Tsangpo River Basin Research Articles

Geochemical behavior of riverine magnesium isotopes in the Yarlung Tsangpo River Basin, southern Tibetan Plateau

The riverine magnesium (Mg) isotope composition is generally controlled by sources and fractionation processes. However, it remains unclear in which cases these factors are predominant at the basin scale. In this study, we investigated the major elements, trace elements, and Mg and strontium (Sr) isotope ratios in the Yarlung Tsangpo River (YTR) Basin, southern Tibetan Plateau (TP), to explore the geochemical behavior of Mg isotopes and the dominant controlling factors. Riverine Mg2+ was shown to derive primarily from the weathering of silicates and carbonates. Riverine δ26Mg, which is first influenced by the mixing of different lithological sources, was detected ranging from −1.63 ‰ to −0.52 ‰. According to the saturation indexes of common Mg-bearing secondary minerals, the basin was divided into two zones. Above Shannan City (Zone I), where river waters mostly were oversaturated with minerals, positive correlations were observed between δ26Mg and the Ca/Mg and Sr/Mg ratios. This indicated that, after mixing, secondary minerals (talc and chlorite), which tend to preferentially incorporate 24Mg, may be formed in most of waters, leading to an increase in riverine δ26Mg values. The Rayleigh and batch fractionation models were fitted with factors ranging from 0.9975 to 0.9997. Below Shannan City (Zone II), where river waters mostly were unsaturated with minerals, riverine δ26Mg was positively correlated with 87Sr/86Sr and negatively correlated with the Ca/Mg, Sr/Mg, and HCO3/Na ratios. This suggested that the riverine δ26Mg were influenced by carbonate dissolution with faster kinetic rates. Our analysis of riverine δ26Mg values in the YTR Basin may be a reference for interpreting the relationships between δ26Mg and δ7Li in river systems worldwide. In minerals-oversaturated waters, secondary mineral formation was shown to lead to isotope fractionation, resulting in a positive correlation between the two parameters, whereas in minerals-unsaturated waters, the δ26Mg and δ7Li values were negatively correlated, possibly due to the predominance of mineral dissolution.

Efficient risk assessment of landslide dam breach floods in the Yarlung Tsangpo river basin

Efficient risk assessment of landslide dam breach floods in the Yarlung Tsangpo river basin

Environmental fate of microplastics in high-altitude basins: the insights into the Yarlung Tsangpo River Basin

Microplastics (MPs) have been found in remote high-altitude areas, but the main source and migration process remained unclear. This work explored the characteristics and potential sources of MPs in the Yarlung Tsangpo River Basin. The average abundances of MPs in water, sediment, and soil samples were 728.26 ± 100.53 items/m3, 43.16 ± 5.82 items/kg, and 61.92 ± 4.29 items/kg, respectively, with polypropylene and polyethylene as the main polymers. The conditional fragmentation model revealed that the major source of MPs lower than 4000 m was human activities, while that of higher than 4500 m was atmospheric deposition. Community analysis was further conducted to explore the migration process and key points of MPs among different compartments in the basin. It was found that Lhasa (3600 m) and Shigatse (4100 m) were vital sources of MPs inputs in the midstream and downstream, respectively. This work would provide new insights into the fate of MPs in high-altitude areas.

Complex spatial and size distributions of landslides in the Yarlung Tsangpo River (YTR) basin

The Yarlung Tsangpo River (YTR), located in the Himalayan orogenic belt, is renowned for its deep gorges and complex tectonic features, as well as its reputation as a landslide-prone region. However, less is known about the distribution of landslides across the entire river basin. To address this gap in knowledge, this study first established a comprehensive landslide inventory across the entire basin using remote sensing mapping and multiple field investigations. Then, a systematic analysis of the spatial and size distributions was conducted. The results indicated that the YTR basin features at least 2390 landslides with areas exceeding 104 m2, spanning a total area and volume of 1087.6 km2 and 48.4 km3, respectively. These landslides can be classified into eight types, and rockslides are the most common (53.1%). Their distributions are highly asymmetric, with the following notable patterns: (1) the Tsangpo suture zone (53.4%) contains a greater number of landslides than other tectonic units; (2) the landslide size is influenced by the relief and elevation conditions, with positive relationships observed between the local relief and landslide area, as well as between the elevation range and landslide area; and (3) the landslide distribution is not significantly correlated with rainfall, and seasonally frozen ground is associated with a greater concentration of landslides. Alternating slate and shale groups in the Tsangpo suture zone may be the factors responding to landslide concentration. A total of 20.6% of landslide-blocked rivers were observed, with some forming river knickpoints. Due to the limited data, spatial and size analyses are perhaps immature, and further systematic analysis remains necessary.

