding regions. Its unique location and extreme environmental conditions contribute to the formation of some of the world largest lakes, crucial components of the regional water cycle. These lakes not only store vast freshwater resources but also play a vital role in regulating the flow and quality of rivers, maintaining a delicate balance in the local ecosystem. Recent decades have witnessed rapid expansion of many plateau lakes, primarily attributed to glacial melt. However, evaluating the contribution of climate forcings to these changes remains challenging. In this study, we reconstructed Zhari Namco's lake-level changes between 5.3 ka and 1.3 ka based on optically stimulated luminescence dating, a period with relatively stable glacial amount on the Tibetan Plateau. Our analysis employed sediment grain size distribution, organic matter contents and their stable carbon isotopes. In contrast to recent expansions, our findings reveal a declining trend in Zhari Namco's lake level since the middle Holocene, consistent with intermittent paleo-shoreline records from major central Tibetan Plateau lakes. This regional decline is likely the result of a weakening of the Indian Summer Monsoon. In addition to the long-term drying trend, we identified high-frequency fluctuations in Zhari Namco's lake level on centennial timescale. Further comparison with hydroclimate records from the tropics suggests that centennial high lake levels correlate with increased monsoonal precipitation during periods when ENSO activities were reduced. This study sheds lights on the historical dynamics and driving mechanisms of Zhari Namco's lake levels, providing valuable insights for predicting the impacts of future climate change on the Tibetan Plateau's water cycle.

Application of a Three‐Dimensional Coupled Hydrodynamic‐Ice Model to Assess Spatiotemporal Variations in Ice Cover and Underlying Mechanisms in Lake Nam Co, Tibetan Plateau, 2007–2017

AbstractA three‐dimensional lake‐ice coupled model is used to investigate the space‐time variations of ice and underlying mechanisms in Lake Nam Co (LNC), the third largest lake over Tibetan Plateau (TP), during 2007–2017. The model reasonably reproduces the in situ measured ice thickness and water temperature profile, and satellite retrieved ice coverage and lake surface temperature. Seasonally, the lake ice first forms in the eastern basin during early January, expands from east to west during January and February, covers nearly the entire LNC in March, starts melting from west to east in April, and eventually disappears in May. The eastward drift of thin ice throughout the ice‐covered phase and the eastward water heat transport during the ice melting phase are key factors to determine the spatial variation of ice and freeze‐thaw processes. A multiple linear regression analysis confirms that the eastward drift of thin ice can be mostly attributed to the prevailing westerly. During 2007–2017, ice volume, duration, ice‐on and ice‐off dates show significant interannual variations, and they are highly correlated with the surface air temperature (T2m) averaged over January‐March, from the preceding December to May, in December and over March–May, respectively, suggesting the “cumulative effects” of T2m. Seasonal and interannual variations of ice drift are attributed to the combined effects of wind and ice volume variations. Sensitivity analysis further points out the important impacts of ice on the lake temperature and circulation structure in winter and spring, hence the necessity of hydrodynamic‐ice coupled models in large TP lakes.

New insights into the distribution, potential source and risk of microplastics in Qinghai-Tibet Plateau

Microplastics (MPs) as emerging contaminants have become a major global concern, however, the distribution and origin of MPs in Qinghai-Tibet Plateau (QTP) and their impacts on ecosystem are poorly known. Hence, we systematically evaluated the profile of MPs on the representative metropolitan locations of Lhasa and Huangshui Rivers and the scenic sites of Namco and Qinghai Lake. The average abundance of MPs in the water samples was 7020 items/m3, which was 34 and 52 times higher than those for the sediment (206.7 items/m3) and soil samples (134.7 items/m3), respectively. Huangshui River had the highest levels, followed by Qinghai Lake, Lhasa River and Namco. Human activities rather than altitude and salinity impacted the distribution of MPs in those areas. Besides the consumption of plastic products by locals and tourists, laundry wastewater and exogenous tributary inputs, the unique prayer flag culture also contributed to the MPs emission in QTP. Notably, the stability and fragment of MPs were crucial for their fate. Multiple assessment models were employed to evaluate the risk of MPs. PERI model took MP concentration, background value and toxicity into account, comprehensively describing the risk differences of each site. The large PVC proportion in Qinghai Lake posed the highest risk. Furthermore, concerns should be raised about PVC, PE and PET in Lhasa and Huangshui Rivers, and PC in Namco Lake. Risk quotient suggested that aged MPs in sediments slowly released biotoxic DEHP and should be cleaned up promptly. The findings offer baseline data of MPs in QTP and ecological risks, providing important support for the prioritization of future control measures.

