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1.
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2.
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.  相似文献   

3.
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.  相似文献   

4.
Pramod Singh 《Chemical Geology》2010,269(3-4):220-236
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.  相似文献   

5.
The Alaknanda and Bhagirathi rivers flow through the Higher and Lesser Himalayas and confluence at Devprayag, which represents the origin of the Ganga (or Ganges) river. In the present study, a vast number of temporal and spatial samples of the river waters were collected and analyzed for major cations and anions. In addition, more recent and time series water flow data have been obtained and based on these inputs, a more refined dissolved flux rates have been estimated. The Alaknanda and Bhagirathi rivers show significant variations in chemical compositions during different seasons. Carbonate rock weathering is responsible for more than 70% of the chemical compositions in the river waters. The chemical weathering rates show seasonal variations and are much higher during non-monsoon season. The dissolved flux of Alaknanda river is much higher (1.80 × 106 tons yr?1) as compared to the Bhagirathi river (0.34 × 106 tons yr?1). The chemical weathering rates in the basin vary between 85 and 155 tons km?2 yr?1, which is significantly higher compared to the global average of ～24 tons km?2 yr?1.  相似文献   

6.
Extensive measurements of dissolved Re and major ion abundances in the Yamuna River System (YRS), a major tributary of the Ganga, have been performed along its entire stretch in the Himalaya, from its source near the Yamunotri Glacier to its outflow at the foothills of the Himalaya at Saharanpur. In addition, Re analysis has been made in granites and Precambrian carbonates, some of the major lithologies of the drainage basin. These data, coupled with those available for black shales in the Lesser Himalaya, allow an assessment of these lithologies’ contributions to the Re budget of the YRS.The Re concentrations in the YRS range from 0.5 to 35.7 pM with a mean of 9.4 pM, a factor of ∼4 higher than that reported for its global average concentration in rivers. Dissolved Re and ΣCations∗ (= Na∗+K+Ca+Mg) are strongly correlated in the YRS, indicating that they are released to these waters in roughly the same proportion throughout their course. The Re/ΣCations∗ in most of these rivers are one to two orders of magnitude higher than the (Re/Na+K+Mg+Ca) measured in granites of the Yamuna basin. This leads to the conclusion that, on average, granites/crystallines make only minor contributions to the dissolved Re budget of the YRS on a basin-wide scale, though they may be important for rivers with low dissolved Re. Similarly, Precambrian carbonates of the Lesser Himalaya do not seem to be a major contributor to dissolved Re in these rivers, as their Re/(Ca+Mg) is much less than those in the rivers. The observation that Re concentrations in rivers flowing through black shales and in groundwaters percolating through phosphorite-black shale-carbonate layers in phosphorite mines are high, and that Re and SO4 are significantly correlated in YRS, seems to suggest that the bulk of the dissolved Re is derived from black shale/carbonaceous sediments. Material balance considerations, based on average Re of 30 ng g−1 in black shales from the Lesser Himalaya, require that its abundance in the drainage basin of the YRS needs to be a few percent to yield average Re of 9.4 pM. Furthermore, the positive correlation between Re and ΣCations∗ would require that these Re-rich sediments (e.g., black shales) and Re-poor lithologies (e.g., crystallines, Precambrian carbonates) contribute Re and cations in roughly the same proportion throughout the drainage basin. The available data on the abundance and distribution of black shales in the basin are not adequate to test if these requirements can be met.The annual fluxes of dissolved Re at the base of the Himalaya from the Yamuna are ∼150 mol at Batamandi and ∼100 mol at Saharanpur, compared to ∼120 mol from the Ganga at Rishikesh. The total flux from the Yamuna and the Ganga account for ∼0.4% of the global riverine Re flux, much higher than their contribution to global water discharge. This is also borne out from the mobilization rate of Re: ∼1 to 3 g km−2 y−1 in the Ganga and Yamuna basins in the Himalaya, compared to the global average of ∼0.1 g km−2 y−1.Black shale weathering can also significantly influence the budgets of Os and U in rivers and CO2 in rivers and the atmosphere. Using dissolved Re in rivers as a proxy, it is estimated that ∼(6-9) × 108 kg y−1 of black shales are being weathered in the Ganga and Yamuna basins in the Himalaya. Weathering of such amounts of black shales can account for the reported concentrations of Os and U in these rivers. Furthermore, if the weathering results in the conversion of organic carbon in the black shales to CO2, it would release ∼2 × 105 mol of CO2 km−2 y−1 in the Yamuna and Ganga basins in the Himalaya, comparable to the CO2 consumption from silicate weathering.  相似文献   

