Water-soluble elements in snow and ice on Mt. Yulong

Investigation of water-soluble organic constituents and their spatio-temporal heterogeneity over the Tibetan Plateau

Investigating the migration and transformation of carbonaceous and nitrogenous matter in the cryosphere areas is crucial for understanding global biogeochemical cycle and earth's climate system. However, water-soluble organic constituents and their transformation in multiple water bodies are barely investigated. Water-soluble organic carbon (WSOC) and organic nitrogen (WSON), and particulate black carbon (PBC) in multiple types of water bodies in eastern Tibetan Plateau (TP) cryosphere for the first time have been systematically investigated. Statistical results exhibited that from south to north and from east to west of this region, WSOC concentrations in alpine river runoff were gradually elevated. WSOC and nitrogenous matter in the alpine river runoff and precipitation in the glacier region presented distinct seasonal variations. WSON was the dominant component (63.4%) of water-soluble total nitrogen in precipitation over high-altitude southeastern TP cryosphere. Water-soluble carbonaceous matter dominated the carbon cycle in the TP cryosphere, but particulate carbonaceous matter in the alpine river runoff had a small fraction of the cryospheric carbon cycle. Analysis of optical properties illustrated that PBC had a much stronger light absorption ability (MAC-_PBC: 2.28 ± 0.37 m² g^-1) than WSOC in the alpine river runoff (0.41 ± 0.26 m² g^-1). Ionic composition was dominated by SO₄^2-, NO₃^-, and NH₄⁺ (average: 45.13 ± 3.75%) in the snow of glaciers, implying important contribution of (fossil fuel) combustion sources over this region. The results of this study have essential implications for understanding the carbon and nitrogen cycles in high altitude cryosphere regions of the world. Future work should be performed based on more robust in-situ observations and measurements from multiple environmental medium over the cryosphere areas, to ensure ecological protection and high-quality development of the high mountain Asia.

Spatial distribution and potential sources of arsenic and water-soluble ions in the snow at Ili River Valley, China

Trace elements and water-soluble ions in snow can be used as indicators to reveal natural and anthropogenic emissions. To understand the chemical composition, characteristics of snow and their potential sources in the Ili River Valley (IRV), snow samples were collected from 17 sites in the IRV from December 2018 to March 2019. Inverse distance weighting, enrichment factor (EF) analysis, and backward trajectory modelling were applied to evaluate the spatial distributions and sources of water-soluble ions and dissolved arsenic (As) in snow. The results indicate that Ca²⁺ and SO₄^2- were the dominant ions, and the concentrations of As ranged from 0.09 to 0.503 μg L^-1. High concentrations of As were distributed in the northwest and middle of the IRV, and the concentrations of the major ions were high in the west of the IRV. The strong correlation of As with F^-, SO₄^2-, and NO₂^- demonstrates that As mainly originated from coal-burning and agricultural activities. Principal component analysis showed that the ions originated from a combination of anthropogenic and crustal sources. The EFs showed that K⁺, SO₄^2-, and Mg²⁺ were mainly influenced by human activities. Backward trajectory cluster analysis suggested that the chemical composition of snow was affected by soil dust transport from the western air mass, the unique terrain, and local anthropogenic activities. These results provide important scientific insights for atmospheric environmental management and agricultural production within the IRV.

Photobleaching reduces the contribution of dissolved organic carbon to glacier melting in the Himalayas and the Tibetan Plateau

