Long-range transport of atmospheric microplastics deposited onto glacier in southeast Tibetan Plateau.

Micoroplastics (MPs) can be transported through atmospheric circulations, and have caused global attentions due to their potential risk to the environment. In this study, MPs in snowpit samples collected from Demula (DML) glacier in southeast Tibetan Plateau were investigated. The results showed that the average abundance of MPs in snow was 9.55 ± 0.9 items L-1, with dominant shapes of plastic fibers and films. MPs size was dominated by MPs <200 µm, with detected minimum size of 48 µm from the DML glacier. MPs in snowpit indicated seasonal variations, showing relatively higher abundance during the monsoon season than that during the non-monsoon season. The chemical composition of MPs and backward air mass trajectory modeling revealed that MPs in DML snowpit mostly originated from the atmospheric long-range transport, suggesting the glacier in southeast Tibetan Plateau can be a temporal sink of atmospheric MPs. The surface structure of the MPs was rough and adhered to a large amount of mineral dust and metallic particles, revealed that these MPs have undergone severe weathering during transportation and after deposition. Based on the MPs data, multi-year average precipitation, and glacier mass balance of DML glacier, the deposition flux of MPs on DML glacier was estimated to be about 7640 ± 720 to 9550 ± 900 items m-2 yr-1 and the export from melting water was about 5.9 ± 1.3 × 109 to 6.6 ± 1.4 × 109 items yr-1, indicating the glacier may be also an important source of MPs to the downstream ecosystems. These results provided the current status of MPs pollution on the Tibetan Plateau glaciers and new data to the study of MPs in typical cryospheric regions.

A review of analytical methods and models used in atmospheric microplastic research.

Microplastic pollution in the environment has become a source of concern in recent years. The transport and deposition of suspended atmospheric microplastics play an important role in the global linkage of microplastic sources and sinks. In this review, we summarized recent research progress on sampling devices, pretreatments, and identification methods for atmospheric microplastics. The total suspended particles and atmospheric deposition, including dust, rainfall, and snow samples, are the environmental carriers for atmospheric microplastic studies. There are active and passive sampling methods. Pretreatment depends on sample types and identification methods and includes sieving, digestion, density separation, filtration, and drying. The measured features for atmospheric microplastics include particle size distributions, shapes, colors, surface morphology, and polymer compositions, using stereomicroscopes, Fourier transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, and liquid chromatography-tandem mass spectrometry. Laser direct infrared spectroscopy and thermochemical methods coupled with mass spectrometry are potential methods for identifying atmospheric microplastics. Currently, models for estimating the fluxes of atmospheric microplastic emission, transport, and deposition are in the initial stages of development; their implementation will enhance our understanding of the "microplastic cycle" globally based on simulated and observed data.

Microplastic characteristic in the soil across the Tibetan Plateau.

Microplastics are widely detected in terrestrial environments. However, microplastic features in the soil of remote areas are still sparse. In this study, microplastic pollution in soil across the Tibetan Plateau was systematically investigated. The results revealed that microplastic was ubiquitous in the soil of the Tibetan Plateau with an average abundance of 47.12 items/kg-dry weight (range: 5-340 items/kg). Compared with the published data of soil microplastic pollution in other regions, the microplastic pollution in the Tibetan Plateau was relatively low. Fibers represented 43.54% of microplastic particles detected, followed by fragments (32.20%) and films (23.78%). They mainly consisted of polyvinyl chloride, polyethylene, polypropylene, and polystyrene. Transparent and white microplastics were prevalent, and small microplastics (50-500 µm) occupied approximately 66% of all microplastics. High values of microplastics were found near Lhasa, Naqu, and Linzhi. Furthermore, microplastic pollution was found to be negatively related to the distance to the nearest city (p < 0.01), wind velocity (p = 0.014), altitude (p = 0.181), yet positively related to precipitation (p = 0.024). This work presents new insights into the magnitude of microplastics contamination in the soil across the Tibetan Plateau and supplies valuable data for future research on ecotoxicology, ecosystem impacts, and earth system feedback of microplastics on terrestrial ecosystems.

