Arsenic mobility in fluvial environment of the Ganga Plain,northern India

In the northern part of the Indian sub-continent, the Gomati River (a tributary of the Ganga River) was selected to study the dynamics of Arsenic (As) mobilization in fluvial environment of the Ganga Plain. It is a 900-km-long, groundwater-fed, low-gradient, alluvial river characterized by monsoon-controlled peaked discharge. Thirty-six water samples were collected from the river and its tributaries at low discharge during winter and summer seasons and were analysed by ICP-MS. Dissolved As and Fe concentrations were found in the range of 1.29–9.62 and 47.84–431.92 μg/L, respectively. Arsenic concentration in the Gomati River water has been detected higher than in its tributaries water and characteristically increases in downstream, attributed to the downstream increasing of Fe₂O₃ content, sedimentary organic carbon and silt-clay content in the river sediments. Significant correlation of determination (r ² = 0.68) was also observed between As and Fe concentrations in the river water. Arsenic concentrations in the river water are likely to follow the seasonal temperature variation and reach the level of World Health Organization’s permissible limit (10 μg/L) for drinking water in summer season. The Gomati River longitudinally develops reducing conditions after the monsoon season that mobilize As into the river water. First, dissolved As enters into pore-water of the river bed sediments by the reductive dissolution of Fe-oxides/hydroxides due to microbial degradation of sedimentary organic matter. Thereafter, it moves upward as well as down slope into the river water column. Anthropogenically induced biogeochemical processes and tropical climatic condition have been considered the responsible factors that favour the release of As in the fluvial environment of the Ganga Plain. The present study can be considered as an environmental alarm for future as groundwater resources of the Ganga–Brahmaputra Delta are seriously affecting the human–environment relationship at present.     

Investigation on the hydrodynamics of Ganga Alluvial Plain using environmental isotopes: a case study of the Gomati River Basin, northern India

An investigation using environmental isotopes (δ¹⁸O and δD) was conducted to gain insight into the hydrological processes of the Ganga Alluvial Plain, northern India. River-water, shallow-groundwater and lake-water samples from the Gomati River Basin were analyzed. During the winter season, the δ¹⁸O and δD compositions of the Gomati River water ranged from ?1.67 to ?7.62 ‰ and ?25.08 to ?61.50 ‰, respectively. Deuterium excess values in the river water (+0.3 to ?13 ‰) and the lake water (?20 ‰) indicate the significance of evaporation processes. Monthly variation of δ¹⁸O and δD values of the Gomati River water and the shallow groundwater follows a similar trend, with isotope-depleted peaks for δ¹⁸O and δD synchronized during the monsoon season. The isotopically depleted peak values of the river water (δ¹⁸O?=??8.30 ‰ and δD?=??57.10 ‰) can be used as a proxy record for the isotopic signature of the monsoon precipitation in the Ganga Alluvial Plain.     

Escalation of salinity levels in the quaternary aquifers of the Ganga alluvial plain,India

A detailed water quality analysis was carried out in the quaternary aquifer system of the marginal alluvial plain (Ganga Plain) in Bah Tahsil, Agra district, India. The electrical conductivity of 50 samples each from dug wells, hand pumps and tube wells was analysed for the study of salinity levels in shallow, intermediate and deep aquifers. Out of 50, 20 samples of each were also analysed for other chemical constituents such as Na⁺, K⁺, Cl⁻, F⁻ and TDS. The analyses show drastic changes in the salinity levels of shallow, intermediate and deep aquifers. The deep aquifers are more saline compared to the shallow and intermediate aquifers. On the contrary, the concentration of chemical constituents such as Na⁺, K⁺, Cl⁻ and F⁻ was more in the shallow aquifers compared to the deep aquifers. Moreover, there is an indication that the salinity and concentration of the above chemical constituents also escalate with time in each aquifer. The chemical constituents such as Na⁺, K⁺, Cl⁻, F⁻ and TDS range from 51 to 165 mg/l, 1 to 14 mg/l, 224 to 1,459 mg/l, 0 to 1.5 mg/l and 750 to 2,650 mg/l, respectively. Over a 3-year period, the salinity levels have sharply increased and the average F level has increased by 0.1–0.3 mg/l. An attempt has been made here to discuss the factors causing the variation and escalation of chemical constituents and salinity in the water of the three aquifers.     

