Spatial variation, source identification, and quality assessment of surface water geochemical composition in the Indus River Basin, Pakistan

Water quality assessment of Upper Ganga and Yamuna river systems during COVID-19 pandemic-induced lockdown: imprints of river rejuvenation

Clean river water is an essential and life-sustaining asset for all living organisms. The upper Ganga and Yamuna river system has shown signs of rejuvenation and tremendous improvement in the water quality following the nationwide lockdown due to the coronavirus pandemic. All the industrial and commercial activity was shut down, and there was negligible wastewater discharge from the industries. This article addresses the water quality assessment from the study area, which is based on the original data of physical parameters, major and trace elements, and stable isotopes (hydrogen and oxygen) systematics during the nationwide lockdown. The impact of the lockdown could be seen in terms of an increase in dissolved oxygen (DO). Water samples were collected from the Upper Ganga and Yamuna river basins (Alaknanda, Bhagirathi, and Tons rivers) during an eight-week lockdown in Uttarakhand, India. We discussed the signs of rejuvenation of riverine based on physical parameters, major ions, trace elements, isotopic ratios, and water pollution index (WPI). Results reveal that the water quality of the entire upper basins of the Ganga has significantly improved by 93%, reflecting the signs of self-rejuvenation of the rivers. Multivariate analysis suggests a negative factor loading for an anthropogenic element (NO 3 - ), implying that they contribute little to the river water during the lockdown. Further, bicarbonate (HCO 3 - ) is a dominant element in both river basins. The geochemical facies are mainly characterized by the (Ca 2 + : Mg 2 + : H C O 3 - ) type of water, suggesting that silicate rock weathering dominates with little influence from carbonate weathering in the area. The positive factor loadings of some cations, likeHCO 3 - ,Ca 2 + , andMg 2 + reflect their strong association with the source of origin in the lockdown phases. Stable isotopic reveals that the glaciated region contributed the most to the river basin, as evidenced by the low d-excess in riverine water compared to anthropogenic contributions. Rivers can self-rejuvenate if issues of human influence and anthropogenic activities are adequately resolved and underline our responsibility for purifying the ecosystem. We observed that this improvement in the river water quality will take a shorter time, and quality will deteriorate again when commercial and industrial activity resumes.

Trace elements in the Upper Indus River Basin (UIRB) of Western Himalayas: Quantification, sources modeling, and impacts

This study conducted a comprehensive analysis of trace element concentrations in the Upper Indus River Basin (UIRB), a glacier-fed region in the Western Himalayas (WH), aiming to discern their environmental and anthropogenic sources and implications. Despite limited prior data, 69 samples were collected in 2019 from diverse sources within the UIRB, including mainstream, tributaries, and groundwater, to assess trace element concentrations. Enrichment factor (EF) results and comparisons with regional and global averages suggest that rising levels of Zn, Cd, and As may pose safety concerns for drinking water quality. Advanced multivariate statistical techniques such as principal component analysis (PCA), absolute principal component scores (APCS-MLR), Monte Carlo simulation (MCS), etc were applied to estimate the associated human health hazards and also identified key sources of trace elements. The 95th percentile of the MCS results indicates that the estimated total cancer risk for children is significantly greater than (>1000 times) the USEPA's acceptable risk threshold of 1.0 × 10-6. The results classified most of the trace elements into two distinct groups: Group A (Li, Rb, Sr, U, Cs, V, Ni, TI, Sb, Mo, Ge), linked to geogenic sources, showed lower concentrations in the lower-middle river reaches, including tributaries and downstream regions. Group B (Pb, Nb, Cr, Zn, Be, Al, Th, Ga, Cu, Co), influenced by both geogenic and anthropogenic activities, exhibited higher concentrations near urban centers and midstream areas, aligning with increased municipal waste and agricultural activities. Furthermore, APCS-MLR source apportionment indicated that trace elements originated from natural geogenic processes, including rock-water interactions and mineral dissolution, as well as anthropogenic activities. These findings underscore the need for targeted measures to mitigate anthropogenic impacts and safeguard water resources for communities along the IRB and WH.

Identification of hydrochemical fingerprints, quality and formation dynamics of groundwater in western high Himalayas

Identifying hydrochemical fingerprints of groundwater is a challenge in areas with complex geological settings. This study takes the Gilgit-Baltistan, a complex geological area in west high Himalayas, Pakistan, as the study area to get insights into the hydrochemcial genesis and quality of groundwater in complex geological mountainous regions. A total of 53 samples were collected across the area to determine the hydrochemical characteristics and formation of groundwater. Results revealed groundwater there is characterized by slightly alkaline and soft fresh feature. Groundwater is dominated by the hydrochemical facies of HCO3·SO4-Ca·Mg type. The factor method yields three components (PCs) of principal component analysis, which together explain 75.71% of the total variances. The positive correlation of EC, TDS, Ca2+, SO42-, K+ in PC1, and NO3-, Cl- in PC2 indicate that a combination of natural and anthropogenic activities influences groundwater hydrochemistry. Water-rock interaction is the main mechanism governing the natural hydrochemistry of groundwater. The negative correlation of Cl-, SO42-, Ca2+, and Na+ with NDVI attributes to inorganic salt uptake by plant roots. Groundwater chemical composition is also affected by the type of land use. Groundwater is characterized as excellent and good water quality based on the entropy-weighted water quality index assessment, and is suitable for drinking purposes except for very few samples, while aqueous fluoride would pose potential health threats to water consumers in western high Himalayas, and infants are most at risk compared to other populations. This study will help to deepen the hydrochemial formation mechanism and exploitation suitability of groundwater resources in the mountainous areas that undergone the combined actions of nature and human activities, and provide insights into the characteristics of water environmental quality in western Himalayas area.