An integrative method for identifying potentially dangerous glacial lakes in the Himalayas.

Glacial lakes in the Himalayas are widely distributed. Since 1900, more than 100 glacial lake outburst floods (GLOFs) have originated in the region, causing approximately 7000 deaths and considerable economic losses. Identifying potentially dangerous glacial lakes (PDGLs) is considered the first step in assessing GLOF risks. In this study, a more thorough inventory of PDGLs was presented that included numerous small-sized glacial lakes (<0.1 km2) that were generally neglected in the Himalayas for decades. Moreover, the PDGL evaluation system was improved in response to several deficiencies, such as the selection of assessment factors, which are sometimes arbitrary without a solid scientific basis. We designed an optimality experiment to select the best combination of assessment factors from 57 factors to identify PDGLs. Based on the experiments on both drained and non-drained glacial lakes in the Sunkoshi Basin, eastern Himalayas, five assessment factors were determined to be the best combination: the mean slope of the parent glacier, the potential for mass movement into the lake, the mean slope of moraine dams, the watershed area, and the lake perimeter, corresponding to the GLOF triggers for ice avalanches, rockfalls and landslides, dam instability, heavy precipitation or other liquid inflows, and lake characteristics, respectively. We then applied the best combination of assessment factors to the 1650 glacial lakes with an area greater than 0.02 km2 in the Himalayas. We identified 207 glacial lakes as very high-hazard and 345 as high-hazard. It is noteworthy that in various GLOF susceptibility evaluation scenarios with different assessment factors, weighting schemes, and classification approaches, similar results for glacial lakes with high outburst potential have been obtained. The results provided here can be used as benchmark data to assess the GLOF risks for local communities.

Plant uptake of CO2 outpaces losses from permafrost and plant respiration on the Tibetan Plateau.

High-latitude and high-altitude regions contain vast stores of permafrost carbon. Climate warming may result in the release of CO2 from both the thawing of permafrost and accelerated autotrophic respiration, but it may also increase the fixation of CO2 by plants, which could relieve or even offset the CO2 losses. The Tibetan Plateau contains the largest area of alpine permafrost on Earth. However, the current status of the net CO2 balance and feedbacks to warming remain unclear, given that the region has recently experienced an atmospheric warming rate of over 0.3 °C decade-1 We examined 32 eddy covariance sites and found an unexpected net CO2 sink during 2002 to 2020 (26 of the sites yielded a net CO2 sink) that was four times the amount previously estimated. The CO2 sink peaked at an altitude of roughly 4,000 m, with the sink at lower and higher altitudes limited by a low carbon use efficiency and a cold, dry climate, respectively. The fixation of CO2 in summer is more dependent on temperature than the loss of CO2 than it is in the winter months, especially at higher altitudes. Consistently, 16 manipulative experiments and 18 model simulations showed that the fixation of CO2 by plants will outpace the loss of CO2 under a wetting-warming climate until the 2090s (178 to 318 Tg C y-1). We therefore suggest that there is a plant-dominated negative feedback to climate warming on the Tibetan Plateau.

Research progresses of microplastic pollution in freshwater systems.

Microplastics (MPs) have received widespread attention as an emerging environmental pollutant. They are ubiquitous in the freshwater system, causing a global environmental issue. The current features and perspectives of MPs in the freshwater systems can provide the concerns of their ecological effects, which has not been addressed widely. Therefore, in this study, we reviewed the characteristics of MPs in freshwater environments and discussed their sources and potential impacts. The abundance of MPs in freshwater system ranged from approximately 3-6 orders of magnitude in different regions. There colors were mainly white and transparent, with polypropylene (PP) and polyethylene (PE) as the major polymers. The main shape of these MPs was fibers with dominant size of less than 1 mm. Analysis indicated MPs in freshwater system mostly originated from human activities such as sewage discharge in highly contaminated areas, while atmospheric long-distance transport and precipitation deposition played an important role in remote areas. Freshwater MPs pollutants also affected drinking water and aquatic organisms. Because the abundance of MPs in organisms was relatively balanced, the pollution level of biological MP pollution cannot accurately characterize the pollution status in the watershed currently. Future research should focus and strengthen on periodic monitoring to characterize the temporal and spatial changes of MPs, and enhance toxicological research to explore MPs pollution impact on biota and humans.

