Characteristics of Rock–Water Interaction in Gangotri Proglacier Meltwater Streams at Higher Altitude Catchment Garhwal Himalaya, Uttarakhand, India
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J. Earth Syst. Sci. (2020) 129:173 Ó Indian Academy of Sciences https://doi.org/10.1007/s12040-020-01426-9 (0123456789().,-volV)(0123456789().,-volV) Characteristics of rock–water interaction in Gangotri proglacier meltwater streams at higher altitude catchment Garhwal Himalaya, Uttarakhand, India SARFARAZ AHMAD and ZABIULLAH ANSARI* Department of Geology, Aligargh Muslim University, Aligarh, India. *Corresponding author. e-mail: [email protected] MS received 18 March 2019; revised 9 March 2020; accepted 23 April 2020 Proglacial streams play an important role in water–rock interaction due to different climatic conditions at different altitudes. The main objective of the present study is to analyze the variation of glacier hydro- chemistry and sedimentation processes at different altitudes. The results show that the bed sediments in higher altitude streams are Bne sand, poorly sorted, leptokurtic in nature and dominated with high proportion of feldspar and biotite. At lower altitude, the bed sediment is coarse sand, moderately sorted and platykurtic in nature with relatively high proportion of quartz. The high concentration of biotite and feldspar in silt/lay size fraction are responsible for high proportion of magnesium in Gangotri proglacier meltwater than others. Meltwater is slightly acidic and hydrochemical facies shows Ca+2– +2 À +2 +2 + + Mg –HCO3 type. The concentration of Ca ,Mg ,Na, and K decreases with altitude due to dilution produced by augmentation of freshly monsoonal recharged groundwater from meadow and forest in downstream. The cation exchange, carbonate/silicate weathering and groundwater, subglacial water sources control the hydrochemistry of proglacial streams at lower altitude. Keywords. Gangotri proglacier streams; sediments texture; streams hydrochemistry; weathering processes. 1. Introduction an important source to supply sediments in the Cuvial ecosystem. Plucking, quarrying, crushing, Gangotri proglacial meltwater stream is the source shearing and abrasion are the main physical of the Ganges–Brahmaputra river system. This weathering processes in Himalayan glacier catch- river system plays an important role in world ments. Studies have demonstrated that the speciBc hydrological, sedimentological budget and aAect yield may increase downstream due to the remobi- the large human population of the world. The lization of sediments pushed by the glaciers (Fer- understanding of the glacier-fed meltwater streams guson 1984; Warburton 1990; Chauhan and processes are closely related with the comprehen- Hasnain 1993). The sediment loads of Himalayan sive knowledge of the sediment budget and hydro- rivers are reported to be highest in the world, logical composition of rivers in Himalaya. The delivering *17% of the global sediment input to the headwater of this river system is covered with gla- oceans (Milliman and Syvitski 1992). Along with cier/ice. In glacier cover catchments, physical sediment load, these rivers also contribute about weathering processes have long been recognized as 5% of the total dissolved solids in the ocean. The 173 Page 2 of 14 J. Earth Syst. Sci. (2020) 129:173 solute acquisition processes of the Himalayan rivers Garhwal Himalaya situated in the Uttarkashi in Ganga–Yamuna plains have been studied by district, Uttarakhand, India. It is bounded by lat- numerous scientists in last four decades (Abbas and itude 30°440–30°560N and longitude 79°040–79°150E Subramanian 1984; Subramanian 1985; Subrama- and streams draining in the south western direction nian et al. 1987; Sarin et al. 1989). Numerous studies (Bgure 1). The proglacial streams originate from have also been completed on hydrochemical aspect Gangotri glacier at an altitude of 4000 amsl and of small glaciers basins in Himalaya (Ahmad and Cow in deep glaciated valley. The famous Gangotri Hasnain 2000; Singh et al. 2012, 2013; Singh and temple is situated on the right side of the proglacial Ramanathan 2015). Most of these studies were river at the altitude of 3000 amsl. Hydrometero- conducted to investigate the hydrochemical pro- logical conditions in the catchment area of pro- cesses in high altitude region with the emphasis to glacial streams vary with altitude. The climate is revealing the rock–water interaction. The hydro- cold and mild warm at Gangotri town and severe logical and hydrochemical variability of glacier cold at Gangotri glacier. A variation with the meltwater streams have been studied in detail by altitude in the study area showing different eco- Singh and Hasnain (1998), Pandey et al. (1999) and logical zones in the catchment; above 3000 amsl Ahmad and Hasnain (2001). forest is sparse and represented