Source Region Of The Yangtze River Research Articles

Contribution of ecological conservation programs and climate change to hydrological regime change in the source region of the Yangtze River in China

Contribution of ecological conservation programs and climate change to hydrological regime change in the source region of the Yangtze River in China

A Study of the Vegetation Growth Dynamics in the Three Rivers Source from 1982 to 2015

The three rivers source area (The source region of the Yangtze River, Yellow River and Lancang River) has the largest area of river source areas in China, and is also an important climate-sensitive area and ecologically fragile zone. Studies on its vegetation growth dynamics are of great significance to the construction of ecological security barriers in China and the construction of ecological civilization in the Qinghai-Tibet Plateau region. The study investigated the vegetation dynamics in the three rivers source area by using the GIMMS NDVI dataset from January 1982 to December 2015. The results show that the monthly NDVI and multi-year average spatial distribution of NDVI values in the three river source areas follow the same trend, with the NDVI values in the Lancang and Nujiang river basins being significantly larger than those in the Yangtze river basin; while the spatial distribution of NDVI annual change rates in the three river source areas is the opposite, with the annual NDVI change rates in the Yangtze river source area being better than those in the Lancang and Nujiang river basins.

Enhanced aridity in the source region of the Yangtze River since 5.8 ka revealed by the sediments of Saiyong Co

The Yangtze River is a major component of the ‘Asian Water Tower’ and it provides freshwater resources for hundreds of millions of people in East Asia. Hence, climatic and environmental changes in the source region of the Yangtze River (SRYR) are of major significance for understanding changes in the status of its freshwater resources. However, due to the contradictory results shown by the available paleoclimatic records from the SRYR and neighboring regions, it remains unclear how the regional climate and hydrology have evolved since the middle Holocene. Here, we present records of hydrological variations based on multiple proxies (grain size, scanned micro-scale X-ray fluorescence (XRF) element composition, and loss on ignition (LOI)) of the sediments of alpine lake Saiyong Co, with the aim of reconstructing hydrological changes in the SRYR since 5.8 ka. The first principal component (PC1) of the XRF scanned element record is dominated by Ti, Fe and K, representing terrigenous inputs from the catchment. The LOI profile shows an inverse pattern of variation to that of PC1, suggesting that the sedimentary organic matter is primarily derived from aquatic plants. Since 5.8 ka the overall decrease in sample scores on PC1 and the increasing LOI, together with the grain-size based lake-level record, indicate an overall drying trend in SRYR. Furthermore, several major droughts are recorded, at ∼4.0 ka, ∼2.8 ka and ∼1.8 ka. The hydrological variations at Saiyong Co are supported by multiple records from the SRYR, suggesting that millennial-scale environmental variations were regionally synchronous and were influenced by Northern Hemisphere summer insolation and movement of the intertropical convergence zone.

Vegetation Index Reconstruction and Linkage with Drought for the Source Region of the Yangtze River Based on Tree-ring Data

Vegetation Index Reconstruction and Linkage with Drought for the Source Region of the Yangtze River Based on Tree-ring Data

Response of hydrological systems to the intensity of ecological engineering

The rapid global construction of ecological engineering has had an important impact on hydrological processes, especially in China. However, previous studies have largely regarded the hydrological system as a “black box” and have formed conclusions by comparing changes before and after ecological engineering; additionally, managers have assumed that the intensity of ecological engineering (IEE) is proportional to the hydrological system effect. The influence processes and mechanisms of the IEE on hydrological systems are unclear. Here, the source region of the Yangtze River (SRYR) in China was adopted as the empirical research area. Based on various data, such as DEM, soil, land use and climate data from 1980 to 1987 and 2004–2015, a Soil and Water Assessment Tool (SWAT) model was constructed, and the response of the hydrological system to the IEE was quantitatively explored. The results showed that the IEE generally displayed an increasing trend, increasing from 10.209 in 2005 to 10.649 in 2015. There was no linear relationship between the IEE and hydrological effects, and the hydrological effects did not increase with increasing IEE but did exhibit obvious stages. Specifically, the four phases – the lag phase, transition phase, sensitive phase, and adaptive phase – had different hydrological response characteristics, sensitivities, structures, and functions. Based on the feedback of the hydrological system, ecological engineering managers should abandon the incorrect assumption of a linear relationship between the two and realize that there is usually a lag phase in the early implementation of ecological engineering that requires a continuous increase in the IEE. Additionally, managers should choose the appropriate IEE, evaluation nodes and periods and prioritize the most sensitive hydrological variables in different stages based on the evaluation purpose and hydrological response, thereby improving the efficiency of ecological engineering and realizing the original goal of ecological protection and restoration.

