Reduced microbial stability in the active layer is associated with carbon loss under alpine permafrost degradation.

Permafrost degradation may induce soil carbon (C) loss, critical for global C cycling, and be mediated by microbes. Despite larger C stored within the active layer of permafrost regions, which are more affected by warming, and the critical roles of Qinghai-Tibet Plateau in C cycling, most previous studies focused on the permafrost layer and in high-latitude areas. We demonstrate in situ that permafrost degradation alters the diversity and potentially decreases the stability of active layer microbial communities. These changes are associated with soil C loss and potentially a positive C feedback. This study provides insights into microbial-mediated mechanisms responsible for C loss within the active layer in degraded permafrost, aiding in the modeling of C emission under future scenarios.

[Mercury in tree rings: Advances, problems and prospects]. / æ ‘æœ¨å¹´è½®æ±žè®°å½•: 进展、问题和展望.

As a highly biotoxic element, mercury (Hg) can be enriched by the food chain and has negative effect on ecosystems. Changes of Hg flux and reserves in forest have important effects on its biogeochemical cycle in forest ecosystem. Due to limitation of temporal and spatial monitoring, there is not comprehensive understanding on Hg distribution. Widely distributed trees can be used as effective bio-monitors and Hg records in tree rings can be used to study Hg temporal and spatial distribution. Hg accumulated by root, leaf, bark, and other tissues can be detained in bole and record environmental Hg variations. Therefore, historical Hg trends can be restructured by analyzing Hg concentration in tree rings and the biogeochemical characteristics can be understood with Hg isotope ratio. We reviewed the method of measurement of Hg concentration and isotope ratio and application of reconstruction using Hg concentration in tree ring. We suggested the great application potential of Hg isotope ratio in atmospheric Hg construction and biogeochemistry cycle and raised concerns in further studies.

Gradient distribution of persistent organic contaminants along northern slope of central-Himalayas, China.

High mountains may serve as condenser for persistent organic pollutants (POPs) and the vegetation in remote areas has been used as a means to characterized atmospheric concentrations of air pollutants. In this study, organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in Himalayan spruce needle samples from Zhangmu-Nyalam region (central-Himalayas) were analyzed and the altitudinal gradient of these pollutants was investigated. Total HCHs and DDTs concentration in needles were in the range of 1.3-2.9 ng g(-1) dry weight and 1.7-11 ng g(-1) dry weight, which were lower than concentrations reported in spruce needles from Alps, however higher than concentrations in conifer needles from mountain areas of Alberta. Total Himalayan spruce needle PAHs was below 600 ng g(-1) and fluorene, phenanthrene and acenaphthene were abundant individual compounds measured. The ratios of alpha-HCH/gamma-HCH in pine needles were similar with the usual values for technical HCH, implying technical HCHs might be used in this region. The high ratios of o-p'-DDT/p-p'-DDT and no p-p'-DDE measured in this study led to the suspicion that a new source of o-p'-DDT and/or p-p'-DDT existed in this region. In addition, higher ratios of low molecular weight-/high molecular weight-PAHs in this region indicated that petroleum combustion, vehicle emission and low-temperature combustion might be the major contributions of PAH source. To examine the POPs distillation, the analyte concentrations were correlated with altitude. The more volatile OCPs, alpha-HCH, gamma-HCH, aldrin and alpha-endosulfan positively correlated with altitude, however, less volatile OCPs (DDT and DDD) inversely related with elevation. Almost all PAHs detected in this area showed positive correlations with altitude. It is worthy to note that heavy PAHs (Benzo[k] fluoranthene and Benzo[a]anthracene) displayed positive correlation, which implied the sources of PAHs were near the sampling sites. The distillation of POPs was strongly affected by the proximity between sampling sites and contaminant sources. If the contaminant sources are close to the mountains, it may be the dominant factor that controls the concentration gradient.

[Mercury Transport from Glacier to Runoff in Typical Inland Glacial Area in the Tibetan Plateau].