Occurrence, spatial distribution, and sources of PFASs in the water and sediment from lakes in the Tibetan Plateau.

Per-and polyfluoroalkyl substances (PFASs) are omnipresent globally and received increasing attention recently. However, there are limited data on PFASs in the Tibetan Plateau (TP), a remote high-altitude mountain region, which is regard as an important indicator region to study long-range transport behaviors of contaminants. This study investigates the occurrence, distribution, partitioning behavior, and sources of 26 PFASs in water and sediments from the four lakes of TP. The ΣPFAS concentrations ranged from 338 to 9766pgL-1 in water, and 12.2-414pgg-1 dry weight in sediments. Perfluorobutanonic acid (PFBA) and perfluorooctane sulfonate (PFOS) were detected in all samples. Qinghai Lake had the highest ΣPFAS concentrations in both water and sediments, while the Ranwu Lake had the lowest. The functional groups and CF2 moiety units were investigated as essential factors influencing the partition behavior. Principal component analysis (PCA) combined back-trajectory was used to infer possible sources of PFASs. The results suggested that the main source of PFASs in Yamdrok Lake, Namco Lake, and Ranwu Lake on southern TP were mainly originated from South Asia via long-range atmospheric transport (LRAT); while for the Qinghai Lake of northern TP, LRAT, local emissions, and tourism activities were the primary sources of PFASs.

INPPTR: An improved retracking algorithm for inland water levels estimation using Cryosat-2 SARin data

As an important technology for measuring water levels, satellite altimetry has been widely using in the lake, river, and wetland in the past two decades. However, the waveform pollution limits its application in areas with complex topography, the accuracy of the existing retracking algorithms need to be further improved. In this study, a new retracking algorithm, named Improved Narrow Primary Peak Threshold Retracking algorithm (INPPTR), based on Narrow Primary Peak Threshold Retracking algorithm (NPPTR) is presented. This retracking algorithm eliminates the noise in the waveform, extracts more accurate main peaks of the waveform, and performs Gaussian fitting on the main peaks with serious waveform pollution. Finally, the more stable water levels in areas with complex terrain can be obtained from Cryosat-2 Synthetic Aperture Radar Interferometer (SARin) waveform. To verify the accuracy of retracking algorithms, the water level time series of eight lakes and one river were retrieved using INPPTR and other three retracking algorithms (NPPTR, NPPOR and MWaPP), then were compared to the in-situ data. For Qinghai Lake, Namco Lake, Selin Lake, Zhair Namco Lake, Issyk Lake, Great Salt Lake, Tahoe Lake and Great Slave Lake, where SARin mode is used, and the root mean squared errors (RMSE) obtained by INPPTR are 18.09 cm, 21.69 cm, 20.48 cm, 34.82 cm, 17.39 cm, 39.68 cm, 26.25 cm and 18.43 cm, respectively. Compared with NPPTR, the RMSE of INPPTR is reduced by 9.91 %, 14.83 %, 7.62 %, 14.74 %, 6.70 %, 4.11 %, 105.37 % and 25.02 %, respectively. For the Amazon River, the RMSE of INPPTR is 58.24 cm, compared with the other three retracking algorithms, the RMSE obtained by INPPTR is the lowest as well. In summary, the accuracy of INPPTR is significantly higher than the other three retracking algorithms, and INPPTR can process Cryosat-2 SARin data effectively and provide more stable and effective water levels, laying the foundation for long-term, high-accuracy water levels monitoring of inland water bodies with complex terrain.