Characteristics of dissolved organic carbon and nitrogen in precipitation in the northern Tibetan Plateau.

Dissolved organic carbon (DOC) and nitrogen (N) play essential roles in global C and N cycles. To address the possible role of DOC and N in precipitation and enrich the related global database, the characteristics of DOC and N in precipitation were investigated in a typical remote permafrost region (upper Heihe River Basin) of the northern Tibetan Plateau (TP) from February 2019 to March 2020. The results demonstrated that the average DOC and total dissolved N (TDN) concentrations in the precipitation were 1.41 ± 1.09 µg mL-1 and 0.84 ± 0.48 µg mL-1, respectively, with relatively lower concentrations in the summer. The annual DOC and TDN fluxes were estimated to be 6.42 kg ha-1 yr-1 and 3.39 kg ha-1 yr-1, respectively, indicating that precipitation was a significant factor in C and N deposition. The light-absorbing properties of precipitation DOC from the SUVA254 and spectral slope revealed that precipitation DOC containing more aromatic components and lower molecular weights mostly was present during the summer; the mass cross-section (at the wavelength of 365 nm) ranged 0.26-1.84 m2 g-1, suggesting the potential impact of DOC on climatic forcing in the area. The principal component analysis combined with air mass backward trajectories indicated that the air masses from west Siberia, Central Asia, and northwestern China most significantly influenced the precipitation C and N in the study area. The WRF-Chem simulations and aerosol vertical distributions further illustrated the air mass transport pathways, demonstrating that dust and anthropogenic emissions could be transported over the studied area by westerlies and monsoonal winds. In the study basin, the precipitation deposition of DOC and N contributed largely to the riverine DOC and N exportation during the summer and had potential ecological effects. These results highlight the importance of DOC and N deposition from precipitation in the northern TP.

Microplastics in glaciers of the Tibetan Plateau: Evidence for the long-range transport of microplastics.

Microplastics are globally prevalent on a large scale in various marine and terrestrial environments, including Arctic snow and precipitation in protected areas of the United Sates. However, reports of microplastics from glaciers are rare, especially for the Tibetan Plateau (TP), which is widely known as the world's Third Pole and Asian Water Tower. Adjacent to human settlements in South Asia, East China, and Central Asia, the TP features regular cross-border air pollution (e.g., black carbon and mercury), which can affect its vulnerable and pristine environments. In previous studies, abundant microplastics have been reported from Tibetan rivers/lakes water and sediments, and surface soils. We detected microplastics in glacier surface snow on the TP, which were isolated from the impact of human activities, indicating that microplastics can be transported over long distances. This evidence is expected to be significant for understanding the atmospheric transport of microplastics to the TP, and provides a global perspective on the microplastic cycle.

Effects of black carbon and mineral dust on glacial melting on the Muz Taw glacier, Central Asia.

Light-absorbing impurities (LAIs), including black carbon (BC) and mineral dust, in snow can trigger a positive feedback. In this study, we estimate the contribution of BC and dust to glacial melting in Central Asia. Average BC and dust concentrations in the surface snow of the Muz Taw glacier are 1788 ± 1754 ng g-1 and 172 ± 178 µg g-1, respectively. Simulation using the Snow Ice and Aerosol Radiation (SNICAR) model indicates that the combined effect of BC and dust reduces the snow albedo by approximately 6.24% to 50.4% relative to clean snow. Radiative forcing (RF) induced by BC and dust deposited in snow ranges from 1.61 to 32.69 W m-2, with an average of 16.74 W m-2 for the central scenario. Thus, glacier melting can be enhanced by 36.37 cm w.e. by BC and dust in snow, accounting for about 16.3% of the total glacier melt. LAIs deposited on the Muz Taw glacier mostly originate from Central Asia, West Siberia and local emissions during the study period. More than 80% of BC deposited is attributed to anthropogenic emissions. These results strengthen the important role of BC and dust in glacier melting in Central Asia, and further highlights the potential benefits of mitigation of BC emissions.