Groundwater chemistry and entropy weighted water quality index of tsunami affected and ecologically sensitive coastal region of India

Quality groundwater is the most essential prerequisite for the better livelihood of the coastal villages and a vital resource for a safe living. Seawater interaction and coastal inundation modify hydro geochemical cycles leading to gross utility as a challenge. Poor quality water intake causes diseases and seriously affects human health. In this study, the suitability of shallow drinking water sources (10-15 m) has been studied with a focus on coastal village in south west of India (Alappad coast, Kollam, Kerala) which is a host of huge placer mineral reserve of the country. This coastal stretch has good deposition of Late Quaternary sediments of heavy mineral placers subjected to severe seawater interactions. Mineralogically, garnet and heavy minerals comprises the beaches and most coastal plains of the Alappad. A concerted geological process where moving water and waves causes erosion, leads to lowering of the earth's surface -is prominent in this fragmented land. This study critically evaluates the temporal-spatial impact of these interactions in an age of varying climatic conditions and hence for reference beyond. Water quality index analysis has been attempted using the entropy weighted water quality index (EWQI) method for a total of 45 samples (15 samples season-wise). It aims to ascertain better choices of groundwater sources for domestic uses for isolated settlers endowed with estuaries, and old coastal plains with barrier beaches. Irrigation suitability was evaluated using sodium adsorption ratio (SAR) and Na%. Observed EWQ Indices (38.2 ± 14.5) for post-monsoon (80% samples), (66.1 ± 77.7) for monsoon (66% samples), and (71.4 ± 71.3) for pre-monsoon (53% samples) fall in excellent category. Post-monsoon is most favoured for a better quality groundwater as evidenced by WQI of 80% among the samples tested. Ca-HCO3 is the dominant hydrochemical type observed. The mean value of iron (0.9 ± 1.3 mg/L) exceeded the permissible limit of 0.3 mg/L during monsoon season due to mineral-water interactions. In pre-monsoon season the parameters Na+ (95.9 ± 200.7 mg/L), Cl- (173.4 ± 510.2 mg/L), EC (1559.3 ± 2510.6 μS/cm), and TDS (492.5 ± 629.7 mg/L) were observed in higher ranges. Significant correlation (p < 0.05) prevailed between EWQI, and parameters-conductivity (0.75), TDS (0.75), Iron (0.59), Ca2+ (0.66), and Mg2+ (0.74). Principal component analysis (PCA) on chemical parameters accounted for the total variance of 84.2% in pre-monsoon, 89.9% in monsoon and 82.9% in post-monsoon. Groundwater quality is influenced by geochemical processes, salt intrusion, and human activities like fertiliser application and domestic sewage discharge. Hierarchical cluster analysis (HCA) grouped the samples into three clusters. Cluster 3 represents poor quality water (13%) in pre-monsoon (EWQI ranged 32.2-192.7), and monsoon (EWQI ranged 171.8-309.7). Cluster 3 in post-monsoon (20%) indicating good water quality (EWQI ranged 51.4-72.6). Ultimate finding is that post-monsoon groundwater is more suitable for drinking and domestic purposes for the selected coastal area.

Hydrochemistry, water quality and health risk assessment of streams in Bismil plain, an important agricultural area in southeast Türkiye

In this study, the water quality of Ambar, Kuruçay, Pamuk and Salat streams, which are the important tributaries of the Tigris River in the Bismil Plain (Diyarbakır, Türkiye) was assessed using 19 physicochemical parameters. Except for a few exceptions, all parameters in the water samples taken from the streams were below the drinking water limit values. Kuruçay Stream had significantly higher TOC, Na+, NO3-, NO2-, Cl- and SO42- levels and lower DO levels than other streams (p < 0.05) due to sewage water discharges, animal manure storage areas near the stream and irrigation return flows. In all streams, Ca-HCO3 was dominant water type. Gibbs diagram indicated that rock weathering is the major factor controlling the hydrochemistry of the streams. According to the results of water quality index (WQI), all sampling stations of Ambar, Pamuk and Salat streams and K1 station of Kuruçay Stream had "good" quality water for drinking purposes, while K2 station of Kuruçay Stream had "poor" quality water. Irrigation indices (permeability index, sodium percentage, magnesium hazard, residual sodium carbonate, Kelley's ratio, sodium adsorption ratio and potential salinity) revealed that all water samples taken from the streams were suitable for irrigation. The water samples from Ambar, Pamuk and Salat streams were in the C2S1 (medium salinity and low alkalinity) category, while the samples from Kuruçay Stream were in the C2S1 and C3S1 (high salinity and low alkalinity) categories. Both hazard quotient and hazard index values of NO3-N, NO2-N and F- for children and adults were found below 1, indicating that adverse health effects are not expected from exposure to these contaminants via water ingestion and dermal contact. The findings of this study showed that the water quality status of Kuruçay Stream is worse as it receives large amounts of irrigation return flows compared to other streams.