Hydrogeochemistry of groundwater and anthropogenic control over dolomitization reactions in alluvial sediments of the Deoria district: Ganga plain,India

Groundwater is a critical resource in Deoria district, as it is the main source of drinking water and irrigation. The aquifer has deteriorated to a high degree, during the last two to three decades, in quality and quantity due to high population growth and environmental pollution. More than 90% of the population get their drinking water from subsurface waters. Fifteen wells were sampled in June 2006 to probe the hydrogeochemical components that influence the water quality. The results show that groundwater have EC, TDS, Na⁺, Mg²⁺, HCO₃⁻ and TH higher than the WHO, 1997 maximum desirable limits. A hydrogeochemical numerical model for carbonate minerals was constructed using the PHREEQC package. The regression analysis shows that there are three groups of elements which are significantly and positively correlated. The main hydrochemical facies of the aquifer (Ca + Mg–HCO₃) represents 33.33% of the total wells. The geochemical modeling demonstrated that the reactions responsible for the hydrochemical evolution in the area fall into three categories: (1) dissolution of salts, (2) precipitation of dolomite, (3) ion exchange. Solubility of dolomite, calcite, aragonite and gypsum were assessed in terms of the saturation index. The thermodynamic prerequisites for dolomite supersaturation reactions are satisfied by subsurface waters, since they are supersaturated with respect to dolomite, undersaturated (or in equilibrium) with respect to calcite, and undersaturated with respect to gypsum. The Ca²⁺ versus SO₄²⁻ and Mg²⁺ versus SO₄²⁻ trends are also compatible with homologous trends resulting from dolomite supersaturation.     

Sedimentation model of gravel-dominated alluvial piedmont fan,Ganga Plain,India

The Piedmont Zone of the Indo-Gangetic Plain contains numerous, laterally coalescing small alluvial fans. The Latest Pleistocene–Holocene 30 km long Gaula Fan can be divided into gravelly proximal fan (0–14 km down-stream), gravel-sand rich mid fan (14–22 km) and sand–mud dominated distal fan (22–30 km). The fan succession is composed of two fan expansion cycles A and B. Separated by an undulatory erosional contact of regional extent, cycle A is characterized by river borne clast-supported gravelly deposits, and the overlying fan expansion cycle B by matrix-supported gravely debris flows. The main process behind fan development has been lateral migration of channels over the fan surface probably due to rapid sedimentation caused by increased sediment supply, and the fluctuating water budget in response to changing climate. The water laid expansion cycle A represents a humid phase. The debris flow deposits of expansion cycle B suggest a dry phase. Approximately between 8 and 3 Ka, cycle B also indicates a phase of tectonic instability in the Siwalik Hills forming the mountain front. The tectonic activity caused incision of rivers into the fan surface, and in turn resulted in reduced fan-building activity. At present the fan surface is accreting by sheet flow processes.     

Holocene tectono-geomorphic evolution of Haryana plains,Western Ganga plain,India

