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Himalayan glaciers are retreating, and glacial lakes are evolving and proliferating as a result of climate change. Glacier retreat marks in the formation and expansion, and sometimes outburst of moraine-dammed lakes. Lato Lake is one of the high-altitude and unexplored glacial lakes upstream of Gya-Miru village in the Leh-Ladakh region. This study is the first of its kind to assess hydrogeochemistry (HCO3−, SO42−, NO3−, Cl−, F−, Ca2+, Mg2+, Na+, and K+) and studying the dynamics of a moraine-dammed lake in the Ladakh Himalayas. We observed substantial expansion of Lato Lake over the past 50 years between 1969 and 2019, and the areas of the lake have increased while the glacier area is reduced by 16.4% and 4.15%, respectively. The pH values ranging from 7.6 to 8.1 show slightly alkaline. HCO3−, Ca2+, and SO42− were the most dominant ions during the study period 2018–19. The high (Ca2+ + Mg2+) and a low (Na+ + K+) ratio to the total cations show that Lato Lake receives ions from rock weathering, primarily from carbonate rocks. Gibbs and Na-Mixing plot also support the hydrogeochemistry of lake water was primarily controlled by rock weathering. HYSPILT backward trajectory model suggested that atmospheric input mainly originated from the seawater vapor transported by the summer monsoonal and westerly circulation systems. Results show that the lake has a substantial impact on the long-range transport of ocean water relative to local interferences.

In the year 2013, the Northwestern Himalaya witnessed an extreme hydrological event that severely affected the upper Ganga Basin. The unexpected high sediment mobilisation in the basin affected the human population, infrastructure, and ecology in several reaches of the Ganga river and its tributaries. In an exceedingly affected reach, the Kedarnath valley, a considerable sediment volume (∼26243 × 104 m3) was mobilised during the 2013 extreme hydrological event. In the Srinagar valley, up to 50 × 104 m3 of legacy sediment was washed away during the same event. This sediment mobilisation generated sediment pulses in the affected region, which is assessed through remote sensing, field observations and existing literature, in the Kedarnath and Srinagar valleys. Results show that the evolution of translative, dispersive, and their combined sediment pulse pattern in both selected reaches of the upper Ganga Basin. The mountainous region of the upper Ganga basin has very few monitoring stations observing sediment movement, and data from such stations are mostly unavailable due to which our understanding of the sediment movement in the Himalaya remains very poor. Therefore, it is suggested that there is a need for detailed studies of the sediment transport mechanism in the Himalayan river basins especially during such extreme hydrological events when large volume of sediment is mobilised.

This study presents a recent estimate (for year 2017) of ice thickness and volume of a small glacier called Patsio Glacier located in Western Himalayas. Also, the present study aims to examine whether the improvement in GlabTop2 based estimates obtained for Chhota Shigri Glacier through the use of relatively accurate and high-resolution Digital Elevation Model (DEM) and glacier specific model parameterisation is consistent and can be extended to other glaciers. The version of GlabTop2 model used in this study is GlabTop2_IITB (Glacier Bed Topography version 2_Indian Institute of Technology Bombay). For validation purpose, ground penetrating radar (GPR) survey-based ice thickness estimates available at four cross-section profiles collected during July 2017 was used. Root mean square error (RMSE) of the modelled ice thickness estimates is about 14 m. Average and the maximum thickness of the modelled glacier ice is about 45 and 129 m, respectively. The obtained results when compared with an earlier study carried out using velocity-based approach indicate a significant improvement in the modelling accuracy. Moreover, a 16 percentage points reduction in uncertainty of the estimated ice thickness is seen when compared with a previous study involving different version of GlabTop2 model for Himalaya–Karakoram region. This is perhaps due to the use of a relatively accurate and high-resolution DEM and model parameterisation scheme adopted in this study, thus confirming the consistency of the modelling approach for different glaciers. Based on the obtained ice thickness estimates, the modelled volume of the glacier stored ice was calculated to be 0.11198 ± 0.0162 km3 in 2017.

This study mainly focuses on the source identification of various ions in meltwater and estimation of CO2 consumption rate by chemical weathering in the Batal glacier basin on the basis of 2 years of study (2015 and 2017). The glacier meltwater has been monitored as slightly acidic in nature having mean pH value of 6.6. Ca2+ was observed as the most dominant cation contributing about 76% of TZ+ (total cations), whereas SO42− was observed as the most dominant anion contributing about 70% of TZ− (total anions) in the stream meltwater. High ratios of (Ca + Mg) versus TZ+ (mean value: 0.89 ± 0.02) and (Ca + Mg) versus (Na + K) (mean value: 8.51 ± 2.07) elucidate that stream water chemistry of the Batal glacier is largely controlled by carbonate weathering. Concentration of total dissolved solid in the glacial stream water was higher during the low-melt season (September) and lower during the high-melt period (July). The average value of daily mean TDS flux of the study area was calculated to be 12.4 t/day. The mean values of CWR (carbonate weathering rate) and SWR (silicate weathering rate) for the Batal glacier basin were calculated to be 97.4 and 22.8 t/km2/year, showing higher contribution of CWR as compared to SWR in the investigation area. CO2 consumption rate by the combined silicate and carbonate (chemical) weathering was estimated to be 11.1 × 105, 28.8 × 105 and 35.5 × 105 mol/km2/year during the study period September 2015, June 2017 and July 2017, respectively. The annual CO2 drawdown by the Batal glacier basin on the basis of CO2 consumption rate by chemical weathering is much lower as compared to the Gangotri glacier, which may be due to bigger size and higher meltwater runoff of the Gangotri glacier as compared to the Batal glacier.

The nature of groundwater recharge along the mountain front (MF) and riparian zone (RZ) was discerned by multiple tools involving rain/water level relationship, geophysical of subsurface, seasonal hydrochemistry and environmental isotopic signatures. The proposed study has been carried out in Courtallam Hills, the north-western part of Tirunelveli District, South India. The study area is a hilly terrain with narrow valleys endowed with steep slopes. The relationship between water-level fluctuation and precipitation were evaluated by observing daily water level in 8-h interval at three piezometer zones and regular rainfall data. It was inferred that the RZ played a role in storage zone and gets recharged from mountain block (MB) and lateral flow. The seasonal geochemistry of the groundwater was studied to determine the sources of recharge in MF and RZ. Geostatistical treatment of factor analysis revealed that weathering was the dominant recharge process along the foothill. The geophysical studies reveal good quality of groundwater observed in the northern part along with low conductance and high resistivity. The increased level of groundwater conductivity and lower resistivity was noted in southern part of the study area due to the irrigation activities. The isotopic tracers range from − 2.5 to − 12.6‰ for δ18O and from − 91.2 to − 15.5‰ for δ2H. Moreover, the groundwater recharge was evaluated by source of rainfall moisture. High-altitude recharge from MB along the MF was clearly indicated by depleted isotopic content of the water samples. It was also supported by hydrogeochemical and statistical evidences, showing that rainfall over both MB and MF zones provided the recharge to foothill aquifers, while the RZ zone was mainly recharged by local precipitation with less contribution from regional flows.

Arsenic and uranium in the aquatic environment are recognized as a major catastrophic problem worldwide and have natural as well as human-made sources such as mining, industry and agriculture. The severity of this problem is further accelerated by in-situ physio-chemical factors in the fluvial environment which enhances the concentration of arsenic and uranium in groundwater that feeds millions of people in Central Gangetic Plain in India. This study aims to establish a better understanding of the processes responsible for the co-occurrence of arsenic and uranium along with the factors controlling their solubility and mobility in the groundwater of central Gangetic plain. This study is an attempt to bring out the (a) the spatial distribution pattern of arsenic and uranium, (b) insight into the hydrogeochemical characteristics of aquifers that are controlling their co-occurrence and provides (c) information of their source which are validated by statistical tools. Silicate weathering controls U mobilization and distribution whereas carbonate dissolution and ion exchange process controls As in groundwater. The land use and land cover pattern of the North-eastern (NE) part of the study area is agriculture dominated and is composed of Holocene older alluvium. However, the South and South-western areas which are closer to the river are formed by the deposition of river born newer alluvial. Newer alluvium in the SW part has unoxidized organic-rich clay that enhances arsenic mobilization by reductive dissolution of Fe-oxyhydroxide. In the NE region, the abundance of fertilizers in the subsurface oxidizing environment augments the solubility and mobility of uranium.