Paleoclimate changes over the past 13,000 years recorded by Chibuzhang Co sediments in the source region of the Yangtze River, China

Climate change characteristics in the Qinghai-Tibetan Plateau (QTP) exhibit spatial differences. These differences are due to different large circulation systems, comprising Asian summer monsoons and mid-latitude Westerlies. However, the paleoclimate pattern at the transition zone between the two systems existing since the Late Glacial remains unclear. We present a 13,000-year high-resolution record of climate change and monsoon effects in the source region of the Yangtze River at the modern limit of the Indian Summer Monsoon (ISM) influence, which lies in the interaction zone with the Westerlies. Multi-proxy records—such as grain size (GS), total inorganic carbon (TIC) and element geochemistry—suggest four stages of paleoclimate change since the Late Glacial: 1) relatively cold in the Late Glacial, 2) warm-wet conditions in the early Holocene, 3) cool-dry conditions in the mid- and late Holocene and 4) a warming and wetting trend over the last 2000 years. Correspondingly, the lake experienced a shallow-water phase in the Late Glacial and a deep-lake phase during the Holocene. The cold Younger Dryas (YD) event occurred from 12.7 to 11.0 cal. kyr BP in the core, with extremely low total organic carbon (TOC) and coarse GS. In contrast, the Holocene Megathermal occurred between 10.0 and 9.1 cal. kyr BP, as recorded by the TOC maxima, which had a finer grain size. In this study, the TIC (plus the XRF-Ca and Ca/Si ratio) reflected the combined effects of biochemical processes (e.g., algal photosynthesis) and hydrological changes (e.g., precipitation, evaporation and runoff). Comparisons between regional records and reconstructed paleoclimate indexes suggested that the studied area's effective moisture pattern mostly followed fluctuations in the ISM-dominated region. The monsoonal circulation drove the paleoclimate variations on the central QTP since the Late Glacial, mainly controlled by enhanced summer insolation until the mid-Holocene. Further, the effective moisture variation was influenced by the August insolation (increased evaporation), on which the Westerlies effect (related to intensely cold air) and the meltwater runoff were later superimposed. Recently, the hydro-climatic conditions have acquired a temperate-humid status in the study area, which likely approaches that in the early Holocene's late phase. Therefore, the paleoclimate pattern of the source region of the Yangtze River exhibits a transitional nature (phase) between two circulation regions during the Holocene.

Distribution characteristics, enrichment patterns and health risk assessment of dissolved trace elements in river water in the source region of the Yangtze River

Abstract The security of water environment in the source region of the Yangtze River (SRYR) is vital to the water environment security of the whole basin. The results showed that the rivers in the SRYR were weakly alkaline and the values of total solid solubility (TDS), electrical conductivity (EC), turbidity concentration and salinity were higher than the values in the middle and lower reaches of the Yangtze River. The results showed that the dissolved trace elements detected displayed obvious regional distribution characteristics, showing a high concentration trend in the Chumar River, low in the Dangqu, and middle in the Tong River. All water quality indexes in the SRYR met the surface water environmental quality standard of class II based on GB 3838-2002 except Hg, while the average concentration of As exceeded 10 μg/L. The main enrichment elements in the SRYR were Li, Se, As and Pb, and their concentrations were far higher than the average concentration of the world rivers. Moreover, the HI and HQingrstion of children caused by As in the SRYR were greater than 1. This study could provide basic data for water environment protection and water resource management in the SRYR.

Local and geographical factors jointly drive elevational patterns of phytoplankton in the source region of the Yangtze River, China

AbstractLittle information about biodiversity patterns in high‐elevation aquatic systems has been gathered, even though these patterns are important for understanding the impacts of human activities. The source region of the Yangtze River, a typical alpine zone with vulnerable and sensitive ecosystems, was selected. Phytoplankton, which play a critical functional role as freshwater primary producers, serve as an important ecological indicator of aquatic systems. Here, systematic surveys on the water environment and phytoplankton were carried out to examine how the phytoplankton community varies with elevation based on hypothesized structural equation models (SEMs) in 10 typical rivers of the Yangtze River source region in March and October 2018. In total, 58 species of phytoplankton belonging to 28 genera were identified. The relationship between species abundance and elevation for phytoplankton showed unimodal elevational patterns. The results of the SEMs showed that all studied aspects affecting the phytoplankton community were directly or indirectly associated with elevation. The synergistic effects of human activities and basic environmental factors (terrestrial productivity and slope gradient) were the drivers affecting the phytoplankton community in the Yangtze River source region. Climate, topography, human activities and other factors are significantly different with changes in elevation, resulting in significant differences in the structure of aquatic communities at different elevations. Human activities were the major drivers affecting the phytoplankton community along the elevational gradient. As the elevation decreased, the disturbances to aquatic ecosystems caused by human activities intensified in the study area.

