Major World Rivers Research Articles

Floodplain dynamics included in river model

Surface water flow is important to the climate system and to water resources management. Floodplain inundation dynamics is a key part of surface water flow, but most current river routing models do not include realistic representation of floodplain dynamics. A new global river routing model created by Yamazaki et al. does include these dynamics. The researchers tested the model by comparing results of their model simulation with in situ and satellite observations and found that the model improved simulation of river discharge in most of the world's major river basins. (Water Resources Research, doi:10.1029/2010WR009726, 2011)

A physically based description of floodplain inundation dynamics in a global river routing model

Current global river routing models do not represent floodplain inundation dynamics realistically because the storage and movement of surface waters are regulated by small‐scale topography rather than the commonly used spatial resolution of global models. In this study, we propose a new global river routing model, CaMa‐Flood, which explicitly parameterizes the subgrid‐scale topography of a floodplain, thus describing floodplain inundation dynamics. The relationship between water storage, water level, and flooded area in the model is decided on the basis of the subgrid‐scale topographic parameters based on 1 km resolution digital elevation model. Horizontal water transport is calculated with a diffusive wave equation, which realizes the backwater effect in flat river basins. A set of global‐scale river flow simulations demonstrated an improved predictability of daily‐scale river discharge in many major world rivers by incorporating the floodplain inundation dynamics. Detailed analysis of the simulated results for the Amazon River suggested that introduction of the diffusive wave equation is essential for simulating water surface elevation realistically. The simulated spatiotemporal variation of the flooded area in the Amazon basin showed a good correlation with satellite observations, especially when the backwater effect was considered. The improved predictability for daily river discharge, water surface elevation, and inundated areas by the proposed model will promote climate system studies and water resource assessments.

Evaluation of the Global Land Data Assimilation System using global river discharge data and a source‐to‐sink routing scheme

Advanced land surface models (LSMs) offer detailed estimates of distributed hydrological fluxes and storages. These estimates are extremely valuable for studies of climate and water resources, but they are difficult to verify as field measurements of soil moisture, evapotranspiration, and surface and subsurface runoff are sparse in most regions. In contrast, river discharge is a hydrologic flux that is recorded regularly and with good accuracy for many of the world's major rivers. These measurements of discharge spatially integrate all upstream hydrological processes. As such, they can be used to evaluate distributed LSMs, but only if the simulated runoff is properly routed through the river basins. In this study, a rapid, computationally efficient source‐to‐sink (STS) routing scheme is presented that generates estimates of river discharge at gauge locations based on gridded runoff output. We applied the scheme as a postprocessor to archived output of the Global Land Data Assimilation System (GLDAS). GLDAS integrates satellite and ground‐based data within multiple offline LSMs to produce fields of land surface states and fluxes. The application of the STS routing scheme allows for evaluation of GLDAS products in regions that lack distributed in situ hydrological measurements. We found that the four LSMs included in GLDAS yield very different estimates of river discharge and that there are distinct geographic patterns in the accuracy of each model as evaluated against gauged discharge. The choice of atmospheric forcing data set also had a significant influence on the accuracy of simulated discharge.

Seasonal variations of physical and chemical erosion: A three-year survey of the Rhone River (France)

