A Tibetan ice core covering the past 1,300 years radiometrically dated with 39Ar.

Ice cores from alpine glaciers are unique archives of past global and regional climate conditions. However, recovering climate records from these ice cores is often hindered by the lack of a reliable chronology, especially in the age range of 100 to 500 anni (a) for which radiometric dating has not been available so far. We report on radiometric 39Ar dating of an ice core from the Tibetan Plateau and the construction of a chronology covering the past 1,300 a using the obtained 39Ar ages. This is made possible by advances in the analysis of 39Ar using the laser-based detection method atom trap trace analysis, resulting in a twofold increase in the upper age limit of 39Ar dating. By measuring the anthropogenic 85Kr along with 39Ar we quantify and correct modern air contamination, thus removing a major systematic uncertainty of 39Ar dating. Moreover, the 85Kr data for the top part of the ice core provide information on firn processes, including the age difference between the ice and its enclosed gas. This first application of 39Ar and 85Kr to an ice core facilitates further ice cores from nonpolar glaciers to be used for recovering climate records of the Common Era, a period including pronounced anomalies such as the Little Ice Age and the Medieval Warm Period.

Tight coupling between leaf δ13 C and N content along leaf ageing in the N2 -fixing legume tree black locust (Robinia pseudoacacia L.).

N2 -fixing legumes can strongly affect ecosystem functions by supplying nitrogen (N) and improving the carbon-fixing capacity of vegetation. Still, the question of how their leaf-level N status and carbon metabolism are coordinated along leaf ageing remains unexplored. Leaf tissue carbon isotopic composition (δ13 C) provides a useful indicator of time-integrated intrinsic water use efficiency (WUEi). Here, we quantified the seasonal changes of leaf δ13 C, N content on a mass and area basis (Nmass , Narea , respectively), Δ18 O (leaf 18 O enrichment above source water, a proxy of time-integrated stomatal conductance) and morphological traits in an emblematic N2 -fixing legume tree, the black locust (Robinia pseudoacacia L.), at a subtropical site in Southwest China. We also measured xylem, soil and rainwater isotopes (δ18 O, δ2 H) to characterize tree water uptake patterns. Xylem water isotopic data reveal that black locust primarily used shallow soil water in this humid habitat. Black locust exhibited a decreasing δ13 C along leaf ageing, which was largely driven by decreasing leaf Nmass , despite roughly constant Narea . In contrast, the decreasing δ13 C along leaf ageing was largely uncoupled from parallel increases in Δ18 O and leaf thickness. Leaf N content is used as a proxy of leaf photosynthetic capacity; thus, it plays a key role in determining the seasonality in δ13 C, whereas the roles of stomatal conductance and leaf morphology are minor. Black locust leaves can effectively adjust to changing environmental conditions along leaf ageing through LMA increases and moderate stomatal conductance reduction while maintaining constant Narea to optimize photosynthesis and carbon assimilation, despite declining leaf Nmass and δ13 C.

Demonstration of a memory calibration method in water isotope measurement by laser spectroscopy.

RATIONALE: Measuring δ18 O and δ2 H values in water using wavelength-scanned cavity ring down spectroscopy (WS-CRDS) requires multiple injections of up to six (and sometimes eight or more) of one sample to remove the memory effect, which decreases the sample throughput and increases the consumables cost. Thus, improved methods for removing the memory effect are required. METHODS: We calculated the memory coefficients by sequential WS-CRDS measurement of two lab standard waters with isotopic differences, and used them to establish calibration equations. We then used these equations to correct the measured δ18 O and δ2 H values by removing the memory effect, instead of using multiple injections in the routine daily measurements. RESULTS: By using this method, the number of injections per sample was reduced to one. The reproducibility (one standard deviation) of the δ18 O and δ2 H values obtained for quality control sample was less than 0.05‰ and 0.5‰ for an annual average, respectively. CONCLUSIONS: By measuring the memory coefficients and establishing the calibration equations, a highly effective method was developed for determining the δ18 O and δ2 H values of water, which could significantly improve sample throughput for liquid water dual isotope measurement without sacrificing the precision.

