Water quality of the Chhoti Gandak River using principal component analysis,Ganga Plain,India

Chhoti Gandak is a meandering river which originates in the terai area of the Ganga Plain and serves as a lifeline for the people of Deoria district, Uttar Pradesh. It travels a distance of about 250 km and drains into Ghaghara near Gothani, Siwan district of Bihar. It has been observed that people of this region suffer from water-borne health problems; therefore water samples were collected to analyse its quality along the entire length of Chhoti Gandak River.     

Change in carbon flux (1960–2015) of the Red River (Vietnam)

Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555?±?639 kton C year^?1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year^?1 during the 1960s to 1372 kton C year^?1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.     

Total organic carbon transport by the Alaknanda River,Garhwal Himalayas,India

Transport and fate of organic carbon by the fluvial system play a significant role in the global biogeochemical cycle of carbon. Previous studies show that the transportation of modern organic carbon from the Himalayan River system accounts for 10–20% of the total global flux to the oceans. Till date, no study has been published which dealt with the transport of organic carbon in the headwaters of the Ganga River. The Alaknanda River is a headwater stream of the Ganga, which flows in the Western Himalayas of India. Water and freshly deposited channel sediment samples were collected during the months of March 2014 and August 2014 and analysed for dissolved organic carbon (DOC), particulate organic carbon (POC) and channel organic carbon (COC). The observed variability of organic carbon concentration was correlated with factors such as discharge, physiography and suspended sediment concentration (SSC). The results show that seasonal erosivity in the basin influences its DOC concentration and physiography, thus acting as a key parameter which controls transportation, oxidation and residence time of the organic matter. The allochthonous input of sediments from the erosional activities is the major source of organic carbon. At Devprayag, Alaknanda contributes 66% of the total DOC flux carried by the Ganga River. The comparison with the previously published values indicate that due to differences in physiography and chemical weathering rate, the Ganga River transports organic carbon mainly as a dissolved load in its upstream and predominantly as POC down the Himalayan foothills.     

Geochemistry and provenance of stream sediments of the Ganga River and its major tributaries in the Himalayan region,India

Major, trace and REE compositions of sediments from the upper Ganga River and its tributaries in the Himalaya have been examined to study the weathering in the Himalayan catchment region and to determine the dominant source rocks to the sediments in the Plains. The Ganga River rises in the Higher Himalaya from the Higher Himalayan Crystalline Series (HHCS) bedrocks and traverses over the Lesser Himalayan Series (LHS) and the Himalayan foreland basin (Siwaliks) rocks before entering into the Gangetic Plains. The major element compositions of sediments, reflected in their low CIA values (45.0–54.7), indicate that silicate weathering has not been an important process in the Himalayan catchment region of the Ganga River. Along the entire traverse, from the HHCS through LHS and the Siwaliks, the sediments from the tributaries and the mainstream Ganga River show higher Na₂O, K₂O, CaO and silica. This, and the higher ratios of La/Sc, Th/Sc and lower ratios of Co/Th, suggest that the source rocks are felsic. The fractionated REE patterns and the significant negative Eu anomalies (Eu/Eu? = 0.27–0.53) indicate highly differentiated source. Moreover, the comparison of the sediments with different source rock lithologies from the HHCS and the LHS for their major elements clearly suggests that the HHCS rocks were the dominant source. Further, comparison of their UCC (upper continental crust) normalized REE patterns suggests that, among the various HHCS rocks, the metasediments (para-gneiss and schist) and Cambro-Ordovician granites have formed the major source rocks. The Bhagirathi and Alaknanda River sediments are dominantly derived from metasediments and those in the Mandakini River from Cambro-Ordovician granites. The resulting composition of the sediments of the Ganga River is due to the mixing of sediments supplied by these tributaries after their confluence at Devprayag. No further change in major, trace and rare earth element compositions of the sediments of the Ganga River after Devprayag up to its exit point to the Plains at Haridwar, suggests little contribution of the Lesser Himalayan and Siwalik rocks to the Ganga River sediments.     

