Jefferson Mortatti

Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations

Abstract Using the data of the CAMREX project (1982–1984) on the water geochemistry of the Amazon river and its main tributaries, it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric/soil CO2, taking into account seasonal and spatial variations. This study confirms the important role of the Andes in the fluvial transport of dissolved and particulate material by the Amazon, and it shows for the first time that the silicate weathering rate and atmospheric/soil CO2 consumption are higher in the Andes than in the rest of the Amazon basin. The seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge. The average weathering rate estimated for the whole Amazon basin (15 m/My) is comparable to other estimations made for other tropical–equatorial environments. A comparison between physical and chemical weathering rates of silicate rocks for the Amazon basin and for each tributary basin show that in the Andes and in the Amazon trough, the soil thicknesses are decreasing whereas in the Shield the soil profiles are deepening.

Carbon river fluxes and weathering CO2 consumption in the Congo and Amazon river basins

Data on carbon river fluxes recently obtained by the authors for the Congo basin within the framework of the PIRAT Program (INSU-CNRS/ORSTOM) are compared with results previously obtained for the Amazon basin. A special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges. The flux of atmospheric and soil CO2 consumed by rock weathering is estimated to be 3.1 × 105 and 0.5 × 105 moles/a/km2 respectively for the Amazon and the Congo basin. These CO2 fluxes represent, respectively, 67.4% and 74.7% of the total bicarbonate river fluxes. A comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas. A transfer function between the weathering CO2 flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century. These interannual CO2 fluctuations present average increasing trends of 10% for Amazon basin and only 0.7% for the Congo basin during the last century.

REE distribution pattern in river sediments: partitioning into residual and labile fractions

Abstract To assess rare earth element (REE) distribution, fractionation during weathering processes and river transport, a sequential extraction procedure was applied to 36 river sediments collected from different rivers in Argentina, Brazil, France and Morocco. The results show that labile REE fractions are mainly linked to carbonates, iron oxides or organic matter according to the river. Moreover the leached REE do not behave as a coherent group: middle REE are mainly bound to carbonates or organic matter, whereas light REE (except cerium) are preferentially linked to organic matter and heavy REE and cerium are associated with iron oxides.

Hydrograph Separation of the Amazon River: A Methodological Study

The hydrograph separation of the Amazon river was performed using three different methodologies. Were applied isotopic, filter-separation, and mixing methods to estimate the contributions of the surface runoff (event water) and baseflow (pre-event water) components to the total river flow, during the 1973–1974 hydrological years. The importance of the baseflow contribution, mainly during the peak discharge, suggesting that the groundwater plays a much more active and important role in the storm dynamics, was verified. Similar results were obtained for all the methods used, and the applicability of each one was discussed in detail. For the Amazon river basin, the average contribution of the baseflow was 56% of the total river flow, at peak discharge. The average surface runoff contribution, which represents the water capable of mechanical erosion in drainage basins, expressed in terms of the surface runoff coefficient (Kr), was 31.9%, while the mean contribution of the baseflow, expressed by the baseflow coefficient (Kb), was 68.1%.

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 Tardys 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.

Biogeochemistry of the Madeira river basin

A biogeochemical characterization of the Madeira river basin has been made to evaluate the local and global effects of possible alterations in the ecosystem caused by recent intensive occupation in Rondonia state. During the period April 1983—January 1986, sampling was made both by land and river along the tributaries and main channel of the Madeira river. The parameters analysed lead to a detailed study of the physicochemical quality of the waters of the basin and their relationship with the local geology, associated with the transport of solid material and the hydrological behavior of the ecosystem.Penmans method adapted to tropical rainforest conditions was used to evaluate the potential evapotranspiration for the basin. Estimated potential evapotranspiration was 1420 mm/y, 77% due to the energy balance. Real evapotranspiration was 94% of the estimated potential and the main residence time of the rain water in the basin was 2 months. The isotopic behavior of Hydrogen and Oxygen in the river waters of the region was typical of great rivers, the values being more positive during the dry season and more negative during the rainy season. An isotopic gradient of δ 18O 0.038 (‰)/100 km, was established from Porto Velho station to the estuary, which was considered low when compared with the value of 0.063 (‰)/100 km, obtained for the Amazon river.In general, the waters of the tributaries were poor in dissolved ion species when compared with the main channel of the Madeira river. Seasonal variation in the transport of suspended sediment kept the same pattern, greater transport being observed on rising water than during high water. A transport of 2.85 million tons per day was observed in the Madeira river near the mouth.