The influence of memory, sample size effects, and filter paper material on online laser-based plant and soil water isotope measurements.

RATIONALE: The recent development of isotope ratio infrared spectroscopy (IRIS) was quickly followed by the addition of online extraction and analysis systems, making it faster and easier to measure soil and plant water isotopes. However, memory and sample size effects limit the efficiency and accuracy of these new setups. In response, this study presents a scheme dedicated to estimating and eliminating these two effects. METHODS: Memory effect was determined by injecting two standard waters alternately. Each standard was injected nine times in a row and analyzed using induction module cavity ring-down spectroscopy (IM-CRDS). Memory coefficients were calculated using a new "multistage jump" algorithm. Sample size effects were evaluated by injecting water volumes ranging from 1 µL to 6 µL. Finally, the influence of cellulose filter paper on the isotopic measurements, the memory, and the sample size effect was evaluated by comparing it with glass filter paper. RESULTS: Memory effects were detected for both δ18 O and δ2 H values, with the latter being stronger. Isotopic differences between replicates of the same plant or soil sample showed a clear decrease after memory correction. A small water volume effect was found only when the injected water volume was larger than 3 µL. However, while the correction method performed well for laboratory-made samples, it did not for field samples, due to the heterogeneity of the isotopic composition of the samples. Stronger memory and water volume effects were found for cellulose filter paper. CONCLUSIONS: The memory coefficients and the water volume-isotope relationship improved the consistency and accuracy of both laboratory and field data. Our results indicate that cellulose filter paper may not be a suitable medium to measure standard waters and evaluate memory and water volume effects. Finally, a detailed correction and calibration protocol is suggested, along with notes on best practices to obtain good-quality IM-CRDS data. Copyright © 2017 John Wiley & Sons, Ltd.

Monsoon-driven transport of organochlorine pesticides and polychlorinated biphenyls to the Tibetan Plateau: three year atmospheric monitoring study.

Due to the influence of the Indian monsoon system, air mass transport in and to the Tibetan Plateau shows obvious seasonality. In order to assess the responses of atmospheric concentrations of persistent organic pollutants (POPs) to the Indian Monsoon fluctuation patterns, a three year air monitoring program (2008-2011) was conducted in an observation station close to the Yarlung Tsangpo Grand Canyon, southeastern Tibetan Plateau. The air concentrations of polychlorinated biphenyls (PCBs) and hexachlorocyclohexanes (HCHs) are generally comparable to those of other remote regions, whereas the concentrations of DDTs are much higher than reported for the polar regions, the North American Rocky Mountains, and the European Alps. The concentrations of DDTs and PCBs were strongly linked to the cyclic patterns of the Indian monsoon, displaying higher values in the monsoon season (May-September) and lower values in the nonmonsoon season (November-March). A "bimodal" pattern was observed for α- and γ-HCH, with higher concentrations in spring and autumn and lower concentrations in the summer (monsoon season). Rain scavenging in the monsoon season likely resulted in the lower HCH concentrations in the atmosphere. This paper sheds lights on the role the Indian monsoon plays on the atmospheric transport of POPs to the Tibetan Plateau.

Dust dominates the summer melting of glacier ablation zones on the northeastern Tibetan Plateau.