Data on DOC and N from the Muz taw glacier in Central Asia.

This Data in Brief article provides a supplementary information to the dissolved organic carbon and nitrogen from the snow of Muz taw glacier in the Central Asia, which is related to the scientific article titled with "Characterization, sources and transport of dissolved organic carbon and nitrogen from a glacier in the Central Asia"[1]. Meanwhile, major ions (including Na+, K +, NH4 +, Ca2+, Mg2+, Cl-, SO4 2-, NO3 -, and NO2 -) were also reported. These data were analysed using descriptive statistics such as correlations and principle component analysis. Additionally, we conducted a literature review on DOC and N concentrations for the comparison. This article also presents the analysis data of the mass absorption cross section of DOC in snow.

Characterization, sources and transport of dissolved organic carbon and nitrogen from a glacier in the Central Asia.

Glacier melting represents an important flux of carbon and nitrogen (N) and affects the hydrological cycle. In this study, we presented the features of dissolved organic carbon (DOC) and N concentrations, their potential sources and export from the Muz Taw glacier in Central Asia. The average DOC and total dissolved nitrogen concentrations were 1.12 ± 1.66 and 0.62 ± 0.59 mg L-1 in surface snow and 0.21 ± 0.04 and 0.31 ± 0.10 mg L-1 in snowpit samples, respectively. The values from snowpit of the Muz Taw glacier were comparable to data reported from glaciers in the Tibetan Plateau but were considerably higher than those from polar regions. The C/N ratios in snow ranged from 0.7 to 11.7, indicating the high bioavailability of DOC. Mass absorption cross section of DOC at 365 nm in snow indicated that during the snow melting process, light-absorbing DOC was prone to be attached to particles, especially in the ablation zone of the Muz Taw glacier. Radiative forcing caused by DOC contributed approximately 38 ± 26% and 18 ± 9.8% of that caused by black carbon for surface snow and snowpit samples, respectively. DOC and N deposition on the glacier surface were influenced by the combined sources from anthropogenic input, wild biomass burning emission, and dust input from local regions and long range transport. Export of DOC and N from the Muz Taw glacier was estimated to be 3.47-18.5 t C yr-1 and 5.11-10.23 t N yr-1 respectively, based on their concentrations and current glacier mass balance. These results enhanced our understanding of the sources and cycle of DOC and N released from glaciers in Central Asia, where glacier meltwater can protect the population from drought stress.

Importance of atmospheric transport for microplastics deposited in remote areas.

Atmospheric transport is an important pathway for the deposition of micro- and nano-plastics in remote areas. However, the sources and fate of atmospheric microplastics remain poorly understood. A study on atmospheric transport and deposition in the Pyrenean Mountains highlights the movement of microplastics away from known sources (cities, agriculture, and industry) into remote areas. Following this first evidence of atmospheric microplastic deposition in a pristine location, it is necessary to reconsider previous studies on atmospheric microplastic deposition and behavior in remote areas.

Riverine dissolved organic carbon and its optical properties in a permafrost region of the Upper Heihe River basin in the Northern Tibetan Plateau.