Unraveling the Coupled Dynamics between DOM Transformation and Arsenic Mobilization in Aquifer Systems during Microbial Sulfate Reduction: Evidence from Sediment Incubation Experiment

Geogenic arsenic (As)-rich groundwater poses a significant environmental challenge worldwide, yet our understanding of the interplay between dissolved organic matter (DOM) transformation and arsenic mobilization during microbial sulfate reduction remains limited. This study involved microcosm experiments using As-rich aquifer sediments from the Singe Tsangpo River basin (STR) and Jianghan Plain (JHP), respectively. The findings revealed that microbial sulfate reduction remarkably increased arsenic mobilization in both STR and JHP sediments compared to that in unamended sediments. Moreover, the mobilization of As during microbial sulfate reduction coincided with increases in the fluorescence intensity of two humic-like substances, C2 and C3 (R = 0.87/0.87 and R = 0.73/0.66 in the STR and JHP sediments, respectively; p < 0.05), suggesting competitive desorption between DOM and As during incubation. Moreover, the transformations in the DOM molecular characteristics showed significant increases in CHOS molecular and low-O/C-value molecular intensities corresponding to the enhancement of microbial sulfate reduction and the possible occurrence of methanogenesis processes, which suggests a substantial bioproduction contribution to DOM components that is conducive to As mobilization during the microbial sulfate reduction. The present results thus provide new insights into the co-evolution between As mobilization and DOM transformations in alluvial aquifer systems under strong microbial sulfate reduction conditions.

Identifying and Predicting the Responses of Multi-Altitude Vegetation to Climate Change in the Alpine Zone

Global climate change has affected vegetation cover in alpine areas. In this paper, we analyzed the correlation between Leaf Area Index (LAI) and climate factors of the Yarlung Tsangpo River basin, and identified their contributions using the quantitative analysis method. The results show that the vegetation cover in the study area generally exhibited an increasing trend. Grassland in the middle- and high-altitude areas was the main contributing area. Temperature is the dominant climatic factor affecting the change, the effect of which increases with the rise in elevation. The influences of precipitation and radiation had obvious seasonality and regionality. The vegetation illustrated a lag response to climate drivers. With the change in the elevation band, the response time to precipitation was significantly less than that to air temperature in the low-elevation area, while the opposite trend was observed in the high-elevation area. In the future, the LAI of the watershed will show different characteristics at different time points, with the increases in the LAI in autumn and winter becoming the main factors for the future increase in the LAI. This provides a crucial basis upon which to explore hydrological and ecological processes as important components of the Third Pole region.

Assessment of sediment transport in Luxiapuqu watershed using RUSLE-TLSD and InSAR techniques: Yarlung Tsangpo River, China.

The Yarlung Tsangpo River Basin is characterized by its intricate topography and a significant presence of erosive materials. These often coincide with heavy localized precipitation, resulting in pronounced hydraulic erosion and geological hazards in mountainous regions. To tackle this challenge, we integrated the RUSLE-TLSD (Revised Universal Soil Loss Equation-Transportation-limited sediment delivery) model with InSAR (Interferometric Synthetic Aperture Radar) data, aiming to explore the sediment transport process and pinpoint hazard-prone sites within mountainous small watershed. The RUSLE-TLSD model aids in evaluating multi-year sediment transport dynamics in mountainous zones. And, the InSAR data precisely delineates changes in sediment scouring and siltation at sites vulnerable to hazards. Our research estimates that the potential average soil erosion within the watershed stands at 52.33 t/(hm2 a), with a net soil erosion of 0.69 t/(hm2 a), the sediment transport pathways manifest within the watershed's gullies and channels. Around 4.32% of the watershed area undergoes sedimentation, predominantly at the base of slopes and within channels. Notably, areas (d) and (e) emerge as the most susceptible to disasters within the watershed. Further analysis of the InSAR data highlighted four regions in the typical area (e) from 2017 that are either sedimentation- or erosion-prone, referred to as "hotspots." Among them, R1 exhibits a strong interplay between water and sediment, rendering it highly sensitive to environmental factors. In contrast, R4, characterized by a sharp bend in siltation, remains relatively impervious to external elements. The NDVI (normalized difference vegetation index) stands out as the pivotal determinant influencing sediment transport within the watershed, exerting a pronounced impact on the outlet section, especially in spring. By employing this approach, we gained a deeper understanding of sediment transport mechanisms and potential hazards in small watershed in uninformative mountainous areas. This study furnishes a robust scientific framework beneficial for erosion mitigation and disaster surveillance in mountainous watersheds.