The global scenario of hydrogeochemical research on glacier meltwater: a bibliometric and visualization analysis

In recent years, there has been a rapid increase in scientific research into hydrogeochemical research on glacier meltwater. Nevertheless, systematic and quantitative analyses are lacking to investigate how this research field has developed over the years. As a result, this study is aimed at examining and evaluating recent research trends and frontiers in hydrogeochemical research on glacier meltwater throughout the previous 20 years (2002-2022) and at locating collaboration networks. This is the first global-scale study, and visualization of the key hotspots and trends in hydrogeochemical research has been presented here. The Web of Science Core Collection (WoSCC) database aided in the retrieval of research publications related to hydrogeochemical research of glacier meltwater published between 2002 and 2022. From the beginning of 2002 till July 2022, 6035 publications on the hydrogeochemical study of glacier meltwater were compiled. The result revealed that the number of published papers on the hydrogeochemical study of glacier meltwater at higher altitudes had grown exponentially, with USA and China being the main research countries. The number of publications produced from the USA and China accounts for about half (50%) of all publications from the top 10 countries. Kang SC, Schwikowski M, and Tranter M are highly influential authors in hydrogeochemical research of glacier meltwater. However, the research from developed nations, particularly the United States, emphasizes hydrogeochemical research more than those from developing countries. In addition, the research on glacier meltwater's role in streamflow components is limited, particularly in the high-altitude regions and needs to be enhanced.

Hydrochemical variations and driving mechanisms in a large linked river-irrigation-lake system

A linked river-irrigation-lake system exhibits intricate and dynamic hydrochemical variations, closely related to changes in natural conditions and anthropogenic activities. However, little is known about the sources, migration and transformation of hydrochemical composition, and the driving mechanisms, in such systems. In this study, the hydrochemical characteristics and processes in the linked Yellow River-Hetao Irrigation District-Lake Ulansuhai system were studied, based on a comprehensive hydrochemical and stable isotope analysis of water samples collected during spring, summer, and autumn. The results showed that the water bodies in the system were weakly alkaline with a pH range of 8.05-8.49. The concentrations of hydrochemical ions showed an increasing trend in the water flow direction. Total dissolved solids (TDS) were less than 1000 mg/L (freshwater) in the Yellow River and the irrigation canals, and increased to more than 1800 mg/L (saltwater) in the drainage ditches and Lake Ulansuhai. The dominant hydrochemical types varied from SO₄•Cl-Ca•Mg and HCO₃-Ca•Mg types in the Yellow River and the irrigation canals to Cl-Na type in the drainage ditches and Lake Ulansuhai. The ion concentrations in the Yellow River, the irrigation canals, and the drainage ditches were highest during summer, while ion concentrations in Lake Ulansuhai were highest during spring. The hydrochemistry of the Yellow River and the irrigation canals was mainly affected by rock weathering, while evaporation was the principal controlling factor in the drainage ditches and Lake Ulansuhai. Water-rock interactions including the dissolution of evaporites and silicates, the precipitation of carbonates, and cation exchange were the main sources of hydrochemical compositions in this system. Anthropogenic inputs had a low impact on the hydrochemistry. Therefore, greater attention should be paid in future to hydrochemical variations, especially salt ions, in the management of linked river-irrigation-lake system water resources.

Understanding the hydrochemical functioning of glacierized catchments of the Upper Indus Basin in Ladakh, Indian Himalayas

Recent studies have endorsed that surface water chemical composition in the Himalayas is impacted by climate change-induced accelerated melting of glaciers. Chemical weathering dynamics in the Ladakh region is poorly understood, due to unavailability of in situ dataset. The aim of the present study is to investigate how the two distinct catchments (Lato and Stok) drive the meltwater chemistry of the Indus River and its tributary, in the Western Himalayas. Water samples were collected from two glaciated catchments (Lato and Stok), Chabe Nama (tributary) and the Indus River in Ladakh. The mildly alkaline pH (range 7.3-8.5) and fluctuating ionic trend of the meltwater samples reflected the distinct geology and weathering patterns of the Upper Indus Basin (UIB). Gibbs plot and mixing diagram revealed rock weathering outweighed evaporation and precipitation. The strong associations between Ca²⁺-HCO₃^-, Mg²⁺-HCO₃^-, Ca²⁺-Mg²⁺, Na⁺-HCO₃^-, and Mg²⁺-Na⁺ demonstrated carbonate rock weathering contributed to the major ion influx. Principal component analysis (PCA) marked carbonate and silicates as the most abundant minerals respectively. Chemical weathering patterns were predominantly controlled by percentage of glacierized area and basin runoff. Thus, Lato with the larger glacierized area (~ 25%) and higher runoff contributed low TDS, HCO₃^-, Ca²⁺, and Na⁺ and exhibited higher chemical weathering, whereas lower chemical weathering was evinced at Stok with the smaller glacierized area (~ 5%). In contrast, the carbonate weathering rate (CWR) of larger glacierized catchments (Lato) exhibits higher average value of 15.7 t/km²/year as compared to smaller glacierized catchment (Stok) with lower average value 6.69 t/km²/year. However, CWR is high in both the catchments compared to silicate weathering rate (SWR). For the first time, in situ datasets for stream water chemical characteristics have been generated for Lato and Stok glaciated catchments in Ladakh, to facilitate healthy ecosystems and livelihoods in the UIB.