7.
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.  相似文献   

8.
The Alaknanda and Bhagirathi Rivers originate in the mountainous regions of the Himalayas (Garhwal) and result in high sediment yields causing flood hazards downstream of the Ganga River and high sediment flux to the Bay of Bengal. The rivers are perennial, since runoff in these rivers is controlled by both precipitation and glacial melt. In the present study, three locations in the upper reaches of the Ganga River were monitored for 1 yr (daily observations of, more than >1000 samples) for suspended sediment concentrations. In addition, more than one hundred samples were collected from various locations of the Alaknanda and Bhagirathi Rivers at different periods to observe spatial and temporal variations in river suspensions. Further, multi-annual data (up to 40 yrs) of water flow and sediment concentrations were used for inferring the variations in water flow and sediment loads on longer time scales. In most previous studies of Himalayan Rivers, there has been a general lack of long term water flow and sediment load data. In the present study, we carried out high frequency sampling, considered long term discharge data and based on these information, discussed the temporal and spatial variations in water discharge and sediment loads in the rivers in the Himalayan region. The results show that, >75% of annual sediment loads are transported during the monsoon season (June through September). The annual physical weathering rates in the Alaknanda and Bhagirathi River basins at Devprayag are estimated to be 863 tons km−2 yr−1 (3.25 mm yr−1) and 907 tons km−2 yr−1 (3.42 mm yr−1) respectively, which are far in excess of the global average of 156 tons km−2 yr−1 (0.58 mm yr−1).  相似文献   

9.
The river at its origin known as “Bhagirathi” attains the title “Ganga” after its confluence with Alaknanda, originates from the snout of Gangotri glacier. Water samples were collected from the selected sites from Gaumukh to Haridwar (2000–2001) for two seasons (pre-monsoon and post-monsoon) and analyzed for various physico-chemical characteristics. The pH, nitrate (NO3), conductance, chloride, alkalinity, total hardness, fluoride, sulphate and total dissolved solids were found to be in the ranges of 6.0–7.6, 0.225–10.6 mg/l, 73.0–978 μmhos, 5.0–70.0 mg/l, 15–90 mg/l, 10.0–250.0 mg/l, 0.23–1.60 mg/l, 12.0–150.0 mg/l and 37.0–190.6 mg/l respectively.  相似文献   