To investigate the transport of mercury from glacier to runoff in typical inland glacial area in the Tibetan Plateau, we selected Zhadang glacier and Qugaqie river Basin located in the Nyainqentanglha Range region and collected samples from snow pit, glacier melt-water and Qugaqie river water during 15th August to 9'h September 2011. Mercury speciation and concentrations were determined and their distribution and controlling factors in different environmental compartments were analyzed. The results showed that the average THg concentrations were (3.79 +/- 5.12) ng x L(-1), (1.06 +/- 0.77) ng x L(-1) and (1.02 +/- 0.24) ng x L(-1) for glacier snow, glacier melt-water and Qugaqie river water, respectively, all of which were at the global background levels. Particulate-bound mercury accounted for large proportion of mercury in all environmental matrices, while mercury in glacial melt-water was controlled by total suspended particle, and mercury in Qugaqie river water co-varied with runoff. With the increase of temperature, glacier melted and released water as well as mercury into glacier-fed river. Total mercury concentrations in glacier melt water, upstream and downstream peaked at 14:00, 16:00 and after 20:00, respectively, reflecting the process of mercury release from glacier and its subsequent transport in the glacier fed river. The transport of riverine mercury was controlled by multiple factors. Under the context of climate change, glacier ablation and the increasing runoff will play increasingly important roles in mercury release and transport.

[Concentration and Source of Dissolved Organic Carbon in Snowpits of the Tibetan Plateau].

Snowpit samples of three glaciers (Laohugou NO. 12 Glacier (LHG), Small Dongkemadi Glacier on Mount Tanggula (TGL) and East Ronghuk Glacier on Mount Everest (ZF)) in the Tibetan Plateau were collected. Concentrations of DOC and major ions were analyzed. The results showed that average DOC concentrations of the snowpits of LHG, TGL and ZF were (250.30 +/- 157.10), (216.92 +/- 142.82) and (152.50 +/- 56.11) microg x L(-1), respectively. DOC of TGL and ZF accounted for large parts of total values of DOC and ions. Correspondingly, DOC of LHG accounted for small part (only 5%), because LHG was located at north China and intensively influenced by natural mineral dust, which caused high concentrations of Ca2+ (the highest value could reach 5299.18 microg x L(-1)) and consequently low percentage of DOC of snowpit samples. Correlation and PCA analyses were used to study the sources of DOC. DOC was significantly correlated with Ca2+, Mg2+, K+ and SO4(2-). Additionally, PCA further indicated that the main potential source of DOC was the natural source of mineral dust. Meanwhile, anthropogenic pollutants (e.g., biomass, fossil combustion and agricultural related pollutants) could also not be ignored. Moreover, the carbon depositional fluxes of three snowpits were roughly estimated, and the values of LHG, TGL and ZF snowpits were 189.23, 132.76 and 128.44 mg (m2 x a)(-1), respectively, which played a significant role in the carbon cycle in this region and was also helpful for the study of glaciers fluctuation.

[Study on soil element background values of the Hoh Xil area in north Tibet].

Hoh Xil locates at northern part of the Tibetan Plateau. Twenty five surface soil samples were collected from this area in 2007 and 32 elements were analyzed and compared to the element contents of Yarlung Zangbo river sediment, background element value of the Tibetan surface soil and the Chinese Continental crust contents. The results showed that the element contents of the < 20 microm fraction were higher than those of bulk samples; Contents of many elements of this study were similar to those of the Tibetan soil. Meanwhile, contents of Ca and As of the studied area were higher than those of Chinese continental crust, resulting mainly from local alpine arid climate and widely distributed the rocks that enriched in As, respectively. The EOF analysis of the contents of bulk soil samples revealed the sources and chemical properties of studied elements: many elements such as Al, Fe, Ga inherit the characteristics of the parent rocks of this region. Meanwhile, elements with an active chemical property and the element Zr that specially existed in the heavy minerals also had a certain contribution to the contents. The contents of B and Cs revealed contribution of hot springs to the soil of studied area.