Numerous studies of weathering fluxes have been carried out on major world rivers during the last decade, to estimate CO 2 consumption rates, landscape evolution and global erosion rates. For obvious logistical reasons, most of these studies were based on large scale investigations carried out on short timescales. By comparison, much less effort has been devoted to long term monitoring, as a means to verify the temporal variability of the average characteristics, their trends, and the representativeness of short-term investigations. Here we report the results of a three-year survey (November 2000 to December 2003) of the major and trace element composition of dissolved and suspended matter in the lower Rhone River (France), the largest river of the Mediterranean area. Subsurface water samples were collected in Arles, about 48 km upstream of the estuary, twice a month routinely, and at higher frequency during flood events. During each flood event, the suspended particulate matter (SPM) show the usual trend of clockwise hysteresis with higher SPM concentrations on the rising limb of the flood than at the same discharge on the falling limb. We show that the annual average SPM flux of the Rhone River to the Mediterranean Sea (7.3 ± 0.6 × 10 6 tons yr −1) was largely controlled by the flood events (83% of the solid discharge occurred in less than 12% of the time), and that the precision on the total output flux depends strongly on the precise monitoring of SPM variations during the floods. The chemical composition of water and SPM are characterized by the predominance of Ca 2+ due to the abundance of carbonate rocks in the Rhone watershed. Chemical budgets have been calculated to derive the contributions of atmospheric deposition, carbonate, silicate and evaporite weathering, and anthropogenic inputs. The chemical weathering rate of carbonates is estimated to be 89 ± 5 t km −2 yr −1 compared to 14.4 ± 3 t km −2 yr −1 from silicates. By contrast, the physical erosion rate of silicates is about 51 t km −2 yr −1 against 19 t km −2 yr −1 for carbonates. The steady-state model of Gaillardet et al. (1995) has been applied to the chemical composition of dissolved and solid products. The results show that the Rhone River currently exports much less material than produced at steady-state by weathering in its watershed. The sediment flux inferred from the steady-state calculation (21–56 × 10 6 t yr −1) is on the same order as that estimated in literature for the 19th and the beginning of the 20th centuries. This imbalance may suggest that the Rhone is under a transient erosion regime following climate change (i.e. significant decrease of the flooding frequency since the beginning of the 19th century). On the other hand, the imbalance may also be due to the trapping of alluvion by the numerous dams on the river and its tributaries. Our data corroborate with previous studies that suggest a strong coupling between chemical and physical erosion fluxes, during the hydrological seasonal cycle of the Rhone River. The correlation between physical and chemical transport rates is, however, clearly different from that reported for global annual averages in large world rivers.

Towards an Integrated Model of Weathering, Climate, and Biospheric Processes

Research Article| January 01, 2009 Towards an Integrated Model of Weathering, Climate, and Biospheric Processes Yves Goddéris; Yves Goddéris Laboratoire d’étude des Mécanismes et Transferts en Géologie, Observatoire Midi-Pyrénées, CNRS-Université de Toulouse, Toulouse, France Contact e-mail: godderis@lmtg.obs-mip.fr Search for other works by this author on: GSW Google Scholar Caroline Roelandt; Caroline Roelandt Laboratoire d’étude des Mécanismes et Transferts en Géologie, Observatoire Midi-Pyrénées, CNRS-Université de Toulouse, Toulouse, France Search for other works by this author on: GSW Google Scholar Jacques Schott; Jacques Schott Laboratoire d’étude des Mécanismes et Transferts en Géologie, Observatoire Midi-Pyrénées, CNRS-Université de Toulouse, Toulouse, France Search for other works by this author on: GSW Google Scholar Marie-Claire Pierret; Marie-Claire Pierret Centre de Géochimie de la Surface, Université de Strasbourg, Strasbourg, France Search for other works by this author on: GSW Google Scholar Louis M. François Louis M. François Laboratoire de Physique Atmosphérique et Planétaire, Université de Liège, Liège, Belgium Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2009) 70 (1): 411–434. https://doi.org/10.2138/rmg.2009.70.9 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Yves Goddéris, Caroline Roelandt, Jacques Schott, Marie-Claire Pierret, Louis M. François; Towards an Integrated Model of Weathering, Climate, and Biospheric Processes. Reviews in Mineralogy and Geochemistry 2009;; 70 (1): 411–434. doi: https://doi.org/10.2138/rmg.2009.70.9 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Subaerial weathering of the continental rocks is an important component of global biogeochemical cycles. During the dissolution of continental rocks, atmospheric CO2 is consumed resulting in alkalinity production and its transfer to the ocean via river transport. Atmospheric carbon is also consumed during the dissolution reaction itself, as illustrated by the dissolution equation of plagioclase: \begin{eqnarray*}&&4Na_{0.5}Ca_{0.5}Al_{1.5}Si_{2.5}O_{8}\ +\ 17H_{2}O\ +\ 6CO_{2}\ {\rightarrow}\\&&3Al_{2}Si_{2}O_{5}(OH)_{4}\ +\ 2Na^{+}\ +\ 2Ca^{2+}\ +\ 6HCO_{3}^{{-}}\ +\ 4H_{4}SiO_{4}\end{eqnarray*} (1) Plagioclase dissolution produces dissolved species (basic cations, bicarbonate ions, and silica) and clay minerals which can precipitate locally. Dissolution of carbonate minerals also consumes atmospheric carbon, for example: \[CaCO_{3}\... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chemical composition of suspended sediments in World Rivers: New insights from a new database