Haryana plain is the drainage divide between the Ganga plain in the east and the Indus plain in the west. Being a part of the Himalayan foreland, its geomorphology, sedimentation processes, and tectonism are broadly controlled by the Himalayan tectonics. Soil and geomorphological mapping in Haryana plain bring out geomorphic features such as paleochannels, various active drainage patterns, and landforms such as old fluvial plains, floodplains, piedmonts, pediments, terminal fans, and eolian plains. Based on the degree of soil development, and Optical stimulated luminescence (OSL) ages, the soil-geomorphic units were grouped into six members (QIMS-I to VI) (Quaternary Indus Morphostratigraphic Sequence) of a morphostratigraphic sequence: QIMS-VI 9.86–5.38 Ka, QIMS-V 5.38–4.45 Ka, QIMS-IV 4.45–3.60 Ka, QIMS-III 3.60–2.91 Ka, QIMS-II <?2.91–1.52 Ka, and QIMS-I <?1.52 Ka. OSL chronology of different geomorphic features suggests six episodes of tectono-geomorphic evolution in the region since 10 Ka. Neotectonic features such as nine faults, two lineaments, and five fault-bounded tectonic blocks have been identified. Independent tilting and sagging of the blocks in response to neotectonics have resulted in modification of landforms, depositional processes, and hydro-geomorphology of the region. Major rivers like the Yamuna, the Ghaggar, and the Sutlej show different episodes of shifting of their courses. Lineament controlled few extinct channels have been recorded between 20 and 25 m depth below the surface in the ground-penetrating radar (GPR) profiles. These buried channels are aligned along the paleo-course of the Lost Saraswati River interpreted from the existing literature and hence are considered as the course of the lost river. Seven terminal fans have been formed on the downthrown blocks of the associated faults. The Markanda Terminal Fan, the first of such features described, is indeed a splay terminal fan and was formed by a splay distributary system of the Markanda River. Association of three terminal fans of different ages with the Karnal fault indicates the segment-wise development of the fault from west to east. Also, comparison with other such studies in the Ganga plain to further east suggests that the terminal fans formed by streams with distributary drainage pattern occur only in semiarid regions as in the present area and thus are indicators of semiarid climate/paleoclimate. Though the whole region is tectonically active, the region between the Rohtak fault and Hisar fault is most active at present signified by the concentration of earthquake epicenters.     

Heavy metals in freshly deposited sediments of the Gomati River (a tributary of the Ganga River): effects of human activities

 The concentrations of various metals (Cr, Cu, Co, Fe, Mn, Ni, Pb, Zn, and Cd) were determined in recently deposited surface sediments of the Gomati River in the Lucknow urban area. Markedly elevated concentrations (milligrams per kilogram) of some of the metals, Cd (0.26–3.62), Cu (33–147), Ni (45–86), Pb (25–77), and Zn (90–389) were observed. Profiles of these metals across the Lucknow urban stretch show a progressive downstream increase due to additions from 4 major drainage networks discharging the urban effluents into the river. The degree of metal contamination is compared with the local background and global standards. The geoaccumulation index order for the river sediments is Cd>Zn>Cu>Cr>Pb. Significant correlations were observed between Cr and Zn, Cr and Cu, Cu and Zn and total sediment carbon with Cr and Zn. This study reveals that the urbanization process is associated with higher concentrations of heavy metals such as Cd, Cu, Cr, Pb, and Zn in the Gomati River sediments. To keep the river clean for the future, it is strongly recommended that urban effluents should not be overlooked before their discharge into the river. Received: 16 February 1996 · Accepted: 29 February 1996     

Discharge estimation from planform characters of the Shedhi River, Gujarat alluvial plain: Present and past

In the absence of long-term hydrologic and streamflow records an understanding of river morphology (present and past) can help delineate changes in magnitudes of water and sediment discharges. The relict drainage system of Gujarat alluvial plain provides an opportunity to reconstruct the palaeochannel morphology-related discharge estimations. In this paper, based on the geomorphological evidence and channel geometry, an attempt has been made to reconstruct the palaeohydrological condition in the Shedhi River during the Holocene. A comparison of the present day channel of the Shedhi River with that of its palaeo counterpart reveals that the former was carrying much higher bankfull discharge (∼5500m³ s⁻¹) as compared to the present (∼200m³ s⁻¹). This is attributed to a larger drainage area and enhanced precipitation in the Shedhi River basin.     