[Chemical speciation and risk assessment of heavy metals in the middle part of Yarlung Zangbo surface sediments].

Nine heavy metals (Cd, Co, Ni, Cu, Zn, Pb, Cs, As, Cr) of surface sediments collected from the Middle Part of the Yarlung Zangbo River were analyzed by BCR sequential extraction procedure. Based on speciation distributions of these metals, ecological risk of heavy metals was assessed with methods of risk assessment code (RAC) and sediment quality guideline quotient (SQG-Q). The results show that: (1) Large part of Cr and As belong to residual fraction(87%-96%). Ni, Cu, Co and Cs have similar distribution characteristics (non-residual part accounts for approximate 20%). Correspondingly, mass fraction of Cd exists mainly in acid soluble and reducible faction (65% ) , indicating high ecological risk level. (2) Based on calculation of RAC method, Cd is of high risk to the environment (37. 38%). Accordingly, Co, Ni, Cu and Zn are of low risk, and Pb, Cs, As and Cr pose extreme low risk to the environment. According to evaluation of heavy metal speciation distributions, the potential ecological risk of heavy metals is in the descending order of Cd > Co > Ni > Cu > Zn > Pb > Cs > As > Cr. (3) The SQG index of sediments is 0. 804, indicating that studied river sediment has a moderate potential biological toxicity effect. Given most of heavy metals exists in residual fraction, the sediments of this region pose a low ecological risk to the environment.

[Temporal and spatial variations of major ions in Nam Co Lake water, Tibetan Plateau].

In order to investigate the temporal and spatial variations, sources, and major controlling factors of the major ions in Nam Co Lake water, inshore surface water samples were collected at a fixed site (30 degrees 47.27'N, 90 degrees 58.53'E, 4718 m a. s. l.) from 2006 to 2010, at the vertical profiles in the center of the lake in August 2009, and at both the vertical profiles in the center of the lake and at the surface layers of different sites in the Nam Co Lake in October 2010. The results indicated that Na+ was the dominant cation and HCO3- was the dominant anion in the lake water. The concentrations of most ions were higher in monsoon seasons (June - September) and lower in non-monsoon seasons, especially when the lake was frozen (January -April). However, the Ca2+ concentration showed a reverse trend of seasonal variations, namely, higher values in the frozen period and lower in monsoon seasons. Analysis of water samples collected from the vertical profiles indicated that the concentrations of all ions except Ca2+ increased with the depth in nonmonsoon seasons (e. g. October). The major ions in Nam Co Lake were mainly contributed by river input. There were a variety of factors that influenced the temporal and spatial variations of the major ions in the Nam Co Lake, such as evaporation, precipitation, pH values, etc., among which, evaporation was the most important controlling factor, causing the increasing Na+ concentration and decreasing Ca2+ concentration in the lake water.

[Spatial and temporal distribution of total mercury (T-Hg) in different water bodies of Nam Co, Tibetan Plateau].

To investigate the tempo-spatial distribution of total mercury (T-Hg) concentration in water bodies in the Nam Co basin on the Tibetan Plateau, inflowing river water and surface lake water samples were collected from 2007 to 2010. The T-Hg concentration and its relationship with precipitation and river runoff were analyzed. The results showed that the average T-Hg concentration was (1.09 +/- 0.73) ng x L(-1) and (2.87 +/- 2.59) ng x L(-1) for surface lake water and river water, respectively, both of which were significantly lower than those of Hg contaminated waters. T-Hg concentration in off-shore lake water was much higher during the monsoon season than in the non-monsoon season, and its level and spatial variation were significantly greater than those in central lake water. T-Hg concentration in river water showed significant seasonal variations with the highest values during the monsoon season and the lowest during the post-monsoon season, which were in accordance with the variations of precipitation. A fixed point observation at Niyaqu River indicated that the temporal changes of the T-Hg concentrations in river water were in accordance with those of the runoff. The spatial distribution features of T-Hg concentrations in inflowing river water varied in different periods, possibly resulting from the differences in drainage areas, background mercury levels in soils, and water supplies for rivers at different locations of the Nam Co basin.