Riverine dissolved organic carbon (DOC) and its optical properties were investigated in two sub-river basins (Yeniugou and Hulugou river) of the Upper Heihe river basin in the northern Tibetan Plateau. The results showed that DOC concentrations ranged from 0.25 to 12.2 and 0.18-1.04 mg L-1 for Yeniugou and Hulugou river basin with an average of 0.82 and 0.33 mg L-1, respectively. Export of DOC from the studied river (YNG: ~0.86 Gg C yr-1) was lesser compared with other large river in the Tibetan Plateau and Arctic regions because of the small drainage area and lower DOC concentrations. There exhibited significant seasonality for DOC in Yeniugou river basin with higher values observed during late spring and summer; however, no such distinct trend was observed for DOC in the studied rivers of Hulugou river basin. In contrast, total dissolved nitrogen showed a slightly lower value during the summer season. A strong relationship was determined between DOC concentrations and spectral UV absorbance at 254 nm (SUVA254), absorption coefficients and spectral slope for both sub-river basins, attributing that the riverine DOM in the northern Tibetan Plateau has a remarkably high content of aromatic compounds in late spring and summer. Considering the less snow cover percentage, this study highlights the potential impacts of permafrost thaw on the riverine DOC and its characteristics in the permafrost region under climate change.

Dissolved organic carbon in snow cover of the Chinese Altai Mountains, Central Asia: Concentrations, sources and light-absorption properties.

Dissolved organic carbon (DOC) in snow plays an important role in river ecosystems that are fed by snowmelt water. However, limited knowledge is available on the DOC content in snow of the Chinese Altai Mountains in Central Asia. In this study, DOC in the snow cover of the Kayiertesi river basin, southern slope of Altai Mountains, was investigated during November 2016 to April 2017. The results showed that average concentrations of DOC in the surface snow cover (1.01 ±â€¯0.52 mg L-1) were only a little higher than those in glaciers of the Tibetan Plateau, European Alps, and Alaska, but much higher than in Greenland Ice Sheet. Depth variations of DOC concentrations from snowpack profiles indicated higher values in the surface layer. During the observation period, scavenging efficiency for DOC in snow cover is estimated to be 0.15 ±â€¯0.10, suggesting that DOC in snow can be affected more by the meltwater during ablation season than during accumulation season. The average mass absorption cross section at 365 nm and the absorption Ångström exponent of DOC were 0.45 ±â€¯0.35 m2 g-1 and 2.59 ±â€¯1.03, respectively, with higher values in March and April 2017. Fraction of radiative forcing caused by DOC relative to black carbon accounted for about 10.5%, implying DOC is a non-ignorable light-absorber of solar radiation in snow of the Altai regions. Backward trajectories analysis and aerosol vertical distribution images from satellites showed that DOC in the snow of the Altai Mountains was mainly influenced by air masses from Central Asia, Western Siberia, the Middle East, and some even from Europe. Biomass burning and organic carbon mixed with mineral dust contributed significantly to the DOC concentration. This study highlights the effects of DOC in the snow cover for radiative forcing and the need to study carbon cycling for evaluation of quality of the downstreams ecosystems.

Dissolved organic carbon in glaciers of the southeastern Tibetan Plateau: Insights into concentrations and possible sources.

Dissolved organic carbon (DOC) released from glaciers has an important role in the biogeochemistry of glacial ecosystems. This study focuses on DOC from glaciers of the southeastern Tibetan Plateau, where glaciers are experiencing rapid shrinkage. We found that concentrations of DOC in snowpits (0.16±0.054 µg g-1), aged snow (0.16±0.048 µg g-1), and bare ice (0.18±0.082 µg g-1) were similar across the southeastern Tibetan Plateau, but were slightly lower than those in other glaciers on the Tibetan Plateau. Vertical variations of DOC, particulate organic carbon, black carbon, and total nitrate in snowpit showed no systematic variations in the studied glaciers, with high values of DOC occurring in the ice or dusty layers. We estimated the export of DOC and particulate organic carbon from glaciers to be 1.96±0.66 Gg yr-1 and 5.88±2.15 Gg yr-1 in this region, respectively, indicating that organic carbon released from glacier meltwater may be affecting downstream ecosystems. Potential sources of the air masses arriving at the southeastern Tibetan glaciers include South Asia, Central Asia, Middle East, and northwest China. Emissions from biomass burning of South Asia played an important role in the deposition of DOC to the glacier, which can be evidenced by backward trajectories and fire spot distributions from MODIS and CALIPSO images. Our findings suggest that anthropogenic aerosols contribute abundant DOC to glaciers on the southeastern Tibetan Plateau. The pronounced rate of glacial melting in the region may be delivering increased quantities of relic DOC to downstream rivers.