Arsenic in groundwater,Quaternary sediments,and suspended river sediments from the Middle Gangetic Plain,India: distribution,field relations,and geomorphological setting

A groundwater arsenic (As) survey in Mirzapur, Varanasi, Ghazipur, Ballia, Buxar, Ara, Patna, and Vaishali districts of UP and Bihar shows that people from these districts are drinking As-contaminated groundwater (max. 1,300 μg/l). About 66 % of tubewells from Buxar to Mirzapur areas and 89 % of tubewells from Patna to Ballia areas have As?>?10 μg/l (WHO guideline). Moreover, 36 % of tubewells from Buxar to Mirzapur areas and 50 % of tubewells from Patna to Ballia areas have As above 50 μg/l. Most of the As-affected villages are located close to abandoned or present meander channels of the Ganga River. In contrast, tubewells located in Mirzapur, Chunar, Varanasi, Saidpur, Ghazipur, Muhammadabad, Ballia, Buxar, Ara, Chhapra, Patna, and Hazipur towns are As-safe in groundwater because of their positions on the Pleistocene Older Alluvium upland surfaces. The iron (Fe) content in tubewell water samples varies from 0.1 to 12.93 mg/l. About 77 % As-contaminated tubewells are located within the depth of 21 to 40 m in the Holocene Newer Alluvium aquifers. The potential source of As in sediments carried through the rivers from the Himalayas. Maximum As concentrations in the Older and Newer Alluvium sediments are 13.73 and 30.91 mg/kg, respectively. The Himalayas rivers, i.e. Yamuna, Ganga, Gomati, Ghaghara, Gondak, Buri Gandak, and Kosi rivers carrying suspended sediments have high content of As (max. 10.59 mg/kg).     

Re-Os isotope systematics of sediments of the Brahmaputra River system

Re-Os analyses were performed on suspended loads and coarser grained bank sediments of the Brahmaputra River system. Re and Os concentrations of these sediments vary from 7 to 1154 ppt and from 3 to 173 ppt, respectively. ¹⁸⁷Os/¹⁸⁸Os ratios range from 0.178 to 6.8, and thus vary from nearly mantle to very radiogenic crustal values. Nevertheless, most of the sediments have ¹⁸⁷Os/¹⁸⁸Os ratios less than 1.5, and nearly all of the samples of the Brahmaputra main channel have ratios less than 1.2. Thus, as previously suggested, the Brahmaputra is much less radiogenic than the Ganga. The Siang River, the northern extension of the Brahmaputra, is quite radiogenic in Os despite receiving sediments from the Tsangpo River, which flows along a suture zone with ultramafic outcrops. The Brahmaputra main channel has a fairly constant ¹⁸⁷Os/¹⁸⁸Os ratio even though its tributaries contribute sediments with very heterogeneous Os isotopic compositions. These data, along with the corresponding Nd isotopic compositions, suggest that about 60-90% of the sediment in the Brahmaputra system is derived from Himalayan formations (Higher Himalaya and Lesser Himalaya) whereas 10-40% comes from ophiolite-bearing sequences, perhaps eastern equivalents of those of the Transhimalayan Plutonic Belt. Os data also confirm previously published Sr and Nd results, indicating that about half of the sediments delivered to the Brahmaputra are supplied by the Siang River, while the Himalayan and the eastern tributaries account for 40 and 10%, respectively.The lower ¹⁸⁷Os/¹⁸⁸Os of the Brahmaputra River compared to that of the Ganga is due to two factors. One is the more limited presence of the Lesser Himalaya and hence the lower black shale content of the eastern Himalaya. The other is the non-radiogenic Os supplied by the eastern and southern tributaries, reflecting the presence of mantle-derived lithologies in this region. Despite the lower sediment supply from these tributaries, they contribute greatly to the Os budget of the Brahmaputra River. This study indicates that the Brahmaputra River has little effect on the present-day seawater Os budget. However, reconsideration of this budget suggests that the Ganga, which provides the most radiogenic Os of major rivers studied to date, may have significant impact on the marine Os isotopic composition. The Indo-Asian collision cannot be excluded as an important cause of the increase in the marine ¹⁸⁷Os/¹⁸⁸Os over the past 16 million years until the contributions of all of the rivers draining the Himalayan Tibetan Plateau are known.     