Dust and black carbon (BC) can darken snow and ice surface and play pivotal roles in glacier mass loss. Thus, a quantitative assessment of their contributions to glacier summer melting is critical. During the summer of 2018, surface snow and ice were sampled, and the albedo and mass balance were continuously measured in the ablation zone of Laohugou Glacier No. 12 in the western Qilian Mountains. The physical properties of dust and BC were measured in the laboratory, and their impacts on glacier surface albedo reduction and melting were simulated. The results indicate that the ice surface in the ablation zone was enriched with substantial amounts of particles, and the average particle concentrations of these samples were hundreds of times higher than those of fresh snow. The BC mass absorption cross-sections (MACs) ranged from 3.1 m2 g-1 at 550 nm for dirty ice to 4.6 m2 g-1 for fresh snow, largely owing to meltwater percolation and particle collapse. The spectral variations in dust MACs were significantly different in the visible light bands and near-infrared bands from those in the other areas. Moreover, the two-layer surface energy and mass balance model with the new albedo parameterization formula was validated and agreed well with the experimental measurements of spectral albedo, broadband albedo, and mass balance. BC and dust combined resulted in 26.7 % and 54.4 % of the total mass loss on the cleaner and dirtier (particle enriched) surfaces in the ablation zone, respectively, compared to particle-free surfaces, and although both impurities played vital roles, dust was the more prominent factor in accelerating glacier melting on the northeastern Tibetan Plateau. This study emphasizes the importance of dust in cryosphere changes where Tibetan glaciers are strongly affected by Asian dust deposition.

Microbial diversity in the snow, a moraine lake and a stream in Himalayan glacier.

The microbial diversity and abundance in surface snow at different altitudes (5300 and 5504 m above sea level), a moraine lake and a glacial stream in the Yala Glacier on the southern slope of the Himalayas were investigated through a 16S rRNA gene clone library and flow cytometry approaches. Cell abundance in different habitats changed from 1.1 × 10(4) to 25 × 10(4) cells mL(-1), with the highest abundance in the moraine lake and the lowest abundance in the snow at 5504 m. Microbial communities in the snow were significantly different from those in the moraine lake and stream, although they were similar within snow and within the aquatic habitats. The two snow libraries were both dominated by Cyanobacteria, which accounted for about half of the total, followed by the Alphaproteobacteria and Firmicutes. The moraine lake and stream libraries were dominated by the Bacteroidetes and Betaproteobacteria, followed by the Actinobacteria. The results indicated that snow and water were highly diverse systems even in the same glacier. Microbial communities in the snow on the Yala Glacier were distinctly different from those in the East Rongbuk Glacier on the northern slope of Himalayas. However, microbes in the moraine lakes at two glaciers had similar community features. The snow habitat was easily affected by various environmental factors, while the aquatic habitats were comparatively stable in different glaciers.

Canal surface evaporation along the China's South-to-North Water Diversion quantified by water isotopes.

Water stable isotopes have extensive applications in the study of riverine hydrological processes, in particular, isotopic enrichment occurring along flow direction can be used as an indicator to estimate river surface evaporation. However, this application is difficult in natural rivers due largely to complex water exchange along river channel. China's South-to-North Water Diversion Project (SNWDP) is the largest artificial river designed to divert water from south to north through its enclosed, long span open canal, therefore providing a practice to estimate river surface evaporation by using isotope method. In this paper, we carried out hydrometeorological surveys and sampled canal water along the Middle Route of SNWDP (MRP) in two seasons, July 2018 and April 2019, for δ18O and δ2H measurement, then simulated the isotopic enrichment in canal water by using Craig-Gordon (C-G) evaporation model. We found clear increasing trend in heavy isotopes along the long span canal from head water to the end, resulting from evaporation enrichment. We used C-G evaporation model to estimate evaporation ratio E/V of canal water, and results show a ratio of evaporation loss of 2.54% ~ 3.73% in July 2018 and 1.66% ~ 2.39% in April 2019. We also found obvious seasonal differences existed in canal water isotopes, evaporation enrichment and the CWEL (canal water evaporation line), in association with more intensive evaporation in summer. Some large isotope fluctuations along the canal are mostly related to rainfall events, altering the canal water isotope signal. Our result in this study highlights the potential for water isotopes in the application of inter-basin water resources management, in particular, with increasing stress from water shortage and anthropogenic impact.