Tectonic setting and sedimentology of Ganga River sediments, India

The Ganga basin provides a present-day example of a peripheral foreland basin. The course of the river is controlled by Himalayan tectonics. Three main types of architectural elements, such as channels (CH), sandy bedforms (SB) and overbank fines (OF) have been developed in Ganga River sediments. The channels (CH) include gravelly (Gs) and sandy channel (Ss) lithofacies. The sandy bedforms (SB) include trough cross-stratified (St), planar cross-stratified (Sp), horizontal stratified (Sh), sandy massive (Sm) and climbing ripple cross-laminated (Sr) lithofacies, all of which are active channel deposits. The overbank fines (OF) include massive silt and clay (Fm), parallel laminated silt and clay (FI) and climbing ripple cross-laminated (Sr) lithofacies. Mega units have been developed in the lower part of the active channel deposits, while small units have been developed in the upper part of active channel deposits, in inactive channel deposits and overbank fines. This study illustrates the seasonal and tectonic control on sedimentation. Petrofacies studies of the sediments indicate a recycled orogen provenance. The sediments are derived from rapidly uplifted fault blocks comprising granite, gneiss and basic and ultrabasic rocks. Lack of textural and compositional maturity suggests a local source of derivation. The principal control on sand composition is source lithology. The hot and humid climate may slightly increase the content of quartz in sand derived from reworked foreland basin sediments. but the effect is neither sufficient to shift the sand compositions out of the recycled orogen field nor does it obscure composition mixing patterns.     

Natural hazards in the Ghaghara River area, Ganga Plain, India

The Ganga Plain is one of the most densely populated regions of the world due to its fertile soil and availability of water. The rivers of this plain are the lifeline for millions of people of this vast alluvial plain. All rivers of this plain are characterized by narrow channel confined within wide valley. Continuously increasing pressure of population on this plain has led to the intensification of settlement even into the valley of the river. This unplanned expansion has enhanced the damage due to flooding during high-discharge period and lateral erosion during low-discharge period. Flooding and lateral erosion are identified as fluvial hazards in the Ghaghara River area. Extensive studies have been carried out on flooding, but not much attention has been paid to the phenomenon of lateral erosion. However, it has been observed that lateral erosion is an independent fluvial hazard that operates during low-discharge period. Low degree of compaction due to the presence of sandy and silty facies in the river valley deposits, mass movement, palaeocurrent pattern, and fractures initiates and enhances the lateral erosion. The present paper deals with the fluvial hazards in the Ghaghara River area.     

Major and trace element geochemistry in upper Ganga river in the Himalayas, India

Chemical weathering and resulting water compositions in the upper Ganga river in the Himalayas were studied. For the first time, temporal and spatial sampling for a 1 year period (monthly intervals) was carried out and analyzed for dissolved major elements, trace elements, Rare Earth Elements (REE), and strontium isotopic compositions. Amounts of physical and chemical loads show large seasonal variations and the overall physical load dominates over chemical load by a factor of more than three. The dominant physical weathering is also reflected in high quartz and illite/mica contents in suspended sediments. Large seasonal variations also occur in major elemental concentrations. The water type is categorized as HCO₃^––SO₄^2––Ca²⁺ dominant, which constitute >60% of the total water composition. On an average, only about 5–12% of HCO₃^– is derived from silicate lithology, indicating the predominance of carbonate lithology in water chemistry in the head waters of the Ganga river. More than 80% Na⁺ and K⁺ are derived from silicate lithology. The silicate lithology is responsible for the release of low Sr with extremely radiogenic Sr (⁸⁷Sr/⁸⁶ Sr>0.75) in Bhagirathi at Devprayag. However, there is evidence for other end-member lithologies for Sr other than carbonate and silicate lithology. Trace elements concentrations do not indicate any pollution, although presence of arsenic could be a cause for concern. High uranium mobilization from silicate rocks is also observed. The REE is much less compared to other major world rivers such as the Amazon, perhaps because in the present study, only samples filtered through <0.2 m were analysed. Negative Eu anomalies in suspended sediments is due to the excess carbonate rock weathering in the source area.     