10.
Pramod Singh   《Chemical Geology》2009,266(3-4):251-264
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.  相似文献   

11.
Rates of chemical and silicate weathering of the Deccan Trap basalts, India, have been determined through major ion measurements in the headwaters of the Krishna and the Bhima rivers, their tributaries, and the west flowing streams of the Western Ghats, all of which flow almost entirely through the Deccan basalts.Samples (n = 63) for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002. The Total dissolved solid (TDS) in the samples range from 27 to 640 mg l−1. The rivers draining the Western Ghats that flow through patches of cation deficient lateritic soils have lower TDS (average: 74 mg l−1), whereas the Bhima (except at origin) and its tributaries that seem to receive Na, Cl, and SO4 from saline soils and anthropogenic inputs have values in excess of 170 mg l−1. Many of the rivers sampled are supersaturated with respect to calcite. The chemical weathering rates (CWR) of “selected” basins, which exclude rivers supersaturated in calcite and which have high Cl and SO4, are in range of ∼3 to ∼60 t km−2 y−1. This yields an area-weighted average CWR of ∼16 t km−2 y−1 for the Deccan Traps. This is a factor of ∼2 lower than that reported for the Narmada-Tapti-Wainganga (NTW) systems draining the more northern regions of the Deccan. The difference can be because of (i) natural variations in CWR among the different basins of the Deccan, (ii) “selection” of river basin for CWR calculation in this study, and (iii) possible contribution of major ions from sources, in addition to basalts, to rivers of the northern Deccan Traps.Silicate weathering rates (SWR) in the selected basins calculated using dissolved Mg as an index varies between ∼3 to ∼60 t km−2 y−1, nearly identical to their CWR. The Ca/Mg and Na/Mg in these rivers, after correcting for rain input, are quite similar to those in average basalts of the region, suggesting near congruent release of Ca, Mg, and Na from basalts to rivers. Comparison of calculated and measured silicate-Ca in these rivers indicates that at most ∼30% of Ca can be of nonsilicate origin, a likely source being carbonates in basalts and sediments.The chemical and silicate weathering rates of the west flowing rivers of the Deccan are ∼4 times higher than the east flowing rivers. This difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates. The silicon weathering rate (SWR) in the Krishna Basin is ∼15 t km−2 y−1, within a factor of ∼2 to those in the Yamuna, Bhagirathi, and Alaknanda basins of the Himalaya, suggesting that under favourable conditions (intense physical weathering, high runoff) granites and the other silicates in the Himalaya weather at rates similar to those of Deccan basalts. The CO2 consumption rate for the Deccan is deduced to be ∼3.6 × 105 moles km−2 y−1 based on the SWR. The rate, though, is two to three times lower than reported for the NTW rivers system; it still reinforces the earlier findings that, in general, basalts weather more rapidly than other silicates and that they significantly influence the atmospheric CO2 budget on long-term scales.  相似文献   

12.
Major ion composition of waters, δ13C of its DIC (dissolved inorganic carbon), and the clay mineral composition of bank sediments in the Brahmaputra River System (draining India and Bangladesh) have been measured to understand chemical weathering and erosion and the factors controlling these processes in the eastern Himalaya. The time-series samples, collected biweekly at Guwahati, from the Brahmaputra mainstream, were also analyzed for the major ion composition. Clay mineralogy and chemical index of alteration (CIA) of sediments suggest that weathering intensity is relatively poor in comparison to that in the Ganga basin. This is attributed to higher runoff and associated physical erosion occurring in the Brahmaputra basin. The results of this study show, for the first time, spatial and temporal variations in chemical and silicate erosion rates in the Brahmaputra basin. The subbasins of the Brahmaputra watershed exhibit chemical erosion rates varying by about an order of magnitude. The Eastern Syntaxis basin dominates the erosion with a rate of ∼300 t km−2 y−1, one of the highest among the world river basins and comparable to those reported for some of the basaltic terrains. In contrast, the flat, cold, and relatively more arid Tibetan basin undergoes much slower chemical erosion (∼40 t km−2 y−1). The abundance of total dissolved solids (TDS, 102-203 mg/L) in the time-series samples collected over a period of one year shows variations in accordance with the annual discharge, except one of them, cause for which is attributable to flash floods. Na* (Na corrected for cyclic component) shows a strong positive correlation with Si, indicating their common source: silicate weathering. Estimates of silicate cations (Nasil+Ksil+Casil+Mgsil) suggest that about half of the dissolved cations in the Brahmaputra are derived from silicates, a proportion higher than that for the Ganga system. The CO2 consumption rate due to silicate weathering in the Brahmaputra watershed is ∼6 × 105 moles km−2 y−1; whereas that in the Eastern Syntaxis subbasin is ∼19 × 105 moles km−2 y−1, similar to the estimates for some of the basaltic terrains. This study suggests that the Eastern Syntaxis basin of the Brahmaputra is one of most intensely chemically eroding regions of the globe; and that runoff and physical erosion are the controlling factors of chemical erosion in the eastern Himalaya.  相似文献   