Drivers of Warming in Lake Nam Co on Tibetan Plateau Over the Past 40 Years

AbstractThe lake surface water temperature (LSWT) on Tibetan Plateau (TP) is sensitive to climate change. Based on a 1‐D lake model, we have investigated the interdecadal variation and long‐term trend of LSWT in Lake Nam Co (LNC) on TP during 1980–2018 and quantified the relative contributions of atmospheric factors to the LSWT trend. Results show LNC was warmed with a rate of 0.29°C decade−1, which is smaller than the warming of ambient air (0.45°C decade−1). The weakened wind speed, rising air temperature, increased downward longwave radiation, and decreased shortwave radiation contributed about 35%, 30%, 20%, and −15% of the estimated long‐term LSWT trend during 1980–2018, respectively. The contribution rate of 32.5% was from the interactions among all forcing variables. The primary warming was completed before 1997 (0.30°C decade−1) and was followed by a hiatus that the LSWT jumped to a warm level with a slightly negative trend (−0.08°C decade−1) after 1997. During this hiatus, the wind speed recovered from decrease and the deceleratingly increased downward longwave radiation slowed down the LNC warming. Particularly, the specific humidity shifted from increasing to decreasing trend played a key role in the hiatus of LNC warming after 1997, despite its slight contribution (−2.5%) to the LSWT trend during 1980–2018. The results showed the particularity of warming for a TP lake compared to the other ice‐covered lakes worldwide and provided a quantitative perspective for understanding the relative contributions of atmospheric factors to the long‐term trend of LSWT.

Occurrence, distribution, and ecological risk of psychoactive substances in typical lakes and rivers in Qinghai-Tibet Plateau

The occurrence, distribution, and ecological risks of psychoactive substances (PSs) in Qinghai-Tibet Plateau (QTP) was investigated in this study. The surface water samples were collected in July in 2020 from five major water bodies, and 9 PSs were determined by liquid chromatography-mass spectrometry. The mean concentrations of the total PSs were 2.19–96.86 ng/L in lakes and 4.56–34.47 ng/L in rivers. Amphetamine (AMP) was the predominant contaminant both in lakes and rivers with a mean concentration of 12.21 ± 22.76 ng/L and 9.83 ± 6.14 ng/L, respectively. The compositions of PSs in lakes and rivers were significantly different. AMP, methadone (MTD), 3,4-methylenedioxyamphetamine (MDA), and ketamine (KET) were the most detected contaminants in lakes, while in rivers AMP, MDA, heroin (HER), and methamphetamine (METH) were the most detected ones. Concentrations of AMP and MTD, the two predominant drugs, varied spatially, with the decreasing concentration of AMP in the order of Huangshui River > Yamzhog Yumco Lake > Qinghai Lake > Lhasa River > Namco Lake, and of MTD in the order of Qinghai Lake > Namco Lake > Huangshui River > Yamzhog Yumco Lake. The risk quotients (RQs) of PSs ranged from 4.44 × 10−6 to 4.32 × 10−2, indicating a low risk of PSs in the aquatic ecosystem in QTP. Compared with other research in the world, the contamination of psychoactive substances in the Qinghai-Tibet Plateau was at relatively low levels with low ecological risks.

