Mixing and transformation processes of water sources in the lower Yarlung Tsangpo River: Insights from δ18O, Δ17O, 222Rn, and hydrochemistry

The Tibetan Plateau is known as the "Asian water tower," and the Yarlung Tsangpo (YT) River is the largest river that originates in and flows across the southern Tibetan Plateau. Although the solute source of YT River has been extensively and qualitatively analyzed, there is a lack of the quantitative analysis for the whole basin and seasonal variation of hydrochemical characteristics. Here, 212 samples obtained in the mainstream and tributary of YT River in different (wet, normal, and dry) periods were used for the solute apportionment using the mass balance model. The results showed that the solutes in YT River water were mainly derived from the carbonate and silicate rock weathering that accounts 42.2% and 26.9% in the total solute source, respectively, as the complex geological conditions in the basin. A part of the ions (7.5%) was also originated from the atmospheric precipitation as the abundant rainfall in the wet period. Meanwhile, the contribution of solute sources had no significantly seasonal variation in the upstream, whereas it had significantly seasonal variation in the downstream with the tropical climate and heavy rainfall. Importantly, the rock weathering of the basin could consume so much atmospheric CO2 (0.54% of the consumption at global with the only 0.16% of the global surface area) that could mitigate the global warming, which followed an increasing trend from upstream to downstream. The quantitative analysis of the solute source for YT River fills in the gaps in the chemically characteristic cognition of the basin. It is beneficial for the water resource management for the Asian. The proportion of solute sources in the YT River and its tributaries for wet (W), normal (N), and dry (D) periods.

To improve the reliability of methods to trace surface water pollutants in river basins, hydrological and water quality processes in the Fuxi River Basin were continuously monitored from 2013 to 2015, and the main pollution sources in the watershed and δ15N as well as δ18O in the rivers were measured simultaneously. The Soil and Water Assessment Tool (SWAT) model was used to simulate the NH4+ and NO3- migration processes in the hydrological processes of the land surface and rivers. On this basis, the processes of mixing, transformation, and fractionation of δ15N and δ18O in NO3- were coupled, and the simulation methods of δ15N and δ18O in the rivers were developed. The results showed that δ15N and δ18O in the rivers were mainly affected by the pollution sources in the river basin and the variation in runoff conditions during different hydrological periods. The contribution of the mixing process of different isotopes to the isotope abundance was 82.74%. The contribution of isotope fractionation in the process of nitrogen conversion was 16.26%. The influence of NH4+ and NO3- concentration deviation from the SWAT simulation on the simulation errors of δ15N and δ18O was 10.44%. The δ18O simulation errors were 18.72% larger than those of δ15N because of the higher variation range of δ18O in rainfall and the complexity of δ18O. The systematic errors and deviations of the simulated δ15N and δ18O results using the proposed method were less than 10% and 15%, respectively. The simulation method of δ15N and δ18O in the river basin has a clear physical meaning, which provides a useful approach for tracing nitrogen sources in rivers.

Rivers are important routes for material and energy transport between terrestrial and marine ecosystems. Recent global-scale assessments of carbon (C) have suggested that C emission fluxes to the atmosphere are comparable to the fluvial C fluxes to the ocean. However, many previous studies only collected data from inland rivers in low altitude regions. Therefore, it remains unclear how plateau rivers affect C flux. In this study, 20 monitoring sites were set up along the Yarlung Tsangpo (YT) River on the Tibetan Plateau and detailed observations were carried out in the wet and dry seasons. The riverine CO2 fluxes exhibited significant seasonal patterns which ranged from 597.12 ± 292.63 μatm in the wet season to 368.72 ± 123.50 μatm in the dry season. The CO2 emission flux (FCO2) obtained from floating chamber method, ranging from 8.44 ± 6.94 mmol m−2 d−1 in sunmmer to 3.62 ± 6.32 mmol m−2 d−1 in winter, with an average value of 6.03 mmol m−2 d−1. Generally, the river was a weak carbon source with respect to the atmosphere. However, the pCO2 and FCO2 were much lower than that for other large rivers around the globe, which were obviously restrained by the weak microbial activities due to the low primary productivity and carbonate buffer activities in the carbonate background. Carbon loss via atmosphere exchange in the YT River on the plateau accounted for 2.2% and 10.6% of the riverine dissolved carbon fluxes (67.77 × 109 mol a−1) according to the floating chamber and thin boundary layer methods, respectively. The YT River probably acts as a “pipeline” to transport weathered nutrients from the plateau to downstream areas. Our results demonstrated the characteristics of a “weak outgassing effect and a high transport flux of carbon” for the plateau river, which is different from rivers on plains. Considering the global relevance of Tibetan Plateau, further studies with enhanced spatiotemporal resolution are needed to better understand the important role of plateau rivers on carbon budgets and climate change over both regional and global cycles.