Chemistry of the heavily urbanized Bagmati River system in Kathmandu Valley, Nepal: export of organic matter, nutrients, major ions, silica, and metals

Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH₄, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km^?2 year^?1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km^?2 year^?1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km^?2 year^?1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering.     

Sr isotopic signature of the Ganga Alluvial Plain and its implication to Sr flux of the Ganga River System

The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the Ganga River, draining nearly 30,500 km² area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about 335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the alluvial plain rivers. This study establishes that elevated ⁸⁷Sr/⁸⁶Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain.     

Chemical weathering in the plain and peninsular sub-basins of the Ganga: Impact on major ion chemistry and elemental fluxes

Concentrations of major ions, Sr and ⁸⁷Sr/⁸⁶Sr have been measured in the Gomti, the Son and the Yamuna, tributaries of the Ganga draining its peninsular and plain sub-basins to determine their contribution to the water chemistry of the Ganga and silicate and carbonate erosion of the Ganga basin. The results show high concentrations of Na and Sr in the Gomti, the Yamuna and the Ganga (at Varanasi) with much of the Na in excess of Cl. The use of this ‘excess Na’ (Na∗ = Na_riv − Cl_riv) a common index of silicate weathering yield values of ∼18 tons km⁻² yr⁻¹ for silicate erosion rate (SER) in the Gomti and the Yamuna basins. There are however, indications that part of this Na∗ can be from saline/alkaline soils abundant in their basins, raising questions about its use as a proxy to determine SER of the Ganga plain. Independent estimation of SER based on dissolved Si as a proxy give an average value of ∼5 tons km⁻² yr⁻¹ for the peninsular and the plain drainages, several times lower than that derived using Na∗. The major source of uncertainty in this estimate is the potential removal of Si from rivers by biological and chemical processes. The Si based SER and CER (carbonate erosion rate) are also much lower than that in the Himalayan sub-basin of the Ganga. The lower relief, runoff and physical erosion in the peninsular and the plain basins relative to the Himalayan sub-basin and calcite precipitation in them all could be contributing to their lower erosion rates.Budget calculations show that the Yamuna, the Son and Gomti together account for ∼75% Na, 41% Mg and ∼53% Sr and ⁸⁷Sr of their supply to the Ganga from its major tributaries, with the Yamuna dominating the contribution. The results highlight the important role of the plain and peninsular sub-basins in determining the solute and Sr isotope budgets of the Ganga. The study also shows that the anthropogenic contribution accounts for ?10% of the major ion fluxes of the Ganga at Rajmahal during high river stages (October). The impact of both saline/alkaline soils and anthropogenic sources on the major ion abundances of the Ganga is minimum during its peak flow and therefore the SER and CO₂ consumption rates of the river is best determined during this period.     