Integrated constructed wetland into activated sludge process has a potential in improving treated wastewater with high organic loading. However, biological activities on those processes will generate microbial by-products from substrate metabolism and cell lysis. The presence of those compounds in effluent of wastewater treatment causes problems in source water. This study combines fluorescence excitation emission matrices (FEEM) with high-performance size exclusion chromatography with fluorescence detector (HPSEC-FLD) to characterize molecular weight–based fluorescent of organic matter and its removal in combination of constructed wetland with activated sludge process. The results show that three components of fluorescence organic: fulvic acid–like (Ex/Em 250/440 nm), SMP-like (Ex/Em 280/350 nm), humic acid–like (Ex/Em 340/420 nm), have been identified in all samples by the FEEM. Further, the HPSEC-FLD, which was set up based on chosen fluorescence wavelength, revealed two different apparent molecular weight (AMW) fractions: high molecular weight (HMW)/biopolymer (50,000 Da) and medium molecular weight (MMW)/humic substance–like (3000–650 Da). Peak-fitting determines that the area of MMW is higher than the area of HMW of all fluorescence organic components, and the area of HMW of fluorescence fulvic acid–like is comparable with the area of SMP-like, and no HMW of humic acid–like detected. Humic acid–like and fulvic acid–like were removed during treatment, while metabolite by-product were released as shown by increasing fluorescence SMP-like and TOC concentration. This method gives new insight to characterize organic matter for assessing effluent of wastewater quality and determining the appropriate water treatment.

The hydrogeochemical study on glacial meltwater gives important information about the quality of meltwater and weathering processes controlling dissolved ions chemistry in the glacierized area. Anionic abundance in the Manimahesh Glacier meltwater shows a trend of HCO3− > SO42− > Cl− = NO3−, whereas cationic abundance in the meltwater shows a trend of Ca2+ > Mg2+ > K+ > Na+. On the basis of high equivalent ratios of (Ca + Mg) versus (Na + K) and (Ca + Mg) versus TZ+ (total cations) and low equivalent ratio of (Na + K) versus TZ+, carbonate-type weathering has been identified as a major hydrogeochemical process regulating solute chemistry of the Manimahesh Glacier meltwater followed by silicate weathering. About 80% of bicarbonate in the meltwater of investigation area was mainly generated from carbonate weathering, whereas 20% of bicarbonate was produced from silicate weathering. The result of statistical methods (correlation, principal component and cluster analysis) shows that meltwater quality of the Manimahesh Glacier is mainly governed by carbonate and silicate-type weathering, oxidation of pyrite, dissolution of sulphate minerals and atmospheric input. The average value of suspended sediment concentration (SSC) in the glacier meltwater was calculated to be 46 mg/l and 63 mg/l during the month of June and July 2014, respectively, showing higher concentration of SSC during the month of July (peak-flow period) followed by June (low-flow period).

This investigation was carried out with the objective to understand the impacts of landfill leachate on groundwater quality. This study also explained the movement of trace metals in groundwater by using Visual MODFLOW/MT3D. It also delineates the various factors controlling the suitability of groundwater for domestic, agriculture and drinking purpose. The statistical assessment shows ~ 60.09% groundwater are in good condition, ~ 35.38% in poor condition and 4.53% in very poor condition. The spatial distributions of water quality index (LWQI) around landfills indicate landfills are in depleted condition. Hydrogeochemical classification indicates ~ 90.91% groundwater shows Ca–Na water-type cation facies and Cl− water-type anion facies. While 9.09% groundwater shows Ca–Na water-type cation facies and Cl−–SO42−–HCO3− anion hydrogeochemical facies. The mineral equilibrium diagram of groundwater has revealed that it is in equilibrium with silicate minerals and favors kaolinite formation. The saturation index indicates chrysotile (Mg3Si2O5(OH)4) (2.84), dolomite (CaMg(CO3)2) (0.45), ferric hydroxide (Fe(OH)3) (1.97–3.58), goethite (FeOOH) (7.86–9.47), hematite (Fe2O3) (17.73–20.95), hydroxyapatite (Ca5(PO4)3OH) (2.38–4.62), jarosite-K (KFe3(SO4)2(OH)6) (0.22–1.92), cerussite (PbCO3) (0.39), vivianite (Fe3(PO4)2·8H2O) (0.39) and willemite (Zn2SiO4) (0.35) are reactive mineral in groundwater aquifer of study area. The seasonal and temporal variation indicates anthropogenic influence. The calibration and validation of model show > 90% models correct with 95% confidence. The contaminant transport simulated in groundwater aquifer with the high accuracy (estimated standard error 0.049 m) for the large area (~ 300 km2). The trends of contour lines of trace metals concentration indicate; it will contaminate study area within few years of its release through the landfill.

Present study shows suspended sediment dynamics in the meltwater of Chhota Shigri glacier, Himachal Pradesh, India for different melt seasons during the period 2011-2014. Maximum suspended sediment concentration in the meltwater was found during the month of July 2011, 2012 and 2014 constituting to 55.2%, 48.3% and 46.9%, respectively. Whereas in 2013, maximum suspended sediment concentration was observed in August accounting for 46.1% of the total. On the other hand, maximum suspended sediment load was monitored in the month of July 2011, 2012 and 2014 constituting 59.5%, 63% and 55.7% of the total, respectively. Whereas in 2013, maximum suspended sediment load was observed in the month of August accounting for 49.8% of the total suspended sediment load. Annual distribution of suspended sediment concentration (SSC) and suspended sediment load (SSL) in the Chhota Shigri glacier shows higher value of SSC and SSL during the study period 2012 and 2013, which may be due to the presence of high glacial runoff and negative mass balance of the studied area during these time periods. Marked diurnal variation has been observed in the SSC of meltwater. Strong correlation was observed between SSC and SSL with discharge. On the other hand, SSC and SSL also showed strong exponential correlation with air temperature of the studied area. Sediment yield from the catchment of Chhota Shigri glacier is high during the peak melt season (July and August) and low during the late melt season (September and October). The average value of erosion rate for Chhota Shigri glacier basin during the study period 2011-2014 was calculated to be 1.1 mm/yr, which is lower than the average erosion rate of other Himalayan glaciers such as Rakiot, Chorabari and Gangotri glaciers, which may be caused by its geological setting containing high erosion resistant rocks such as granite, granite gneiss and porphyritic granite.

Mountain front recharge (MFR) is the contribution of mountains to recharge the aquifers in the adjacent basins. The estimation of MFR is essential to obtain a detailed investigation of recharge of the groundwater at the mountain front. This study summarises the current understanding of recharge processes by comparing daily groundwater fluctuation to daily rainfall and identifies the recharge rates. The recharge rates vary with time due to difference in water table depth and travel time. Thus to understand the MFR along the foothills of Courtallam, a total of 14 surface water, rainwater and groundwater samples were collected and measured for stable isotopes. The isotopic data were used to investigate the recharge process and to identify the elevations to recharge. The study findings also suggest that predominantly rainfall along the foothills contributes recharge to the riparian zone (basin block region), whereas foothill regions receive recharge from rainfall over mountain block.

The present study aims at assessing water quality of river Yamuna in one of the world's most polluted and populated megacities, Delhi. Conductivity, salinity and sodium content were within the permissible categories. Chloride concentration exceeded acceptable levels of drinking water guidelines. Water quality was poor at all locations with respect to heavy metal contamination, especially along the lower section of the Delhi stretch. Heavy metal concentrations were manifold higher than the acceptable limits of drinking water according to the BIS guidelines and reached similar to 29, 4.9, 10, 31, 27, 83, 7.3 and 27 times higher, respectively, for metals aluminum, copper, chromium, cadmium, iron, lead, manganese and nickel. The Najafgarh and the Shahdara drains are major point sources. Low oxidation-reduction potential reflected high organic loads and traces of eutrophication together with significant levels of nitrate and total phosphate. Discharges from agriculture, sewage and power plants could be important sources of high metal concentration. This calls for urgent measures to be taken for prevention of metal contamination in the river, through both, technology as well as implementation of regulations in order to sustain huge populations in megacities like Delhi. Waste water treatment from point sources needs tremendous improvement on the city. Treatment of the entire waste generated up to the tertiary level is required for minimizing dissolved solids, especially toxic metals, and rendering reuse in agriculture suitable. Treatment plants need proper operation, maintenance, uninterrupted power supply and regular monitoring. Various measure and programmes need to be undertaken to ensure safe reuse of wastewater.