13.
Sr and 87Sr/86Sr have been measured in the Yamuna river headwaters and many of its tributaries (YRS) in the Himalaya. These results, with those available for major ions in YRS rivers and in various lithologies of their basin, have been used to determine their contributions to riverine Sr and its isotopic budget. Sr in the YRS ranges from 120 to 13,400 nM, and 87Sr/86Sr from 0.7142 to 0.7932. Streams in the upper reaches, draining predominantly silicates, have low Sr and high 87Sr/86Sr whereas those draining the lower reaches exhibit the opposite resulting from differences in drainage lithology. 87Sr/86Sr shows significant co-variation with SiO2/TDS and (Na* + K)/TZ+ (indices of silicate weathering) in YRS waters, suggesting the dominant role of silicate weathering in contributing to high radiogenic Sr. This is also consistent with the observation that streams draining largely silicate terrains have the highest 87Sr/86Sr, analogous to that reported for the Ganga headwaters. Evaluation of the significance of other sources such as calc-silicates and trace calcites in regulating Sr budget of these rivers and their high 87Sr/86Sr needs detailed work on their Sr and 87Sr/86Sr. Preliminary calculations, however, indicate that they can be a significant source to some of the rivers.It is estimated that on an average, ∼25% of Sr in the YRS is derived from silicate weathering. In the lower reaches, the streams receive ∼15% of their Sr from carbonate weathering whereas in the upper reaches, calc-silicates can contribute significantly (∼50%) to the Sr budget of rivers. These calculations reveal the need for additional sources for rivers in the lower reaches to balance their Sr budget. Evaporites and phosphorites are potential candidates as judged from their occurrence in the drainage basin. In general, Precambrian carbonates, evaporites, and phosphorites “dilute” the high 87Sr/86Sr supplied by silicates, thus making Sr isotope distribution in YRS an overall two end member mixing. Major constraints in quantifying contributions of Sr and 87Sr/86Sr from different sources to YRS rivers are the wide range in Sr and 87Sr/86Sr of major lithologies, limited data on Sr and 87Sr/86Sr in minor phases and on the behavior of Sr, Na, and Ca during weathering and transport.The Ganga and the Yamuna together transport ∼0.1% of the global Sr flux at the foothills of the Himalaya which is in the same proportion as their contribution to global water discharge. Dissolved Sr flux from the Yamuna and its mobilization rate in the YRS basin is higher than those in the Ganga basin in the Himalaya, a result consistent with higher physical and chemical erosion rates in the YRS.  相似文献   

14.
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––SO42––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.  相似文献   

15.
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∗ = Nariv − Clriv) 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.  相似文献   

16.
青藏高原东部长江流域盆地陆地化学风化研究   总被引：4，自引：0，他引：4  
长江河水主要离子由流域盆地碳酸盐岩的风化所控制,沱沱河和楚玛尔河受蒸发盐岩影响较为明显;河水溶质载荷Si,Si/TZ *,Si/(Na* K)等指标表明,长江流域盆地地表硅酸盐岩风化还是浅表层次的;金沙江地表化学剥蚀速率为1.74×103mol/yr.km2,雅砻江为1.69×103mol/yr.km2,大渡河为1.57×103mol/yr.km2,岷江为1.88×103mol/yr.km2,长江河源区楚玛尔河为2.32×103mol/yr.km2,沱沱河为1.37×103mol/yr.km2,流域地表化学剥蚀速率可与世界上其它造山带的河流进行对比。  相似文献   