Sources and distribution of polycyclic aromatic hydrocarbons (PAHs) and organic matter in surface sediments of an estuary under petroleum activity influence, Todos os Santos Bay, Brazil

The present study evaluated the origin and distribution of polycyclic aromatic hydrocarbons (PAHs) and the organic matter (OM) in the surface sediment of the São Paulo River estuary, Todos os Santos Bay (TSB), Brazil. The samples were collected in the rainy (CP1) and the dry (CP2) seasons. We analyzed the 16 PAHs from the United States Environmental Protection Agency (US EPA) priority pollutant list, total organic carbon (TOC), total nitrogen (N), and stable carbon isotope (δ13C). The total concentration of PAHs ranged from 11.45±1.28 to 1825.35±107.96ngg-1, while TOC ranged from 3.8 to 27.7gkg-1. CP1 showed the highest concentrations for all parameters. The δ13C ratio indicated terrigenous OM (-23.81 to -26.63‰). The TOC/N ratio (C/N) indicated transitional OM (12.32 to 24.39), in addition to the continental origin. The diagnostic ratios of PAHs origin revealed only pyrolytic source, although close to areas with a history of petroleum contamination.

Hydroclimatology and biogeochemistry of the Amazon: 1. Erosion

Abstract The Amazon is the largest stream in the world. Its basin covers at least 7 · 10 6 km 2 , which represents ∼ 5% of the global continental area and almost 70% of the area of the continents localized in the equatorial zone, between 5°S and 5°N of latitude. The global tropical moist forest covers ∼ 9.35 · 10 6 km 2 , so that the Brazilian evergreen rain forest represents at least 50% of this area. At Obidos, the most accessible downstream station for collecting data, the area concerned is 4.619 · 10 6 km 2 . The purpose of these two extended abstracts is to show how changes and oscillations of climate can significantly affect erosion as well as carbon and nitrogen cycles, and may also mask the degradations of the environment due to deforestation.

RADICULAR UPTAKE KINETICS OF 15NO− 3, CO(15NH2)2, AND 15NH4 + IN WHOLE RICE PLANTS

The mechanism of uptake of nitrate, urea, and ammonium by roots of intact plants (Oryza sativa L.) was studied using enriched nitrogen 15N as a tracer in order to establish an absorption kinetic model and the influence of external concentration on uptake. Rice plants at 30 and 60 days after germination were submitted to different contact times with two concentrations of an external solution containing these nitrogenous sources. In the treatment with nitrate, the relative uptake rate decreased with increasing plant age, for both concentrations tested. For urea, this rate was higher in dry matter of old plants at low external concentration (1.0 μmol g−1) and for ammonium a higher relative rate of uptake was found in young plants at low external concentration and at high concentration, old plants had higher relative rate of uptake, as had been seen with nitrate and urea uptake. In the experiment related to the influence of external concentration on the radicular uptake, plants were used at 30 days after germination and have shown the occurrence of a multiphasic system (4 isotherms) for the three treatments. Each isotherm is associated with the Michaelis-Menten kinetics and the transition between phases is carried out by jumps. The Vmax (maximum uptake rate) and Km (affinity of carrier to ion) values, calculated by Lineweaver-Burk and Hofstee transformations, increased with the increasing external concentration.

Mechanical Erosion in a Tropical River Basin in Southeastern Brazil: Chemical Characteristics and Annual Fluvial Transport Mechanisms

This study aims to evaluate the mechanical erosion processes that occur in a tropical river basin, located in the Sao Paulo state, southeastern Brazil, through the chemical characterization of fine suspended sediments and the transport mechanisms near the river mouth, from March 2009 to September 2010. The chemical characterization indicated the predominance of SiO2, Al2O3, and Fe2O3 and showed no significant seasonal influences on the major element concentrations, expressed as oxides. The concentration variations observed were related to the mobility of chemical species. The evaluation of the rock-alteration degree indicated that the physical weathering was intense in the drainage basin. The fine suspended sediments charge was influenced by the variation discharges throughout the study period. The solid charge estimate of the surface runoff discharge was four times higher in the rainy season than the dry season. The transport of fine suspended sediments at the Sorocaba River mouth was 55.70 t km−2 a−1, corresponding to a specific physical degradation of 37.88 m Ma−1, a value associated with the mechanical erosion rate that corresponds to the soil thickness reduction in the drainage basin.