Fluid production rate during the regional metamorphism of a pelitic schist

Phase equilibria modeling of the pressure–temperature (P–T) path of regional metamorphism and associated fluid expulsion, combined with constraints on the timescale of garnet growth by Sm–Nd geochronology, elucidates the fluid production rate and fluid flux during Barrovian metamorphism of pelitic rocks from Townshend Dam, VT, USA. This modeling builds on a published companion study that utilized Sm–Nd geochronology of concentric growth zones in multiple garnet grains, to constrain the duration of garnet growth in a large sample of schist at Townshend Dam to 3.8?±?2.2 million years (Gatewood et al., Chem Geol 401:151–168, 2015). P–T pseudosections combined with observed mineral compositions constrain garnet growth conditions, and were utilized to construct P–T path-dependent thermodynamic forward models. These models determine that garnet growth was initiated at ~?0.6 GPa and ~?525 °C, with a roughly linear loading and heating P–T trajectory to >?0.8 GPa and ~?610 °C. Loading and heating rates of 2.4 km·Myear^?1 (with a range of 1.6 to 5.8 km·million year^?1) and 23 °C·million year^?1 (with a range of 14 to 54 °C·million year^?1), respectively, are consistent with model estimates and chronologic constraints for tectono-metamorphic rates during orogenesis. Phase equilibria modeling also constrains the amount of water release during garnet growth to be ~?0.7 wt% (or >?2 vol%), largely resulting from the complete consumption of chlorite. Coupling this estimate with calculated garnet growth durations provides a fluid production rate of 5.2 kg·m^?3·million year^?1 (with a range of 3.2 to 12.2 kg·m^?3·million year^?1) and when integrated over the overlying crustal column, a regional-scale fluid flux of 0.07–0.37 kg·m^?2·million year^?1. This range of values is consistent with those derived by numerical models and theory for regional-scale, pervasive fluid flow. This study signifies the first derivation of a fluid production rate and fluid flux in regional metamorphism using a direct chronology of water-producing (garnet-forming) reactions and can provide a framework for future studies on elucidating the nature and timescales of fluid release.     

Major ion chemistry of the Ganga source waters: Weathering in the high altitude Himalaya

A systematic study of the major ion chemistry of the Ganga source waters—the Bhagirathi, Alaknanda and their tributaries—has been carried out to assess the chemical weathering processes in the high altitude Himalaya. Among major ions, Ca, Mg, HCO₃ and SO₄ are the most abundant in these river waters. These results suggest that weathering of carbonate rocks by carbonic and sulphuric acids dominates in these drainage basins. On an average, silicate weathering can contribute up to ∼ 30% of the total cations. The concentration of total dissolved salts in the Bhagirathi and the Alaknanda is 104 and 115mg/l, respectively. The chemical denudation rate in the drainage basins of the Bhagirathi and the Alaknanda is, respectively, 110 and 137 tons/km²/yr, significantly higher than that derived for the entire Ganga basin, indicating intense chemical erosion of the Himalaya.     

Net Ecosystem Metabolism and Nonconservative Fluxes of Organic Matter in a Tropical Mangrove Estuary, Piauí River (NE of Brazil)

Net ecosystem metabolism (NEM) was measured in the Piauí River estuary, NE Brazil. A mass balance of C, N, and P was used to infer its sources and sinks. Dissolved inorganic carbon (DIC) concentrations and fluxes were measured over a year along this mangrove dominated estuary. DIC concentrations were high in all estuarine sections, particularly at the fluvial end member at the beginning of the rainy season. Carbon dioxide concentrations in the entire estuary were supersaturated throughout the year and highest in the upper estuarine compartment and freshwater, particularly at the rainy season, due to washout effects of carbonaceous soils and different organic anthropogenic effluents. The estuary served as a source of DIC to the atmosphere with an estimated flux of 13 mol CO₂ m^?2 year^?1. Input from the river was 46 mol CO₂ m^?2 year^?1. The metabolism of the system was heterotrophic, but short periods of autotrophy occurred in the lower more marine portions of the estuary. The pelagic system was more or less balanced between auto- and heterotrophy, whereas the benthic and intertidal mangrove region was heterotrophic. Estimated annual NEM yielded a total DIC production in the order of 18 mol CO₂ m^?2 year^?1. The anthropogenic inputs of particulate C, N, and P, dissolved inorganic P (DIP), and DIC were significant. The fluvial loading of particulate organic carbon and dissolved inorganic nitrogen (DIN) was largely retained in two flow regulation and hydroelectric reservoirs, promoting a reduction of C:N and C:P particulate ratios in the estuary. The net nonconservative fluxes obtained by a mass balance approach revealed that the estuary acts as a source of DIP, DIN, and DIC, the latter one being almost equivalent to the losses to the atmosphere. Mangrove forests and tidal mudflats were responsible for most of NEM rates and are the main sites of organic decomposition to sustain net heterotrophy. The main sources for this organic matter are the fluvial and anthropogenic inputs. The mangrove areas are the highest estuarine sources of DIP, DIC, and DIN.     