17.
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.  相似文献   

18.
The Hanjiang River, the largest tributaries of the Changjiang (Yangtze) River, is the water source area of the Middle Route of China’s South-to-North Water Transfer Project. The chemical and strontium isotopic compositions of the river waters are determined with the main purpose of understanding the contribution of chemical weathering processes and anthropogenic inputs on river solutes, as well as the associated CO2 consumption in the carbonate-dominated basin. The major ion compositions of the Hanjiang River waters are characterized by the dominance of Ca2+ and HCO3 −, followed by Mg2+ and SO4 2−. The increase in TDS and major anions (Cl−, NO3 −, and SO4 2−) concentrations from upstream to downstream is ascribed to both extensive influences from agriculture and domestic activities over the Hanjiang basin. The chemical and Sr isotopic analyses indicate that three major weathering sources (dolomite, limestone, and silicates) contribute to the total dissolved loads. The contributions of the different end-members to the dissolved load are calculated with the mass balance approach. The calculated results show that the dissolved load is dominated by carbonates weathering, the contribution of which accounts for about 79.4% for the Hanjiang River. The silicate weathering and anthropogenic contributions are approximately 12.3 and 6.87%, respectively. The total TDS fluxes from chemical weathering calculated for the water source area (the upper Hanjiang basin) and the whole Hanjiang basin are approximately 3.8 × 106 and 6.1 × 106 ton/year, respectively. The total chemical weathering (carbonate and silicate) rate for the Hanjiang basin is approximately 38.5 ton/km2/year or 18.6 mm/k year, which is higher than global mean values. The fluxes of CO2 consumption by carbonate and silicate weathering are estimated to be 56.4 × 109 and 12.9 × 109 mol/year, respectively.  相似文献   

19.
Chemical weathering in the Three Rivers region of Eastern Tibet   总被引：2，自引：0，他引：2  
Three large rivers - the Chang Jiang (Yangtze), Mekong (Lancang Jiang) and Salween (Nu Jiang) - originate in eastern Tibet and run in close parallel over 300 km near the eastern Himalayan syntaxis. Seventy-four river water samples were collected mostly during the summer season from 1999 to 2004. Their major element compositions vary widely, with total dissolved solids (TDS) ranging from 31 to 3037 mg/l, reflecting the complex geologic makeup of the vast drainage basins. The major ion distribution of the main channel samples primarily reflects the weathering of carbonates. Evaporite dissolution prevails in the headwater samples of the Chang Jiang in the Tibetan Plateau interior, as evidenced by the high TDS (928 and 3037 mg/l) and the Na-Cl dominant major element composition. Local tributary samples of the Mekong and Salween, draining the Lincang Batholith and the Tengchong Volcano, show distinctive silicate weathering signatures. We used five reservoirs - rain, halite, sulfate, carbonate, and silicate - in a forward model to calculate the contribution from silicate weathering to the total dissolved load and to estimate the consumption rate of atmospheric CO2 by silicate weathering. Carbonate weathering accounts for about 50% of the total cationic charge (TZ+) in the samples of the Mekong and the Salween exiting the Tibetan Plateau. In the “exit” sample of the Chang Jiang, 45% of TZ+ is from halite dissolution inherited from the extreme headwater tributaries in the interior of the plateau, and carbonates contribute only 26% to the TZ+. The net rate of CO2 consumption by silicate weathering is (103-121) × 103 mol km−2 year−1, lower than the rivers draining the Himalayan front. GIS-based analyses indicate that runoff and relief can explain 52% of the spread in the rate of atmospheric CO2 drawdown by silicate weathering, but other climatic (temperature, precipitation, potential evapotranspiration) and geomorphic (elevation, slope) factors also show collinearity. Only qualitative conclusions can be drawn for the significance of lithology due to lack of digitized lithologic information. The effect of the peculiar drainage pattern due to tectonic forcing is not readily apparent in the major element composition or in increased chemical weathering rates. The 87Sr/86Sr ratios and the silicate weathering rates are in general lower in the Three Rivers than in the rivers draining the Himalayan front.  相似文献   

20.
New Nd and Sr isotope data are presented in this paper for sediments from the Yellow and Yangtze River drainage basins. The average 143Nd/144Nd isotope compositions of fine-grained sediments from two drainage basins seem similar. The T DMNd ages of sediments from the two drainage basins are relatively uniform but exhibit subtle differences. This reflects the different underlying bedrocks, in association with the unique tectonic terranes that comprise central and southeastern China, including the North China Block, the Yangtze Block, the South China Block, the Tibet Plateau and the Qinling-Dabie Orogenic Belt. In contrast, there is an obvious difference in the 87Sr/86Sr ratios between fine-grained sediments of the Yellow and Yangtze Rivers, which actually reflects an increase in chemical weathering intensity from northwestern to southeastern China.  相似文献   

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