The aim of this paper is to present a new database on the chemical composition of suspended matter in World Rivers, together with the associated elemental fluxes. There is a lack of any recent attempt in the literature to update the pioneering work of Martin and Meybeck [Martin, J.-M., Meybeck, M., 1979. Elemental mass balance of material carried by major world rivers. Mar. Chem. 7, 173–206.] and Martin and Whitfield [Martin, J.-M., Whitfield, M., 1983. The significance of the river input of chemical elements to the ocean. Trace metals in sea water Wong, Boyle, Bruland, Burton, Goldberg (Eds) Plenum Publishing Corporation.] regarding the worldwide average major and trace element chemistry of riverine particulate matter. Apart from compiling a new database on particulate matter, this paper also aims to give a “snap-shot” of elemental fluxes for each continent. This approach should allow us to obtain new insights on weathering conditions in different environments and assess the influence of human activities on natural geochemical cycles. Finally, this study demonstrates the large uncertainties currently associated with estimating the flux of sediments transported by rivers. By comparing the riverine suspended sediment fluxes of some metals (Cd, Zn, Ni, Cu, Cr and Pb) given in this study with estimates of the anthropogenic fluxes of these metals to the atmosphere, soils and waters (natural ecosystems) [Nriagu, J.O., 1988. A silent epidemic of environmental poisoning. Environ. Pollut. 50, 139–161.], we can see that riverine fluxes are similar to anthropogenic fluxes. This casts light on the effect of human activities on the cycles of trace elements at the Earth's surface.

How polluted is the Yangtze river? Water quality downstream from the Three Gorges Dam

The concentrations of major anions and cations, nitrogen and phosphorus, dissolved and particulate trace elements, and organic pollutants were determined for the middle and lower reaches of the Yangtze River (Changjiang) from below the Three Gorges Dam (TGD) to the mouth at Shanghai in November 2006. The concentration of dissolved inorganic phosphate (DIP) was constant at a low level of 6–8 µgP/L, but the concentration of nitrate (NO 3 −) approximately doubled downstream and was closely correlated with K +. This translated to a daily load of well over 1000 t of dissolved inorganic nitrogen (DIN) at Datong. The average concentrations of dissolved Pb (0.078 ± 0.023 µg/L), Cd (0.024 ± 0.009 µg/L), Cr (0.57 ± 0.09 µg/L), Cu (1.9 ± 0.7 µg/L), and Ni (0.50 ± 0.49 µg/L) were comparable with those in other major world rivers, while As (3.3 ± 1.3 µg/L) and Zn (1.5 ± 0.6 µg/L) were higher by factors of 5.5 and 2.5, respectively. The trace element contents of suspended particles of As (31 ± 28 µg/g), Pb (83 ± 34 µg/g), and Ni (52 ± 16 µg/g) were close to maximum concentrations recommended for rivers by the European Community (EC). The average concentrations of Cd (2.6 ± 1.6 µg/g), Cr (185 ± 102 µg/g), Cu (115 ± 106 µg/g), and Zn (500 ± 300 µg/g) exceeded the EC standards by a factor of two, and Hg (4.4 ± 4.7 µg/g) by a factor of 4 to 5. Locally occurring peak concentrations exceed these values up to fourfold, among them the notorious elements As, Hg, and Tl. All dissolved and particulate trace element concentrations were higher than estimates made twenty years ago [Zhang, J., Geochemistry of trace metals from Chinese river/estuary systems: an overview. Estuar Coast Shelf Sci 1995; 41: 631–658.]. The enormous loads of anthropogenic pollutants disposed to the river were diluted by the large water discharge of the Yangtze even during the lowest flow resulting in the relatively low concentration levels of trace elements and organic pollutants observed. We estimated loads of e.g. As, Pb and Ni to the East China Sea to be about 4600 kg As d − 1 , 3000 kg Pb d − 1 , and 2000 kg Ni d − 1 . About 6000 t d − 1 of dissolved organic carbon (DOC) was delivered into the sea at the time of our cruise. We tested for 236 organic pollutants, and only the most infamous were found to be barely above detection limits. We estimated that the load of chlorinated compounds, aromatic hydrocarbons, phenols, and PAHs were between 500 and 3500 kg d − 1 . We also detected eight herbicides entering the estuary with loads of 5–350 kg d − 1 . The pollutant load, even when at low concentrations, are considerable and pose an increasing threat to the health of the East China Sea ecosystem.