Black carbon and dust in the Third Pole glaciers: Revaluated concentrations, mass absorption cross-sections and contributions to glacier ablation.

In snow and ice, light-absorbing particles (LAPs), such as black carbon (BC) and dust, accelerate the melting of Third Pole glaciers (TPGs). In this study, we revaluated LAP concentrations in the snow pits of TPGs (SP-TPGs), measured LAP mass absorption cross-sections (MACs), and simulated their effects on glacier darkening and melting based on the Spectral Albedo Model for Dirty Snow and a surface energy and mass balance model. The results indicated that because of their short distances to emission sources, the average BC concentrations measured in snow pits in the periphery of Third Pole were much higher than those measured in the inland Tibetan Plateau, and the average dust concentrations generally decreased from north to south. The average MACs of BC in the SP-TPGs varied from 3.1 to 7.7 m2 g-1 at 550 nm, most of the average spectral values were comparable in the visible and near-infrared bands to those calculated by Mie theory, except those in Urumqi Glacier No. 1 (UR), Syek Zapadniy Glacier (SZ), and Laohugou Glacier No.12 (LH), while the average spectral MACs of dust in the SP-TPGs were considerably smaller in magnitude than most of the variations measured in other regions. Compared with the pure snow surfaces, BC and dust played comparable roles in reducing albedo in UR, SZ, LH, and Renlongba Glacier, whereas BC was the most prominent absorber in the other glaciers. The combined effect of BC and dust accelerated melting by 30.4-345.9 mm w.e. (19.7-45.3% of the total mass balance) through surface albedo darkening (0.06-0.17) and increased radiation absorption (25.8-65.7 W m-2) within one month of the ablation season. This study provides a new data set of LAP concentrations and MACs and helps to clarify the roles of these factors in the cryospheric environment of the Third Pole.

Thin debris layers do not enhance melting of the Karakoram glaciers.

The assessment of meltwater sourcing from the clean and debris-covered glaciers is scarce in High Mountain Asia (HMA). The melting rate varies with the debris cover thickness and glacier orientation. The present study quantifies glacier melting rate attributed to varying thickness of debris cover in the Karakoram. We observed daily melting rates by installing ablation stakes over debris-free and debris-covered ice during a field expedition. The stakes were installed on glacier surface with debris cover thickness ranges between 0.5 and 40 cm at selected experimental sites during the ablation period (September and October 2018) and (July to August 2019). We selected three glaciers including Ghulkin, Hinarchi, and Hoper facing east, south, and north, respectively to assess the role of glacier orientation on melting rates. We observed that the debris-free ice melts faster than the debris-covered ice. Intriguingly, a thin debris layer of 0.5 cm does not enhance melting compared to the clean ice which is inconsistent with the earlier studies. The melting rate decreases as the thickness of debris cover increases at all the three selected glaciers. Furthermore, south-facing glacier featured the highest melting (on average ~ 25% more). However, the north and east-facing glaciers revealed almost same melting rates. We observed that the average degree-day factors (DDF) slightly varies within a range of 0.58-0.73 and 0.55-0.68 cm °C-1 day-1 for debris-free and 0.5 cm debris-covered ice, respectively, however, DDF largely reduces to 0.13-0.25 cm °C-1 day-1 for 40 cm debris-covered ice. We suggest continuous physical glacier ablation observations for various debris cover throughout the ablation zone to better understand the role of debris on melting.

Isotopic evidence that recent agriculture overprints climate variability in nitrogen deposition to the Tibetan Plateau.