Spatiotemporal variations in frozen ground and their impacts on hydrological components in the source region of the Yangtze River

The source region of the Yangtze River (SRYR), located on the eastern Tibetan Plateau, is an essential part of the Asian Water Tower and plays an important role in the downstream water resources. Significant changes in frozen ground caused by increases in air temperature have been widely reported in the past several decades, which has greatly affected regional runoff. This study evaluated the spatiotemporal variations in frozen ground and hydrological components by utilizing a geomorphology-based eco-hydrological model (GBEHM) and investigated the reasons for runoff changes based on the Budyko framework. The results showed that the area with an elevation range of 4700–4800 m located in the permafrost region was the main source area of runoff generation from 1981 to 2015. Compared with the permafrost region, the seasonally frozen ground (SFG) region had a larger ratio of annual evapotranspiration to annual precipitation, although the aridity indices in the two regions were very similar. From 1981 to 2015, the mean value of the maximum frozen depth of SFG (MFDSFG) decreased by 12.3 cm/10 a and the mean value of the active layer thickness (ALT) of permafrost increased by 4.2 cm/10 a. The annual runoff in the SFG region decreased, while that in the permafrost region increased. Runoff change was more sensitive to precipitation change in the higher altitude regions that were mainly covered by permafrost than in the lower altitude regions that were mainly covered by the SFG, while the evapotranspiration change in the transition zone was more sensitive to climate change. An abrupt change in the annual runoff time series was detected in 1989, 2004, and 2004 in the SFG region, the permafrost region and the entire SRYR, respectively, and the annual runoff change from period 1 (1981 to change point) to period 2 (change point + 1 to 2015) were −25.7 mm, 33.8 mm and 25.8 mm respectively. Frozen ground degradation contributed changes of −15.0 mm, −8.8 mm and −11.6 mm to the annual runoff in the SFG region, the permafrost region and the entire SRYR, respectively. This result implied that frozen ground degradation had a negative impact on regional runoff in the SRYR. These findings deepen our understanding of frozen ground and its hydrological changes and are helpful for water resource management in the SRYR.

Estimation of glacier mass loss and its contribution to river runoff in the source region of the Yangtze River during 2000–2018

With rapid climatic warming, glaciers in the source region of the Yangtze River (SRYR) generally experienced apparent terminus retreats over the past several decades. However, the influence of glacier melting in the river runoff of the SRYR remains poorly known due to lack of glacier mass balance measurements. In this study, we derived the glacier mass changes of the SRYR in 2000–2018 by comparing the digital elevation models (DEMs) produced from ZiYuan-3 tri-stereo scenes with the SRTM DEM. Glacier mass balances were spatially heterogeneous (range from −0.55 ± 0.12 to −0.14 ± 0.05 m w.e. yr−1) in the SRYR, which may be mainly attributed to the spatial difference in snowfall variation. Overall, the glacier mass loss of −0.343 ± 0.055 Gt yr−1 was estimated for the entire SRYR. By using the hydrological data recorded by the Zhimenda station, we calculated the annual runoff of 17.84 Gt yr−1 between 2000 and 2018. Therefore, the contribution of glacier mass loss to the river runoff of the SRYR was only 1.9 ± 0.3% in 2000–2018. Our results reveal that glacier melting was not the major water resource in the SRYR during recent decades.