The Changing Sediment Load of the Mekong River

The sediment loads of many of the world's major rivers have changed significantly in recent years due to land-use change, reservoir construction, and other human impacts on their drainage basins. For many rivers, the loads have decreased, whereas for others, they have increased. Such changes can have important implications for both the natural functioning of the system as well as for human exploitation of the river system. This paper considers the evidence for recent changes in the sediment load of the Mekong River. The available data have a number of limitations in terms of both sampling frequency and the period of coverage, but they have been processed to provide a basis for considering the changes in the sediment load of the river over the period extending from the early 1960s to 2002. Although there is evidence of increasing loads at some measuring stations, the overall trends show little evidence of major changes, and the system provides evidence of buffering through storage. As of 2002, the construction of major dams on the headwaters in China appears to have had little impact on the sediment load, although as further larger dams are commissioned, the sediment load of the Mekong can be expected to decrease.

A comparative overview of weathering intensity and HCO 3− flux in the world's major rivers with emphasis on the Changjiang, Huanghe, Zhujiang (Pearl) and Mississippi Rivers

In this paper, general relationships of riverine bicarbonate concentrations and fluxes as a function of drainage basin mineral content and runoff are examined using a database of the 25 largest rivers in the world. Specific HCO 3 − flux normalized to unit basin area, which peaks in the mid latitudes, was found to be strongly correlated with the carbonate mineral content of river basins, while river HCO 3 − concentration was related to the balance of precipitation and evaporation. Within this global context, the weathering patterns of CO 2 in a few large rivers (Changjiang, Huanghe, Pearl, and Mississippi rivers) were examined in further detail. The Zhujiang (Pearl River), especially its largest branch (Xijiang), was characterized by the highest specific weathering rate among all the world's large rivers due to an exceptionally high carbonate mineral content (over 80%) in its drainage basin and its warm and wet environment. It has a moderate level of HCO 3 − concentration, however, due to dilution by relatively high precipitation in the watershed. In stark contrast, the Huanghe (Yellow River) has one of the lowest specific weathering rates because of low carbonate mineral content and a dry climate. However, it has a high HCO 3 − concentration due largely to the concentrating effects of high evaporative water loss, as a result of arid weather and the agricultural use of water through irrigation systems, as well as carbonate-containing surficial deposits (i.e., loess). The strong correlation between specific HCO 3 − fluxes and discharge in all four rivers with different discharge seasonality suggests that higher precipitation in drainage basins promotes higher weathering rates. For the 25 large rivers studied here, rivers in low (<30°), mid (30–60°) and high (>60°) latitudes have an average HCO 3 − concentration of 0.584, 1.649, and 1.154 mM, respectively, and they account for 42.6%, 47.3% and 10.1%, respectively, of the total global dissolved inorganic carbon flux to the ocean. Thus the mid-latitude rivers carry a disproportionally high dissolved inorganic carbon flux with a relatively small (26%) amount of freshwater discharge. The discharge-averaged global river HCO 3 − concentration was estimated to be 1.1 mM.

Temporal variability of uranium concentrations and 234U/ 238U activity ratios in the Mississippi river and its tributaries

234U/ 238U activity ratios and total dissolved uranium concentrations in the Lower Mississippi River at New Orleans, LA have been analyzed on a bi-weekly basis over 2003–2004. During this time period, the range in 234U/ 238U activity ratios is approximately 17% (from 1.241 to 1.473), while uranium concentrations span an even greater range of 130% (0.28 to 1.33 ppb). There is no correlation between uranium activity ratio and discharge, and only a very weak correlation between uranium concentration and discharge. In order to examine the cause of the substantial variability in the lower river concentrations and 234U/ 238U activity ratios, we sampled the four major tributaries of the Mississippi River (Ohio, Missouri, Upper Mississippi, and Arkansas Rivers). Each river was sampled four times, each time representing a unique discharge season. In general, lithological and climatological parameters in the tributary sub-basins exert the greatest control on Lower Mississippi River uranium concentration and isotope signatures. These parameters may also be influenced by groundwater infiltration below the confluences of the major tributaries. Our temporal analysis suggests that if one were to estimate Mississippi River uranium fluxes to the ocean based on single-point sampling during 2003–2004, significant over- or under-estimations of these values would ensue. Our two-year average Mississippi River uranium-flux values suggest that previous best estimates of the contribution of Mississippi River uranium to the global average riverine 234U/ 238U activity ratio are too high by 36%. If other major world rivers are as poorly constrained with respect to uranium systematics as the Mississippi River, then the global average riverine U flux and 234U/ 238U activity ratio need to be revised.