The stable isotopes of nitrogen in nitrate archived in polar ice have been interpreted as reflecting a shift in reactive nitrogen sources or changes in atmospheric chemical reactivity. Here, we present a novel concentration and isotopic record of nitrate (δ15N-NO3-) from a central Tibetan Plateau ice core over the last ~200 years. We find that nitrate concentration increased from 6.0 ± 2.3 µeq/L (mean ± 1σ) in the preindustrial period (prior to 1900s) to 7.3 ± 2.7 µeq/L in post-1950. Over the same time period, the δ15N-NO3- decreased from 8.7 ± 3.7‰ to 4.2 ± 3.1‰, with much larger interannual variation in δ15N-NO3- during the preindustrial period. We present a useful framework for quantifying the sensitivity of the isotopic composition of atmospheric nitrate to changes in both sources and chemistry (gas and aerosol phase). After 1950, nitrogen deposition is primarily driven by fertilizer use, leading to significant increases in concentration and decreases in δ15N-NO3-. The large interannual variability of ice core δ15N-NO3- in the preindustrial reflects natural processes, namely the El Niño Southern Oscillation (ENSO) and dust events. Our results highlight a new connection between the nitrogen cycle and ENSO, and the overprinting of natural climate signals by recent anthropogenic increases in reactive nitrogen release.

The recent deposition of persistent organic pollutants and mercury to the Dasuopu glacier, Mt. Xixiabangma, central Himalayas.

High mountains may serve as condensers for persistent organic pollutants (POPs) and the ice/snow core can provide long-term records of atmospheric deposition of pollutants. In this study, organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in firn core from Dasuopu Glacier were analyzed and the seasonal variation and deposition flux of these pollutants were investigated. PCB 28 was always detected in samples from different firn core layers and concentrations of PCB 28 were in the range of 0.09-0.3 ng/l. Hexachlorobenzene (HCB) and total DDTs (p-p'-DDD and p-p'-DDT) were not always detected and were only present in some samples. No p-p'-DDE and hexachlorocyclohexane (HCH) were detected above the level of determination limits. Concentrations of HCB ranged from 0.04 to 0.07 ng/l, and total DDTs were in the range of 0.15-0.3 ng/l. Total glacier PAHs was below 26 ng/l. The levels of OCPs and PAHs in Dasuopu glacier were roughly similar to values from the European mountain areas but lower than those from Lys glacier (Italy) and glacier from Rocky Mountain. Hg concentration (2-35 ng/l) in firn core samples was higher than that of remote region of Arctic. PCB 28 didn't show obvious variation in different seasons, however for major PAH compounds higher values were observed in summer than in winter. With regard to Hg, it displayed winter maximum. Deposition flux of OCPs, PAHs and mercury showed similar results with maximum flux occurring in the 2000s. After 2000/2001, deposition flux decreased and reflected the possible decrease of emissions of these atmospheric pollutants in the adjacent region.

Dramatic mass loss in extreme high-elevation areas of a western Himalayan glacier: observations and modeling.

Rapid climate change at high elevations has accelerated glacier retreat in the Himalayas and Tibetan Plateau. However, due to the lack of long-term glaciological measurements, there are still uncertainties regarding when the mass loss began and what the magnitude of mass loss is at such high elevations. Based on in situ glaciological observations during the past 9 years and a temperature-index mass balance model, this study investigates recent mass loss of the Naimona'nyi Glacier in the western Himalayas and reconstructs a 41-year (1973/74-2013/14) equilibrium line altitude (ELA) and glacier-wide mass loss. The result indicates that even at 6000 m above sea level (a.s.l.), the annual mass loss reaches ~0.73 m water equivalent (w.e.) during the past 9 years. Concordant with the abrupt climate shift in the end of 1980s, the ELA has dramatically risen from ~5969 ± 73 m a.s.l. during 1973/74-1988/89 to ~6193 ± 75 m a.s.l. during 1989/90-2013/14, suggesting that future ice cores containing uninterrupted climate records could only be recovered at least above 6200 m a.s.l. in the Naimona'nyi region. The glacier-wide mass balance over the past 41 years is averaged to be approximately -0.40 ± 0.17 m w.e., exhibiting a significant increase in the decadal average from -0.01 ± 0.15 to -0.69 ± 0.21 m w.e.