Weathering and Geochemical Processes Controlling Solute Acquisition in Ganga Headwater–Bhagirathi River, Garhwal Himalaya, India

Water and suspended sediment samples were collected along a longitudinal transect of the Bhagirathi – a headwater stream of the river Ganga, during the premonsoon and postmonsoon seasons, in order to assess the solute acquisition processes and sediment transfer in a high elevation river basin. Study results show that surface waters were dominated by HCO₃ and SO₄ in anionic abundance and Ca in cationic concentrations. A high concentration of sulphate in the source region indicates oxidative weathering of sulphide bearing minerals in the drainage basin. The combination of high concentrations of calcium, bicarbonate and sulphate in river water suggests that coupled reaction involving sulphide oxidation and carbonate dissolution are mainly controlling the solute acquisition processes in the drainage basin. The sediment transfer reveals that glacial weathering and erosion is the major influence on sediment production and transfer. The seasonal and spatial variation in ionic concentration, in general, is related to discharge and lithology. The sediment mineralogy and water mineral equilibrium indicate that water composition is in equilibrium with kaolinite. The river Bhagirathi annually delivers 0.74 M.tons of dissolved and 7.88 M.tons of suspended load to the river Ganga at Devprayag. The chemical and physical denudation rate of the Bhagirathi is 95 and 1010 tons/km²/yr, higher than the Indian and global average.     

Riverine organic carbon in the Xijiang River (South China): seasonal variation in content and flux budget

. Riverine water samples were collected from the lower reach hydrometric station Makou of the Xijiang River, in four hydrological seasons during 1997 and 1998. The samples were analyzed for their particulate and dissolved organic carbon. The contents of riverine particulate and dissolved organic carbon changed synchronously during different hydrological processes. The contents of organic carbon and total suspended substances in the riverine water increased with increasing discharge. The mass of organic carbon in the total suspended substances decreased logarithmically with increasing total suspended substances. The transported flux of organic carbon in the Xijiang River drainage is about 10.18᎒⁶ g of C km^–2 year^–1, which is two to three times larger than that of the average value in other river systems. Particulate organic carbon is the main component of riverine organic carbon, with a flux of about 8.30᎒⁶ g of C km^–2 year^–1.     

Hydrological and biogeochemical dynamics of the minor and trace elements in the St. Lawrence River

Surface water samples from the St. Lawrence River were collected in order to study the processes controlling minor and trace elements concentrations (Al, Fe, Mn, Cd, Co, Cu, Ni and Zn), and to construct mass balances allowing estimates of the relative importance of their natural and anthropogenic sources. The two major water inputs, the upper St. Lawrence River, which drains waters originating from the Lake Ontario, and the Ottawa River were collected fortnightly over 18 months. In addition, other tributaries were sampled during the spring floods. The output was monitored near Quebec City at the river mouth weekly between 1995 and 1999. Dissolved metal concentrations in the upper St. Lawrence River carbonated waters were lower than in the acidic waters of the tributaries draining the crystalline rocks of the Canadian shield and the forest cover. Biogeochemical and hydrodynamic processes occurring in Lake Ontario drive the seasonal variations observed in the upper St. Lawrence River. Biogeochemical processes relate to biological uptake, regeneration of organic matter (for Cd and Zn) and oxyhydroxide formation (for Mn and Fe), while hydrodynamic processes mainly concern the seasonal change in vertical stratification (for Cd, Mn, and Zn). In the Ottawa River, the main tributary, oxyhydroxide formation in summer governs seasonal patterns of Al, Fe, Mn, Cd, Co and Zn. The downstream section of the St. Lawrence River is a transit zone in which seasonal variations are mainly driven by the mixing of the different water masses and the large input of suspended particulate matter from erosion. The budget of all dissolved elements, except Fe and Zn, was balanced, as the budget of particulate elements (except Cd and Zn). The main sources of metals to the St. Lawrence River are erosion and inputs from tributaries and Lake Ontario. Direct anthropogenic discharges into the river accounted for less than 5% of the load, except for Cd (10%) and Zn (21%). The fluxes in transfer of dissolved Cd, Co, Cu and Zn species from the river to the lower St. Lawrence estuary were equal to corresponding fluxes calculated for Quebec City since the distributions of dissolved concentrations of these metals versus salinity were conservative. For Fe, the curvature of the dilution line obtained suggests that dissolved species were removed during early mixing.     

