Chemical Erosion Rates Research Articles

Hydrological and geochemical characteristics of the Jamari and Jiparana river basins (Rondonia, Brazil)

The authors investigate the hydrological and geochemical characteristics of the Jamari (30430 km2) and Jiparana (60350 km2) river basins (Amazonia), during the period 1978–1984. A spectral analysis of Fourier is applied to time series of mean monthly river discharges, in order to assess the contribution (7 to 8%) of the surface runoff to the total river flow. The mean annual runoff coefficient calculated for the Jiparana river basin (36%), is higher than for the Jamari (32%), and this coefficient increases during the study period, only for the Jiparana. The total specific suspended sediment discharge calculated for both rivers shows the same value 13 t/km2/y, and the estimated suspended sediment concentration in the surface runoff is slightly superior for the Jiparana river (0.3 g/l) than for the Jamari one (0.2 g/l). The river suspended sediments are mainly composed of kaolinite, quartz and feldspar, but the Jiparana is more enriched in quartz. For both rivers, the dominant clay mineral is the kaolinite which is in agreement with the rock weathering type determined for both basins using the Tardy's weathering index: the monosiallitisation. The total chemical erosion rate calculated after correction for the atmospheric inputs (ions and CO2), is higher for the Jiparana (10.11 t/km2/y) than for the Jamari river basin (7.75 t/km2/y). These values are lower than the mechanical denudation rate calculated previously for both river basins.

Salinities and sediment transport in the Bolivian highlands

Salinities and sediment loads of the rivers of the entire interior drainage basin of the Lake Titicaca, Rio Desaguadero, Lake Poopo and salars, as well as their evolution from upstream to downstream, have been characterized on the basis of the results of four samplings during runoff periods. On the other hand, the regimes of dissolved and suspended matter transport are characterized with periodic measurements and samplings at hydrometrical stations over several years. The junction of Lake Poopo and the Salar of Coipasa, since 1985 is noted, which recalls that an unique terminal lake of large area existed during some parts of the Quaternary. Mechanical and chemical erosion rates have been calculated for the basins that drain the Western (Rio Mauri) and Eastern (Rio Suches) Cordilleras of the Bolivian Andes. Most of the sediment comes from the Western Cordillera, with a mechanical erosion rate of 640 t km 2 yr −1 for the basin of the Rio Mauri. On the other hand, Lake Titicaca is the main source of dissolved matter to Lake Poopo via the Rio Desaguadero.

Deuterium pumping and erosion behavior of selected graphite materials under high flux plasma bombardment in PISCES-A — effects of surface pores and machined grooves

The deuterium plasma recycling and chemical erosion behavior of selected graphite materials have been investigated using the PISCES-A facility. These materials include: Pyro graphite; 2D-graphite weave; 4D-graphite weave; and POCO graphite. Deuterium plasma bombardment conditions are: fluxes around 7 × 10 17 ions s −1 cm −2; exposure time in the range from 10 to 100 s; bombarding energy of 300 eV; and graphite temperatures between 20 and 120 °C. To reduce deuterium plasma recycling, several approaches have been investigated. Erosion due to high-fluence helium plasma conditioning significantly increases the surface porosity of POCO graphite and 4D-graphite weave whereas little changes for 2D-graphite weave and Pyro graphite. The increased pore openings and refreshed in-pore surface sites are found to reduce the deuterium plasma recycling and chemical erosion rates at transient stages. It is also found that deuterium recycling even at the steady state tends to be suppressed as the surface porosity increases by materials selection. Surface topographical modification by machined-grooves noticeably reduces the steady state deuterium recycling rate and the impurity emission from the surface. These surface topography effects are attributed to continuous co-deposition of reemitted deuterium, chemically sputtered hydrocarbon and physically sputtered carbon under deuterium plasma bombardment. The co-deposited groove surface exhibits a characteristic morphology with dens-packed dendritic microstructures.

Chemical and sediment mass transfer in the Yamuna River — A tributary of the Ganges system

Maximum mass transfer, in the Yamuna River takes place during the monsoon season. The sediment load constitutes 58–86% of the total load carried by the river depending upon the sites. Tributaries are chemically more active than the mainstream. The total load of the river seems to be controlled by lithology. At Allahabad, the Yamuna carries 42 × 10 6t dissolved chemical load and 64 × 10 6t sediment load to the Ganges river. The TSM/TDS ratio shows that upstream physical weathering is more dominant than chemical weathering. The negative relation between basin area and total erosion rate and the positive relation between the chemical and sediment erosion in the Yamuna basin is in agreement with the global trend. The average chemical erosion rate (165 t km −2yr −1) of the Yamuna is much higher than that of the Ganges and the Indian average. The total erosion rate (973 t km −2yr −1) is 1.7 times greater than that of the Ganges. Upstream the Yamuna removes 1.04 mm yr −1 of the basin surface; the removal rate decreases downstream to 0.19 mm yr −1 at Allahabad, the point of confluence with the Ganges.