To study hydrological regime over Marshyangdi (area: 3006.77 km2) and Tamor River basins (area: 4005.22 km2), an integrated approach was performed in particular to emphasize glacio-hydrological model development. Glacio-hydrological degree-day model (GDM) version 1.0, a physical-based gridded glacio-hydrological model, developed on C-Sharp (C#) and Python-programming language is developed. GDM is calibrated for the period 2004–2007 for Marshyangdi River basin (MRB) and from 2001 to 2005 for Tamor River basin (TRB) with Nash–Sutcliffe Efficiency (NSE) of 0.81 and 0.64, respectively. Furthermore, the model is validated for the period 2008–2009 for MRB and from 2006 to 2010 for TRB with NSE of 0.84 and 0.68, respectively. The snow and ice melt contribution to total discharge in MRB during calibration period is found to be 12.3% and 11.2%, respectively, whereas, during validation period, it is 9.9% and 11.8%, respectively. In case of TRB, contribution during calibration period is found to be 14.5% and 7.3%, respectively, and during validation period 12.9% and 10.6%, respectively. The highest rate of increment in minimum temperature trend over TRB and MRB is 0.027 °C/year and 0.008 °C/year. In case of maximum temperature trend, both basins show an increment rate of 0.018 °C/year. The morphometric analysis shows low drainage densities and length of overland flows of 3.66 km and 3.73 km over MRB and TRB, respectively. In Representative Concentration Pathways (RCPs) 4.5 scenario for the period 2021–2050, an average decrease in simulated discharge as − 0.087 m3/year and − 0.366 m3/year for MRB and TRB, respectively, is seen.

This manuscript discusses about the solute acquisition processes controlling hydrogeochemistry and suspended sediment characteristics of meltwater of the Batal glacier, Western Himalaya, India. The predominance of anions and cations in meltwater follows the order: SO4 2− > HCO3 − > Cl− > NO3 − and Ca2+> Mg2+> Na+> K+, respectively. High excess of (Ca + Mg) over (Na + K), high input of (Ca + Mg) to the TZ+ (total cations) and very low input of (Na + K) to the total cations (TZ+) demonstrate that meltwater chemistry of Batal glacier is predominantly regulated by carbonate type weathering along with minor input from silicate type weathering. Sulphide oxidation is the dominant mechanism responsible for delivery of hydrogen ions (protons) for weathering in the glacier environment, which is revealed by C-ratio of meltwater. The Piper trilinear plot indicates that Ca–SO4 is the prevalent water type in the study area with dominancy of (Ca + Mg) (alkaline earth metals) over (Na + K) (alkali metals) and dominancy of (SO4 + Cl) (strong acid) over (HCO3) (weak acid). Interrelation among the different chemical constituents of meltwater and various factor regulating meltwater chemistry of the Batal glacier are evaluated by multivariate statistical analysis. Average suspended sediment concentrations in meltwater of the study area for August and September 2014 were computed to be 706 and 98.3 mg/l, respectively. These results show that in August suspended sediment concentrations is high and in September its concentration is low.

The occurrence of arsenic in drinking water and its detrimental effects have drawn much attention in recent years. Several studies have been conducted in the deltaic plains of River Ganga, NE part of the India, and in other countries, but no systematic study was conducted in South India on occurrence of arsenic in groundwater. The main aim of this study is to determine the level of arsenic in groundwater and to understand the relation with other geochemical parameters of groundwater in the south-eastern coastal aquifer at Kalpakkam region, India. This region is represented by three different lithologies, viz. charnockites, flood plain alluvium and marine alluvium. Twenty-nine representative samples of groundwater were collected and analysed for major ions, metals and isotopes such as 2H and 18O. In addition, geophysical method was also attempted to understand the subsurface condition. The spatial variation in arsenic (As) indicates that higher concentration was observed around the landfill sites and irrigated regions, which was supported by geochemical, statistical and isotopic inferences. The variation in the As with depth, lithology and sources has been clearly brought out. Though the values of As does not exceed the drinking water permissible limit (10 mg/l), it has reached a near permissible level of 8.7 ppb. Hence, it is essential to understand the geochemical behaviour of As for a proper future management of the water resource in the study area.

The expedited advent of urbanization and industrialization for economic growth has adversely affected the biological diversity, which is one of the major concerns of the developing countries. Microbes play a crucial role in decontaminating polluted sites and degrades pollution load of textile effluent. The present study was based on identification of microbial diversity along the Noyaal river of Tirupur area. River water samples from industrial and non-industrial sites and effluent samples of before and after treatment were tested and it was found that microbial diversity was higher in the river water at the industrial site (Kasipalayam) as compared to the non-industrial site (Perur). Similarly, the microbial populations were found to be high in the untreated effluent as compared to the treated one by conventional treatment systems. Similar trends were observed for MBR treatment systems as well. Pseudomonas sp., Achromobacter sp. (bacterial species) and Aspergillus fumigates (fungal species), found exclusively at the industrial site have been reported to possess decolorization potential of dye effluent, thus can be used for treatment of dye effluent. The comparison of different microbial communities from different dye wastewater sources and textile effluents was done, which showed that the microbes degrade dyestuffs, reduce toxicity of wastewaters, etc. From the study, it can be concluded that the microbial community helps to check on the pollutants and minimize their affect. Therefore, there is a need to understand the systematic variation in microbial diversity with the accumulation of pollution load through monitoring.

A geochemical assessment of seasonal dynamics in the groundwater chemistry of the National Capital Territory (NCT), Delhi, was attempted through geochemical modelling, mineral precipitation sequences with rainfall and water evaporation cycle. Saturation indices calculated using PHREEQC indicated that the degree of water–rock equilibrium changes significantly from pre-monsoon to post-monsoon. The schematic model of SI change with water table fluctuation showed that during monsoon, as rainwater percolates through the soil, partial pressure of CO2 becomes higher than that of the atmospheric value and led to the formation of more carbonic acid that react with the carbonate minerals to produce $${{{\text{HCO}}_{3}^{-} }}$$ , Mg2+ and Ca2+. The thermodynamic stability relationships of water chemistry in the Na, K, Ca and Mg silicate systems showed that for the samples with higher EC equilibrium between clay and primary minerals is not likely to be the main processes controlling variation in the groundwater chemistry. Chloro-alkaline indices (CAI) are positive when the groundwater level is high and become negative with the lowering of water level, i.e. when water level is high, reverse ion exchange is dominant. In case of pre-monsoon season, lower and negative value of CAI-1 and CAI-2 indicates dominance of ion exchange process and increases dissolved solid concentration in groundwater. The conceptual geochemical model depicted that water table fluctuation resulting from heavy pumping/withdrawal and recharge in association with the variation in DO, $${{{\text{HCO}}_{3}^{-} }}$$ and Fe regulates the water–mineral equilibrium. The conceptual geochemical model explained the hydrogeochemical processes and their variations with water table fluctuation and, thus, highlighted the descriptive capabilities of PHREEQC. The study suggested that in the subsurface environment, complex interactions are simultaneously functioning, and hence, significant seasonal variations are likely to be very influential due to monsoonal recharge and subsequent changes in the saturation states of the water.

The systematic and comprehensive geochemical analysis of fluoride (F) in twenty agricultural soil samples was carried out to understand spatial variability, mechanism of retention and release, and the areas of potential risk due to high concentrations of F in soil around Sidhi District, Central India. The spatial variations in physico-chemical parameters revealed significant difference in the methods of cultivation due to geomorphological constraints, availability of surface water and ground water etc., in the study area. The north and small pocket in central Sidhi were rich in fertile soils due to availability of surface and ground water. The southern and eastern Sidhi were rainfed areas, hence, the monocropping system by traditional methods showed less impact on the soil physico-chemical parameters. The soil F varied from 366.94 to 1178 mg/kg and 2-4 times greater than the background soil value (320 mg/kg) of the world. The pollution indexes were > 1 indicating prevalence of elevated soil fluorine.