Changes in soil organic carbon and its response to environmental factors in the Yarlung Tsangpo River basin

The distribution of terrestrial soil organic carbon changes with climate and substrate conditions. This study investigated the spatial and temporal distribution of soil organic carbon and its influencing elements in the Yarlung Tsangpo River Basin using meteorological, subsurface, and remotely sensed data over the past 39 years, combined with random forests and geodetector. The results of the study showed that soil organic carbon has been increasing in the study area over the past 39 years, and this change has been concentrated in the central part of the watershed. Among the environmental factors, precipitation, temperature, and leaf area index were the main contributors to the soil organic carbon changes, and the effects of the three factors were more significant at higher altitudes, with a 33 % increase in the significance level. Notably, the interactions among the factors exceeded their individual effects, and the combination of climate and leaf area index showed a significant two-factor enhancement effect, with q-value enhancements generally ranging from 0.15 to 0.3. The two-factor enhancement effect was more pronounced below 3000 m above sea level, where the topography of the study area concentrates soil organic carbon in the gently sloping areas of the catchment.

Insights from distribution and fractionation of the rare earth elements into As enrichment in the Singe Tsangpo River Basin

The geogenic As enrichment occurs extensively in the major river basin from the Tibetan Plateau, while the knowledge involved with the underlying mechanisms is far from completion. The present study utilized the geochemical behaviors of rare earth elements (REE) to study the hydrogeochemical evolution and As enrichment in the Singe Tsnagpo River basin, a typical As-rich river basin in the Tibetan Plateau. The river water was characterized by significant positive Eu anomalies and slight negative Ce anomalies, indicating the hydrogeochemical control of oxidative weathering of sourcing rocks and the contribution of felsic rocks. The PHREEQC modeling results suggested that the carbonate weathering contributed to the complexation of REE in the river water, where REE(CO3)+ and REE(CO3)2− were the predominant complex species. Besides, the reversing scenarios of HREE/LREE enrichment in the river water/sediments suggested a critical control of iron (hydr)oxides on the REE fractionation due to the preferential adsorption of LREE compared with HREE. Interestingly, the variations in Y/Ni and Cr/V ratios from the river sediments suggested a different contribution of sourcing rock weathering along the river flow path, where ultramafic rock showed a substantial contribution to the river sediments in the lower reaches and granite source is predominant in the upper reaches. It was also notable that the concurrent enrichment of REE and As in the river waters showed a response to the substantial enhancement of chemical weathering in the upper reaches of the STR basin, which was evidenced by the corresponding increases in the electrical conductivity and the δ18O values in the river waters. The present study thus provides new insights into utilizing REE as environmental tracers for studying hydrogeochemical evolution and As enrichment in the STR basin, which could also apply to similar alpine arid and cold river basins.

Quaternary sediment datasets for spatial distribution and accumulation on the Yarlung Tsangpo River Basin based on remote sensing and field on‐site measurements

AbstractQuaternary unconsolidated sediments are pronouncedly widespread features on the planetary surface, documenting significant geological signals of earth surface processes, climate change and biogeochemical cycles. The extensive unconsolidated deposits play a vital role in natural hazards and Anthropogenic activities, especially in alpine regions where massive unconsolidated materials are produced. However, the spatial distribution and total volume of unconsolidated sediments across the Yarlung Tsangpo River Basin (YTRB) remain largely unknown due to the limitation of traditional field surveys and on‐site measurements as well as the complex landscape in the remote area. This study presents the datasets for the systematic distribution and spatial accumulation of unconsolidated sediments across the Yarlung Tsangpo River Basin, southern Tibet. Combining remotely sensed data with numerous field investigations, an integrated method based on image processing and kriging interpolation‐pixel integration was performed to semi‐automatically classify and quantify the unconsolidated sediments. Eleven categories of sediments were mapped and their total accumulation is estimated at approximately 4.97 × 1011 t. Ultimately, 17 groups of classification and thickness maps were derived, revealing the distribution and volume of unconsolidated and Quaternary sediments. The datasets fill the gaps in comprehensive investigations of unconsolidated sediments for YTRB, and provide a fundamental database to support the scientific understanding of potential linkages between the distribution of unconsolidated sediments with environmental changes and human activities.