Effects of agricultural activities on hydrochemistry in the Shiyang River Basin, China

Agricultural water accounts for more than 80% of the available water in arid areas. Agricultural activities have a great impact on surface water and groundwater. If the impact of agricultural activities on hydrochemistry is not prevented, the risk of water quality change in arid areas may be greatly intensified. Based on the hydrochemical data of the whole Shiyang River Basin from April 2014 to October 2019, this paper analyzes the impact of agricultural activities on hydrochemistry in the basin. The results show that (i) in the middle and lower reaches of farmland with high intensity of agricultural activities, the ion concentration of groundwater in summer and autumn is significantly higher than that in winter and spring due to the influence of irrigation; (ii) the runoff ion concentration in the backflow of the river reaches recharged by irrigation water is significantly higher than that of other reaches; (iii) due to strong evaporation, different types of reservoirs will lead to an overall increase in ion concentration, which is more obvious in plain reservoirs and river tail lakes. In addition, the reservoirs have a certain removal effect on nitrates.

Impacts of Stressors on Riparian Health Indicators in the Upper and Lower Indus River Basins in Pakistan

Riparian zones along rivers and streams provide ecosystem services that may change over time as disturbances increase and deteriorate these buffer zones globally. The effect of stressors on ecosystem services along the rivers in underdeveloped countries is unclear, which impacts the environment directly in the form of riparian health indicators (RHIs). This study fills this gap and measures the impact of stressors on RHIs (parameters of habitat, plant cover, regeneration, exotics, and erosion) in the Indus River basin (IRB) in Pakistan. Data on 11 stressors and 27 RHIs were collected using a field-based approach in 269 transects in the upper and lower Indus basins (UIB and LIB) in 2020 and analyzed using multivariate statistical methods. The Kruskal-Wallis tests (p < 0.05) indicated that RHIs varied significantly under the influence of stressors in the UIB and LIB. However, their highest mean values were found in the UIB. Principal component analysis revealed the key RHIs and stressors, which explained 62.50% and 77.10% of the variance, respectively. The Pearson correlation showed that stressors had greater impacts on RHIs in LIB (with r ranging from -0.42 to 0.56). Our results also showed that stressors affected RHI indices with r ranging from -0.39 to 0.50 (on habitat), -0.36 to 0.46 (on plant cover), -0.34 to 0.35 (on regeneration), -0.34 to 0.56 (on erosion), and -0.42 to 0.23 (on exotics). Furthermore, it was confirmed by the agglomerative hierarchical cluster that indices and sub-indices of RHIs and stressors differ across the UIB and LIB. These findings may serve as guidance for managers of large rivers and ecosystem service providers to minimize the environmental impact of stressors in terms of RHIs.

Hydrogeochemical characterization and water quality assessment in Altay, Xinjiang, northwest China

The safety of drinking and irrigation water is an issue of great concern worldwide. The rational development and utilization of water resources are vital for the economic and societal stability of Altay, an extremely arid area. In this study, three types of water samples (25 river waters, 10 groundwaters, 6 lake waters) were collected from main rivers and lakes in Altay and analyzed for electrical conductivity, total dissolved solids, pH, major ions (i.e., K⁺, Na⁺, Ca²⁺, Mg²⁺, HCO₃^-, Cl^-, SO₄^2-, NO₃^-, NO₂^-, F^-), and trace elements (i.e., Al, Li, B, Sc, Ti, Mn, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, I, Ba, U). The water quality index (WQI), hazard quotient, carcinogenic risk, Na percentage, and Na adsorption ratio were then calculated to evaluate the water quality for drinking and irrigation. The results showed that the main hydrochemical type of river waters and groundwaters was Ca-HCO₃, whereas that of lake water was mainly Na-SO₄. The WQIs (9.39-170.69) indicated that the water quality in Altay ranged from poor to excellent. The concentrations of As, Ni, and U need to be carefully monitored since their average carcinogenic risks (for all waters collected, for adults) reached 0.05686, 0.06801, and 0.14527 and exceeded the safety risk levels (10^-4-10^-6) by at least 568 times, 680 times, and 1452 times, respectively. The result of Na% and SAR indicated that lake waters (with Na% of 62.92 and SAR of 41.63) and groundwaters (with Na% of 37.88 and SAR of 5.58) in Altay were unsuitable for irrigation, while river water (with Na% of 29.24 and SAR of 3.33) could meet the irrigation quality requirements. The results of this study could help promote reasonable water resource use among three types of waters and population protection in Altay.