Precipitation chemistry in the Source Region of the Yangtze River

A study of ions sources and water vapor sources was carried out from April 1, 2016 to October 31, 2018, at Zhimenda(ZMD), Qumalai(QML) and Tuotuohe(TTH) in the source region of the Yangtze River to obtain preliminary quantitative results for the contributions of the ion and water vapor sources. In the study, 489 precipitation samples analyzed for pH, EC, and ionic concentrations were evaluated by using neutralization factor analysis, factor analysis, and trajectory analysis. The results revealed that Na+ was derived mainly from crustal sources. However, K+, Mg2+, and Ca2+ were only mainly controlled by crustal sources, with contribution rates of 93.60%, 58.88%, and 98.10%, respectively. Marine sources made the greatest contribution to Cl− (99.03%). The most important contributor of NO3− (99.52%) and SO42− (83.23%) was anthropogenic sources. F− was mainly controlled by crustal sources and anthropogenic sources. Although there were different water vapor paths in different seasons at different sample sites, water vapor in the study area was mainly controlled by westerly circulation and monsoon circulation. The largest contributions of westerly circulation were for Cl− and K+, whereas monsoon circulation mainly contributed the ionic concentration of NH4+. However, the largest number of ions was contributed by a westerly circulation–monsoon circulation pattern. These ions were F−, NO2−, SO42−, Li+, Na+, Mg2+, and Ca2+, with contributions of 51.20%, 41.60%, 42.30%, 53.68%, 40.36%, 40.22%, and 34.20% of the total, respectively. NO3− was mainly contributed by westerly circulation–regional circulation.

Geochemical evidence of ions’ sources and influences of meteorological factors on hydrochemistry of glacier snow meltwater in the source region of the Yangtze River

This study discusses the hydrochemical components of glacier snow meltwater using the correlation analysis, factor analysis, enrichment factor, and the Gibbs diagram. Water samples were collected from June to September in 2016 and 2017. The results obtained the monthly changes for anions and cations in Yuzhufeng (YZG) and Jianggudiru Glacier (JGG) were notably, with highest concentration of ions recorded in September. The effect of seasonal variation on the chemical characteristics of glacier snow meltwater was determined by studying the interaction between the glacier snow meltwater and the control source. The change of hydrochemical characteristics and hydrological cycle is positive in cold areas under the climate warming. The hydrochemical characteristics of glacier snow meltwater in study area were mainly contributed by crustal sources such as evaporates and carbonate rocks. Certainly, a small part of human input cannot be ignored. There was a close relationship between temperature and hydrochemical characteristics, and the relationship between meteorological factors and other ions except K+ was not clear. It is concluded that the water chemistry of glacier snow meltwater in the Alpine region is mainly controlled by the temperature factor-led ablation.

Impact of the Westerly Jet on Rainfall/Runoff in the Source Region of the Yangtze River during the Flood Season

Based on runoff data collected at the Zhimenda station, reanalysis data from the National Centers of Environmental Prediction/National Centers of Atmospheric Research (NCEP/NCAR), and observation data from ground stations in China, this study analyzes the characteristics of changes in runoff in the source region of the Yangtze River (SRYR) during the flood season (from July to September), the relationship between runoff and antecedent rainfall, and the impact of the westerly jet (WJ) on rainfall in the coastal zone of the SRYR. The results show the following. The runoff in the SRYR displays a significant interannual and interdecadal variability. The runoff in the SRYR during the flood season is most closely related to 15-day (June 16 to September 15) antecedent rainfall in the coastal zone of the SRYR. In turn, the antecedent rainfall in the coastal zone of the SRYR is mainly affected by the intensity of the simultaneous WJ over a key region (55–85°E, 45–55°N). When the intensity of the WJ over the key region is greater (less) than normal,the jet position moves northward (southward), and the easterly (westerly) wind anomalies over the region to the west of the SRYR become unfavorable (favorable) to the transport of water vapor from high-latitude regions to the SRYR. In addition, the southerly wind over the equatorial region cannot (can) easily advance northward, which is unfavorable (favorable) to the northward transport of water vapor from the low-latitude ocean. Hence, these conditions result in a decrease (increase) in the water vapor content in the SRYR. Furthermore, the convergence (divergence) anomalies in the upper level and the divergence (convergence) anomalies in the lower level result in the descending (ascending) motion over the SRYR. These factors decrease (increase) the rainfall, thereby decreasing (increasing) the runoff in the SRYR during the flood season.