Combination of mineral protection and molecular characteristics rather than alone to govern soil organic carbon stability in Qinghai-Tibetan plateau wetlands

Wetlands in the Yarlung Tsangpo River Basin (YTR) on the Qinghai-Tibet Plateau provide immense soil organic carbon (SOC) storage, which is highly susceptible to climate warming and requires urgent deciphering SOC stabilization mechanisms of long-term protection of SOC against decomposition. Conflicting views exist regarding whether persistent SOC is controlled by molecular features or by mineral protection. As such, this study quantified SOC stability using two thermal indices (TG-T50, and DSC), described molecular features of SOC using pyrolysis-gas chromatography-mass spectrometry, and measured SOC protection by minerals using a chemical extraction method. Results indicated SOC of topsoils had higher thermal stability, with TG-T50 and DSC-T50 of 337.61 °C and 384.58 °C, than that of subsoils with TG-T50 and DSC-T50 of 337.32 and 382.67 °C, respectively. We found subsoils had significantly higher proportions of aliphatic and aromatic compounds, while existed higher SOC associated with minerals. It seemed SOC stabilization differed with soil depths, in which mineral protection dictated SOC thermal stability in topsoils while molecular features posed a more important constraint on SOC stabilization in subsoils. Overall, our findings support the hypothesis of physical and chemical protection but emphasized that SOC thermal stability largely depended on to extent of the combination between molecular features and mineral protection, which explained 55% in topsoils and 73% in subsoils, respectively.

Chemical weathering rates and controlling mechanisms of glacial catchments within different climate regimes in the Tibetan Plateau.

Continental weathering plays an important role in regulating atmospheric CO2 levels. Chemical weathering in glacial areas has become an intensely focused topic in the background of global change compared with other terrestrial weathering systems. However, research on the weathering of the glacial areas in the Yarlung Tsangpo River Basin (YTRB) is still limited. In this article, the major ions of the Chaiqu and Niangqu catchments in the YTRB have been investigated to illustrate the chemical weathering rates and mechanisms of the glacier areas in the YTRB. Ca2+ and HCO dominate the major ions of the Chaiqu and Niangqu rivers, accounting for about 71.3% and 69.2% of the TZ+ of the Chaiqu (the total cations, TZ+ = Na+ + K+ + Ca2+ + Mg2+, in µeq/L), and about 64.2% and 62.6% of the TZ+ of the Niangqu. A Monte Carlo model with six end-members is applied to quantitatively partition the dissolved load sources of the catchments. The results show that the dissolved loads of the Chaiqu and Niangqu rivers are mainly derived from carbonate weathering (accounting for about 62.9% and 79.7% of the TZ+, respectively), followed by silicate weathering (about 25.8% and 7.9% of the TZ+, respectively). The contributions of precipitation and evaporite to the Chaiqu rivers are about 5.0% and 6.2%, and those to the Niangqu rivers are about 6.3% and 6.2%. The model also calculated the proportion of sulfuric acid weathering in the Chaiqu and Niangqu catchments, which account for about 21.1% and 32.3% of the TZ+, respectively. Based on the results calculated by the model, the carbonate and silicate weathering rates in the Chaiqu catchment are about 7.9 and 1.8 ton km-2 a-1, and in the Niangqu catchment, the rates are about 13.7 and 1.5 ton km-2 a-1. The associated CO2 consumption in the Chaiqu catchment is about 4.3 and 4.4 × 104 mol km-2 a-1, and about 4.3 and 1.3 × 104 mol km-2 a-1 in the Niangqu catchment. The chemical weathering rates of the glacier areas in the YTRB show an increasing trend from upstream to downstream. Studying the weathering rates of glacier catchments in the Tibetan Plateau (TP) reveals that the chemical weathering rates of the temperate glacier catchments are higher than those of the cold glacier catchments and that lithology and runoff are important factors in controlling the chemical weathering of glacier catchments in the TP. The chemical weathering mechanisms of glacier areas in the YTRB were explored through statistical methods, and we found that elevation-dependent climate is the primary control. Lithology and glacial landforms rank second and third, respectively. Our results suggest that, above a certain altitude, climate change caused by tectonic uplift may inhibit chemical weathering. There is a more complex interaction between tectonic uplift, climate, and chemical weathering.