Effects of Lake Nam Co and Surrounding Terrain on Extreme Precipitation Over Nam Co Basin, Tibetan Plateau: A Case Study

AbstractThousands of lakes and complex topography on Tibetan Plateau (TP) have important impacts on the local weather and climate, especially extreme weather events. In this study, the Weather Research and Forecasting model was adopted to quantify the impacts of Lake Nam Co (LNC) and surrounding topography on the extreme snowfall event over Nam Co basin on 24 October 2006 based on numerical experiments. The accumulated precipitation of 12 hr in this event is characterized by a maximum precipitation center with an intensity exceeding 20 mm over eastern LNC and downwind regions. Results show that the precipitation regionally averaged over eastern LNC and downstream regions can be reduced by 53%, 26%, and 68% when LNC, surrounding terrain, and both of them are absent, respectively, suggesting that LNC plays a dominant role in the formation of this event while the surrounding mountains further amplify the lake effect precipitation/snow over the downwind of LNC. Mechanism analysis indicates that the low‐level convective instability and water vapor convergence induced by LNC are essential for the formation of this extreme snowfall event, while the wind deflection and topographic lifting further strengthen the precipitation over the downwind of LNC and shift the snow belt distribution. This study is not only important to deepen the understanding of the complex interactions between the lake and orography and their combined influences on regional extreme precipitation, but also helpful for further improving the refined forecasting of the extreme precipitation induced by the lake and surrounding terrain in other regions over TP.

Numerical Study of the Thermal Structure and Circulation in a Large and Deep Dimictic Lake Over Tibetan Plateau

AbstractA three‐dimensional (3‐D) hydrodynamic model based on the Princeton Ocean Model (POM) was applied to simulate the thermal structure and circulation of Lake Nam Co (LNC), the third largest lake over the Tibetan Plateau (TP), during May–December 2013. Compared with a spatially distributed set of one‐dimensional thermal diffusion lake models, POM better reproduced the observed seasonal evolution of the horizontal distribution of lake surface temperature and the vertical thermal structure. A heat budget analysis confirmed that the lateral heat exchange made significant contributions to the horizontal variability of lake temperature. The model results showed that LNC was thermally stratified in summer, had a weak inverse stratification since mid‐December, and was fully turned over during late spring and autumn. During both overturning phases, the modeled “thermal bar” was developed as a result of the density‐driven convection in response to the radiative heating (surface cooling) during spring (autumn). The 3‐D model results showed that the monthly mean circulation featured a predominant mid‐lake cyclonic gyre throughout the ice‐free period; upwelling along the western coast and strong coastal currents occurred in all months except in July–August. Model sensitivity experiments confirmed that the lake circulation was primarily driven by the barotropic dynamics of the prevailing southwesterly wind, while the baroclinic process made a secondary contribution. The results pointed out the necessity to resolve lateral processes when modeling large TP lakes.

Black Carbon: The Concentration and Sources Study at the Nam Co Lake, the Tibetan Plateau from 2015 to 2016

We measured black carbon (BC) with a seven-wavelength aethalometer (AE-31) at the Nam Co Lake (NCL), the hinterland of the Tibetan Plateau (TP) from May 2015 to April 2016. The daily average concentration of BC was 145 ± 85 ng m−3, increasing by 50% since 2006. The seasonal variation of BC shows higher concentrations in spring and summer and lower concentrations in autumn and winter, dominated by the adjacent sources and meteorological conditions. The diurnal variation of BC showed that its concentrations peaked at 9:00–16:00 (UTC + 8), significantly related to local human activities (e.g., animal-manure burning and nearby traffic due to the tourism industry). The concentration-weighted trajectory (CWT) analysis showed that the long-distance transport of BC from South Asia could also be a potential contributor to BC at the NCL, as well as the biomass burning by the surrounding residents. The analyses of the absorption coefficient and absorption Ångström exponent show the consistency of sourcing the BC at the NCL. We suggest here that urgent measures should be taken to protect the atmospheric environment at the NCL, considering the fast-increasing concentrations of BC as an indicator of fuel combustion.