The short term climatic sensitivity of carbonate and silicate weathering fluxes: Insight from seasonal variations in river chemistry

Large seasonal variations in the dissolved load of the headwater tributaries of the Marsyandi river (Nepal Himalaya) for major cations and ⁸⁷Sr/⁸⁶Sr ratios are interpreted to result from a greater dissolution of carbonate relative to silicate at high runoff. There is up to a 0.003 decrease in strontium isotope ratios and a factor of 3 reduction in the Si(OH)₄/Ca ratio during the monsoon. These variations, in small rivers sampling uniform lithologies, result from a different response of carbonate and silicate mineral dissolution to climatic forcing. Similar trends are observed in compiled literature data, from both Indian and Nepalese Himalayan rivers. Carbonate weathering is more sensitive to monsoonal runoff because of its faster dissolution kinetics. Silicate weathering increases relative to carbonate during the dry season, and may be more predominant in groundwater with longer water-rock interaction times. Despite this kinetic effect, silicate weathering fluxes are dominated by the monsoon flux, when between 50% and 70% of total annual silicate weathering flux occurs.     

Major ion chemistry of the Yarlung Tsangpo-Brahmaputra river: Chemical weathering, erosion, and CO2 consumption in the southern Tibetan plateau and eastern syntaxis of the Himalaya

The Yarlung Tsangpo-Brahmaputra river drains a large portion of the Himalaya and southern Tibetan plateau, including the eastern Himalayan syntaxis, one of the most tectonically active regions on the globe. We measured the solute chemistry of 161 streams and major tributaries of the Tsangpo-Brahmaputra to examine the effect of tectonic, climatic, and geologic factors on chemical weathering rates. Specifically, we quantify chemical weathering fluxes and CO₂ consumption by silicate weathering in southern Tibet and the eastern syntaxis of the Himalaya, examine the major chemical weathering reactions in the tributaries of the Tsangpo-Brahmaputra, and determine the total weathering flux from carbonate and silicate weathering processes in this region. We show that high precipitation, rapid tectonic uplift, steep channel slopes, and high stream power generate high rates of chemical weathering in the eastern syntaxis. The total dissolved solids (TDS) flux from the this area is greater than 520 tons km⁻² yr⁻¹ and the silicate cation flux more than 34 tons km⁻² yr⁻¹. In total, chemical weathering in this area consumes 15.2 × 10⁵ mol CO₂ km⁻² yr⁻¹, which is twice the Brahmaputra average. These data show that 15-20% of the total CO₂ consumption by silicate weathering in the Brahmaputra catchment is derived from only 4% of the total land area of the basin. Hot springs and evaporite weathering provide significant contributions to dissolved Na⁺ and Cl⁻ fluxes throughout southern Tibet, comprising more than 50% of all Na⁺ in some stream systems. Carbonate weathering generates 80-90% of all dissolved Ca²⁺ and Mg²⁺ cations in much of the Yarlung Tsangpo catchment.     