Impacts of the active layer on runoff in an upland permafrost basin, northern Tibetan Plateau.

The paucity of studies on permafrost runoff generation processes, especially in mountain permafrost, constrains the understanding of permafrost hydrology and prediction of hydrological responses to permafrost degradation. This study investigated runoff generation processes, in addition to the contribution of summer thaw depth, soil temperature, soil moisture, and precipitation to streamflow in a small upland permafrost basin in the northern Tibetan Plateau. Results indicated that the thawing period and the duration of the zero-curtain were longer in permafrost of the northern Tibetan Plateau than in the Arctic. Limited snowmelt delayed the initiation of surface runoff in the peat permafrost in the study area. The runoff displayed intermittent generation, with the duration of most runoff events lasting less than 24 h. Precipitation without runoff generation was generally correlated with lower soil moisture conditions. Combined analysis suggested runoff generation in this region was controlled by soil temperature, thaw depth, precipitation frequency and amount, and antecedent soil moisture. This study serves as an important baseline to evaluate future environmental changes on the Tibetan Plateau.

Characteristics of black carbon in snow from Laohugou No. 12 glacier on the northern Tibetan Plateau.

Black carbon (BC) emitted from the incomplete combustion of biomass and fossil fuel impacts the climate system, cryospheric change, and human health. This study documents black carbon deposition in snow from a benchmark glacier on the northern Tibetan Plateau. Significant seasonality of BC concentrations indicates different input or post-depositional processes. BC particles deposited in snow had a mass volume median diameter slightly larger than that of black carbon particles typically found in the atmosphere. Also, unlike black carbon particles in the atmosphere, the particles deposited in snow did not exhibit highly fractal morphology by Scanning Transmission Electron Microscope. Footprint analysis indicated BC deposited on the glacier in summer originated mainly from Central Asia; in winter, the depositing air masses generally originated from Central Asia and Pakistan. Anthropogenic emissions play an important role on black carbon deposition in glacial snow, especially in winter. The mass absorption efficiency of BC in snow at 632nm exhibited significantly seasonality, with higher values in summer and lower values in winter. The information on black carbon deposition in glacial snow provided in this study could be used to help mitigate the impacts of BC on glacier melting on the northern Tibetan Plateau.

Chemical Records in Snowpits from High Altitude Glaciers in the Tibetan Plateau and Its Surroundings.

Glaciochemistry can provide important information about climatic change and environmental conditions, as well as for testing regional and global atmospheric trace transport models. In this study, δ18O and selected chemical constituents records in snowpits collected from eight glaciers in the Tibetan Plateau and adjacent areas have been investigated. Drawing on the integrated data, our study summarized the seasonal and spatial characteristics of snow chemistry, and their potential sources. Distinct seasonal patterns of δ18O values in snowpits indicated more negative in the south TP controlled by Indian monsoon, and less negative in the north TP and Tien Shan. Overall increasing concentrations of microparticles and crustal ions from south to north indicated a strength of dust deposition on glaciers from semi-arid and arid regions. Principal component analysis and air mass trajectories suggested that chemical constituents were mainly attributable to crustal sources as demonstrated by the high concentrations of ions occurring during the non-monsoon seasons. Nevertheless, other sources, such as anthropogenic pollution, played an important role on chemical variations of glaciers near the human activity centers. This study concluded that air mass transport from different sources played important roles on the spatial distributions and seasonality of glaciochemistry.