Atmospheric concentrations of halogenated flame retardants at two remote locations: the Canadian High Arctic and the Tibetan Plateau.

Atmospheric concentrations of halogenated flame retardants (FRs) were monitored for approximately one year at two remote stations, namely Nam Co on the Tibetan Plateau and Alert in the Canadian High Arctic. BDE-47 and 99 were the dominant polybrominated diphenyl ether (PBDE) congeners at both sites. Atmospheric PBDE concentrations in Nam Co were generally lower than those at Alert. While significant seasonal variations were observed for PBDEs at Alert, the FR concentrations at Nam Co showed no significant seasonality, even though air masses originated from distinctly different regions during different seasons. This suggests that FRs in Tibet do not have regional sources, but are reflective of truly global background contamination. Three new FRs, namely 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), 2-ethyl-1-hexyl-2,3,4,5-tetrabromobenzoate (EHTeBB) and bis(2-ethyl-1-hexyl)tetrabromophthalate (TBPH) were detected at relatively high concentrations at both sites. This is the first report of these FRs in the remote global atmosphere and suggests significant potential for long-range atmospheric transport.

[Mineral and elemental characteristics of microparticles with different size fraction in snowpits from Zadang Glacier].

In order to study the mineral and elemental composition of insoluble microparticles (IP) in snow/ice, two snowpits were collected from the Zadang Glacier in Mt. Nyainqentanglha (30.47 degrees N, 90. 65 degrees E, 5 800 m a. s. l) in May and July, 2009, and IP samples were investigated. The measurements of mineral composition with different size fractions (d > 10 microm and 0.22 microm < d < 10 microm) were carried out using Particle-induced X-ray emission (PIXE) and X-ray diffraction analysis (XRD). The main mineral components of both coarse and fine IP are quartz, mica and calcite, accounting for 71.5% and 76.5%, respectively. The crustal elements concentrations (e.g. Si, Al, Fe, K, Mg and Ca) are 97% and 85.1% of total coarse/fine IP, while S, Cl and P take fairly proportion in fine microparticles (d < 10 microm). Seasonal variability of mineral composition in coarse microparticles (d >10 microm) is not obviously; However it's significantly in fine IP. Enrichment factors (EF) analysis reveals that several elements (e.g. Sc, P, Cr, S and Cl) in fine IP during monsoon season have high values which indicate these elements may be influenced by anthropogenic activities. Backward air mass trajectory analysis suggests that air masses in this region mainly originate from the South Asia areas during monsoon season, and air masses mainly come from arid/semi-arid region in the South and West Asia during non-monsoon season. Therefore, anthropogenic pollutants from the South Asia may be transported by the summer Indian monsoon to the Zadang glacier area. The coarse IP may derive from the local or remote mineral dust, and chemical compositions of fine IP interfere with anthropogenic pollutants.

[Indoor air pollution in the Nam Co and Ando Regions in the Tibetan Plateau].

Concentrations and variations of fine particulate matter (PM2.5) and carbon monoxide (CO) within tents from the Nam Co and Ando regions were observed at summer 2009, in order to understand the concentrations and variations of PM2.5 and CO in these tents (or in rooms) and their main affect factors, as well as the exposure of different residents. The result indicates that the twenty-four hour average concentrations of PM2.5 and CO (V/V) in the tents without chimney are 1.272 mg x m(-3) and 5.035 x 10(-6), which are significantly higher than those of tents installed chimneys (0.097 mg x m(-3) and 0.089 x 10(-6)). Diurnal variations of PM2.5 and CO are similar and show multiple peaks, which is different with those in the eastern rural areas of China and closely connected with the behaviors of the residents within the tents. Generally, women and children spend three or four hours longer in tents than other family members every day. Children have the highest exposure of 0.972 mg x m(-3) and 0.132 x 10(-6) for PM2.5 and CO, respectively. Therefore, although the outdoor air in the Tibetan Plateau is very clean, the air of the Tibetan tents are seriously polluted and mainly caused by yak dung combustion.