Multiple discriminant analysis of the Drava River alluvial plain sediments

Three discriminant function models are raised and cross-compared in order to distinguish geochemical patterns characteristic for the Drava River floodplain sediments. Based on data representing total element concentrations in samples collected from alluvium (A), terrace (T), and unconsolidated bedrock (B) at the border of a floodplain, four element clusters emerged accounting for discrimination between the referred groups of sediments. The most prominent is contaminant/carbonate cluster characteristic for alluvium. The other two are: silicate cluster typical for unconsolidated geological substrate (Neogene sedimentary rocks); and naturally dispersed heavy metal cluster separating terrace from the former two groups. Models introducing depth intervals and single profiles as grouping criteria reveal identical sediment-heavy metal matrices. The second important issue of this paper is possibility of reclassification of samples originally assigned to one of the a priori defined groups of sediments, based on established geochemical pattern. The mapped geological units can be reconsidered by the post hoc assignments to a different group if geological border between alluvium and terrace or between terrace and bedrock can not be established geologically with absolute certainty.     

Tectonic controls on the geomorphic evolution of alluvial fans in the Piedmont Zone of Ganga Plain,Uttarakhand, India

The Piedmont Zone is the least studied part of the Ganga Plain. The northern limit of the Piedmont Zone is defined by the Himalayan Frontal Thrust (HFT) along which the Himalaya is being thrust over the alluvium of the Ganga Plain. Interpretation of satellite imagery, Digital Terrain Models (DTMs) and field data has helped in the identification and mapping of various morphotectonic features in the densely forested and cultivated Piedmont Zone in the Kumaun region of the Uttarakhand state of India. The Piedmont Zone has formed as a result of coalescing alluvial fans, alluvial aprons and talus deposits. The fans have differential morphologies and aggradation processes within a common climatic zone and similar litho-tectonic setting of the catchment area. Morphotectonic analysis reveals that the fan morphologies and aggradation processes in the area are mainly controlled by the ongoing tectonic activities. Such activities along the HFT and transverse faults have controlled the accommodation space by causing differential subsidence of the basin, and aggradation processes by causing channel migration, channel incision and shifting of depocentres. The active tectonic movements have further modified the landscape of the area in the form of tilted alluvial fan, gravel ridges, terraces and uplifted gravels.     

Fluvial geochemistry of Subarnarekha River basin,India

The fluvial geochemistry of the Subarnarekha River and its major tributaries has been studied on a seasonal basis in order to assess the geochemical processes that explain the water composition and estimate solute fluxes. The analytical results show the mildly acidic to alkaline nature of the Subarnarekha River water and the dominance of \(\hbox {Ca}^{2+}\) and \(\hbox {Na}^{+}\) in cationic and \(\hbox {HCO}_{3}^{-}\) and \({\hbox {Cl}}^{-}\) in anionic composition. Minimum ionic concentration during the monsoon and maximum concentration in the pre-monsoon seasons reflect concentrating effects due to decrease in the river discharge and increase in the base flow contribution during the pre-monsoon and dilution effects of atmospheric precipitation in the monsoon season. The solute acquisition processes are mainly controlled by weathering of rocks, with minor contribution from marine and anthropogenic sources. Higher contribution of alkaline earth \((\hbox {Ca}^{2+}{+}\,\hbox {Mg}^{2+})\) to the total cations \((\hbox {TZ}^{+})\) and high \((\hbox {Na}^{+}+\hbox {K}^{+})/\hbox {Cl}^{-}\), \((\hbox {Na}^{+}+\hbox {K}^{+})/\hbox {TZ}^{+}\), \(\hbox {HCO}_{3}^{-}/(\hbox {SO}_{4}^{2-}+\hbox {Cl}^{-})\) and low \((\hbox {Ca}^{2+}+\hbox {Mg}^{2+})/(\hbox {Na}^{+}+\hbox {K}^{+})\) equivalent ratios suggest that the Subarnarekha River water is under the combined influence of carbonate and silicate weathering. The river water is undersaturated with respect to dolomite and calcite during the post-monsoon and monsoon seasons and oversaturated in the pre-monsoon season. The pH–log \(\hbox {H}_{4}\hbox {SiO}_{4}\) stability diagram demonstrates that the water chemistry is in equilibrium with the kaolinite. The Subarnarekha River annually delivered \(1.477\times 10^{6}\) ton of dissolved loads to the Bay of Bengal, with an estimated chemical denudation rate of \(77\hbox { ton km}^{-2}\hbox { yr}^{-1}\). Sodium adsorption ratio, residual sodium carbonate and per cent sodium values placed the studied river water in the ‘excellent to good quality’ category and it can be safely used for irrigation.     