Changes of the Bacterial Abundance and Communities in Shallow Ice Cores from Dunde and Muztagata Glaciers, Western China.

In this study, six bacterial community structures were analyzed from the Dunde ice core (9.5-m-long) using 16S rRNA gene cloning library technology. Compared to the Muztagata mountain ice core (37-m-long), the Dunde ice core has different dominant community structures, with five genus-related groups Blastococcus sp./Propionibacterium, Cryobacterium-related., Flavobacterium sp., Pedobacter sp., and Polaromas sp. that are frequently found in the six tested ice layers from 1990 to 2000. Live and total microbial density patterns were examined and related to the dynamics of physical-chemical parameters, mineral particle concentrations, and stable isotopic ratios in the precipitations collected from both Muztagata and Dunde ice cores. The Muztagata ice core revealed seasonal response patterns for both live and total cell density, with high cell density occurring in the warming spring and summer months indicated by the proxy value of the stable isotopic ratios. Seasonal analysis of live cell density for the Dunde ice core was not successful due to the limitations of sampling resolution. Both ice cores showed that the cell density peaks were frequently associated with high concentrations of particles. A comparison of microbial communities in the Dunde and Muztagata glaciers showed that similar taxonomic members exist in the related ice cores, but the composition of the prevalent genus-related groups is largely different between the two geographically different glaciers. This indicates that the micro-biogeography associated with geographic differences was mainly influenced by a few dominant taxonomic groups.

Summer rainfall over the southwestern Tibetan Plateau controlled by deep convection over the Indian subcontinent.

Despite the importance of precipitation and moisture transport over the Tibetan Plateau for glacier mass balance, river runoff and local ecology, changes in these quantities remain highly uncertain and poorly understood. Here we use observational data and model simulations to explore the close relationship between summer rainfall variability over the southwestern Tibetan Plateau (SWTP) and that over central-eastern India (CEI), which exists despite the separation of these two regions by the Himalayas. We show that this relationship is maintained primarily by 'up-and-over' moisture transport, in which hydrometeors and moisture are lifted by convective storms over CEI and the Himalayan foothills and then swept over the SWTP by the mid-tropospheric circulation, rather than by upslope flow over the Himalayas. Sensitivity simulations confirm the importance of up-and-over transport at event scales, and an objective storm classification indicates that this pathway accounts for approximately half of total summer rainfall over the SWTP.

Influence of long-range transboundary transport on atmospheric water vapor mercury collected at the largest city of Tibet.

Monsoon circulation is an important process that affects long-range transboundary transport of anthropogenic contaminants such as mercury (Hg). During the Indian monsoon season of 2013, a total of 92 and 26 atmospheric water vapor samples were collected at Lhasa, the largest city of the Tibet, for Hg and major ions analysis, respectively. The relatively low pH/high electronic conductivity values, together with the fact that NH4(+) in atmospheric water vapor was even higher than that determined in precipitation of Lhasa, indicated the effects of anthropogenic perturbations through long-range transboundary atmospheric transport. Concentrations of Hg in atmospheric water vapor ranged from 2.5 to 73.7ngL(-1), with an average of 12.5ngL(-1). The elevated Hg and major ions concentrations, and electronic conductivity values were generally associated with weak acidic samples, and Hg mainly loaded with anthropogenic ions such as NH4(+). The results of principal component analysis and trajectory analysis suggested that anthropogenic emissions from the Indian subcontinent may have largely contributed to the determined Hg in atmospheric water vapor. Furthermore, our study reconfirmed that below-cloud scavenging contribution was significant for precipitation Hg in Lhasa, and evaluated that on average 74.1% of the Hg in precipitation could be accounted for by below-cloud scavenging.

Response of Glacier and Lake Dynamics in Four Inland Basins to Climate Change at the Transition Zone between the Karakorum And Himalayas.