Characteristics and Influencing Factors of Stable Hydrogen and Oxygen Isotopes in Groundwater in the Permafrost Region of the Source Region of the Yangtze River

We use 84 rainfall samples collected during June to September 2017 from the Dongkemadi basin, source region of the Yangtze River, China, to analyze the characteristics and influencing factors of stable isotopes in groundwater, and further discuss the groundwater recharge sources. The results showed that the range of groundwater δ18 O values in this permafrost region varied from -15.3‰ to -12.5‰ (mean -14.0‰). The range of δD values in groundwater varied from -108.9‰ to -91.7‰ (mean -100.2‰). Compared with local atmospheric precipitation, groundwater isotopes were relatively enriched. The slope and intercept of the groundwater line (GL) in the study area were both lower than of those of the global and local meteoric water lines (GMWL and LMWL), thus indicating that groundwater in the study area was subjected to evaporation during rainfall recharge of groundwater. The d-excess values of groundwater varied from 4.9‰ to 25.0‰ (mean 11.6‰), which was close to the average d-excess value determined for global average rainfall (10‰), but lower than that of rainfall in the study area (15.1‰). The influencing factors on the composition and variation of groundwater isotopes were different in different periods. The permafrost active layer was relatively thin during periods of increasing air temperature, and groundwater isotopes were significantly affected by air temperature. A temperature decrease during the latter part of the sampling period, when the thickness of the permafrost active layer was still increasing, further increased the retention time of infiltrating rainfall in the soil, thereby eventually leading to evaporation that strengthened the enrichment of heavy isotopes in the groundwater. According to the topographic characteristics of the Dongkemadi basin, the isotopic characteristics of the groundwater, and the factors influencing the isotopic composition, we conclude that rainfall was the main source of groundwater recharge. The results of this study provide a scientific basis for studying water cycle processes in the permafrost regions of the source region of the Yangtze River.

Modeling past and future variation of glaciers in the Dongkemadi Ice Field on central Tibetan Plateau from 1989 to 2050

ABSTRACT Glacier mass balance change is among the best indicators of glacier response to climate change. Due to its inaccessibility and limited observation, little is known about the change to the Dongkemadi Ice Field (DIF) in the Tanggula Mountains located in the source region of the Yangtze River in central Tibetan Plateau. Here, an enhanced temperature index–based glacier model considering glacier area change was applied to study the temporal–spatial variation in mass balance on the DIF from 1989 to 2012 and to assess its response to climate change. The model was forced by reconstructed temperature and precipitation from adjacent national meteorological stations and validated by comparing with field observations from the Xiao Dongkemadi Glacier (XDG). Results show that the simulated mass balance is in good agreement with the observations (R 2 = 0.75, p < .001), and the model can reasonably reproduce well the glacier mass change. Then the model was applied to twenty individual glaciers in DIF and forced by the high-resolution regional climate model (RegCM3) from 2013 to 2050 to project their further variation. In the future, the mass balance of glaciers in DIF shows a continuously negative trend with a linear rate of −0.16 m water equivalent (w.e.) a−1 in representative concentration pathway (RCP) 4.5 and −0.35 m w.e. a−1 in RCP 8.5. Most of the glaciers’ equilibrium line altitudes (ELAs) will reach or exceed their maximum elevation after the 2030s. By coupling a modified volume–area scaling method with the mass balance model, results showed that areas of the individual glaciers in DIF will lose about 12.10 to 30.66 percent under RCP4.5 and 14.06 to 38.76 percent under RCP8.5, and the volume of the DIF will lose about 1.18 km3 in RCP4.5 and 1.44 km3 in RCP8.5 by the end of 2050. In addition, the terminuses of glaciers experienced the largest percentage losses and most of the glaciers’ front position will reach ~5,520 m a.s.l. in RCP 4.5 and 5,570 m a.s.l. in RCP 8.5, the latter of which is nearly close to the DIF average ELA in 1989. The clearly increasing summer air temperature may be the main reason for glacier shrinkage in the DIF. If the warming trend continues, glaciers in DIF may further retreat with continued glacial melt or even mostly disappear by the end of the century.

Camera-trapping survey of the diversity of mammals and birds in the Tuotuo River basin of the source region of the Yangtze River

Camera-trapping survey of the diversity of mammals and birds in the Tuotuo River basin of the source region of the Yangtze River

Runoff dominated by supra-permafrost water in the source region of the Yangtze river using environmental isotopes