A New Digital Lake Bathymetry Model Using the Step-Wise Water Recession Method to Generate 3D Lake Bathymetric Maps Based on DEMs

The availability of lake bathymetry maps is imperative for estimating lake water volumes and their variability, which is a sensitive indicator of climate. It is difficult, if not impossible, to obtain bathymetric measurements from all of the thousands of lakes across the globe due to costly labor and/or harsh topographic regions. In this study, we develop a new digital lake bathymetry model (DLBM) using the step-wise water recession method (WRM) to generate 3-dimensional lake bathymetric maps based on the digital elevation model (DEM) alone, with two assumptions: (1) typically, the lake’s bathymetry is formed and shaped by geological processes similar to those that shaped the surrounding landmasses, and (2) the agent rate of water (the thickness of the sedimentary deposit proportional to the lake water depth) is uniform. Lake Ontario and Lake Namco are used as examples to demonstrate the development, calibration, and refinement of the model. Compared to some other methods, the estimated 3D bathymetric maps using the proposed DLBM could overcome the discontinuity problem to adopt the complex topography of lake boundaries. This study provides a mathematically robust yet cost-effective approach for estimating lake volumes and their changes in regions lacking field measurements of bathymetry, for example, the remote Tibetan Plateau, which contains thousands of lakes.

Significant differences exist in lake-atmosphere interactions and the evaporation rates of high-elevation small and large lakes

Lakes impact atmosphere boundary layer processes and are thus important for catchment scale climate modeling and regional water and heat budgets. To explore the differences in lake-atmosphere interaction parameters, meteorological variables and turbulent heat fluxes in small and large water bodies, we collected eddy covariance observations and meteorological data during ice-free periods of the Lake small Nam-Co (“small lake”) in 2012–2013 and Lake Nam-Co (“large lake”) in 2015–2016 on the Tibetan Plateau. Significant differences exist in their lake-atmosphere interaction processes due to differences in their inherent attributes and environmental backgrounds. Relative to the “small lake”, the maximum surface temperature of the “large lake” in summer is approximately 3 °C lower; “large lake” also has a larger wind speed, a higher monthly average air temperature and delayed peaks of the seasonal variation of water and air temperature. The typical values of the roughness length and standard bulk transfer coefficient for momentum are approximately 80% and 21% higher, respectively, for the “large lake”. The typical values of the roughness lengths for heat and water are one order of magnitude lower in the “large lake” while the corresponding standard bulk transfer coefficients are only 7% lower. The latent and sensible heat fluxes of the two lakes have quite different seasonal variations, with evaporation peaking in November for the “large lake” and in June for the “small lake”. The estimated evaporation during the ice-free season of the “large lake” (approximately 981±18 mm) is also higher than that (812 mm) of the “small lake” and this is mainly related to the observed lower Bowen ratio in the “large lake”.

Influence of local geoid variation on water surface elevation estimates derived from multi-mission altimetry for Lake Namco

Water surface elevation (WSE) is an essential quantity for water resource monitoring and hydrodynamic modeling. Satellite altimetry has provided data for inland water bodies. The height that is derived from altimetry measurement is ellipsoidal height. In order to convert the ellipsoidal height to orthometric height, which has physical meaning, accurate estimates of the geoid are needed. This paper evaluates the suitability of geodetic altimetric measurements for improvement of global geoid models over a large lake in the Tibetan Plateau. CryoSat-2 and SARAL/AltiKa are used to derive the high-frequency geoid correction. A validation of the local geoid correction is performed with data from in-situ observations, a laser altimetry satellite (ICESat), a Ka-band radar altimetry satellite (SARAL) and a SAR radar altimetry satellite (Sentinel-3). Results indicate that the geodetic altimetric dataset can capture the high-resolution geoid information. By applying local geoid correction, the precision of ICESat, SARAL and Sentinel-3 retrievals are significantly improved. We conclude that using geodetic altimetry to correct for local geoid residual over large lakes significantly decreases the uncertainty of WSE estimates. These results also indicate the potential of geodetic altimetry missions to determine local geoid residual with centimeter-level accuracy, which can be used to improve global and regional geopotential models.