Carbonate system and CO 2 degassing fluxes in the inner estuary of Changjiang (Yangtze) River, China

We examined the carbonate system, mainly the partial pressure of CO 2 ( pCO 2), dissolved inorganic carbon (DIC) and total alkalinity (TAlk) in the Changjiang (Yangtze) River Estuary based on four field surveys conducted in Sep.–Oct. 2005, Dec. 2005, Jan. 2006 and Apr. 2006. Together with our reported pCO 2 data collected in Aug.–Sep. 2003, this study provides, for the first time, a full seasonal coverage with regards to CO 2 outgassing fluxes in this world major river–estuarine system. Surface pCO 2 ranged 650–1440 μatm in the upper reach of the Changjiang River Estuary, 1000–4600 μatm in the Huangpujiang River, an urbanized and major tributary of the Changjiang downstream which was characterized by a very high respiration rate, and 200–1000 μatm in the estuarine mixing zone. Both DIC and TAlk overall behaved conservatively during the estuarine mixing, and the seasonal coverage of these carbonate parameters allowed us to estimate the annual DIC export flux from the Changjiang River as ∼ 1.54 × 10 12 mol. The highly polluted Huangpujiang River appeared to have a significant impact on DIC, TAlk and pCO 2 in the lower reaches of the inner estuary. CO 2 emission flux from the main stream of the Changjiang Estuary was at a low level of 15.5–34.2 mol m − 2 yr − 1 . Including the Huangpujiang River and the adjacent Shanghai inland waters, CO 2 degassing flux from the Changjiang Estuary may have represented only 2.0%–4.6% of the DIC exported from the Changjiang River into the East China Sea.

GRACE observations of changes in continental water storage

Signatures between monthly global Earth gravity field solutions obtained from GRACE satellite mission data are analyzed with respect to continental water storage variability. GRACE gravity field models are derived in terms of Stokes' coefficients of a spherical harmonic expansion of the gravitational potential from the analysis of gravitational orbit perturbations of the two GRACE satellites using GPS high–low and K-band low–low intersatellite tracking and on-board accelerometry. Comparing the GRACE observations, i.e., the mass variability extracted from temporal gravity variations, with the water mass redistribution predicted by hydrological models, it is found that, when filtering with an averaging radius of 750 km, the hydrological signals generated by the world's major river basins are clearly recovered by GRACE. The analyses are based on differences in gravity and continental water mass distribution over 3- and 6-month intervals during the period April 2002 to May 2003. A background model uncertainty of some 35 mm in equivalent water column height from one month to another is estimated to be inherent in the present GRACE solutions at the selected filter length. The differences over 3 and 6 months between the GRACE monthly solutions reveal a signal of some 75 mm scattering with peak values of 400 mm in equivalent water column height changes over the continents, which is far above the uncertainty level and about 50% larger than predicted by global hydrological models. The inversion method, combining GRACE results with the signal and stochastic properties of a hydrological model as ‘a priori’ in a statistical least squares adjustment, significantly reduces the overall power in the obtained water mass estimates due to error reduction, but also reflects the current limitations in the hydrological models to represent total continental water storage change in particular for the major river basins.

Spatial and temporal analysis of water chemistry records (1958–2000) in the Huanghe (Yellow River) basin