The distribution, enrichment, and ecotoxicity potential of Bangladesh part of Sundarban mangrove was investigated for eight trace metals (As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) using sediment quality assessment indices. The average concentration of trace metals in the sediments exceeded the crustal abundance suggesting sources other than natural in origin. Additionally, the trace metals profile may be a reflection of socio-economic development in the vicinity of Sundarban which further attributes trace metals abundance to the anthropogenic inputs. A total of eleven surficial sediment samples were collected along a vertical transect along the freshwater-saline water gradient. The sediment samples were digested using EPA 3051 method and were analyzed on ICP-MS. Geo-accumulation index suggests moderately polluted sediment quality with respect to Ni and As and background concentrations for Al, Fe, Mn, Cu, Zn, Pb, Co, As, and Cd. Contamination factor analysis suggested low contamination by Zn, Cr, Co, and Cd, moderate by Fe, Mn, Cu, and Pb while Ni and As show considerable and high contamination, respectively. Enrichment factors for Ni, Pb, and As suggests high contamination from either biota or anthropogenic inputs besides natural enrichment. As per the three sediment quality guidelines, Fe, Mn, Cu, Ni, Co, and As would be more of a concern with respect to ecotoxicological risk in the Sundarban mangroves. The correlation between various physiochemical variables and trace metals suggested significant role of fine grained particles (clay) in trace metal distribution whereas owing to low organic carbon content in the region the organic complexation may not be playing significant role in trace metal distribution in the Sundarban mangroves.

The Himalayan Mountains and valley glaciers within it are coupled in such a way that they maintain the ecosystem along the draining stream from the young to old stage. They produce meltwater and nutrient-rich sediments, which serve as precious resources for low-lying areas. Meltwater is assumed to be an important agent of transportation and deposition of sediments in warm-based valley glaciers. Overall, the glacial environment acts as a good erosional system, and the sediments produced form a good-quality aquifer above the hard bedrock in the outwash plain. The glaciofluvial and glaciolacustrine sediments were collected from the Chandra Basin and analysed for the permeability, porosity, density and statistical parameters. Correlation among the different parameters was explained through the regression analysis. The correlation between permeability and mean grain size showed a good regression coefficient, R2 = 0.86 and R2 = 0.97, for glaciofluvial and glaciolacustrine sediments respectively. Correlation between density and porosity was also established against the mean grain size with a good regression coefficient. The physioempirical parameters, effective diameter (D10) and coefficient of uniformity (Cu) were also examined for their dependability on permeability. Hence, this preliminary study attempts to use sediment grain size and texture as a tool to understand the permeability, porosity, density and movement and mobility of water through the glaciofluvial and glaciolacustrine sediments. Also, the correlation study showed that the mean grain size could be used as a factor for predicting the physioempirical model in that region.

This systematic study was carried out with objective to delineate the various sources responsible for $$\hbox {NO}_{3}^{-}$$ contamination and $$\hbox {F}^{-}$$ enrichment by utilizing statistical and graphical methods. Since Central Ground Water Board, India, indicated susceptibility of $$\hbox {NO}_{3}^{-}$$ contamination and $$\hbox {F}^{-}$$ enrichment, in most of the groundwater, $$\hbox {NO}_{3}^{-}$$ and $$\hbox {F}^{-}$$ concentration primarily observed $${>}45$$ and $${>}1.5~\hbox {mg/L}$$ , respectively, i.e., higher than the permissible limit for drinking water. Water Quality Index (WQI) indicates $${\sim }22.81\%$$ groundwater are good-water, $${\sim }71.14\%$$ groundwater poor-water, $${\sim }5.37\%$$ very poor-water and 0.67% unsuitable for drinking purpose. Piper diagram indicates $${\sim }59.73\%$$ groundwater hydrogeochemical facies are Ca–Mg– $$\hbox {HCO}_{3 }$$ water-types, $${\sim }28.19\%$$ Ca–Mg– $$\hbox {SO}_{4}$$ –Cl water-types, $${\sim }8.72\%$$ Na–K– $$\hbox {SO}_{4}$$ –Cl water-types and 3.36% Na–K– $$\hbox {HCO}_{3 }$$ water-types. This classification indicates dissolution and mixing are mainly controlling groundwater chemistry. Salinity diagram indicate $${\sim }44.30\%$$ groundwater under in low sodium and medium salinity hazard, $${\sim }49.66\%$$ groundwater fall under low sodium and high salinity hazard, $${\sim }3.36\%$$ groundwater fall under very-high salinity hazard. Sodium adsorption ratio indicates $${\sim }97\%$$ groundwater are in excellent condition for irrigation. The spatial distribution of $$\hbox {NO}_{3}^{-}$$ indicates significant contribution of fertilizer from agriculture lands. Fluoride enrichment occurs in groundwater through the dissolution of fluoride-rich minerals. By reducing the consumption of fertilizer and stress over groundwater, the water quality can be improved.

Intense agricultural and mining/industrial activities make groundwater quality vulnerable to contaminants. This study conducted in one of the mining areas of Panna district evaluated the factors influencing the groundwater hydrogeochemistry using water quality parameters and multi-isotopic approach considering the fact that groundwater is the only major source of drinking water. Forty-five water samples comprising both shallow and deep aquifers were collected and analyzed for major ions, δ 18O, and δD. The geochemical data were used to characterize and classify water samples based on a multitude of ion plots and diagrams. The groundwater in the region is found to be contaminated with fluoride and nitrate. The sources for fluoride are mostly geogenic in nature. The alkaline nature of groundwater triggers replacement of the exchangeable fluoride from minerals like biotite/muscovite and results in its enrichment. In addition, it is contributed through leaching of fluorides from granitic rocks, abundantly present in the study area. The weathering of these fluoride-bearing minerals releases fluoride into the groundwater. On the other hand, nitrate enrichment is mainly attributed to leaching from untreated sewerage system and agricultural runoff containing nutrients from excess use of fertilizers. The stable isotopic composition for most of the collected samples was found to be near the local meteoric water line (LMWL), i.e., origin of ground water is meteoric in principle; however, the point away from the LMWL might favor exchange with rock minerals and evaporation processes. This study sets an important background for decision makers to take the suitable countermeasures from the public health perspective for sustainable water resources management.

Various physico-chemical parameters of meltwater samples from Bara Shigri glacier collected during 2012–2013 were analysed to understand the dissolved ion chemistry and solute acquisition processes regulating major ion chemistry of the study area. Ionic dominance of anions followed the trend as HCO3 − > SO4 2− > Cl− > NO3 −, whereas ionic dominancy of cations varied as: Ca2+> Mg2+> K+> Na+ for both the years. High share of (Ca + Mg) in the total cations and also dominancy of (Ca + Mg) over (Na + K) for both the years demonstrate that solute acquisition processes in the meltwater of Bara Shigri glacier are mainly governed by the weathering of carbonates. The Piper plot identified Ca-HCO3 as the dominant water type followed by CaSO4 type of water in the study area. The average value of partial pressure of carbon dioxide (Pco2) for meltwater of the Bara Shigri glacier was 10−2.6 atm in 2012 and 10−2.3 atm in 2013 and were higher than the Pco2 value of atmosphere (10−3.5 atm). It indicates that the meltwater is in disequilibrium with respect to the atmosphere. Contents of suspended sediment in the meltwater were 1432 mg/l in July and 596 mg/l in September 2012, whereas in 2013, suspended sediment contents were 1093 mg/l in August and 425 mg/l in September, following discharge pattern of the Bara Shigri glacier. We found that Bara Shigri and Gangotri glaciers demonstrate the higher rate of regional melting.

Discharge and transportation of suspended sediment from the Patsio glacier have been studied for 2 years. During the study period 2011 and 2012, daily mean discharge was measured to be 0.70 and 0.94 m 3 /s, respectively. Daily mean suspended sediment concentra- tion during the study period 2011 and 2012 was found to be 28.1 and 48.8 mg l -1 , respectively. Whereas, daily mean suspended sediment load during the study period was estimated to be 1.70 and 3.96 t day -1 . Suspended sediment concentrations generally follow the discharge pattern of the glacier for both years. High average TDS/TSM ratio of the Patsio glacier meltwater for both years shows the domi- nancy of chemical weathering over the physical weath- ering. The physical weathering rate of the study area during year 2011 and 2012 was estimated to be 79.3 and 185 t km -2 year -1 , respectively. The chemical (cation) weathering rate of the Patsio glacier is much higher than other Himalayan glaciers, which may be due to high intensity of chemical weathering in this glacier.