Arsenic exposure through groundwater in the middle Ganga plain in the Varanasi environs,India: A future threat

The study area covers an about 100 km² of the middle Ganga plain in Uttar Pradesh, experiencing intensive groundwater extraction. In order to recognize the arsenic contamination zones of the Varanasi environs, sixty eight groundwater samples have been collected and analyzed for major ions, iron and arsenic. Twenty one sediment samples in the four boreholes were also collected to deduce the source of arsenic in the groundwater. The preliminary survey reports for the first time indicates that part of rural and urban population of Varanasi environs are drinking and using for irrigation arsenic contaminated water mostly from hand tube wells (<70 m). The study area is a part of middle Ganga plain which comprises of Quaternary alluvium consists of an alternating succession of clay, clayey silt and sand deposits. The high arsenic content in groundwater samples of the study area indicates that 14% of the samples are exceeding the 10 μg/l and 5% of the samples are exceeding 50 μg/l. The high arsenic concentration is found in the villages such as Bahadurpur, Madhiya, Bhojpur, Ratanpur, Semra, Jalilpur, Kateswar, Bhakhara and Kodupur (eastern side of Ganga River in Varanasi), situated within the newer alluvium deposited during middle Holocene to Recent. The older alluvial aquifers situated in the western side of the Ganga River are arsenic safe (maximum As concentration of 9 μg/l) though the borehole sediments shows high arsenic (mean 5.2 mg/kg) and iron content (529 mg/kg) in shallow and medium depths. This may be due to lack of reducing conditions (i.e organic content) for releasing arsenic into the groundwater. Rainfall infiltration, organic matter from recently accumulated biomass from flood prone belt in the newer alluvium plays a critical role in releasing arsenic and iron present in sediments. The main mechanism for the release of As into groundwater in the Holocene sandy aquifer sediments of Varanasi environs may be due to the reductive dissolution of Fe oxyhydroxide present as coatings on sand grains as well as altered mica content. The high societal problems of this study will help to mitigate the severity of arsenic contamination by providing alternate drinking water resources to the people in middle Ganga plain and to arrange permanent arsenic safe drinking water source by the authorities.     

Major, trace and REE geochemistry of the Ganga River sediments: Influence of provenance and sedimentary processes