The chemistry of major dissolved ions (Ca2+, Mg2+, Na+ + K+, HCO3−, SO42−, Cl−) and dissolved silica (SiO2) in the river water of the Huanghe (Yellow River), China, was studied from historical records at 100 stations in the drainage basin for the period 1958–2000 (not all the parameters were continuously monitored during the entire period). This river system (750,000 km2) presents an exceptional temporal and spatial water chemistry variability compared to other major rivers. The total dissolved solid (TDS) concentration of the Huanghe varied over 2 to 3 orders of magnitude throughout the basin, with a median TDS concentration of 452 mg/L, which is about 4 times the world spatial median value (WSM). In particular, the concentrations of Na+ + K+, SO42−, and Cl− were 10–20 times higher than in other major world rivers. Similar to the Changjiang (Yangtze River) and many other Himalayan rivers, the TDS at a given station is seasonally variable and inversely related to river runoff with a variation factor less than 2.0, despite a water dilution of fourfold to fivefold in the summer flood season. In addition to chemical weathering of sedimentary rocks, evaporation and fractional crystallization were found to be the major natural process controlling the major element chemistry of the Huanghe, owing to the abundance of loess and clastic rocks under arid and semiarid climates. A persistent increasing trend from year to year has been observed in the concentrations of TDS and all the salts except for HCO3− at all main‐channel stations except for the uppermost Lanzhou. The rate of increase in the TDS concentration was the highest in the middle reaches (10.52 mg/L yr−1 at Toudaoguai) and remained to be unusually high in the lower reaches (5.5 mg/L yr−1 at Stations Luokou and Lijin). The increasing trend coincided with a significant decrease in water discharge at most of the main‐channel stations in the past 40 years, and is attributed to increasing regulations of reservoirs and intensive water withdrawal for irrigation and diversions, as well as many other anthropogenic processes. Despite the increasing trend in TDS concentrations, the seaward TDS flux to the sea by the Huanghe has decreased dramatically from more than 20 × 109 kg/yr in the 1960s to less than 10 × 109 kg/yr at present, due to the sharp decrease in water discharge (sometimes completely dried up) in the lower reaches of the river. The significant decreases in sea‐ward fluxes of water and dissolved salts are expected to have profound physical, ecological, and socio‐economic impacts on the lower reaches of the river, the coastal areas and the Bohai Sea.

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−–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 Σ 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 μm were analysed. Negative Eu anomalies in suspended sediments is due to the excess carbonate rock weathering in the source area.

Organic carbon transport and C/N ratio variations in a large tropical river: Godavari as a case study, India

This study gives an insight into the source of organic carbon and nitrogen in the Godavari river and its tributaries, the yield of organic carbon from the catchment, seasonal variability in their concentration and the ultimate flux of organic and inorganic carbon into the Bay of Bengal. Particulate organic carbon/particulate organic nitrogen (POC/PON or C/N) ratios revealed that the dominant source of organic matter in the high season is from the soil (C/N = 8–14), while in the rest of the seasons, the river-derived (in situ) phytoplankton is the major source (C/N = l–8). Amount of organic materials carried from the lower catchment and flood plains to the oceans during the high season are 3 to 91 times higher than in the moderate and low seasons. Large-scale erosion and deforestation in the catchment has led to higher net yield of organic carbon in the Godavari catchment when compared to other major world rivers. The total flux of POC, and dissolved inorganic carbon (DIC) from the Godavari river to the Bay of Bengal is estimated as 756 × 109 and 2520 × 109 g yr−1, respectively. About 22% of POC is lost in the main channel because of oxidation of labile organic matter, entrapment of organic material behind dams/sedimentation along flood plains and river channel; the DIC fluxes as a function of alkalinity are conservative throughout the river channel. Finally, the C/N ratios (∼12) of the ultimate fluxes of particulate organic carbon suggest the dominance of refractory/stable soil organic matter that could eventually get buried in the coastal sediments on a geological time scale.

Solute Sources and Processes in the Achankovil River Basin, Western Ghats, Southern India/Sources de Solute?s et Processus Associe?s Dans le Bassin du Fleuve Achankovil, Ghats Occidentaux, Inde du Sud

Abstract A time series survey was carried out in 2002 to understand the hydrogeochemical processes taking place in the Achankovil River of the Western Ghats Range. The water is neutral with pH and EC ranges from 6.32 to 7.56 and 24–54 µS cm−1, respectively. Chloride and sodium are the dominant anion and cation in the water respectively. Correlation analysis of the chemical parameters of the water shows that few ions have additional sources. The majority of carbonate is derived from carbonate weathering followed by silicate weathering. Cation concentrations show decreasing trend from upstream to downstream in contrast to the increasing trend in the major world rivers. Dissolved silica in pre-monsoon water is low. The river chemistry is dominated by rock weathering induced by precipitation. Thermodynamic plots show that dolomite, kaolinite, albite and chlorite are in equilibrium with the river water. Chemical weathering is predominant here compared to physical weathering. The overall material transport seems to be lower compared to the other Indian rivers; nevertheless, the solute loads are comparable to certain large rivers such as the River Cauvery in southern India. The solute flux including the nutrient flux is very high among the Western Ghats rivers in relation to its size, which will certainly supplement the productivity of the lake/estuary and the coastal waters. Since this study is restricted to a one-year period, long-term data procurement and analysis along with micro nutrients studies are needed, which are lacking in the present study, to gain insight into the material flux by this river into the Arabian Sea.