Key Factors Dominating the Groundwater Chemical Composition in a Grain Production Base: A Case Study of Muling–Xingkai Plain, Northeast China

Groundwater quality in the Muling–Xingkai Plain (MXP) is closely related to food security and human health. The chemical composition of groundwater in MXP has attracted great attention. A total of 168 groundwater samples were collected in MXP, and principal component analysis, chemical ion analysis and stable isotopic analysis were used to explore key factors affecting the chemical composition and hydrochemical evolution process of groundwater. Results show sources of chemical ions in groundwater are silicate minerals, carbonate minerals and domestic sewage. Domestic sewage is responsible for groundwater with high levels of Cl−, SO42− and NO3−, but a reduction environment can lead to groundwater with a high level of NH4+ due to nitrification. Human activity and soil media together influence groundwater chemical composition. Groundwater with a high level of chemical ions is mainly collected from wells near river channels, where coarse-textured soils are overlying aquifers. The black soil far away from river channels can retard the infiltration of wastewater. Agricultural activities do not directly lead to deterioration of groundwater qualities, and agricultural non-point-source pollution does not occur in MXP. Nearly 70% of the population in MXP is living in the southern plain, where the influence of sewage on groundwater chemical composition is obvious. Thus, shallow groundwater far away from river channels is the best choice for irrigation. Some measures should be implemented to control the discharge of domestic sewage for the protection of groundwater. In addition, it is necessary to avoid the transformation of the redox environment of groundwater in the northern plain.

Assessment of spatio-temporal variations of selected water quality parameters of Lake Ziway, Ethiopia using multivariate techniques

Excess agrochemicals input from agricultural activities and industrial effluent around Lake Ziway catchment can pose a serious threat on the lake ecosystem. Lake Ziway is a shallow freshwater lake found in the northern part of the Ethiopian Rift Valley. It is characterized as semi-arid to sub-humid type of climate. Expansions of the flower industry, widespread fisheries, intensive agricultural activities, fast population growth lead to deterioration of water quality and depletion of aquatic biota. The spatial and temporal variations of selected water quality parameters were evaluated using multivariate techniques. The data were collected from nine sampling stations during dry and wet seasonal basis for analysis of fifteen water quality parameters. The physicochemical parameters were measured in-situ with portable multimeter and nutrients were determined by following the standard procedures outlined in the American Public Health Association using UV/Visible spectrophotometer. Mean nutrient concentrations showed increasing trend in all seasons. These sites were also characterized by high electrical conductivity and total dissolved solid (TDS). All the nine sampling sites were categorized into three pollution levels according to their water quality features using cluster analysis (CA). Accordingly, sampling sites Fb and Ketar River (Kb) are highly and moderately polluted in both seasons, respectively. On the other hand, sampling sites at the center (C), Meki river mouth (Ma), Ketar river mouth (Ka), Meki River (Mb), Korekonch (K_o) and Fa in dry season and Ka, C, Ma, Ko, Bulbula river mouth (B) and Fa during wet season were less polluted. Principal component analysis (PCA) analysis also showed the pollutant sources were mainly from Fb during dry season Mb and Kb during wet season. The values of comprehensive pollution index illustrated the lake is moderately and slightly polluted in dry and wet seasons, respectively. Comparatively, the pollution status of the lake is high around floriculture effluent discharge site and at the two feeding rivers (Kb and Mb) due to increasing trends in agrochemical loads. In order to stop further deterioration of the lake water quality and to eventually restore the beneficial uses of the lake, management of agrochemicals in the lake catchments should be given urgent priority.

Effects of anthropogenic activities on hydrochemical characteristics of ground water of Da'an irrigation area in Western of Jilin Province

The groundwater environment changes under the influence of anthropogenic activities. Because of the construction of the Da'an irrigation area, the amount of irrigation and fertilizer there has changed. Achieving the coordinated development of groundwater resources and economic benefits requires a deeper understanding of the impact of the construction of irrigation areas on groundwater chemistry. In this study, the variations in groundwater chemistry characteristics were studied using statistics and hydrogeochemical methods. Further, the groundwater quality was assessed using the support vector machine method. The results show that the primary water chemistry type was the HCO3 - Ca - Mg type, with local Fe3+ and F- pollution. After the construction of irrigation area, the SO42-, HCO3-, K+  + Na+, and Ca2+ contents decreased, but the Cl- and Mg2+ contents increased. The main nitrogen source in phreatic water was anthropogenic activities, and the main pollution component was NH4+. After the construction of the irrigation area, the NH4+ concentration increased significantly, and the ratio of samples exceeding the standard increased by 37.5%. The over-standard regions spread to the northwest, east, and southeast of Da'an City and east and southeast of the irrigation area. The groundwater quality was predominantly grade IV and V, which accounted for an increase of 16.35%, widely distributed in the south, east, and southwest of the irrigation area and urban areas. The construction of the irrigation area reduced the suitability of phreatic water for agricultural irrigation in the southeast but increased in the west and north.

Hydrochemical characterization and irrigation suitability of the Ganges Brahmaputra River System: review and assessment