[Composition and seasonal variations of carbon isotopes in aerosols of Lhasa, Tibet].

A total of 30 samples of total suspended particles were collected at an urban site in western of Lhasa city, Tibet from August 2006 to July 2007 for investigating carbonaceous aerosol features. 14C was taken as a reference to quantitatively distinguish the fossil and biogenic-derived origins along with the characteristics of seasonal variations of all carbonaceous materials in Lhasa are discussed. The results showed that the f(c) values in Lhasa ranged from 0.357 to 0.702, with an average of 0.493, which is higher than Beijing and Tokyo, but are far lower than that of remote/rural regions such as Launceston, indicating a major biogenic influence in Lhasa. Values of f(c) displayed clear seasonal variations with higher mean value in winter, a decreasing trend in spring, while relatively lower values in summer and autumn. Higher f(C) values in winter demonstrate that carbonaceous aerosol is mainly dominated by wood burning and incineration of agricultural wastes during the winter. The lower f(c) values in summer and autumn might be caused by increased diesel engines, motor vehicles emissions, which are related to the tourism in Lhasa. delta13C values ranged from -26.40% per hundred to approximately -25.10% per hundred, with an average of -25.8% per hundred, and showed no clear seasonal variation. The relative higher values in summer reflected the increment of fossil carbon emissions. 13C(TC) values are relatively homogeneous at -25.8% per hundred, considering the characteristics of seasonal variations of f(c) values, it can be concluded that carbonaceous aerosol of Lhasa was mainly influenced by a constant mixing of several pollution sources such as motor vehicles and wood burning emissions.

[Major ionic features and their sources in the Nam Co Basin over the Tibetan Plateau].

A preliminary study of major ions in water of three rivers (Niyaqu, Qugaqie, Angqu) in the Nam Co Basin has been carried out in June-October 2006. An obvious difference is found among these rivers, whose ionic characteristics are mainly influenced by the length of rivers and their supply sources. Among the three rivers, the contents of total dissolve solids (TDS) is 79.48 mg/L, 23.44 mg/L, and 111 mg/L in the Niyaqu, Qugaqie, and Angqu, respectively. The hydro-chemical type is CCa for the Qugaqie, between CNa and CCa for the Angqu, and between the Angqu and Qugaqie for the Qugaqie. Changes in ionic concentrations are also related with discharges of the rivers. According to principal component analysis and correlation analysis, the main chemical contents derive from Ca2+ and HCO3(-) in carbonate for the Niyaqu, glacier meltwater and carbonate for the Qugaqie, and Na+, Mg2+ and Cl(-) in evaporates for the Angqu.

[Microparticle variations in snowpits from Mt. Geladaindong in the source region of Yangtze River and its environmental significance].

To study the variations of microparticles and their origins, microparticles concentrations, stable oxygen isotope (delta18 O) and major ion concentrations were analyzed in snow samples collected from Mt. Geladaindong in the source region of Yangtze River. The correlation coefficents of different size microparticles in three snowpits are above 0.9 (significant at the 99% level), respectively. Microparticle concentrations have distinct seasonal variations, about 2-4 times higher in non-monsoon season than those in monsoon season, and are consistent with variations of delta18 O, Ca2+, Mg2+ and SO4(2-). Microparticle fluxes in non-monsoon season in three snowpits are 73.6%, 92.3% & 97% of total annual fluxes, respectively. Air mass backward trajectories over Mt. Geladaindong region were analyzed using the HYSPLIT_4 model, and microparticles in Mt. Geladaindong snow were mostly influenced by dust aerosols from the northwestern Tibetan Plateau, South Asia. Coarse particles may come from the local rocks near glaciers. Research of seasonality of microparticle in snow could provide the information on modern environment processes, and is the base of further interpretation of ice core records.