Dissolved organic carbon (DOC) makes an important contribution to glacier melting in the Himalayas and the Tibetan Plateau (HTP). Photobleaching can effectively reduce the light absorption ability of DOC, further changing its impact on glacier melting, which is not yet well researched in the HTP. Therefore, snowpit samples from the Bayi, Ganglongjiama (GLJM), Jiemayangzong (JMYZ) and Demula (DML) glaciers were collected to study the influence of photobleaching on the light absorption ability of DOC and its impact on glacier melting. The results showed that the DOC concentration of snowpit samples, which was affected by the melting state and photobleaching, decreased from the northern HTP to the southern HTP. At an early stage of melting, the mass absorption cross-section value at 365 nm (MAC₃₆₅) values showed a negative correlation with DOC concentrations in the snowpit at the JMYZ and DML glaciers, indicating that colored DOC tended to be concentrated in the snowpit during the melting process. With the aggravation of ablation, some snowpit samples in the GLJM and Bayi glaciers had both low concentrations and MAC₃₆₅ values of DOC due to the reduced influence of photobleaching on the light absorption ability of DOC. Similarly, two fluorescence components (one protein-like component and one humic-like component) were identified in the extracted DOC at the JMYZ and DML glaciers, while those components were not detected in the GLJM glacier. Based on the sources of fluorescent DOC and five-day backward air mass trajectories, long-distance transport of pollutants from South Asia was an important source of snowpit DOC in the southern HTP. In this study, photobleaching can effectively remove colored and fluorescent DOC from snowpit samples in the HTP, further reducing the radiation forcing and glacier melting caused by DOC.

Bacterial Diversity and Communities Structural Dynamics in Soil and Meltwater Runoff at the Frontier of Baishui Glacier No.1, China

Comprehensive knowledge of bacterial ecology mainly in supraglacial habitats is pivotal particularly at the frontier of accelerated glacier retreat. In this study, bacterial diversity and community composition in glacial soil and meltwater runoff at the frontier of Baishui Glacier No.1 were evaluated using high throughput sequencing. Significant variations in the physiochemical parameters formed an ecological gradient between soil and meltwater runoff. Based on the richness and evenness indexes, the bacterial diversity was relatively higher in soil compared with meltwater runoff. Hierarchical clustering and bi-plot ordination revealed that the taxonomic composition of soil samples was highly similar and significantly influenced by the ecological parameters than the meltwater runoff. The overall relative abundance trend of bacterial phyla and genera were greatly varied in soil and water samples. The relative abundance of Proteobacteria was higher in water runoff samples (40.5-87%) compared with soil samples (32-52.7%). Proteobacteria, Firmicutes, and a little part of Cyanobacteria occupied a major portion of water runoff while the soil was dominated by Acidobacteria (6-16.2%), Actinobacteria (5-16%), Bacteroidetes (0.5-8.8%), and Cyanobacteria (0.1-8.3%) besides Proteobacteria and Firmicutes. Higher numbers of biomarkers were found in soil group compared with the water group. The study area is diverse in terms of richness, while community structures are not evenly distributed. This study provides a preliminary understanding of the bacterial diversity and shifts in community structure in soil and meltwater runoff at the frontier of the glacial. The findings revealed that the environmental factors are a significantly strong determinant of bacterial community structures in such a closely linked ecosystem.

Ecological indication based on source, content, and structure characteristics of dissolved organic matter in surface sediment from Dagu River estuary, China

Dissolved organic matter (DOM) controls the fate of a variety of nutrients and trace metals in river estuary systems. The aim of our study is to explore the sources, structure characteristics of sediment DOM, and potential ecological release risk (heavy metal, N and P) under the environmental conditions of Dagu River estuary. The relative contribution of DOM source was calculated by carbon stable isotope (combining δ¹³C_DOM and C/N ratios). The structural characteristics of sediment DOM in Dagu River estuary were determined by ultraviolet-visible spectroscopy (UV-vis) absorbance and fluorescence spectroscopy. The potential ecological risks of heavy metals and N and P release were also assessed. Results show that the relative contributions of rural area and aquaculture are high in Dagu River estuary. The humification degree of DOM in downstream river is higher than that in the estuary, and the sediment DOM in Dagu River estuary is influenced by both terrestrial input and biological metabolism. The potential risk of eutrophication in the estuary is high. Moreover, under the effect of aquaculture and rural area, there is higher potential ecological release risk of heavy metal in the estuary. And samples in the middle transect have the highest potential ecological risks of heavy metal. Therefore, a framework has been proposed to predict the ecological status of the estuary by analyzing the sources, content, and structural characteristics of sediment DOM. These results provide a new insight on ecological indication of DOM in Dagu River estuary.