Inland glacier and lake dynamics on the Tibetan Plateau (TP) and its surroundings over recent decades are good indicators of climate change and have a significant impact on the local water supply and ecosystem. The glacier and lake changes in Karakoram are quite different from those of the Himalayas. The mechanisms of the complex and regionally heterogeneous behavior of the glacier and lake changes between the Karakorum and Himalayas are poorly understood. Based on satellite images and meteorological data of Shiquanhe, Hetian, and Yutian stations, we demonstrate that the overall retreat of glaciers and increase of lake area at the transition zone between the Karakoram and Himalayas (TKH) have occurred since 1968 in response to a significant global climate change. Glacial areas in the Songmuxi Co basin, Zepu Co basin, Mang Co basin and Unnamed Co decreased by -1.98 ± 0.02 km2, -5.39 ± 0.02 km2, -0.01 ± 0.02 km2, and -0.12 ± 0.02 km2 during the study period, corresponding to losses of -1.42%, -2.86%, -1.54%, and -1.57%, respectively. The lake area of the Songmuxi Co, Zepu Co, Mang Co and Unnamed Co increased by 7.57 ± 0.02 km2, 8.53 ± 0.02 km2, 1.35 ± 0.02 km2, and 0.53 ± 0.02 km2, corresponding to growths of 30.22%, 7.55%, 11.39%, and 8.05%, respectively. Increases in temperature was the main reason for glacier retreat, whereas decreases in potential evapotranspiration of lakes, increases in precipitation, and increases in melt water from glaciers and frozen soil all contributed to lake area expansion.

A comparison of pelagic, littoral, and riverine bacterial assemblages in Lake Bangongco, Tibetan Plateau.

Lakes of the Tibetan Plateau lack direct anthropogenic influences, providing pristine high-altitude (> 4000 m) sites to study microbial community structure. We collected samples from the pelagic, littoral, and riverine zones of Lake Bangongco, located on the western side of the Plateau, to characterize bacterial community composition and geochemistry in three distinct, but hydrologically connected aquatic environments during summer. Bacterial community composition differed significantly among zones, with communities changing from riverine zones dominated by Bacteroidetes to littoral and pelagic zones dominated by Gammaproteobacteria. Community composition was strongly related to the geochemical environment, particularly concentrations of major ions and total nitrogen. The dominance of Gammaproteobacteria in the pelagic zone contrasts with typical freshwater bacterial communities as well as other lakes on the Tibetan Plateau.

Heavy metals of the Tibetan top soils: level, source, spatial distribution, temporal variation and risk assessment.

OBJECTIVE: Due to its high elevation, rare human activities and proximity to south Asia where industries are highly developed, it is required to investigate the fragile environment of the Tibetan Plateau. We are aiming to obtain the concentration level, source, spatial distribution, temporal variation and potential environmental risk of Tibetan soils. METHODS: A total of 128 surf ace soil samples were collected and analyzed f or V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd and Pb, and an additional 111 samples were analyzed f or Hg and total organic carbon. Concentration comparisons coupled with multivariate statistics were used to analysis the sources of elements of soils. We also carried out Risk assessment on the soils. RESULTS: Concentrations of Hg, Cr, Ni, Cd and Pb are slightly higher than those of the late 1970s. Concentrations of Cr and Ni are higher than averaged world background values. Tibetan soils present a high natural As concentration level. DISCUSSION: Anthropogenic sources may partly contribute to the elevated Hg, Cd and Pb concentrations. Cr and Ni are mainly originated from soil parent materials. Soil elements in Anduo and Qamdo regions may threaten the health of local people. CONCLUSION: Heavy metal elements of Tibetan Plateau are mainly from the natural source. Arsenic present a high background level. Soil elements in Anduo and Qamdo regions may threaten the health of local people, which should be of concern to scientists and the government.