Accelerating multiphase water transformation affects runoff processes and components greatly and have changed the spatiotemporal patterns of water resources in the Third Polar Region. The source region of the Yangtze River is one location where accelerated warming has resulted in the gradual extension of the ablation period since 1990. This has caused the acceleration of multiphase water transformation, characterized by increases in the rate of glacial retreat, maximum freezing depth, and annual actual evapotranspiration and by decreased snowfall. In response, the total runoff increased by 53% at the Tuotuohe national hydrological station (TTH) and 6% at the Zhimenda national hydrological station (ZMD) during the periods 1961–1990 and 1991–2017, respectively. Under these conditions, runoff components were being determined based on stable isotope tracing. Substantial seasonal differences in δ18O (δD) among precipitation, river water, supra-permafrost water, and glaciers snow meltwater indicate that the runoff has been replenished by multiple components, and that these first infiltrate the ground, becoming part of the groundwater, and then recharge river water. Supra-permafrost water rather than precipitation now dominates river water. Based on the end-member mixing analysis model, supra-permafrost water, precipitation, and glaciers snow meltwater accounted for 51%, 26%, and 23% of river water at the TTH station from June 2016 to May 2018; the corresponding values at the ZMD station were 49%, 34%, and 17%. Additionally, there are also differences in the seasonal contributions of runoff components to river water. Seasonal variations in the freezing and thawing of the active layer directly trigger the runoff process. Future research should be focused on determining the mechanisms underlying the dynamics of precipitation-supra-permafrost water-runoff, which will aid the assessment of the impacts of an unstable Asian Water Tower on water resources.

Multi-Space Seasonal Precipitation Prediction Model Applied to the Source Region of the Yangtze River, China

This paper developed a multi-space prediction model for seasonal precipitation using a high-resolution grid dataset (0.5° × 0.5°) together with climate indices. The model is based on principal component analyses (PCA) and artificial neural networks (ANN). Trend analyses show that mean annual and seasonal precipitation in the area is increasing depending on spatial location. For this reason, a multi-space model is especially suited for prediction purposes. The PCA-ANN model was examined using a 64-grid mesh over the source region of the Yangtze River (SRYR) and was compared to a traditional multiple regression model with a three-fold cross-validation method. Seasonal precipitation anomalies (1961–2015) were converted using PCA into principal components. Hierarchical lag relationships between principal components and each potential predictor were identified by Spearman rank correlation analyses. The performance was compared to observed precipitation and evaluated using mean absolute error, root mean squared error, and correlation coefficient. The proposed PCA-ANN model provides accurate seasonal precipitation prediction that is better than traditional regression techniques. The prediction results displayed good agreement with observations for all seasons with correlation coefficients in excess of 0.6 for all spatial locations.

Characterizing braided rivers in two nested watersheds in the Source Region of the Yangtze River on the Qinghai-Tibet Plateau

Large and complex braided channels (>1 km wide) in the Source Region of the Yangtze River (SRYR) on the Qinghai-Tibet Plateau, China, are characterized by a unique alpine environment with very high elevations and glacier sources. Yet, little is known about the morphological complexity and changes of large braided channels owing to the scarcity of hydrological and topographical data. In this study, we provided the first insight into these issues using compiled long-term (several decades) climatic and suspended sediment data, and Landsat images of braided channels in two nested headwater watersheds (i.e., Tuotuo and Tongtian river watersheds) in the SRYR. Analysis of annual and monthly mean temperature, precipitation, and water discharges illustrated the nature of the hydrological regime and their response to glacier melting in the two watersheds. Examination of annual mean suspended sediment loads and concentrations (C) led to two sediment rating curves and generally similar C values between the two watersheds. Among a suite of morphological indices for braided rivers, braiding intensity may be quantified using four different ones. After comparing the indices, we showed that they had similar ability of characterizing braiding patterns and adopted branch count index (BIT3) for further analysis. We found that BIT3 was linearly correlated with active valley width (WR) during both flood and dry seasons for the 17 selected braided reaches distributed within the two nested watersheds. In addition, braiding density, defined as the ratio of BIT3 to WR, remained approximately unchanged irrespective of elevations and locations of these reaches, indicating clearly that morphological structures of braided channels are spatially uniform in the SRYR. Along the main channels of the two nested watersheds over the entire study period, BIT3 always reached the maximum as RW, defined as the ratio of water body to exposed active riverbed area, was around 0.43. Furthermore, RW was always positively correlated with the associated water discharge (Q). Variable degrees of braiding adjustment in response to changes of hydrological regime were represented by hysteresis loops between BIT3 and Q. These results revealed relatively homogeneous morphologic properties of braided channels across the two nested watersheds and provided an important benchmark for future morphodynamic research on braided rivers in the SRYR.

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+-SO42-, 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-, SO42-, Mg2+, Ca2+, and between precipitation, relative humidity, and SO42- 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.