Investigation of the spatio-temporal heterogeneity and optical property of water-soluble organic carbon in atmospheric aerosol and snow over the Yulong Snow Mountain, southeastern Tibetan Plateau

Atmospheric aerosols are a branch of active research in recent decades. The deposition of light-absorbing substances on high-altitude glaciers causes substantial adverse impacts on the cryospheric environment, cryosphere-hydrology, and climate system. Although, the concentrations of water-soluble organic carbon (WSOC) in snow/ice on glaciers of Tibetan Plateau (TP) have been reported, their transfer processes and optical properties in the context of summer precipitation-atmosphere-snow-river water continuum are seldom studied. In this study, we have systematically examined some scientific issues associated with WSOC concentrations and light absorption properties of WSOC in various forms of samples from the Mt. Yulong region. Statistical results demonstrate that the spatial distribution of WSOC in the snow of Baishui glacier was heterogeneous. The average WSOC concentrations of each snowpit were significantly decreased, and its light-absorbing properties were significantly elevated with the time extension. Aerosol WSOC concentrations and light absorption have distinct spatial disparity and seasonal variation. Pre-monsoon and monsoon have the highest and lowest WSOC content, respectively. Whereas the light-absorbing properties present contrasting seasonal trends. Rivers of which runoff was supplied by glacier meltwater have significantly lower WSOC concentrations (e.g., 0.42 ± 0.03 mg L^-1) compared with other forms of water bodies. Mass absorption cross-section of WSOC (MAC-_WSOC) in multiple snow and meltwater samples was significantly different and type-dependent. Atmospheric aerosol has the lowest MAC-_WSOC value among the four types of samples, which was likely associated with exhaust emissions from private vehicles and tour buses. Statistical results indicated that the average AAE_330-400 values of various snow/ice samples are subequal. Snow of glaciers supplies a desirable platform for the deposition of gaseous materials which experienced long-range transport in high altitude zones. Biomass-burning emissions made an immense contribution to the WSOC deposition over the study area, as demonstrated by the distribution of active fire points. However, this preliminary study represents the first systematic investigation of WSOC deposition in southeastern TP. Further robust in-situ field investigations and laboratory measurements are urgently necessary to improve our understanding of the transfer process and optical property of WSOC.

Response mode of hydrochemical types of river water to altitude gradient in alpine regions

The study investigates the hydrochemical type and characteristics of river water in permafrost regions in the Tibetan Plateau by analyzing 532 samples collected from the source region of the Yangtze River. The hydrochemical type of the river water was Cl^--Na⁺-SO₄^2-, and its hydrochemical characteristics were primarily influenced by the soil sources, though the influence of the sea sources and anthropogenic factors could not be ignored. Significant negative correlations were found between temperature and NO₃^-, SO₄^2-, Mg²⁺, Ca²⁺, and between precipitation, relative humidity, and SO₄^2- and Mg²⁺ in the river water. River water in the higher altitudes of over 5000 m above sea level was mainly recharged from glacier snowmelt water and by the supra-permafrost water and precipitation at the altitudes between 3500 and 5000 m above sea level. The controlled sources of hydrochemical characteristics of glacier snowmelt water were different for different ablation rates in the area with elevations of over 5000 m above sea level. Different hydrochemical types in different ablation rates implied the hydrochemical type was extremely sensitive to ablation periods in areas with elevation of over 5000 m above sea level. However, hydrochemical type was not sensitive to ablation periods from 3500 to 5000 m above sea level. The ionic concentration of glacier snowmelt water was mainly controlled by pollutants in glaciers and snow. Melting rates of glacier snowmelt water also had a certain effect on ionic concentration. Meanwhile, the stability of the hydrochemical type implied river water mainly controlled the hydrochemical type from 3500 to 5000 m above sea level. Hydrochemical type had no effect on elevation in end ablation.