Comments on the importance of black carbon in the global carbon cycle

Comments on the importance of black carbon in the global carbon cycle

Statistical modelling of compositional trends in sediments

Trends in compositional diagrams are frequently used to describe and interpret the imprint of certain processes on sediment composition. Most of these trends are intuitive and “hand-drawn”, although a numerical description of compositional changes involved with these processes would allow for a quantitative assessment of the observed sediment compositions and the proposed processes. This paper suggests a statistical approach to model compositional linear trends, which allows for a mathematically rigorous description of changes in sediment composition related to a specific process or a combination of processes. Three case studies dealing with different aspects of the sedimentary cycle demonstrate the usefulness of the approach. In the first example, a modelled average global chemical weathering trend is used to calculate an appropriate measure for the degree of chemical weathering of the suspended load from some of the world's major rivers. In the second example, data on precipitation and relief from different watersheds are quantitatively related to the petrographic composition of fine-grained sands from low-order streams derived from these watersheds. The third example is an attempt to quantify the interdependence of chemical sediment composition and grain size in the absence of chemical weathering. Superposition of individual compositional linear trends allows for modelling sediment composition in more complicated case studies. Although primarily a forward modelling approach, it can be also used inversely, and, therefore, has strong potential for tracing back the sediment-forming processes in order to reconstruct the original source rocks of the sediment.

Oceanic export of relict carbon by small mountainous rivers

Small mountainous rivers (SMR) export globally significant quantities of particulate organic carbon (POC) to the oceans, the composition of which may be distinct from POC delivered by major world rivers. To better constrain the controls on the Δ14C signatures of POC suspended in SMR, we examined the temporal variability of Δ14C and δ13C of POC suspended in the Santa Clara River, a SMR in California, USA. Our data suggest mixing of bedrock and contemporary soil, which can be applied to other SMR in contrasting climate zones and with varying land cover. The data also suggest that chemical denudation is incomplete, but effective to the point that only the most recalcitrant moieties of the parent POC are exported. We further propose sediment yield as a potentially useful proxy for the Δ14C of riverine POC. A preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis.

A sediment and organic carbon budget for the greater Strait of Georgia

Recent efforts to construct global ocean budgets for carbon have recognized the importance of continental margins. In this study, we constructed budgets for the Strait of Georgia, a temperate, North American west coast basin that receives the inflow of one of the world's major rivers. Drawing from published and unpublished data, we have estimated the magnitude of the various sources and sinks of fresh water, sediment and organic carbon. The Fraser River is the dominant source of fresh water and particles to the strait, contributing approximately 73% of the 158×10 9 m 3 year −1 of water and 64% of the 30×10 9 kg year −1 of particles. Other rivers supply most of the remainder, while rain, groundwater and anthropogenic sources of water and particles are negligible in comparison. Fresh water escapes the Strait of Georgia through Juan de Fuca Strait, but particulate inputs are approximately balanced by sedimentation within the greater Strait of Georgia, implying almost complete trapping of particles. Dissolved and particulate organic carbon are derived mainly from in situ primary production (855×10 6 kg year −1) and from the Fraser River (550×10 6 kg year −1). Other rivers contribute 200×10 6 kg year −1 of organic carbon, and anthropogenic sources (ocean dumping, sewage, pulp mills and aquaculture) a further 119×10 6 kg year −1. Particulate organic carbon is predominantly buried (428×10 6 kg year −1) or oxidized (90×10 6 kg year −1) in the sediments of the strait. About 70% of the organic carbon that enters or is produced in the strait is dissolved. Most of the dissolved organic carbon is oxidized within the strait (784×10 6 kg year −1), but the remainder (400×10 6 kg year −1) is exported to the Pacific Ocean. Although the particulate organic carbon budget by itself implies net autotrophy, dissolved organic carbon oxidation may make the Strait of Georgia slightly net heterotrophic.