This study was an attempt to understand the role of biogeochemical processes in controlling the heavy metal distribution in the mangroves and to assess heavy metal pollution load (viz. Cr, Fe, Mn, Co, Ni, Cu, Zn, Cd, and Pb) in the Gulf of Kachchh, India. Various biogeochemical processes and anthropogenic factors were playing an important role in altering the concentration of heavy metals in the sediments. A significant correlation of Mn, Fe and Pb with Zn implies the role of diffused anthropogenic activities. The organic carbon content (1.47–3.25 %) and clay content (0.1–2.5 %) seem to play a significant role in the metal concentration. Factor analysis suggested two different processes, Factor I strongly indicating anthropogenic activities and Factor II indicating the combination of natural, marine in situ reduction processes (biogeochemical) with partial anthropogenic influence. The enrichment factor (EF) and Geochemical Index (I geo) of Cu were higher at Old Bedi Port (S5), whereas both these values were higher for Cu as well as Cd at Jam-Salaya (S8). I geo values indicate that sediments around the estuarine mouths were polluted with heavy metals as compared to other locations. Except Chodeshwar (S9), PLI value >1 was reported in almost all the locations, with a slightly higher value reported at Narara (S7); (1.57) and New Bedi Port (S4); (1.56). The findings of this study would help in formulating guidelines for controlling the pollution and suggest the ways by which the mangroves of the Gulf of Kachchh could be revitalized.

Mangrove forests are highly productive ecosystems distributed along the tropical coast line. Nutrient biogeochemistry of mangroves are primarly driven by both allochthonous and autochthonous sources. Characterization of organic matter in coastal ecosystems enables to understand the biogeochemical transformation of organic matter and its influence on ecosystem productivity in response to various changing environmental conditions. Therefore, the elemental and stable carbon and nitrogen levels were employed to understand the organic matter (OM) dynamics in the Sundarban mangrove ecosystem (India-Bangladesh). Differences in stable isotope values indicate that variable sources influence the OM dynamics in Sundarban sediments. The progressive enrichment in δ 13C levels along the land-coastal continuum indicates that the terrestrial and marine inputs are dominant at the landward and seaward ends, respectively. The CuO oxidation-derived lignin phenol monomers describe significant levels of total lignin are preserved in Sundarban mangrove sediments during diagenesis. The phenol monomer ratios are lower than the plant litter explaining that aromatic ring cleavage is the dominant mechanism for the lignin degradation. Furthermore, the Ad/Al ratios were higher than the plant litter explaining the oxidation of propyl side chain of vascular OM influencing the carbon cycling in Sundarban sediments. Largely, the Ad/Al ratios describe the vascular OM degradation is through the oxidation of propyl side chain. The regional variability in land-use regulates the spatial variability in C, N, OC/TN ratio, δ 13C and δ 15N between the Indian and the Bangladesh Sundarban mangroves and indicates that in the upstream terrestrial organic matter and/or mangrove plant litter contribute significant amount of organic matter, whereas the marine POC influences the organic matter dynamics in downstream. The three end-member mixing model applying terrestrial plant litter, seston, and marine POC as end-members explains the relative contribution of OM from various sources, and marine inputs were dominant in Sundarban sediments.

The chemical compositions of various ions in meltwater of the Chhota Shigri glacier were analysed during the observation period from May to October 2010. Total 164 samples of meltwater were collected in two times a day at 8.0 a.m and 6.0 p.m. Bicarbonate and calcium were the dominant anion and cation in meltwater of the investigation area. High ratios of (Ca + Mg) versus TZ+ and (Ca + Mg) versus (Na + K) demonstrate that hydrogeochemistry of the study area was mainly governed by carbonate type weathering. The average sulphate mass fraction of meltwater was computed to be 0.31 ± 0.12, showing dominancy of bicarbonate over sulphate. This excess bicarbonate would be generated by an alternative proton supply mechanism due to biological activities in the bed rock lithology and sulphide oxidation may be about the same as carbonation as a driver of chemical weathering at Chhota Shigri glacier. In general, major ions and total dissolved solid concentrations showed decreasing trend with increasing discharge from the study area. The average daily mean dissolved load of this glacier was much lower than that of the Gangotri glacier, which may be due to low meltwater runoff and lithology of the investigation area. The cation weathering rates of study area for early, peak and late melt seasons were computed to be 694, 1631 and 481 meq m−2 a−1, respectively. The average value of chemical denudation rates of the Chhota Shigri glacier meltwater was found lower than that of the Dokriani glacier.

A hydrochemical analysis of meltwater draining from Chaturangi glacier was conducted to determine the dissolved ions chemistry and to evaluate the geochemical processes controlling major ions chemistry of the study area. Ca2+, Mg2+ and SO4 2− are the dominant ions in the glacier meltwater. The ratio of (Ca + Mg) versus TZ+ varied from 0.79 to 0.86 with an average value of 0.82 ± 0.02 indicating larger contribution of Ca and Mg to the total cations. (Ca + Mg)/(Na + K) ratio is also high, varying from 3.77 to 6.33 with an average value of 4.77 ± 0.79. This shows the dominancy of carbonate weathering in the study area. The scatter diagram between (Ca + Mg) versus SO4 2− shows a linear trend throughout the range of data, indicating the dissolution of sulphate minerals as one of the possible source of SO4 2− in the Chaturangi glacier meltwater. The C-ratio of meltwater of the study area shows that sulphide oxidation is the major proton producing mechanism. Correlation matrix and principal component analysis (factor analysis) were applied for identification of various processes controlling solute acquisition in the Chaturangi glacier meltwater.

Hydrogeochemical assessment of meltwater quality draining from Bara Shigri glacier was carried out in the year 2011. The concentration of cations varied as Ca2+ > Mg2+ > K+ > Na+. Whereas, anions concentration followed the pattern HCO3 − > SO4 2− > Cl− > NO3 − > PO4 3−. High values of Ca+Mg/TZ+ and (Ca+Mg)/(Na+K) indicate that carbonate weathering is the most dominant mechanism controlling the major ions chemistry of the study area. However, the low ratio of (Na+K)/TZ+ also shows relatively smaller contribution of dissolved ions in the meltwater by silicate weathering as compared to carbonate weathering. The ratios of Na/Cl and K/Cl are higher than marine aerosols, indicating relatively small contribution from atmospheric precipitation to the chemical composition of meltwater of the study area.

The variation of biogenic silica (BiSi) in the surface sediments of mangroves of Gulf of Kachchh were due to the nutrients of overlying surface water, depositional environment and distance from supplying channels. In the current study, sediment BiSi is used as geochemical indicators of depositional environments. BiSi in the surface sediment does follows the trend of organic carbon (OC) content in the surface sediments, nutrients (NO3 −) of overlaying surface water, sand proportion in the surface sediment and distance from Arabian sea as reported higher concentration at Sachana (S3), New Bedi Port (S4), Old Bedi Port (S5) and Narara (S7). Higher concentration of NO3 − (30.09 ± 4.55 mg/l) and PO4 3− (1.51 ± 1.18 mg/l) leads to lower BiSi at Mundra (S1). Strong correlation of dissolved silica (DSi) (r = 0.91) indicates its significant influence on BiSi accumulation in the sediments. No significant correlation observed between BiSi in the surface sediments and SO4 2−. Lack of significant correlations among the nutrients indicates the influx of anthropogenic input and waste discharge containing high nitrogen and phosphorous compounds into the environment. Principal component (factor) analysis indicates that accumulation of BiSi in the sediments was highly enhanced by DSi in the surface water and anthropogenic phosphate inputs. Nutrient status of overlying surface water got affected by the accumulation of the BiSi in the surface sediments and may alter its productivity. N:P ratio is maintained by NO3 − oxidation in the ecosystem, which resist the replacement of diatoms by algal communities.