Abstract: Headwater streams are critical repositories of biodiversity and are important sources of water, nutrients, and energy to downstream rivers. I investigated relationships between stream geomorphology and habitat, benthic macroinvertebrates, and fish assemblages between headwater and network streams (n = 18) of mountain drainages in northern Idaho, United States. I found that a stream geomorphic condition assessment (rapid geomorphic assessment, RGA) designed to evaluate channel adjustment explained more variation in habitat assessment scores in headwater (R2 = 0.79) than in larger streams (R2 = 0.51). Results from redundancy analysis indicated that geomorphic‐biotic relationships were stronger in headwater than in network streams. For aquatic macroinvertebrates, relationships in headwaters were largely related to sediment size and slope. Fish‐geomorphic associations in both headwater and network streams were quite variable, although the RGA was correlated with fish diversity in both systems. Large wood was related to macroinvertebrate and fish descriptors in both headwater and network streams, but in distinct ways. This work supports an ecogeomorphic approach to the conservation of headwater streams including the use of tailored stream geomorphic assessment protocols.

The future will be fought on water and not on any other issues. The word has witnessed many disputes on water in the recent past but fortunately they have not crossed the critical threshold of becoming a world war. There are many bilateral or multi- lateral agreements which have the potential for water exploitation (Ashok swain, 2001). This has been seen that world has witnessed more human causalities in the past than the natural disasters and this is indicative of water as an emerging threat to the world peace (Angelakis, A.N. et al 2021). Emergence of water as a threat requires strong legal landscape across the countries (Peter Gleick, 2023). The Helsinki rules on the uses of water in not legally binding therefore, it doesn’t serve the purpose for which it was structured (International law association, 1966). The Chinese have weaponised water and building many dams on the Yarlung Tsangpo River, possibly the China plans to make 360 dams on slope with a gradient of 60o on the Himalayas which is very young and Fissile Mountain. Chinese government has taken a decision to lift a decade-long embargo on hydropower ‘projects in the lower reaches of the Yarlung Tsangpo (Brahmaputra) river in Tibet.

Major ions, stable isotopes, and trace elements, including rare earth elements (REEs), are used as natural tracers in the qualitative assessment of potential water sources in lakes and rivers of the upper Yana River basin, between Verkhoyansk and Chersky Ranges, during the late summer period. Three distinct regions were sampled, and a dominant water source in each region was qualitatively inferred from water chemistry data. The REE distribution pattern was found to be highly regional and controlled by pH and carbonate contents. Mountain headwater stream at the Verkhoyansk Range north slope, the Dulgalakh River, shows an input from a mixture of shallow groundwater and icing meltwater, with a depleted isotopic signature (δ18O below –21‰), d-excess (dex = δ2H − 8·δ18O) above 18, enrichment in Mg and Sr, and depletion in heavy REEs. The Derbeke Depression lakes and streams are fed by rainfall having ultra-low total dissolved solids (TDS) content, below 25 mg/L, and a convex-up REE pattern. In a medium mountainous river at the Chersky Range flank, the Dogdo River, leaching through fissured Jurassic carbonates is a dominant runoff pathway. Riverine water is heavily depleted in light REEs, but enriched in Mo, Rb, Sb, W and U. In the Dulgalakh River water, high positive Sm and Gd anomalies were observed, attributed either to local geology (greenshists), historical mining legacy, or contemporary winter road operations.