The sediments of the Ganga River from different depositional regimes in the Plain region such as the river channel, active flood-plain and the older flood-plain sediments from the inter-fluve region were analysed for major, trace and the rare earth elements (REEs). These are compared with catchment zone sediments of the river and probable source rocks in the Himalaya. The lower CIA values between 48 and 54.7 for the catchment sediments indicates that the sediments supplied to the Ganga Plain are chemically immature and subjected mostly to physical weathering due to higher erosion rates in the Himalaya. The CIA values ranging between 55 and 74, with average value of 59, 61.4 and 67 for sediments from the Plain's bed-load, active flood-plain and older flood-plain from the inter-fluve region indicates that silicate weathering of Ganga River sediments has occurred only after entering into the plains. This is likely because of higher residence time and change in the climate from cold-frigid in the Himalaya to tropical sub-humid in the plains. Therefore, the use of geochemical data on ancient system to infer climate in their source region may not always be true. Although the CIA values indicate a moderate chemical weathering in the plains, it is far from impressive. Dominance of physical weathering in the catchment region and lower degree of chemical weathering in the Plains indicate that weathering of sediments supplied by Himalayan Rivers, particularly the Ganga River may not have affected the atmospheric CO₂ to a significant level as is generally believed. Thus the net effect of the Himalaya on the CO₂ sequestration and consequent global cooling needs a re-evaluation.The plots of sediments in ternary diagram among La, Th, Sc and ratios involving Co/Th, La/Sc and Sc/Th indicate granitic to granodioritic source rocks to the sediments. The ratio plots involving relatively immobile Al₂O₃, TiO₂ and FeO along with REE plots suggest that out of the major Himalayan lithologies, gneisses and Cambro-Ordovician granites of HHCS have acted as the dominant source to the sediments.The plots of LogNa₂O/K₂O vs. LogSiO₂/Al₂O₃ and FeO/SiO₂ vs. Al₂O₃/SiO₂ diagrams show that the combination of processes including erosion, weathering, sorting and aeolian activity has together played a major role in progressively changing the chemistry from source rock to catchments bed-load to Plains bed-load, active flood-plains and the older inter-fluve sediments in the Ganga River system. The above plots demonstrate that as a result of above processes the ratios between the elements generally thought to be immobile and used in provenance studies does not always remain invariant and the linear trend line in the scatter gram between the two immobile elements show rotation around the fine grained end member.     

Hydrogeological environment and groundwater occurrences of the alluvial aquifers in parts of the Central Ganga Plain, Uttar Pradesh, India

A detailed hydrogeological investigation was carried out in parts of the Central Ganga Plain, India, with the objective of assessing the aquifer framework and its resource potential. The area was studied because of its dual hydrogeological situation, that is water logging and soil salinization in the canal command areas and depletion of aquifers in the western part of the basin. A comprehensive investigation of the aquifer system between the Ganga River and Kali River revealed its lateral and vertical dimensions and hydrogeological characteristics. Moreover, study of the groundwater occurrences, movements and behaviour, in terms of water level fluctuation with time and space, confirms the coexistence of over exploitation as well as water logging in the area.

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Electronic Supplementary Material Supplementary material is available for this article at

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Resumen Una investigación hidrogeológica detallada se llevó a cabo en partes de la Llanura de Ganga Central, India, con el objetivo de evaluar la estructura del acuífero y su potencial del recurso. El área fue estudiada por su doble situación hidrogeológica, es decir la saturación con agua y salinización de suelos en las áreas dominadas por el canal y vaciamiento de acuíferos en el la parte occidental de la cuenca. Una investigación completa del sistema acuífero entre el Río Ganga y el Río Kali, reveló sus dimensiones verticales y laterales y las características hidrogeológicas. Además, los estudios sobre la ocurrencia del agua subterránea, sus movimientos y comportamiento, en lo que se refiere al nivel de agua, y a su fluctuación en el tiempo y el espacio, confirma la co-existencia en el área de sobre- explotación así como de saturación con agua.

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Résumé L'objectif de cette étude hydrogéologique détaillée de portions de la Plaine Centrale du Gange est de déreminer la structure aquifère et la ressource potentielle. L'intérêt de la zone repose sur sa dualité du point de vue hydrogéologique, les zones influencées par le canal présentent une remontée de la nappe avec une salinisation des sols, la portion Ouest du bassin présente une baisse du niveau des aquifères. Par cette étude, le système aquifère compris entre la rivière du Gange et la rivière Kali révèle ses dimensions latérales et verticales ainsi que ses caractéristiques hydrogéologiques. De plus, l'étude des événements, des mouvements et du régime hydrogéologique affectant le niveau phréatique confirme la co-existence de surexploitation et de saturation des sols dans la région.