Utilizing a new soil effective temperature scheme and archived satellite microwave brightness temperature data to estimate surface soil moisture in the Nagqu region, Tibetan Plateau of China

Since the early 2000s, many satellite passive microwave brightness temperature (BT) archives, such as the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) BTs, have become the useful resources for assessing the changes in the surface and deep soil moistures over both arid and semi-arid regions. In this study, we used a new soil effective temperature (Teff) scheme and the archived AMSR-E BTs to estimate surface soil moisture (SM) over the Nagqu region in the central Tibetan Plateau, China. The surface and deep soil temperatures required for the calculation of regional-scale Teff were obtained from outputs of the Community Land Model version 4.5 (CLM4.5). In situ SM measurements at the CEOP-CAMP/Tibet (Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau) experimental sites were used to validate the AMSR-E-based SM estimations at regional and single-site scales. Furthermore, the spatial distribution of monthly mean surface SM over the Nagqu region was obtained from 16 daytime AMSR-E BT observations in July 2004 over the Nagqu region. Results revealed that the AMSR-E-based surface SM estimations agreed well with the in situ-based surface SM measurements, with the root mean square error (RMSE) ranging from 0.042 to 0.066 m3/m3 and the coefficient of determination (R2) ranging from 0.71 to 0.92 during the nighttime and daytime. The regional surface soil water state map showed a clear spatial pattern related to the terrain. It indicated that the lower surface SM values occurred in the mountainous areas of the northern, mid-western and southeastern parts of Nagqu region, while the higher surface SM values appeared in the low elevation areas such as the Tongtian River Basin, Namco Lake and bog meadows in the central part of Nagqu region. Our analysis also showed that the new Teff scheme does not require special fitting parameters or additional assumptions, which simplifies the data requirements for regional-scale applications. This scheme combined with the archived satellite passive microwave BT observations can be used to estimate the historical surface SM for hydrological process studies over the Tibetan Plateau regions.

WATER LEVEL CHANGES OF NAM-CO LAKE BASED ON SATELLITE ALTIMETRY DATA SERIES

Abstract. Nam-Co Lake is the largest saltwater lake in Tibet and less influenced by human activity. In order to study the change of water level of Nam-Co Lake over the past decades and the impacts of climate change on the region, this paper combined height measurements of ERS-1, ERS-2, ENVISAT, ICESat-2 and CryoSat-2. We found that the water level of Nam Co Lake experienced three periods of change, namely, slightly decreasing period (1992–1993), significantly increasing period (1995–2005), and stable period (2006–2015). The change is consistent with the change of meteorological factors in the Nam-Co Basin. The increase of glacier melt water and precipitation in the basin is considered to be the cause of the overall trend of water level.

Climate-driven changes in grassland vegetation, snow cover, and lake water of the Qinghai Lake basin

Qinghai Lake basin and the lake have undergone significant changes in recent decades. We examine MODIS-derived grassland vegetation and snow cover of the Qinghai Lake basin and their relations with climate parameters during 2001 to 2010. Results show: (1) temperature and precipitation of the Qinghai Lake basin increased while evaporation decreased; (2) most of the grassland areas improved due to increased temperature and growing season precipitation; (3) weak relations between snow cover and precipitation/vegetation; (4) a significantly negative correlation between lake area and temperature (r=−0.9, p<0.05); and (5) a positive relation between lake level (lake-level difference) and temperature (precipitation). Compared with Namco Lake (located in the inner Tibetan Plateau) where the primary water source of lake level increases was the accelerated melt of glacier/perennial snow cover in the lake basin, for the Qinghai Lake, however, it was the increased precipitation. Increased precipitation explained the improvement of vegetation cover in the Qinghai Lake basin, while accelerated melt of glacier/perennial snow cover was responsible for the degradation of vegetation cover in Namco Lake basin. These results suggest different responses to the similar warming climate: improved (degraded) ecological condition and productive capacity of the Qinghai Lake basin (Namco Lake basin).