Major ion chemistry of meltwater draining from Patsio glacier was carried out between 2010 and 2012 to understand the meltwater chemistry and geochemical processes controlling hydrogeochemistry of the study area. Among the anions, bicarbonate is the major anion on average accounting for 52.5 % in 2010, 58.5 % in 2011 and 58.9 % in 2012 of the total anions (TZ−). Sulphate is the next dominant anion after bicarbonate on average accounting for 45.9 % in 2010, 36.3 % in 2011 and 39.8 % in 2012 of the total anions (TZ−). On the other hand, calcium is the major cation on average accounting for 71.9 % in 2010, 70.3 % in 2011 and 72.5 % in 2012 of the total cations (TZ+). The comparatively higher contribution of (Ca + Mg) to the total cations (TZ+), high value of (Ca + Mg)/((Na + K), good positive correlation between Ca-HCO3 and low value of (Na + K)/TZ+ for all 3 years indicate that carbonate weathering is a dominant geochemical process controlling meltwater chemistry of the study area. The average Na/Cl and K/Cl ratios in the meltwater draining from Patsio glacier are much higher than marine aerosols indicating comparatively minor contribution from atmospheric precipitation to the chemical composition of meltwater of the study area. The average pCO2 (effective CO2 pressure) values of the meltwater of study area are higher than the atmospheric pCO2 showing disequilibrium with respect to atmosphere and open system weathering. Statistical analysis (correlation matrix and factor analysis) was applied for identification of different factors controlling hydrochemistry of the Patsio glacier meltwater.

Studies on dissolved ion chemistry and suspended sediment concentration of meltwater draining from Chhota Shigri Glacier were carried out in the year 2008 and 2009. The cationic and anionic concentrations follow the trend: Ca2+ > Mg2+ > Na+ > K+ and HCO3 − > SO4 2− > Cl− > NO3 − > PO4 3−, respectively. The higher ratios of (Ca + Mg)/TZ+ and (Ca + Mg)/(Na + K); strong correlations between Ca-Mg, Ca-HCO3 and Mg-HCO3; and low ratio of (Na + K)/TZ+ for both the years indicate that chemical characteristics of Chhota Shigri Glacier meltwater are mostly controlled by carbonate weathering followed by silicate weathering. The C ratio shows that dissolution and dissociation of atmospheric CO2 is the major proton producer for glacier meltwater. Statistical analysis was used to identify different factors controlling dissolved ions chemistry of study area. There have been marked seasonal and diurnal variations in the total dissolved solid (TDS) and suspended sediment concentration of glacier meltwater observed during the sampling periods. TDS of meltwater is high during October (low discharge) and low during August (high discharge) in both years, implying that TDS is inversely correlated with discharge. On the other hand, suspended sediment concentration is higher during August (high flow regime) and low during October (low flow regime) during the sampling periods, generally following the discharge pattern of the glacier.

Removal of excess fluoride (F - ) from the water has been attempted by several authors by using different materials both natural and artificial. The main aim of this paper was to attempt the fluoride removal by using the locally available red soil adopting column method. The red soil was mixed in different proportion with sand in order to increase the porosity and permeability property of the medium. It was optimized for 4:1 ratio of red soil to sand and it was used for the following experiment. The experi- ment was conducted in 11 batches for a period of about 9,213 min. Fresh standard solution of F was used in each batch, prepared from Orion 1,000 ppm solution. The samples were collected and analyzed for pH, EC (Electrical Conductivity) and HCO3. Rate of flow of water and effi- ciency of adsorption were calculated and compared with the fluoride removal capacities of the medium. The med- ium used for the fluoride removal was subjected to FTIR analysis before and after the experiment. The variation of IR spectrum before and after treatment signifies the chan- ges in the OH bonding between Al and Fe ions present in the soil. The variation in pH decreased during the course of defluoridation. Higher F removal was noted when flow rate was lesser. An attempt on the regeneration of the fluoride adsorbed soil was also made and found to be effective.

Glaciers, while commonly regarded as sensitive indicators of climate change, can also be affected by various factors like atmospheric deposition. Study of major ions (Mg2+, Ca2+, Na+, K+, HCO3 −, SO4 2− and Cl−) of meltwater draining from Chhota Shigri glacier was carried out to understand weathering and geochemical processes controlling the major ion chemistry of the glacier meltwater. Chhota Shigri glacier meltwater was sampled in August 2008. Mg2+ is the dominant cation followed by Ca2+, K+ and Na+. Whereas HCO3 − is the dominant anion followed by SO4 2− and Cl−. The high ratio of Ca + Mg/TZ+ i.e. 0.77 and low ratio of Na + K/TZ+ i.e. 0.23 shows that carbonate weathering is the dominant mechanism controlling major ion chemistry followed by silicate weathering in the study area. In this paper we aim to evaluate the possible effect of various processes that affect the chemistry of meltwater of Chhota Shigri glacier. Decadal variation in the major ion chemistry of Chhota Shigri glacier meltwater was carried out by comparing the hydrochemistry of August 2008 with previous study carried out in 1987. Comparison between the two data sets shows that cations like Ca2+ increased nearly 6 times, Mg2+ 87 times, Na+ 10 times and K+ 19 times, while anions like Cl− increased nearly 12 times, HCO3 − 85 times and SO4 2− 49 times between 1987 and 2008. This could be attributed to increased weathering rates due to climate warming, atmospheric deposition or a combination of both. Annual specific mass balance of Chhota Shigri glacier was often sharply negative during 2002–2010, pointing to glacier recession, which may be also attributed to global climatic change.

Adverse effect of rapid industrialization on groundwater quality and quantity is widely known problem especially in developing countries. Tirupur, which is situated on the bank of Noyyal River in India, is known for intensive textile processing activities. As groundwater is the main water source for drinking water, there is an urgency to assess the groundwater quality. Twenty groundwater samples were collected for each post and pre-monsoon sampling during August 2009 and March 2010, respectively. Chemical and statistical analysis along with numerical modelling has been performed to assess the current status. The hydro-geochemical study revealed that the dominance of Mg–Cl and Na–HCO3 groundwater type in the upstream region Tirupur industrial hub of Noyyal River basin. Na–Cl groundwater type was found increasing in industrial hub (Kasipalayam) and downstream of the industrial hub (Anaipalayam) sites. The dominance of Na–Cl type of water is mainly due to the impact of salts like NaCl, Na2SO4, etc. used in textile processing, which after discharge, percolate and accumulate in the aquifers. Seasonal groundwater quality of Tirupur region as a whole showed the dominance of Ca–HCO3 −, Na–HCO3 − and Na–Cl water types. PHREEQC model output indicates that nearly all the groundwater samples were oversaturated with respect to calcite and dolomite and undersaturated with respect to gypsum and halite. The results obtained in this study were then compared with groundwater quality of the Noyyal River basin for the year 2008–2009. Among the two sites, Kasipalayam was found to be most contaminated due to incessant industrial discharge. But with the advent of new treatment technologies like CETPs having zero liquid discharge system and MBR, there has been slight decline in the concentration of different physicochemical parameters from 2002–2003 to 2008–2009. This study not only makes situation alarming but also calls for immediate attention for sustainable management of water resources.

A total of 30 water samples and 8 sediment samples were collected and chemically analysed for major ions (Na+, K+, Mg2+, Ca2+, HCO3 −, SO4 2−, Cl−, NO3 −, silica, PO4 3−, F−), trace elements (Fe, Mn, Ni, Cd, Zn, Pb, Cu), minerals and nutrients to determine the factors that control the chemistry of water in the Kawar-Tal and Kusheshwar-Asthan wetlands in the Bihar State of India. These analyses indicate that Ca2+ and HCO3 − ions are the most dominant ions in both of the wetlands. It also indicates rock weathering is a major source of ions in these wetlands, particularly the dissolution of carbonate minerals. The hydrogeochemistry of water in Kusheshwar-Asthan is favouring kaolinite formation and in Kawar-Tal favouring kaolinite–gibbsite formation. Quartz (~36%), clay minerals (~21%) and chlorite (~10%) are the dominant minerals in both the wetlands. Orthoclase (~12.49%), calcite (~7.51%) and illite (4.89%) minerals are only available in Kawar-Tal surface sediment, while albite (6.29%) and biotite (~13.6%) minerals are only available in Kusheshwar-Asthan. Total carbon (~3%), inorganic carbon (0.9%), organic carbon (~2.1%), total sulphur (~0.0008%), nitrogen (~0.55%) and phosphate (~0.96%) are available in Kawar-Tal surface sediments, while total carbon (~2.38%), inorganic carbon (0.55%), organic carbon (~1.84%), total sulphur (~0.001%), nitrogen (~0.62%) and phosphate (~0.64%) are available in Kusheshwar-Asthan surface sediments. The study indicates wetlands are rich in nutrient for biological activities and are sufficient to support the biodiversity, but few locations are influenced by anthropogenic activities which cause the increase of sulphur, chloride, iron and lead.