by the Bhojpatra Hydrochemical researches in the glacier cover and near the glacier snout hardly any vegetation catchments of Himalaya have been conducted to survived except few herbs. The Gangotri proglacial characterize the hydrochemical species, temporal streams receive water mainly from two types of changes with season, glacial and subglacial path- sources; glacier meltwater and groundwater from ways. However, the interactions of proglacial melt- forest/meadows. water stream with channel sediments and forest The basement rocks of the Gangotri proglacial streams have found a little attention among hydro- stream catchment are Gangotri granite and chemists and hydrologists. In recent years, the Bhaironghati granite (Bgure 2). The Gangotri interactions of lithology, geomorphology, weather- granite is the western end of the Badrinath granite, ing kinetics and land cover with proglacial stream one of the largest bodies of the higher Himalayan have been studied (Wu et al. 2005; Baraer et al. 2009; leucogranite (HHL) belt in the Garhwal Himalaya. Chakrapani et al. 2009; Han et al. 2009; Panwar et al. It was exposed along the upper reaches of the 2016). The results indicated that the chemistry of Bhagirathi river around the Gangotri glacier meltwater controlled by groundwater interactions of region. The granite was Brst described by Heim the proximal environment has very high velocity in and Gannser (1939) from the higher Himalaya proglacial streams in headwater. The understanding along upper Alaknanda valley near Badrinath of evolution of the hydrochemical characteristics of tample. Later, Auden (1949) described, the Bne headwater stream water is crucial to predict the fate grain granite constituted by tourmaline, mus- of chemical interaction with pollutant in down- covite, biotite and garnet. The Gangotri granite is stream. These complex interactions cannot be intruded as lenses either the metamorphosed base identiBed in main composite streams in Ganga of the Tethyan sedimentary as mica porphyritic plains. Therefore, the higher altitude pristine envi- granite (Scaillet et al. 1990; Searle et al. ronment provides unique opportunity to reveal the 1993, 1999), which has been named as Bhairong- processes of sediment–water interaction. In the hati granite by Pant (1986) and mainly constituted present study, an integrated approach was applied by quartz, feldspar and muscovite. to investigate the variation in hydrochemical, geo- chemical, sedimentologoical and mineralogical characteristics with altitude to envisage the inter- 3. Materials and methods action of proglacial streams water in different environmental parameters. For revealing the rock–water interaction, different types of rock/water/stream bed samples were col- lected during 25–31 October, 2014 from Gangotri 2. Study area snout to Gangotri town during post-monsoon in proglacier environment. The altitude, longitude, The Gangotri proglacial stream drains from the and latitude information of the samples were doc- Gangotri glacier and the total catchment of the umented from GPS Garmin Etrex-10 and slope stream is 873 km2. It is the longest valley glacier in information along the meltwater stream were being J. Earth Syst. Sci. (2020) 129:173 Page 3 of 14 173 Figure 1. Sample location map along the Gangotri proglacial streams. Figure 2. Geology and rock types in Gangotri region (after Jowhar 2010). extracted from SRTM DEM (Shuttle Radar topo- different gravel samples were viewed and graphic Mission) using PCI Geomatica 9.1.1. photographed under the microscope with magniB- Stream bed sediment samples were collected in cation factor of 20 and 50 lm. The major mineral zip-lock polythene bags using a plastic scoop. The compositions were analyzed through Trinocular sediment grain size distributions were determined stereo zoom microscope (Nikon-SMZ1500). In each by sieve shaker (Fritsch Analysette 03.502) and sample, minerals were identiBed and perform based textural analysis was carried out by Folk and Ward on physical method for the 200 particles in a method (1957). The pebble size fraction of bed sample (Ingersoll et al. 1984). The mineralogy of sediment samples were analyzed under thin section clay fraction of bed sediments were studied using studies (Hamphries 1992). In thin sections, an X-ray diAractogram technique (Carrols 1970; centration of Ca nm using awas determined UV/VIS by the spectrophotometer. molybdosilicate method at Thewas 812 determined con- by titration Gibbs 173 run di sediments were identi Morphological features of the clay fraction of bed at420nmbyusingaUV/VISspectrophotometer.Cl the turbidimetric method, absorbance wasend measured point. Sulphate concentration was determinedpotentiometric by titration method keeping 4.5 pH asand the pH meter.samples were Bicarbonate measured was usingcollection, analyzed a electrical conductivity by meter washed