<p>The Yarlung Tsangpo River follows the Indus-Tsangpo suture through the southern Tibetan Plateau, and then becomes the Brahmaputra, following a bend into India through the Yarlung Tsangpo Gorge. In the middle reaches, narrow gorges alternate with broad valleys (Zhang, et al. 1998). In the section with steep and narrow gorges, the river is easily dammed by landslides, glaciers and/or moraines, rock avalanches and debris flows. Palaeo-lake sediments were discovered in the broad Xigazê valley and Dazhuka-Yueju gorge in the middle reach of the Yarlung Tsangpo River in Tibet. The river was likely dammed by a glacier and/or moraine at the eastern end of the Dazhuka-Yueju gorge. AMS <sup>14</sup>C and OSL ages of lacustrine sediments indicate the palaeo-lake was formed during the period from ~30.2 to 32.3 cal. kyr BP, and failed at ~13.2 cal. kyr BP (Hu et al., 2018). The elevation of the dammed lake was 3811 m a.s.l., and its length, maximum water depth, and volume were 185 km, 211 m, and ~22.55 km<sup>3</sup>, respectively (Hu et al., 2022). The volume of the sediment was ~11.56 km<sup>3</sup>, which was calculated from the dam location, sediment surface elevation, and the ASTER GDEM2 data. Therefore, the backwater volume was 10.99 km<sup>3</sup>, and the peak flood possibly exceeded 3.4 × 10<sup>5</sup> m<sup>3</sup>/s during the dam failure. The dammed palaeo-lakes in the vallyes downstream of the middle Yarlung Tsangpo River were also discharged during ~13 ka, and they were likely interconnected by hydrological processes. Hence, the failure of the dam and related flooding from the Dazhuka-Yueju gorge probably triggered a chain reaction of dam failures downstream, forming a megaflood. However, the dammed event in the Dazhuka-Yueju valley probably had a limited effect on the landforms at downstream because of the presence of another dammed palaeo-lake in the broad Zetang valley. So the ages of the dammed palaeo-lakes at the middle Yarlung Tsangpo River need to constrained more precisely.</p><p><strong>References</strong></p><p>Hu, H.-P., Feng, J.-L., Chen, F., 2018. Sedimentary records of a palaeo-lake in the middle Yarlung Tsangpo: Implications for terrace genesis and outburst flooding. Quaternary Science Reviews, 192, 135-148.</p><p>Hu, H.-P., Liu, J.-H., Feng, J.-L., Ye, C.-S., Lv, F., Chen, F., Gong, Z.-J., Chen, L.-Q., Du, D.-D., 2022. Geomorphic processes of a dammed palaeo-lake in the middle Yarlung Tsangpo River, Tibet. Science of the Total Environment, 811C, 151949.</p><p>Zhang, D.D., 1998. Geomorphological problems of the middle reaches of the Tsangpo River, Tibet. Earth Surface Processes and Landforms, 23(10): 889-903.</p>

The evolution of Yarlung Tsangpo River: Constraints from the age and provenance of the Gangdese Conglomerates, southern Tibet

Headwater streams dominate stream channel length in catchments. They are important sources of water, sediment and biota for downstream reaches and critical sites for organic matter and nutrient processing. Aquatic biodiversity in headwater streams has been overlooked in comparison to higher-order rivers, and few studies have considered spatial biodiversity patterns in headwater streams, or streams in general. I reviewed studies of macroinvertebrate diversity in headwater streams and found equivocal evidence to support the view that headwater streams harbour high biodiversity. Headwater streams might still make an important contribution to γ (regional) diversity at the landscape (catchment) scale by virtue of high β (among-assemblage) diversity. I studied eight headwater streams from three forested, upland catchments along the Great Dividing Range, Victoria, Australia to test my hypothesis of high β diversity and to understand the spatial patterns and determinants of macroinvertebrate diversity in headwater stream networks. Diversity partitioning showed that reaches each had high α (within-assemblage) diversity, while β diversity made only a small contribution to γ diversity at both the reach and catchment scales. β diversity may have been lower than hypothesized due to relatively small distances between sites and high levels of dispersal among reaches and catchments in the study area. Contrary to other studies that have found environmental factors to be important for explaining variation in macroinvertebrate assemblage structure in headwater streams, I found a limited role for environmental factors structuring macroinvertebrate assemblages in the study area. In one year (2008), spatial factors (independent of environmental factors) were the dominant factor structuring macroinvertebrate assemblages. Therefore, metacommunity structure in the study area aligns most closely with the neutral/patch dynamic metacommunity model. This pattern of spatial structuring, coupled with low β diversity, suggests that high neighbourhood dispersal might be the main factor structuring macroinvertebrate assemblages in the study area. Flow permanence had only a seasonal effect on macroinvertebrate diversity and so there is a temporal component to the spatial diversity patterns in this system. The explicit recognition of stream ecosystems as spatially structured networks has increased our understanding of ecological patterns and processes, and provided the impetus for this research. Recent advances in the study of networks, particularly in the fields of physics and network theory, offer an opportunity to considerably extend the current application of the network concept in stream ecology. Determining the relative contributions of α and β diversity to γ diversity, and the scale dependence of α and β components, provides vital information for conservation planning because optimal reserve designs will differ depending on the relative contributions of α and β diversity. My finding of high α and low β diversity indicates that each stream in the study area can be considered to have low irreplaceability and the capacity to contribute a large portion of species to regional conservation targets. Information on spatial patterns of diversity is urgently required for systematic conservation planning for freshwater reserves if we are to halt the rapid decline in global freshwater biodiversity.