Quantitative Estimation of Groundwater Leakage from Namco Lake by SAR Monitoring

Quantitative Estimation of Groundwater Leakage from Namco Lake by SAR Monitoring

Quantifying the impact of cloud cover on ground radiation flux measurements using hemispherical images

Linking observed or estimated ground incoming solar radiation with cloud coverage is difficult since the latter is usually poorly described in standard meteorological observation protocols. To investigate the benefits of detailed observation and characterization of cloud coverage and distribution, a fieldwork campaign has been set up in order to collect data about cloud cover conditions and daily evolution to directly analyse their impacts on solar radiation fluxes. To do so, daytime hemispherical images have been collected at a very high frequency, simultaneously to ground measurements of solar radiation fluxes in a scientific station close to Lake NamCo, China. After calibration, one of the main tasks was the classification of those hemispherical images and the extraction of meaningful indices to describe the cloud cover, such as cloud fraction or cloud cover distribution. The classification is based on automatic detection of threshold on the red channel histogram. The results show that several cloud indices could be successfully derived from the hemispherical images, even if very thin clouds can be difficult to detect. The indices are then correlated to the measured solar radiation values and the impact of cloud cover on surface radiation fluxes were analysed. This analysis highlights that, more than the cloud fraction, the cloud distribution in the hemisphere is of importance when modelling radiation fluxes in the solar domain.

Changes of the three holy lakes in recent years and quantitative analysis of the influencing factors

Namco Lake, Yamzho Yumco Lake, and Mapam Yamco Lake are the “three holy lakes” of Tibet. Based on the topographic map of 1970 and the Landsat TM/ETM + remote sensing images of 1970 and from 1990 to 2012, satellite altimetry data, observed data from meteorological stations, and the changes of the “three holy lakes” in area, water level and water storage, the lake status and causes of the changes have been analyzed in a comparative manner. From 1970 to 2012, Namco Lake rapidly expanded in area, Yamzho Yumco Lake sharply declined, and Mapam Yamco Lake showed a slight decline with no great changes. The increase in precipitation was the main reason for the expansion of Namco Lake from 1970 to 1998, but the increase in glacial meltwater caused by temperature rise, and the decrease in evaporation from the lake surface, are the main reasons for the expansion and water storage increase of Namco Lake after 1998. Yamzho Yumco Lake significantly expanded from 1991 to 2004 mainly because the evaporation was limited, and shrank after 2004 because of the decrease in precipitation and the increase in evaporation. Mapam Yamco Lake was shrinking due to higher evaporation and lower precipitation. In addition to glacier meltwater, there are other forms of supply, such as groundwater, wetlands, and permafrost ablation.

Bacterial Community Structure in Two Permafrost Wetlands on the Tibetan Plateau and Sanjiang Plain, China

Permafrost wetlands are important methane emission sources and fragile ecosystems sensitive to climate change. Presently, there remains a lack of knowledge regarding bacterial communities, especially methanotrophs in vast areas of permafrost on the Tibetan Plateau in Northwest China and the Sanjiang Plain (SJ) in Northeast China. In this study, 16S rRNA-based quantitative PCR (qPCR) and 454 pyrosequencing were used to identify bacterial communities in soils sampled from a littoral wetland of Lake Namco on the Tibetan Plateau (NMC) and an alluvial wetland on the SJ. Additionally, methanotroph-specific primers targeting particulate methane monooxygenase subunit A gene (pmoA) were used for qPCR and pyrosequencing analysis of methanotrophic community structure in NMC soils. qPCR analysis revealed the presence of 10(10) 16S rRNA gene copies per gram of wet soil in both wetlands, with 10(8) pmoA copies per gram of wet soil in NMC. The two permafrost wetlands showed similar bacterial community compositions, which differed from those reported in other cold environments. Proteobacteria, Actinobacteria , and Chloroflexi were the most abundant phyla in both wetlands, whereas Acidobacteria was prevalent in the acidic wetland SJ only. These four phyla constituted more than 80 % of total bacterial community diversity in permafrost wetland soils, and Methylobacter of type I methanotrophs was overwhelmingly dominant in NMC soils. This study is the first major bacterial sequencing effort of permafrost in the NMC and SJ wetlands, which provides fundamental data for further studies of microbial function in extreme ecosystems under climate change scenarios.