     

Provenance, tectonics and source weathering of modern fluvial sediments of the Brahmaputra–Jamuna River, Bangladesh: Inference from geochemistry

This present study describes the elemental geochemistry of fluvial sediments in the Kurigram (upstream) to Sirajganj–Tangail (downstream) section of the Brahmaputra–Jamuna River, Bangladesh, with the aim of evaluating their provenance, weathering and tectonic setting. Petrographically, the sediments are rich in quartz (68%), followed by feldspars (8.5%) and lithic grains (7%). The bulk sediment chemistry is influenced by grain size. Concentrations of TiO₂, Fe₂O₃, MgO, K₂O, P₂O₅, Rb, Nb, Cr, V, Y, and, Ce, Th and Ga slightly decrease with increasing SiO₂/Al₂O₃ and grain size, suggesting clay matrix control. In contrast, concentrations of CaO, Na₂O, Sr and Pb increase with increasing SiO₂/Al₂O₃ and grain size, suggesting residence of these substances in feldspar. Decrease in Zr as grain size increases is likely controlled both by clay matrix and heavy minerals. In addition, heavy minerals' sorting also influences Ce, Th, Y and Cr abundances in some samples. The sediments are predominantly quartzose in composition with abundant low-grade metamorphic and sedimentary lithics, low feldspars and trace volcanic detritus, indicating a quartzose recycled orogen province as a source of the sediments. Discriminant diagrams together with immobile element ratio plots show that, the Brahmaputra–Jamuna River sediments are mostly derived from rocks formed in an active continental margin. Moreover, the rare earth element ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate derivation of the sediments of Brahmaputra–Jamuna River from felsic rock sources of upper continental crust (UCC). The chemical indices of alteration suggest that Brahmaputra–Jamuna River sediments are chemically immature and experienced low chemical weathering effects. In the A–CN–K ternary diagram, most of the samples close to the plagioclase–K-feldspar join line and to the UCC plot, and in the field of various lithologies of Higher Himalayan Crystalline Series, suggesting that rocks in these series are likely source rocks. Therefore, the elemental geochemistry of the Brahmaputra–Jamuna River sediments is controlled mostly by mechanical breakdown of lithic fragments and subsequent preferential attrition of muscovite > albite > quartz.     

Weathering of the zinc-lead lode, Dugald River, northwest Queensland: II. surface mineralogy and geochemistry

Gossans associated with the Dugald River zinc-lead lode contain anomalous concentrations of Zn, Pb, Ag, As, Cd, Cu, Sb, Se, Tl and Ba and differ from those on the more pyritic Western Lode (Zn, Pb, Cu, As, Tl) and those associated with copper mineralization in the hanging wall (As, Bi, Co, Cu, Mo, Ni, Sb). Mineralogical and geochemical variations in gossans along strike reflect changes in primary ore and gangue mineralogy, particularly towards the north, where the Dugald River lode and hanging wall copper mineralization merge. Leaching of more soluble elements from the surface and re-precipitation below have resulted in large geochemical variations in the top metre of the profile.Dispersion into wall rocks has occurred over two distinct periods: hydromorphic dispersion, before erosion removed much of the gossan and surrounding Corella Formation, has resulted in very high Zn contents (up to 9%) in the footwall, whereas a more even dispersion of target and pathfinder elements into hanging and footwall rocks is from recent weathering of the slightly elevated gossan.     

Implication of drainage basin parameters of Chhoti Gandak River,Ganga Plain,India

The drainage basin parameters of the groundwater-fed Chhoti Gandak River originating in the terai area of the Ganga Plain were analyzed using topographical sheets, satellite data, and field documentation with emphasis to its implication for flood mitigation and recharging of groundwater. The analyses indicate dominance of first order streams, gentle slope gradient, low surface run-off, low sediment production, high infiltration rate, and low value of basin relief. The low water storage capacity, spreading of water and concentration of peak discharge in the distal part of the river basin explain that whenever precipitation is high in the catchment area there is flood in the distal part of the basin. The bifurcation ratio value (4.34) of this basin describes that the drainage is carved naturally by slope and local relief and not influenced by geological structures like lineaments and faults.