Available published literatures on glacier mass loss and climate studies like temperature and precipitation are reviewed for Lahaul and Spiti region in northern India, which is a part of the western Himalayas. Chhota Shigri and Hamtah Glaciers are both located in the Lahaul and Spiti region and have the longest record of in situ glaciological mass balance (MB) measurements. We have compiled and compared all the dataset (different methods) related to glacier change with climate in the past few decades. Both the glaciers have experienced a significant mass loss during the study period. Different methods show diverse results for the glaciers studied for the same year; however, all results depicts overall unsteady state of both the glaciers. Data of Indian Meteorological Department (IMD) shows a significant increase in average temperature for the entire country and huge variability in precipitation particularly in the state of Himachal Pradesh. Temperature and precipitation are found to be the two main governing factors controlling the glacier health in this region. Thus, it can be said that the glaciers of Lahaul and Spiti region are losing mass due to changing weather conditions, especially the increasing air temperature. However, long-term MB and climate data will give a better insight into understand and predict the future scenario of glacier health in this region.

Groundwater evaluation indices, multivariate statistical techniques, and geostatistical models are applied to assess the source apportionment and spatial variability of groundwater pollutants at the Lakshimpur district of Bangladesh. A total of 70 groundwater samples have been collected from wells (shallow to deep wells, i.e., 10–375 m) from the study area. Groundwater quality index reveals that 50 % of the water samples belong to good-quality water. The degrees of contamination, heavy metal pollution index, and heavy metal evaluation index present diversified results in samples even though they show significant correlations among them. The results of principal component analysis (PCA) show that groundwater quality in the study area mainly has geogenic (weathering and geochemical alteration of source rock) sources followed by anthropogenic source (agrogenic, domestic sewage, etc.). Cluster analysis and correlation matrix also supported the results of PCA. The Gaussian semivariogram models have been tested as the best fit models for most of the water quality indices and PCA components. The results of semivariogram models have shown that most of the variables have weak spatial dependence, indicating agricultural and residential/domestic influences. The spatial distribution maps of water quality parameters have provided a useful and robust visual tool for decision makers toward defining adaptive measures. This study is an implication to show the multiple approaches for quality assessment and spatial variability of groundwater as an effort toward a more effective groundwater quality management.

Glacial runoff and suspended sediment transport characteristics of the Chhota Shigri glacier were studied during the whole ablation period (May–October 2010). Discharge patterns of this glacier show that August experiences maximum runoff accounting for 34.2 % of the total runoff, followed by July 32.9 %, June 14.3 %, September 12.5 %, May 5.2 % and October 0.9 %. During the study period, the maximum runoff (Q max) was observed in the evening (4–6 p.m.), whereas minimum runoff (Q min) was observed in the morning (7–9 a.m.). The lag time between generation of meltwater from the glacier and its emergence as runoff varied from 1 to 4 h depending on the condition of melting during the melt season. A good correlation (r 2 = 0.71) was found between daily mean glacier-specific runoff and air temperature of the study area. Daily mean concentrations of suspended sediment for May, June, July, August, September and October were found as 155, 506, 577, 591, 80.9 and 30.8 mg l−1, respectively, showing maximum concentration of suspended sediment in August, followed by July. Suspended sediment load also follows a similar trend. Diurnal variations in the concentration of suspended sediment of the investigation area are directly associated with diurnal variations in meltwater runoff. There is a strong relationship between concentration of suspended sediment and discharge (r 2 = 0.79) and suspended sediment load with discharge (r 2 = 0.94). The average sediment yield of the Chhota Shigri glacier basin was computed as 1689 t km−2 year−1 during the melt season, much higher than the worldwide and Indian averages.

Major ion chemistry of lake water provides important information about the sources of dissolved ions, weathering, and hydrogeochemical processes as well as anthropogenic activities taking place in the lake environment. Surface water samples were collected from 23 different locations of the Chandra Tal (Lake) situated in the Western Himalaya and analyzed for 12 different physicochemical parameters for understanding hydrogeochemistry of the study area. The average value of pH in the lake water was measured to be 8.1, showing alkaline nature. HCO3 − was the most dominant anion and Ca2+ and Mg2+ were major cations in the Chandra Tal water. The high ratios of (Ca2+ + Mg2+)/TZ+ (total cations), (Ca2+ + Mg2+)/(Na+ + K+), Ca2+/Na+, Mg2+/Na+, and HCO3 −/Na+ show the dominancy of carbonate weathering as a major source of dissolved ions in the lake water of the study area. On the other hand, equivalent ratios of Na+/Cl− and K+/Cl− are significantly higher than the sea aerosol indicating relatively minor contribution of these ions from atmospheric fallout to the chemical composition of the Chandra Tal water. The carbon dioxide partial pressure (Pco2) of the lake water (10–2.9 atm) was significantly higher than Pco2 value of the atmosphere (10–3.5 atm), showing disequilibrium with respect to the atmosphere and open system weathering in the catchment. The correlation and R-mode principal component analysis indicate that Chandra Tal water chemistry is mainly controlled by weathering processes such as carbonate and silicate weathering, oxidation of pyrite, dissolution of sulphate minerals along with small contribution from atmospheric precipitation, and anthropogenic activities.

Clay mineral found in rivers, estuaries, and marine sedimentary environments is an important group of minerals which is the by-product of chemical weathering. The main constituents of this fine-grained sediment include mudstones, clay stones, and shales. This is probably the first report of a Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) investigation on the clay minerals to characterize them in the Sundarban mangrove core sediments of Moipith Matla and Belamati Island. This study was carried out in the selected stretch for FTIR and SEM analyses. The study reveals the dominant association of kaolinite with subordinate amount of quartz, illite, and chlorite. The abundance of kaolinite, illite, chlorite, and clay with quartz helps in increasing the sediment in the island region. The geochemical and mineralogical evolution of mangrove sediment results in the interaction of biotic and abiotic parameters, whose balance is conditioned by the climate that governs the hydrologic regime, the sedimentation dynamics, and of the organic matter. This study on the characterization of clay provides substantial impact in the water-holding capacity, productivity, and mineralogical and chemical transformation in order to establish much more and intermediate equilibrium between marine influence and continental contribution, as a part of the estuarine environment.

Glaciers are widely recognized as sensitive indicators for regional climate change. Very few studies have been conducted to investigate the long term deglaciation status in the Himalaya. In the present study, glaciers in the Beas basin, Himachal Pradesh, India were mapped by interpretation of various glacio-morphological features using the Landsat and IRS images. The mapping of 224 glaciers during the period 1972–2006 reveals that the glacier cover reduced from 419 to 371 km2, witnessing approximately 11.6% deglaciation in the Beas basin. A higher rate of retreat of the glaciers was observed during 1989–2006 as compared to the retreat during 1972–1989. Also, the loss has been more prominent in the glaciers with an areal extent of 2–5 km2. The number of glaciers increased from 224 to 236 due to fragmentation in this period. The average elevation of the ablation zone basin showed an upward shift from 3898 m (1972) to 4171 m (2006) which may be a consequence of a shift in Equilibrium Line Altitude (ELA) reflecting imbalance.

The Begnas Lake in the Pokhara Valley is one of the threatened habitats in Nepal. The major ion chemistry explains the status of most of the inorganic nutrients and their possible sources. However, the earlier studies mostly cover limnological investigations, and phytoplankton and zooplankton diversity. Thus, the present study has been conducted to investigate the geochemical processes and to examine the seasonal variation of chemical composition within Begnas Lake. The results showed that SO 4 2- , PO 4 3- , and NO 3 - increased compared with the previous values. The domination of Ca2+, Mg2+, and HCO 3 - explains the influence of carbonate weathering on the major ion concentration. In general, pH and dissolved oxygen decreased with the depth of water-column, while electric conductivity, total dissolved solids, HCO 3 - , Cl-, H4SiO4, K+, Mg2+, Ca2+, Mn2+, and Fe increased. Among the cations, the predominance of Ca2+ and Mg2+ as characterized by high (>0.6) (Ca2+ + Mg2+)/(Tz+) and (>0.8) (Ca2+ + Mg2+)/(Na+ + K+) equivalent ratios, also suggests prevalence of carbonate weathering. The low value of (Na+ + K+)/Tz+ ratio shows deficiency of Na+ and K+, suggesting low contribution of cations via aluminosilicate weathering. The C-ratio suggests a proton source derived both from oxidation of sulfide and dissolution and dissociation of atmospheric CO2 during different seasons. Though the major hydro-chemical parameters are within permissible limit, the increase in trophic state of the lake suggests that inherent biogeochemical processes make the limiting nutrients available, rendering eutrophic effect. Therefore, further comprehensive studies incorporating sediment–water interaction ought to be carried out to explain the ongoing phenomena and curb the eutrophication process in the lake.