Summary1. Headwater streams are ubiquitous in the landscape and are important sources of water, sediments and biota for downstream reaches. They are critical sites for organic matter processing and nutrient cycling, and may be vital for maintaining the ‘health’ of whole river networks.2. Macroinvertebrates are an important component of biodiversity in stream ecosystems and studies of macroinvertebrate diversity in headwater streams have mostly viewed stream systems as linear reaches rather than as networks, although the latter may be more appropriate to the study of diversity patterns in headwater systems.3. Studies of macroinvertebrate diversity in headwater streams from around the world illustrated that taxonomic richness is highly variable among continents and regions, and studies addressing longitudinal changes in taxonomic richness of macroinvertebrates generally found highest richness in mid‐order streams.4. When stream systems are viewed as networks at the landscape‐scale, α‐diversity may be low in individual headwater streams but high β‐diversity among headwater streams within catchments and among catchments may generate high γ‐diversity.5. Differing ability and opportunity for dispersal of macroinvertebrates, great physical habitat heterogeneity in headwater streams, and a wide range in local environmental conditions may all contribute to high β‐diversity among headwater streams both within and among catchments.6. Moving beyond linear conceptual models of stream ecosystems to consider the role that spatial structure of river networks might play in determining diversity patterns at the landscape scale is a promising avenue for future research.

Enhanced chemodiversity, distinctive molecular signature and diurnal dynamics of dissolved organic matter in streams of two headwater catchments, Southeastern China

Headwater streams are the primary sources of water in a drainage network and serve as a critical hydrologic link between the surrounding landscape and larger, downstream surface waters. Many states, including North Carolina, regulate activity in and near headwater streams for the protection of water quality and aquatic resources. A fundamental tool for regulatory management is an accurate representation of streams on a map. Limited resources preclude field mapping every headwater stream and its origin across a large region. It is more practical to develop a model for headwater streams based on a sample of field data that can then be extrapolated to a larger area of interest. The North Carolina Division of Water Quality has developed a cost‐effective method for modeling and mapping the location, length, and flow classification (intermittent and perennial) of headwater streams. We used a multiple logistic regression approach that combined field data and terrain derivatives for watersheds located in the Triassic Basins ecoregion. Field data were collected using a standard methodology for identifying headwater streams and origins. Terrain derivatives were generated from digital elevation models interpolated from bare‐earth Light Detection and Range data. Model accuracies greater than 80% were achieved in classifying stream presence and absence, stream length and perennial stream length, but were not as consistent in predicting intermittent stream length.

<p>Baseflow is fed by groundwater to a large fraction. Estimating water quantity and quality from groundwater stores is essential for water management. However, there are few datasets available that contain detailed water chemistry analysis on high spatial resolution across multiple headwater catchments in (high) Alpine environments. This information is essential to analyze mixing processes on catchment scale from distinct landscape features.</p><p>We use two data sets: i) water chemistry analysis snapshot sampling campaigns in 7 headwater streams during low‑flow periods across Switzerland, and ii) a detailed chemical screening (every 25 m) in one selected catchment during baseflow, including electric conductivity and temperature. Major ions, stable isotopes, TOC, DOC, trace elements were analyzed for some of the samples (> 80). These data reveal the chemical fingerprint of the contributing groundwater sources. The chemical composition of these contributing sources to baseflow is largely influenced by weathering products depended on lithology and geomorphology. Using maximum likelihood calculations, we define the ion composition and the isotopic signature of the potential major endmembers (up to three), based on the mixed samples along the main stem.</p><p>The proposed methodology allows to i) reduce uncertainty of the endmembers, and ii) quantify the relative contribution of different lithology and geomorphological features to streamflow and shows iii) which spatial scale of input information is needed to analyze mixing processes from various groundwater sources. Our results show how the contribution of different lithologies, along with topography and geomorphological features, varies spatially throughout Alpine headwater catchments.</p>

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.

Spatial-temporal differentiation of eolian sediments in the Yarlung Tsangpo catchment, Tibetan Plateau, and response to global climate change since the Last Glaciation