Lithium as a Silicate Weathering Proxy: Problems and Perspectives

The lithium concentration of the dissolved load from the Lena River, together with major element chemistry and GIS-based area and runoff data demonstrate the importance of evaporites in controlling dissolved Li in river waters. Eighty-four percent of the Li in the dissolved load of upper Lena tributaries comes from evaporites in these drainage basins. Altogether, at least ~20% of the total Li flux of the Lena River originates from this source. This finding has important implications for using lithium as a proxy for silicate weathering. The Li flux and the ⁸⁷Sr/⁸⁶Sr ratio are compared in order to address a difference between the two silicate weathering rate proxies. The proposed controls on the dissolved δ⁷Li values in rivers (kinetic vs. equilibrium isotopic fractionation; Rayleigh-type preferential extraction of the heavy isotope) (Huh et al., Earth Planet Sci Lett 194:189–199, 2001) are evaluated using data from both the Siberian rivers and the Orinoco River. Neither of the proposed mechanisms satisfactorily explains the comprehensive data set. Instead, a ‘mineralogy-specific view’ that emphasizes the difference in the secondary mineralogy (i.e., fractionation factor) is presented as a potential rationalization in the form of the refined Rayleigh-type extraction.     

Dissolved fluoride in the Lower Ganges-Brahmaputra-Meghna River system in the Bengal Basin, Bangladesh

The dissolved fluoride (F⁻) in the Lower Ganges-Brahmaputra-Meghna (GBM) river system, Bengal basin, Bangladesh, was studied during 1991–1993 to determine its distribution and source in the basin, and its annual flux to the Bay of Bengal. The concentration of dissolved F⁻ varied between 2 and 11 μmol l⁻¹ with statistically significant variations both spatially and temporally in the basin. Such variations are attributable to the geology of the individual subbasins (Ganges, Brahmaputra and Meghna), dilution by rainwater during monsoon and groundwater contribution to the river systems during dry season. Correlation coefficients among F⁻ and major cations and anions suggest diverse inorganic processes responsible for regulating the concentration of F⁻ in these river systems. However, fluorite seems to be one of the major sources of dissolved F⁻. The concentration of F⁻ in the Lower GBM river system is low compared to the rivers draining Deccan Plateau and arid regions of the subcontinent, for example, Yamuna and its tributaries. However, it is within the range of most of the other Peninsular and Himalayan rivers. The GBM system contributes about 115×10³ tonnes year⁻¹ of dissolved F⁻ into the Bay of Bengal, and thus accounts for about 3% of the global F⁻ flux to the oceans annually. Received: 19 May 1999 · Accepted: 11 October 1999     

Geochemistry,dissolved elemental flux rates,and dissolution kinetics of lithologies of Alaknanda and Bhagirathi rivers in Himalayas,India

Alaknanda and Bhagirathi (AB) river basins in the Himalayan region in India expose lithologies comprising mainly of granites, low–high-grade metamorphics, shales and carbonates which, in conjunction with the monsoon rains and glacial melt, control water chemistry and dissolved elemental flux rates. In the present study, we monitored two locations: (a) Srinagar on the Alaknanda river and (b) Maneri on the Bhagirathi river for daily variations in total suspended sediments, major ions and dissolved silica over one complete year (July 2004–June 2005). Based on long-term discharge data, discharge-weighted composition and dissolved elemental flux rates (with respect to Ca, Mg, HCO₃, Si) of the river were estimated. The information thus obtained has substantially added up to the existing chemical data of these rivers and has refined the flux rates. Our high-frequency samples provide informations such as (a) water chemical compositions that show a large temporal and spatial variation and (b) carbonate lithology that controls water chemistry predominantly. The dissolution kinetics of various lithologies namely leucogranite, gneiss, quartzite, phyllite and shale of the AB river basins were studied through batch experiments at controlled temperature (25 and 5°C) and pH (8.4) condition. In laboratory, these lithologies undergo slow rates of dissolution (10⁻¹³ to 10⁻¹⁵ mol/m² s), while field weathering rates based on dissolved elemental flux rates in the AB rivers are much higher (10⁻⁸ to 10⁻⁹ mol/m² s). Extremely high physical weathering rates in AB rivers, which enhance chemical weathering significantly, mainly attribute this wide discrepancy in laboratory-derived rates of representative basin rocks and dissolved elemental fluxes in the field. However, laboratory-simulated experiments facilitate to quantify elemental release rates, understand the kinetics of the dissolution reactions, and compare their roles at individual level.