The hydrochemical characterization and irrigation suitability assessment of the Ganges-Brahmaputra River System (GBRS) has immense importance for the livelihoods of people and ecosystem sustainability in the region. This study aims to assess the hydrochemical characteristics and evaluate the irrigation suitability of water in the GBRS by reviewing published literature of the major tributaries. The studied rivers were categorized into two groups namely Group-1 and Group-2 considering the similarities of climatic patterns, hydrochemical attributes, and drainage characteristics. The hydrochemistry of the river water was characterized by the Piper diagram, Gibbs plot, mixing plots, and ionic ratios. Furthermore, irrigation water qualities were evaluated by electrical conductivity (EC), sodium percentage (Na%), sodium adsorption ratio (SAR), magnesium hazard (MH), and Wilcox diagram. The results indicated that the hydrochemistry of the GBRS was slightly alkaline to alkaline (7.42-8.78) in nature. The average concentrations of most of the chemical attributes showed higher in Group-1, whereas the average concentrations of K+ and NO3 - were found higher in Group-2. The average concentration of the major ions followed the dominancy order Ca2+ > Mg2+ > Na+ > K+ for cations and HCO3 - >SO4 2- > Cl- > NO3 - for anions in both groups. Gibbs plot and mixing plot indicated that carbonate rock weathering dominates the hydrochemical process, which was further confirmed by the Piper diagram and the ionic ratios. From the analyses of irrigational water quality, almost all the rivers (except Gomti River in terms of MH and Rangit River in terms of Na%) in the GBRS were found to be suitable based on EC, SAR, Na%, MH, and Wilcox diagram. Finally, the majority of river systems in the GBRS were characterized by carbonate dominated lithology and irrigational water quality is mostly suitable for utilization. This study could be useful for water quality management in the glacial-fed Himalayan river under the context of global climate change.

Sustainable water resources development and management in large river basins: an introduction

Water resources are important in large basins which are important places for human habitation and industrial and agricultural development. The background of editing this thematic issue was introduced and the general water resources situation and water quality status in four major large river basins in the Asian and African continents were briefly summarized to give readers general pictures of water resources development and management in these basins, and these large river basins are the Yellow River Basin, the Yangtze River Basin, the Indus Basin, and the Nile Basin. The thematic issue papers were classified into four clustered topical categories, and the main points of the papers in this thematic issue were summarized. Finally, the perspectives of future sustainable water resources development and management in large river basins were proposed.

Characterization of Volatile Compounds of Rosa roxburghii Tratt by Gas Chromatography-Olfactometry, Quantitative Measurements, Odor Activity Value, and Aroma Intensity

Rosa roxburghii tratt (RRT), widely distributed in the southwest of China, is favored by consumers for its good taste and healthy functions. In this study, thirty-seven compounds of Rosa roxburghii Tratt (RRT) were identified and quantified by gas chromatography-olfactometry (G-O) and gas chromatography-mass spectrometry (GC-MS) analysis. Furthermore, ethyl 2-methylpropanoate, ethyl butanoate, ethyl 2-methylbutyrate, and ethyl hexanoate were present with much higher odor activity values (OAVs) than other compounds. The key notes were confirmed by omission tests. Possible interaction among key notes was investigated through odor intensity determination and sensory analysis. It showed fruity and woody notes had synergistic effects. Full factorial design was used to evaluate the notes contribution to the whole odor. One important finding is the major effect of order interactions, fruity note (X1) and woody note (X4) especially, emphasizing the existence of complex interactions occurring between odor notes. The interaction X1X4 was further investigated. The woody note has a positive effect when the fruity note is also in the mixture but tends to show a negative effect otherwise.

Hydrochemical appraisal and solute acquisitions in Seti River Basin, Central Himalaya, Nepal

The chemical characterization and assessment of the water quality in the headwater areas of the Himalaya are necessary for securing the water in the future. This study aims to assess the hydrochemistry and water quality concerning drinking and irrigational uses in the Seti River Basin (SRB), Nepal. A total of 45 water samples were collected in 2016 from the SRB during pre-monsoon, monsoon, and post-monsoon seasons, and pH, EC, TDS, and DO were measured on-site, whereas Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-, SO₄^2-, NO₃^-, and dissolved Si were analyzed in the laboratory. The results revealed mildly alkaline pH (8.40 ± 0.43) with the pattern of average ionic dominancy: Ca²⁺  > Mg²⁺  > Na⁺  > K⁺ and HCO₃^- > SO₄^2- > Cl^- > NO₃^- for cations and anions, respectively. Gibbs diagram implied that the lithogenic weathering mainly controlled the solute acquisition process, which was further confirmed by the Piper diagram, exhibiting Ca-HCO₃ as the governing hydrochemical facies (91%). The average molar ratios were 0.88, 8.33, and 6.86 of (Ca²⁺ + Mg²⁺)/TZ⁺, (Ca²⁺ + Mg²⁺)/(Na⁺ + K⁺), and HCO₃^-/(Na⁺ + K⁺), respectively, which specified that the carbonate weathering largely controlled the solute acquisition processes with a minor contribution of silicates. The mass budget calculation also confirmed the dominance of carbonate weathering (72.0%, 78.9%, and 62.0% in Pre-Monsoon, Monsoon, and Post-Monsoon, respectively) and the high monsoon rainfall's dilution effect to anthropogenic input of cations. Principal component analysis and correlation matrix exhibited that the major sources of ions in the basin were geogenic with minor anthropic signatures. Furthermore, water quality in connection to drinking and irrigation uses revealed that the basin has mostly retained its natural water quality. This investigation suggests that regular monitoring and assessment are essential for maintaining the water quality and ecological integrity in the Himalayan river basins.