Nature of solute transport in the Godavari Basin, India

The nature of solute transport of the Godavari basin has been studied based on 59 river and four rain water samples collected four times during 1977–1980. The Godavari basin annually transports 16.8 × 10 6t of solute load representing 6% of chemical load from the Indian subcontinent. The annual chemical erosion rate is 49 t km −1 yr −1 after correcting for atmospheric recycling. The tributaries flowing through the Deccan traps (basalt) covering 48% of the basin area are responsible for 85% of the dissolved transport. The remaining 15% is contributed by granites and other rock types. The sedimentary rocks located in the lower part of the basin covering 7% of the basin area actually retain 7 × 10 6t of the annual dissolved load. Individual elemental fluxes and their rates have also been calculated. Temporal variations in the dissolved transport are quite pronounced. The mean TDS of the Godavari River, 250 mg l −1 is much higher than the Indian and world average river water composition.

Nature of the dissolved load of the Krishna River Basin, India

River water samples were collected four times during a three year period (1981–1984) at sixteen stations in the entire region of Krishna River and its major tributaries. On the basis of our analytical results, the discharge weighted average chemical composition of the Krishna River has been computed and compared to major river systems of the world. The total dissolved transport of Krishna to the Bay of Bengal is estimated to be 10.4 × 10 6 t yr −1 which accounts 4% of the chemical load of the Indian subcontinent. The average annual chemical erosion rate at the river mouth is estimated to be 41 t km −2 yr −1. The fluxes of individual dissolved species of Krishna River water to the Bay of Bengal are in the following order: HCO 3 > SO 4 > Na > Cl > dissolved Si > Mg > K > F > PO 4. The observed chemical data of Krishna River water have been used to predict theoretically the mineral assemblages in the carbonate and in alumino-silicate systems and compared to observed mineralogical composition of suspended sediments.

Dissolved and suspended matter transported by the Girou River (France): mechanical and chemical erosion rates in a calcareous molasse basin

ABSTRACT The mean mechanical and chemical erosion rates of the Girou basin are calculated from the amount of suspended and dissolved material transported by the river. The chemical and mineralogical characteristics of the river load and its behaviour are studied during the water year 1980–1981. Finally, the origins of major compounds in the drainage basin are determined and the contribution of mechanical and chemical erosion to the fluvial transport of each compound are calculated. The separation of the streamflow components on the storm hydrograph allows the calculation of the suspended sediment concentration in the surface runoff.

A comparison of the rock tablet and water hardness methods for determining chemical erosion rates on karst surfaces

A comparison of the rock tablet and water hardness methods for determining chemical erosion rates on karst surfaces

Chemical erosion in a forested watershed in the oesling, Luxembourg

AbstractHydro‐pedological investigations were carried out in a small forested watershed on the Lower Emsian formations of the Lower Devonian in the Luxembourg Ardennes. These rocks consist of weakly metamorphosed shales and quartzites, of which only the shales are undergoing appreciable weathering, and are composed of quartz, sericite, albite and chlorite, with minor amounts of haematite (goethite) and traces of pyrite, rutile and apatite. The alumino‐silicates react with CO2 charged water, forming kaolinite, with vermiculite and smectite as intermediate phases and releasing cations and silica for solution. From a hydrological study and a detailed programme of soil, spring and river water sampling the year could be subdivided into three characteristic hydrological periods. The runoff during these periods could be separated into various components, some of which have a characteristic water chemistry. The amount of material removed in solution was 7,448 kg for the years 1973/1974 and 1974/1975 (220 kg/ha/year). The output of material in solution is probably much greater than the output of material in suspension and as bedload. The chemical erosion rate could be calculated with these output data, after making allowance for atmospherically supplied materials and biomass recycling; it amounts to 4,435 kg (131 kg/ha/year), which is 59.5 per cent of the total solutional output.

Weathering in the Ganga Alluvial Plain: Geochemical signatures linking of the Himalayan source and the Bay of Bengal sink

DOI = 10.3126/hjs.v5i7.1327 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.146