Concentration, spatiotemporal distribution, and sources of mercury in Mt. Yulong, a remote site in southeastern Tibetan Plateau

The unique geographic location of Mt. Yulong in the Tibetan Plateau (TP) makes it a favorable site for mercury (Hg) study. Various snow samples, such as surface snow, snow pit, and snowmelt water were collected from Mt. Yulong in the southeastern TP. The average concentration of Hg was found to be 37 ± 26 ng L^-1 (mean ± SD), comparable to Hg concentration from other parts of TP in the same year, though it was comparatively higher than those from previous years, suggesting a possible increase of Hg concentration over the TP. The concentration of Hg was higher in the lower elevation of the glaciers possibly due to the surface melting concentration of particulates. Higher concentration of Hg was observed in the fresh snow, suggesting the possibility of long-range transportation. The average concentration of Hg from the snow pit was 1.49 ± 0.78 ng L^-1, and the concentration of Hg in the vertical profile of the snow pit co-varied with calcium ion (Ca²⁺) supporting the fact that the portion of Hg is from the crustal origin. In addition, the principal component analysis (PCA) confirmed that the source of Hg is from the crustal origin; however, the presence of anthropogenic source in the Mt. Yulong was also observed. In surface water around Mt. Yulong, the concentration of Hg_T was found in the order of Lashihai Lake > Reservoirs > Rivers > Swamps > Luguhu Lake. In lake water, the concentration of Hg_T showed an increasing trend with depth. Overall, the increased concentration of Hg in recent years from the TP can be of concern and may have an adverse impact on the downstream ecosystem, wildlife, and human health.

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.

Review of brown carbon aerosols: Recent progress and perspectives

Brown carbon (BrC), a carbonaceous aerosol which absorbs solar radiation over a broad range of wavelengths, is beginning to be seen as an important contributor to global warming. BrC absorbs both inorganic and organic pollutants, leading to serious effects on human health. We review the fundamental features of BrC, including its sources, chemical composition, optical properties and radiative forcing effects. We detail the importance of including photochemical processes related to BrC in the GEOS-Chem transport model for the estimation of aerosol radiative forcing. Calculation methods for BrC emission factors are examined, including the problems and limitations of current measurement methods. We provide some insight into existing publications and recommend areas for future research, such as further investigations into the reaction mechanisms of the aging of secondary BrC, calculations of the emission factors for BrC from different sources, the absorption of large and long-lived BrC molecules and the construction of an enhanced model for the simulation of radiative forcing. This review will improve our understanding of the climatic and environmental effects of BrC.

In-situ measurements of light-absorbing impurities in snow of glacier on Mt. Yulong and implications for radiative forcing estimates

The Tibetan Plateau (TP) or the third polar cryosphere borders geographical hotspots for discharges of black carbon (BC). BC and dust play important roles in climate system and Earth's energy budget, particularly after they are deposited on snow and glacial surfaces. BC and dust are two kinds of main light-absorbing impurities (LAIs) in snow and glaciers. Estimating concentrations and distribution of LAIs in snow and glacier ice in the TP is of great interest because this region is a global hotspot in geophysical research. Various snow samples, including surface aged-snow, superimposed ice and snow meltwater samples were collected from a typical temperate glacier on Mt. Yulong in the snow melt season in 2015. The samples were determined for BC, Organic Carbon (OC) concentrations using an improved thermal/optical reflectance (DRI Model 2001) method and gravimetric method for dust concentrations. Results indicated that the LAIs concentrations were highly elevation-dependent in the study area. Higher contents and probably greater deposition at relative lower elevations (generally <5000masl) of the glacier was observed. Temporal difference of LAIs contents demonstrated that LAIs in snow of glacier gradually increased as snow melting progressed. Evaluations of the relative absorption of BC and dust displayed that the impact of dust on snow albedo and radiative forcing (RF) is substantially larger than BC, particularly when dust contents are higher. This was verified by the absorption factor, which was <1.0. In addition, we found the BC-induced albedo reduction to be in the range of 2% to nearly 10% during the snow melting season, and the mean snow albedo reduction was 4.63%, hence for BC contents ranging from 281 to 894ngg^-1 in snow of a typical temperate glacier on Mt. Yulong, the associated instantaneous RF will be 76.38-146.96Wm^-2. Further research is needed to partition LAIs induced glacial melt, modeling researches in combination with long-term in-situ observations of LAIs in glaciers is also urgent needed in the future work.