Distribution and risk appraisal of dissolved trace elements in Begnas Lake and Rupa Lake, Gandaki Province, Nepal

Contamination of the trace elements (TEs) in the freshwater ecosystems is becoming a worldwide problem. This study was carried out to investigate the TEs contamination, and their associated health risk in Begnas Lake and Rupa Lake, Gandaki Province, Nepal. A total of 30 water samples were collected from both lakes during the pre-monsoon season in 2016. The samples were analyzed for the TEs including copper (Cu), lead (Pb), zinc (Zn), nickel (Ni), cobalt (Co), chromium (Cr), cadmium (Cd), manganese (Mn), cesium (Cs), and arsenic (As) using inductively coupled plasma mass spectrometry. The results exhibited that the mean concentrations of all the TEs were higher in Rupa Lake as compared to Begnas Lake except Pb. Principal component analysis and cluster analysis revealed that both the geogenic and anthropic sources were the major contributors of TEs in the lake water. Anthropic activities were considered to contribute the TEs like Zn and Mn in lake water mainly via agricultural runoff, while evaluating the risk of TEs on human health all the elements showed HQ < 1 and CR < 10−4 indicating currently very low health risk concerns. In good agreement with above, the water quality index (WQI) of the Begnas Lake and Rupa Lake was 2.67 and 5.66, respectively, specifying the lake water was safe for drinking and public health concern. This appraisal would help the policymakers and concerned stakeholders for the sustainable management of Ramsar listed freshwater lakes in the Himalayas.

Hydrochemical assessment of the Beeshazar and associated lakes in Central Nepal

Water quality deterioration has threatened aquatic life around the world including Nepal, which has been a serious issue for environmental sustainability and economic development. This study evaluated and interpreted hydrochemical parameters of the Beeshazar and associated lakes in Central Himalaya, Nepal. The study revealed that the water in the lake was slightly alkaline as the average pH was 7.52. The correlation and principal component analysis (PCA) identified both geogenic and anthropogenic processes as the controlling factors of hydrochemistry whereas the cluster analysis (CA) showed relatively more pollution in the associated Laxmi Lake. Also, the water quality index (WQI) classified the water as “good” for drinking purposes (i.e., WQI = 33.90), while the pollution index (PI) values were characterized as sub-cleanness and slightly polluted. In general, both the WQI and PI signify that water in the lake complex is currently safe for drinking purposes. It is further confirmed from the comparative analysis of chemical variables with other lakes in the region, WHO and national water quality guidelines for aqua culture that the most of the analyzed water parameters exhibited relatively low concentrations and were within the prescribed guidelines. However, the elevated concentrations of NO3−and PO43−may pose serious problems for retaining water quality in the future. The results could be considered for future planning and management of the Ramsar Lakes of the lowland areas in the Himalaya and also as a valuable reference for the freshwater researchers at the national and international levels.

Monitoring of pre- and post-monsoon groundwater quality of north-eastern Haryana region using GIS

The present paper is the result of an investigation carried out to analyse the quality of sub-surface water in the districts of Yamunanagar and Ambala of the province of Haryana in India. The investigation was necessitated as the area combines the presence of industrial, commercial and residential units close to each other. A total of 30 groundwater samples were taken each during the months of April and September of 2017 and were appraised for analytical parameters, hydro-geochemical constituents and metal ions. Eight locations were observed to have an abnormal presence of only one element and were, therefore, classified to be falling in the 'Grey-Zone'. Matedi Bus Stand (Sample number - 23) was found to be adversely influenced by the presence of the most of chemical elements and thus was categorized as the 'Red Zone'. For the combined data of post-monsoon and pre-monsoon periods of 2017, the spatial distribution of pH, TDS, TA and TH showed that 100%, 90%, 91.67% and 93.33% of samples, respectively, fall under allowable limits of groundwater quality. Spatial distribution of hydro-chemical elements and metal ions showed that 96.11% of samples for cations, 98.33% for anions and 93.33% for Fe are in the 'allowable' category of groundwater. A comparison of laboratory results with the GIS maps prepared during the study has been found to be in good agreement. The classification of samples pursuance to their hydro-chemical facies indicated that most of the samples fall in Ca²⁺-Mg²⁺- H C O 3 - -Cl^- and Na⁺- H C O 3 - -Cl^- type.

Hydrochemical composition and potentially toxic elements in the Kyrgyzstan portion of the transboundary Chu-Talas river basin, Central Asia

Water chemistry and the assessment of health risks of potentially toxic elements have important research significance for water resource utilization and human health. However, not enough attention has been paid to the study of surface water environments in many parts of Central Asia. Sixty water samples were collected from the transboundary river basin of Chu-Talas during periods of high and low river flow, and the hydrochemical composition, including major ions and potentially toxic elements (Zn, Pb, Cu, Cr, and As), was used to determine the status of irrigation suitability and risks to human health. The results suggest that major ions in river water throughout the entire basin are mainly affected by water-rock interactions, resulting in the dissolution and weathering of carbonate and silicate rocks. The concentrations of major ions change to some extent with different hydrological periods; however, the hydrochemical type of calcium carbonate remains unchanged. Based on the water-quality assessment, river water in the basin is classified as excellent/good for irrigation. The relationship between potentially toxic elements (Zn, Pb, Cu, Cr, and As) and major ions is basically the same between periods of high and low river flow. There are significant differences between the sources of potentially toxic elements (Zn, Pb, Cu, and As) and major ions; however, Cr may share the same rock source as major ions. The risk assessment revealed low non-carcinogenic and carcinogenic risks for human health; however, the maximum carcinogenic risk for As exceeded the allowable value, which requires further consideration. These results provide a scientific basis for the management of agricultural irrigation uses and also infill existing gaps regarding the hydrochemical composition in the Chu-Talas river basin, Central Asia.