Clay minerals, byproducts of chemical weathering, are important group of minerals found in rivers, estuaries, and marine sedimentary environments, which include mudstones, clay stones, and shales. In the present study, FTIR and SEM investigation on the clay minerals in Sundarban mangrove core sediments collected from Moipith Matla and Belamati Island are carried out. The study indicated the dominant association of kaolinite with subordinate amount of quartz, illite and chlorite. The abundance of kaolinite, illite chlorite and clay with quartz helps in increasing sediment in the islands region. The geochemical and mineralogical evolution of mangrove sediments are results of the interaction of biotic and abiotic parameters, whose balance is conditioned by the climate that governs the hydrologic regime, the sedimentation dynamics and the organic matter. This study on the charaterstation of clay provides us with substantial impact in the water holding capacity, productivity and mineralogical and chemical transformation in order to establish much more and intermediate equilibrium between marine influence and continental contribution, as part of the estuarine environment, than to the tropical climate conditions.

Sophisticated geochemical models have been used to describe and predict the chemical behaviour of complex natural waters and also to protect the groundwater resources from future contamination. One such model is used to study the hydrogeochemical complexity in a mine area. Extraction of groundwater from the coastal aquifer has been in progress for decades to mine lignite in Neyveli. This extraction has developed a cone of depression around the mine site. This cone of depression is well established by the geochemical nature of groundwater in the region. 42 groundwater samples were collected in a definite pattern and they were analysed for major cations, anions and trace elements. The saturation index (SI) of the groundwater for carbonate, sulphate and silica minerals was studied and it has been correlated with the recharge and the discharge regions. The SI of alumino silicates has been used to decipher the stage of weathering. The SIGibbsite − SIK-feldspar has been spatially distributed and the regions of discharge and recharge were identified. Then two flow paths A1 and A2 were identified and inverse modelling using PHREEQC were carried out to delineate the geochemical process that has taken place from recharge to discharge. The initial and final solutions in both the flow paths were correlated with the thermodynamic silicate stability diagrams of groundwater and it was found that the state of thermodynamic stability of the end solutions along the flow path were approaching similar states of equilibrium at the discharge.

Assessment of groundwater quality is essential to ensure sustainable use of it for drinking, agricultural, and industrial purposes. The chemical quality of groundwater of Gaya region has been studied in detail in this work to delineate the potable groundwater zones. A total of 30 groundwater samples and 2 surface water samples were collected in and around Gaya district of Bihar. The major cations follow the trend: Ca2+ > Mg2+ > Na+ > K+. The domination of calcium ions in the groundwater is due to weathering of rocks. The K+ ranged between 0.2 and 47.95 ppm, suggesting its abundance the below desired limit; but some samples were found to be above permissible limit. K+ weathering of potash silicate and the use of potash fertilizer could be the source. The major anions abundance followed the order HCO3− > Cl− > SO42− > NO3− > PO43−. Dissolution of carbonates and reaction of silicates with carbonic acid accounts for the addition of HCO3− to the groundwater and oxidation of sulphite may be the source of SO42−. Principal component analysis was utilized to reflect those chemical data with the greatest correlation and seven major principal components (PCs) representing >80 % of cumulative variance were able to interpret the most information contained in the data. PC1, PC2 and PC3 reflect the hydrogeochemical processes like mineral dissolution, weathering and anthropogenic sources. PC4, PC5, PC6 and PC7 show monotonic, random and independent relationships.

A detailed analytical study of major cations (Ca2 + , Mg2 + , Na + , K + ) and anions (SO $_{4}^{2-}$ , HCO $_{3}^{-}$ , Cl − , NO $_{3}^{-})$ of meltwater draining from Gangotri Glacier was carried out to understand major ion chemistry and to get an insight into geochemical weathering processes controlling hydrochemistry of the glacier. In the meltwater, the abundance order of cations and anions varied as follows: Ca2 + > Mg2 + > K + > Na + and SO $_{4}^{2-}$ > HCO $_{3}^{-}$ > Cl − > NO $_{3}^{-}$ , respectively. Calcium and magnesium are dominant cations while sulphate and bicarbonate are dominant anions. Weathering of rocks is the dominant mechanism controlling the hydrochemistry of drainage basin. The relative high contribution of (Ca+Mg) to the total cations (TZ + ), high (Ca+Mg)/(Na+K) ratio (2.63) and low (Na+K)/TZ + ratio (0.29) indicate the dominance of carbonate weathering as a major source for dissolved ions in the glacier meltwater. Sulphide oxidation and carbonation are the main proton supplying geochemical reactions controlling the rock weathering in the study area. Statistical analysis was done to identify various factors controlling the dissolved ionic strength of Gangotri Glacier meltwater.

This work gives us an overview of the groundwater quality and problems pertaining to the occurrence of arsenic (As) and other chemical contaminants in the groundwater of Begusarai district of Bihar, India. The total As concentration in the analyzed water samples varies between 21.5–94.3 μg/L. Through the saturation index using PhreeqC, it was found that most of the samples are saturated for mineral goethite, calcite and dolomite. It was observed that mobilization of arsenic from the alluvial aquifers is mainly affected through the means of reductive dissolution of the iron oxyhydroxides within the sediments. Reductive dissolution of iron oxyhydroxide present as coatings on and around clay layer seems to be the main process responsible for the release of As into groundwater. Close to the Gangetic flood plain most of the tube wells (shallow aquifers) are affected. Groundwater is characterized by slightly alkaline pH with a moderate to strong reducing nature. The water type mainly falls in two categories i.e. Ca–HCO3 and Ca–Cl (with contribution of 75 and 25% of total water type, respectively). Enrichment of $\mathrm{NO}_{3}^{-}$ at few locations is an indicator of agriculture practice well supported by effluent leaching.

The pollution of aquifer sediments by heavy metals has assumed serious concern due to their toxicity and accumulative behavior. Changes in environmental conditions can strongly influence the behavior of both essential and toxic elements by altering the forms in which they occur and therefore quantification of the different forms of metal is more meaningful than total metal concentrations. In this study, fractionation of metal ions in aquifer sediments of Semria Ojhapatti area, Bhojpur district, Bihar has been studied to determine the ecotoxic potential of metal ions. The investigations suggest that iron, copper, and arsenic have a tendency to remain associated in the following order residual > reducible > acid-soluble > oxidizable; manganese and zinc have tendency to be associated as residual > acid-soluble > reducible > oxidizable. The risk assessment code reveals that manganese and zinc occur in significant concentration in acid-soluble fraction and therefore comes under the high risk category and can easily enter the food chain. Most of the iron, copper, and arsenic occur as immobile fraction (i.e. residual) followed by its presence in reducible fraction and would pose threat to the water quality due to changing redox conditions. The metal enrichment factor in the study area shows moderate to significant metal enrichment in the aquifer sediments which may pose a real threat in near future. The geo-accumulation index of metals also shows that the metals lie in the range of strongly contaminated (for iron at shallow depths) to moderately contaminated to uncontaminated values.

Recharge zones and sources in an urban setup (NCT of Delhi, India) were identified using environmental isotopes (2H, 3H, 18O); they were then correlated with hydrogeological conditions. The isotopic results showed that groundwater is being recharged by surface water during the dry season, while recharge associated with local precipitation becomes prominent during the monsoon. The effect of source-water evaporation and altitude on the isotopic characteristics of groundwater was clearly noted. A gradual increase in groundwater age, i.e. decrease in tritium content, while moving away from the river/canals/drains, suggests a degree of mixing of old-aged groundwater with relatively young recharging water. Further, to substantiate the findings of isotopic investigations, surface recharge conditions were differentiated into potential pervious (recharge prone) and impervious (recharge resistant) surfaces through mapping of potential recharge areas based on soil type and water-table depth, to depict a three-dimensional illustration of hydrogeologically mediated recharge zones of the area. The hydrogeological evidence thus obtained about the spatial distribution of permeable zones, slope and boundary conditions, aptly substantiates the isotopic findings. The study seeks its impact by correlation of the isotopic findings with the regional groundwater flow regime which has been altered by the urban development.