Automatic Monitoring Alarm Method of Dammed Lake Based on Hybrid Segmentation Algorithm

Mountainous regions are prone to dammed lake disasters due to their rough topography, scant vegetation, and high summer rainfall. By measuring water level variation, monitoring systems can detect dammed lake events when mudslides block rivers or boost water level. Therefore, an automatic monitoring alarm method based on a hybrid segmentation algorithm is proposed. The algorithm uses the k-means clustering algorithm to segment the picture scene in the RGB color space and the region growing algorithm on the image green channel to select the river target from the segmented scene. The pixel water level variation is used to trigger an alarm for the dammed lake event after the water level has been retrieved. In the Yarlung Tsangpo River basin of the Tibet Autonomous Region of China, the proposed automatic lake monitoring system was installed. We pick up data from April to November 2021, during which the river experienced low, high, and low water levels. Unlike conventional region growing algorithms, the algorithm does not rely on engineering knowledge to pick seed point parameters. Using our method, the accuracy rate is 89.29% and the miss rate is 11.76%, which is 29.12% higher and 17.65% lower than the traditional region growing algorithm, respectively. The monitoring results indicate that the proposed method is a highly adaptable and accurate unmanned dammed lake monitoring system.

Impact of Climate Change on the Hydrological Regimes of the Midstream Section of the Yarlung Tsangpo River Basin Based on SWAT Model

Water resources and the water cycle in high mountain areas are significantly impacted by climate change. In this study, the midstream section of the Yarlung Tsangpo River basin, situated in the southern part of the Tibetan Plateau, was chosen as the target area, and the Soil Water Assessment Tool (SWAT) was used to assess how climate change may affect hydrological processes. The SWAT model proved effective for runoff and snow cover area simulation. Surface runoff, interflow, and groundwater accounted for 47.2%, 24.4%, and 28.4% of the total runoff, respectively. The spatial distribution of runoff was mainly influenced by precipitation and glacier distribution, whereas the spatial distributions of individual runoff components were mainly influenced by soil properties. Overall, the total runoff as well as its components (surface runoff, interflow, and groundwater) increased at a rate of 0.03–0.83%/10 yr (p > 0.05) in the study area during 1983–2017, which could be attributed to the increase in precipitation. Surface runoff peaked earlier (August) than interflow and groundwater (September), owing to the longer convergence time of interflow and groundwater. Future predictions showed a warming and wetting trend (p < 0.05) in the study area from 2020 to 2100 under the SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios. The total runoff was projected to increase at a rate of 0.92–3.56%/10 yr, and the change of total runoff mainly came from the increase of surface runoff.

Hydrochemical Characteristics and Ion Source Analysis of the Yarlung Tsangpo River Basin

In order to investigate the hydrochemical characteristics and their controlling factors, 212 water samples from the Yarlung Tsangpo River and its tributaries were collected over three precipitation periods in 2018 and analyzed using mathematical statistics, the Gibbs and ion ratio methods, and principal component analysis. The results showed the following: (1) The cations in the water were mainly Ca2+, Na+ and Mg2+, and the anions HCO3− and SO42− were predominant, accounting for more than 97% of the total anion concentrations. The concentration of total dissolved solids (TDS) was 204.51 mg/L. The water chemistry type was SO4·(HCO3)−Ca·(Mg) water. (2) The concentrations of major ions in the Yarlung Tsangpo River fluctuate, but in general, the vast majority of the major ions in the water follow the trend of both first increasing and then decreasing in the three precipitation periods. The hydrochemical features of the Yarlung Tsangpo Basin have seasonal differences. (3) The Gibbs model and the PCA analyses showed that the Yarlung Tsangpo River water chemical components are mainly affected by rock weathering. In addition, the influence of the mining industry also plays an important role. The heavy metal concentrations in the three precipitation periods of the Yarlung Tsangpo River could reach the standard of first-class surface water quality.