Spatiotemporal characterization of dissolved trace elements in the Gandaki River, Central Himalaya Nepal

A comprehensive investigation was conducted on trace elements (TEs) in the glacier-fed Gandaki River Basin, Central Himalayas Nepal. A total of 93 water samples were collected from 31 locations in pre-monsoon, monsoon and post-monsoon seasons in 2016 to evaluate the concentrations of TEs. Multivariate statistical techniques such as analysis of variance, cluster analysis, principal component analysis, and correlation analysis were applied to investigate the spatiotemporal variations and identify the major sources of the TEs. The results classified most of the TEs into two groups. Group 1 including Cs, Li, Ni, Rb, Sc, Sr, Tl, U and V were from geogenic sources, while Group 2 including Cd, Co, Cr, Cu, Pb, Ti, Y and Zn were impacted by anthropogenic activities. Group 1 showed lower concentrations in the lower-middle and downstream segments with higher precipitation and the highest concentrations during pre-monsoon. In contrast, Group 2 demonstrated higher concentrations in the densely populated lower segments with more agriculture and industries, and the highest concentrations during the post-monsoon season. Comparing to the drinking water limits suggested that special attention should be paid to the elevated concentrations of Zn and As. The results of the study provide a basic guideline for future environmental protection in the Himalaya.

Evaluating CO2 flux and recharge source in geothermal springs, Garhwal Himalaya, India: stable isotope systematics and geochemical proxies

Evaluation of geogenic carbon fluxes between solid Earth and its atmosphere is essential to understand the global geological carbon cycle. Some of the key geogenic CO₂ suppliers are the magmatic mantle and metamorphic degassing from active and quiescent volcanoes, fault zones, geothermal systems and CO₂ rich groundwater. Indian Himalayan geothermal field hosts about 340 geothermal springs in natural as well as artesian condition that eject hot waters and volatiles with varied temperature and chemical composition. These sites provide an opportunity to analyse tectonically driven gas emissions and their impact on regional and global climate. Here we adopt a method for direct measurement of Dissolved Inorganic Carbon (DIC ≈ HCO₃) concentration in the geothermal springs to estimate geogenic CO₂ flux from an active region based on water discharge and area of geothermal system between the tectonic boundaries of the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) of the Garhwal (Northwest) Himalaya. In the study area, geothermal spring water contain high δ¹³C_DIC ratio (- 8.5‰ to + 4.0‰ _VPDB), and among the major ions, bicarbonate (HCO₃^-) varies by an order of magnitude from 1697 to 21,553 μEq/L; chloride and sodium vary from 90 to 19,171 μEq/L and 436 to 23181 μEq/L. The elevated concentration of Cl^- and Na⁺ in geothermal spring waters suggests affinity towards their deeper origin. These geothermal springs cover a large area of nearly 10,000 km² of the Garhwal region showing a significant discharge of CO₂ rich water with an estimated carbon dioxide degassing flux of ~7.2 × 10⁶ mol/year to the atmosphere. Considering widespread occurrences of geothermal springs in tectonically active areas worldwide, the proposed direct measurement of DIC may be used as a reliable tool to estimate CO₂ fluxes in different active orogenic settings within the Earth system. Results of stable isotopes of δ¹⁸O _(VSMOW) and δD _(VSMOW) in these geothermal spring waters follow the Global Meteoric Water Line (GMWL), suggesting affinity of their recharge through the meteoric origin.

Meltwater hydrochemistry at four glacial catchments in the headwater of Indus River

Glacier runoff shows significant change under global warming in the headwater region of the Indus River with great impact on its highly populated downstream area, but the hydrochemistry characteristics of meltwater and the changing mechanism remain unclear in this region. In this study, runoff water samples were collected during May and June, 2015, from four glacial catchments in the Upper Indus Basin to investigate general characteristics and daytime dynamics of meltwater runoff together with sediment and chemical contents. Results showed that glacier runoff in the studied area had an alkaline pH and much higher sediment yields than the local average of the non-glacier areas. The carbonate-dominated geological feature in the four catchments resulted in single chemical facies of Ca-HCO₃. The dominant process determining the glacier runoff chemistry was rock-water interaction, with less soluble minerals and less intensive evaporate weathering in the Passu and Gulmit catchments than the B&B and Hinarchi catchments. Comparing the investigated catchments, the larger glacier with longer flow path exhibited higher runoff but lower melting rate, higher SSC resulting from higher erosive power of flow, and higher solute concentrations as a consequence of more intensive contact of meltwater with rock minerals along the longer flow path. For individual catchments, a negative correlation between TDS and flow rate (R² = 0.26~0.53) and changing trends of ion ratios with flow rate demonstrated that under intensive melting conditions, rock-water interactions were reduced, resulting in dilution of solutes. Overall, the general chemical characteristics of the investigated glacier runoff indicated geological control, whereas individual glacier illustrated hydrological control on the daytime dynamics of glacier runoff chemistry. The presence of glacier terminal lake and agriculture land can significantly alter the hydrochemistry of downstream runoff.