Mapping Potential Soil Water Erosion and Flood Hazard Zones in the Yarlung Tsangpo River Basin, China

The ubiquity of soil water erosion in the Yarlung Tsangpo River Basin leads to a series of natural hazards, including landslides, debris flows and floods. In this study, the Revised Universal Soil Loss Equation model (RUSLE) was used to quantify potential soil water erosion, while the Height Above Nearest Drainage model (HAND) was used to delimit potential flood hazard zones. Remote sensing and geographic information system technologies were employed to spatialize the results, which showed that the annual soil loss from water erosion was less than 1239 t ha−1 y−1. The total soil loss was estimated to be over 108 × 106 tons, of which about 13 × 106 tons (12.04% of the total) occurred from the agricultural land in the downstream valley. Soil erosion mapping was performed using six levels of soil erosion intensity and the effects of precipitation, land use/land cover and topography on soil erosion were revealed. Increases in precipitation and slope gradient significantly increased the soil loss rate, while the maximum rate of soil loss occurred from densely vegetated land, reaching 9.41 t ha−1 y−1, which was inconsistent with erosion preconceptions for this land type. This may be due to a combination of the region’s unique climate of high intensity rainfall and steep slopes. Flood hazard mapping showed that all regional cities were located in a flood hazard zone and that, within the total basin area (~258 × 105 ha), 9.84% (2,537,622 ha) was in a high flood occurrence area, with an additional 1.04% in aa vulnerable to moderate flood hazard area. Approximately 1.54% of the area was in a low flood risk area and 4.15% was in a very low flood risk area. The results of this study provide an initial identification of high-risk soil water erosion and flood hazard locations in the basin and provide a foundation upon which decision-makers can develop water and soil conservation and flood prevention policies.

Hydrogeochemical processes regulating the enrichment and migration of As and B from the river sediments in the Singe Tsangpo River Bain, Western Tibetan plateau

Although the enrichment of arsenic (As) and boron (B) has been extensively observed in the major river basin within the Tibetan Plateau, little is known about the hydrogeochemical processes regulating the enrichment and mobility of As and B within river sediments. The present study conducted geochemical investigations of river sediments along the river flow path of the Singe Tsangpo River (STR) basin, and examined the mobility of As and B within river sediments under various environmental conditions through incubation experiments. The results suggested that the weathering of Cs-bearing silicate minerals could be a potential origin for As in the river sediments, which was evidenced by the corresponding variations between Cs and As (R = 0.60, P < 0.01). In contrast, carbonate weathering has contributed to the B enrichment, supported by the correlation between CaO and B concentrations (R = 0.60, P < 0.01). The incubation experiments showed intense mobilizations of As and B (∼12 mg/kg) under varying environmental conditions, where the increases in HCO3− concentration and temperature could enhance both As and B mobilization. Additionally, the As mobilization was enhanced by the anaerobic and alkaline conditions. These scenarios are relevant to the hydrogeochemical processes that regulate the As and B enrichment in both river water and groundwater from the STR basin, including the redox fluctuations that resulted from flood and draught cycling and the variations in the water/sediment particle ratios. The present study thus provided new insights into the hydrogeochemical control on the enrichment and mobility of As and B in the river sediments from the STR basin, which is also applicable in other riverine systems under similar conditions.

Changes in the Suitable Habitats of Three Endemic Fishes to Climate Change in Tibet.

As one of the most sensitive regions to global climate change, Tibet is subject to remarkable changes in biota over the past decades, including endemic fish species. However, no study has attempted to predict the changes in the distribution of Tibetan fishes, leaving a great blank for aquatic conservation in Tibet. Based on the Maximum Entropy model (MaxEnt), this study predicted the changes in the suitable habitats of three endemic fish species, including two species mainly inhabiting the rivers (Glyptosternon maculatum, Oxygymnocypris stewartii) and one species mainly inhabiting lakes (Gymnocypris selincuoensis) in Tibet under two representative concentration pathways (RCP2.6 and RCP8.5) under two future scenarios (2050 and 2090), and explored the impact of the barrier effects of hydropower projects on the suitable habitats of fish. The results showed that under the four scenarios, the net change in the suitable habitats of the G. maculatum was negative (-2.0--18.8%), while the suitable habitats of the O. stewartii and G. selincuoensis would be expanded, with the net change of 60.0-238.3% and 46.4-56.9%, respectively. Under different scenarios, the suitable habitats of the three species had a tendency to migrate to a higher elevation, and the largest expansion in the range of migration was projected to occur under the 2090-RCP8.5 scenario. In addition, due to the impact of the hydropower projects, the ability of G. maculatum to obtain new suitable habitats from climate change would be reduced by 2.0-8.1%, which was less than the loss induced by climate change (5.5-25.1%), while the suitable habitats of O. stewartii would be reduced by 3.0-9.7%, which was more than the impact of climate change (about 1%). The results of this study have guiding significance for the conservation and management of fish resources diversity in the Yarlung Tsangpo River basin and Siling Co basin of Tibet, and also provide a reference for the coordination and scientific planning of hydropower projects in Tibet.

Spatiotemporal variation of Li isotopes in the Yarlung Tsangpo River basin (upper reaches of the Brahmaputra River): Source and process

The increase in marine Li isotope composition (δ7Li, ∼9‰) since the Cenozoic is possibly related to continental chemical weathering associated with tectonic uplift (e.g., the Tibetan Plateau [TP]). However, the reasons for the spatiotemporal variations of δ7Li in the rivers flowing through the TP are still under debate, hindering the understanding of the changes in seawater δ7Li. Herein, various geological samples, i.e. river waters, river suspended particulate materials, river sediments, hot springs and silicate rocks, from the Yarlung Tsangpo River basin, the largest river system in the TP, have been analyzed to understand the source and isotopic fractionation of dissolved Li in rivers flowing through high-altitude and tectonic regions. The Yarlung Tsangpo River has an unusually high dissolved Li concentration ([Li]dis) (0.5–313 μg/L, mean 58.4 μg/L, n=93) and low δ7Lidis values (+1.0‰–+14.7‰, mean +6.4‰, n=92) compared with most river waters. These results can be explained by the input of geothermal water with extremely high [Li]dis (5.5–34.4 mg/L, mean 15.7 mg/L, n=9) and low δ7Lidis (−1.7‰–+3.1‰, mean +1.0‰). Silicate weathering is probably responsible for elevated δ7Lidis in river water compared to geothermal water, but the binary mixture model results of silicate weathering and geothermal water do not support this speculation. Ongoing Li isotope fractionation between dissolved loads and secondary minerals has been suggested to be the main reason for the increased δ7Lidis in river water. Field study and adsorption experiment results support the view of continuous Li isotope fractionation in rivers. Physical erosion and chemical weathering processes that provide fresh secondary minerals to rivers as well as dissolved Li from geothermal water transported in rivers over long residence times promote Li isotope fractionation. Hence, with the emergence of a continental geothermal system, the tectonic activity may directly or indirectly induce the simultaneous increase in dissolved Li flux and δ7Lidis in rivers that eventually flow into the ocean. This can partially explain the increase in seawater δ7Li in the Late Cenozoic.

Chemical weathering characteristics and controls in the Yarlung Tsangpo River Basin: Evidence from hydrochemical composition

The uplift of the Tibetan Plateau (TP) is thought to be closely related to the global climate. For the Yarlung Tsangpo River (YTR), the largest river on the TP, the hot spring input is an important source of solutes. Without considering hot spring input will lead to an overestimation of chemical weathering and CO2 consumption rate. Two sample series were collected in the basin before and after the monsoon season to evaluate the chemical weathering rates and controlling factors based on the hydrochemical composition. The results of improved forward model indicate that the highest contribution to the total cations comes from rock weathering (59%–99%, average value 93%), of which carbonate dissolution contributes the most (25%–79%, average value 61%), followed by evaporite dissolution (5%–42%, average value 19%) and silicate weathering (1%–29%, average value 13%). The hydrochemistry of tributaries in the middle reaches (Dogxung Tsangpo and Lhasa River) is affected by hot springs significantly, and the maximum contribution reaches 40%. The chemical weathering rates for the sub-basins show a sequence of Lhasa River > Dogxung Tsangpo > Nyang Qu, primarily controlled by lithology and runoff. For the mainstream above the YTR canyon and tributaries in the upper and middle reaches, chemical weathering is controlled by a transport limited regime, and the rest of the basin is governed by a kinetically limited regime. Overall, after deducting the hot spring input from the solutes, the silicate and carbonate weathering rates in the YTR Basin are 1.8 t/km2/yr and 6.3 t/km2/yr, respectively. The atmospheric CO2 consumption by silicate and carbonate weathering in the YTR Basin accounts for ∼0.17% and ∼0.28% of global, respectively, on ∼0.21% of the global land surface area. The carbon sink caused by chemical weathering and its effect on global carbon cycle in the YTR Basin are insignificant.