Amazon River dissolved load: temporal dynamics and annual budget from the Andes to the ocean

The aim of the present study is to estimate the export fluxes of major dissolved species at the scale of the Amazon basin, to identify the main parameters controlling their spatial distribution and to identify the role of discharge variability in the variability of the total dissolved solid (TDS) flux through the hydrological cycle. Data are compiled from the monthly hydrochemistry and daily discharge database of the “Programa Climatologico y Hidrologico de la Cuenca Amazonica de Bolivia” (PHICAB) and the HYBAM observatories from 34 stations distributed over the Amazon basin (for the 1983–1992 and 2000–2012 periods, respectively). This paper consists of a first global observation of the fluxes and temporal dynamics of each geomorphological domain of the Amazon basin. Based on mean interannual monthly flux calculations, we estimated that the Amazon basin delivered approximately 272 × 106 t year−1 (263–278) of TDS during the 2003–2012 period, which represents approximately 7 % of the continental inputs to the oceans. This flux is mainly made up by HCO3, Ca and SiO2, reflecting the preferential contributions of carbonate and silicate chemical weathering to the Amazon River Basin. The main tributaries contributing to the TDS flux are the Marañon and Ucayali Rivers (approximately 50 % of the TDS production over 14 % of the Amazon basin area) due to the weathering of carbonates and evaporites drained by their Andean tributaries. An Andes–sedimentary area–shield TDS flux (and specific flux) gradient is observed throughout the basin and is first explained by the TDS concentration contrast between these domains, rather than variability in runoff. This observation highlights that, under tropical context, the weathering flux repartition is primarily controlled by the geomorphological/geological setting and confirms that sedimentary areas are currently active in terms of the production of dissolved load. The log relationships of concentration vs discharge have been characterized over all the studied stations and for all elements. The analysis of the slope of the relationship within the selected contexts reveals that the variability in TDS flux is mainly controlled by the discharge variability throughout the hydrological year. At the outlet of the basin, a clockwise hysteresis is observed for TDS concentration and is mainly controlled by Ca and HCO3 hysteresis, highlighting the need for a sampling strategy with a monthly frequency to accurately determine the TDS fluxes of the basin. The evaporite dissolution flux tends to be constant, whereas dissolved load fluxes released from other sources (silicate weathering, carbonate weathering, biological and/or atmospheric inputs) are mainly driven by variability in discharge. These results suggest that past and further climate variability had or will have a direct impact on the variability of dissolved fluxes in the Amazon. Further studies need to be performed to better understand the processes controlling the dynamics of weathering fluxes and their applicability to present-day concentration–discharge relationships at longer timescales

Contaminant transfer and hydrodispersive parameters in basaltic lava flows: artificial tracer test and implications for long-term management

International audienceThe aim of this paper is to evaluate the vulnerability after point source contamination and characterize water circulations in volcanic flows located in the Argnat basin volcanic system (Chaine des Puys, French Massif Central) using a tracer test performed by injecting a iodide solution. The analysis of breakthrough curves allowed the hydrodispersive characteristics of the massive lava flows to be determined. Large Peclet numbers indicated a dominant advective transport. The multimodal feature of breakthrough curves combined with high values of mean velocity and low longitudinal dispersion coefficients indicated thatwater flows in an environment analogous to a fissure system, and only slightly interacts with a low porosity matrix (n(e) < 1%). Combining this information with lava flow stratigraphy provided by several drillings allowed a conceptual scheme of potential contaminant behaviour to be designed. Although lava flows are vulnerable to point source pollution due to the rapid transfer of water within fractures, the saturated scoriaceous layers located between massive rocks should suffice to strongly buffer the transit of pollution through dilution and longer transit times. This was consistent with the low recovery rate of the presented tracer test

Contaminant transfer and hydrodispersiveparameters in basaltic lava flows: artificial tracertest and implications for long-term management

The aim of this paper is to evaluate the vulnerabilityafter point source contamination and characterizewater circulations in volcanic flows located in theArgnat basin volcanic system (Chaîne des Puys, FrenchMassif Central) using a tracer test performed by injectinga iodide solution. The analysis of breakthrough curves allowedthe hydrodispersive characteristics of the massivelava flows to be determined. Large Peclet numbers indicateda dominant advective transport. The multimodal featureof breakthrough curves combined with high valuesof mean velocity and low longitudinal dispersion coefficientsindicated thatwater flows in an environment analogousto a fissure system, and only slightly interacts with alow porosity matrix (ne < 1%). Combining this informationwith lava flow stratigraphy provided by several drillingsallowed a conceptual scheme of potential contaminant behaviourto be designed. Although lava flows are vulnerableto point source pollution due to the rapid transfer of waterwithin fractures, the saturated scoriaceous layers locatedbetween massive rocks should suffice to strongly bufferthe transit of pollution through dilution and longer transittimes. This was consistent with the low recovery rate ofthe presented tracer test

Suspended sediment and dissolved load budgets of two Amazonian rivers from the Guiana Shield : Maroni River at Langa Tabiki and Oyapock River at Saut Maripa (French Guiana)

This study presents the data collected within the framework of an Observatory of Research in Environment on the Amazonian Basin-the ORE HYBAM. It relates to the dissolved and solid loads of the two main rivers of French Guiana, the Maroni and Oyapock rivers, running on the Guiana Shield and draining respectively 64 230 and 24 630 km(2). The low coefficient of variation of the average annual flows of the two rivers indicates an inter-annual hydrological stability probably related to the immediate vicinity of the Atlantic Ocean. The sedimentary load is mainly composed of quartz and kaolinite. The total suspended solid (TSS) concentrations are among the world's lowest values; they range from 1 to 130 mg l(-1) during the hydrological cycle, with averages of 22 and 12 mg l(-1), for the Maroni and Oyapock rivers, respectively. The seasonal variability of these values is significantly higher than that of hydrologic flows, but without simple relationship with the discharge. Water chemical composition of the two rivers indicates a very weak mineralization, very similar to that found in the Amazonian rivers running on the Brazilian and Guianese shields, and in the Congo River and its tributaries in the Central African Shield. Seasonal variations are observed in both basins; they correspond to higher concentrations during low water stage (from October to February) and to more diluted water during the flood, from April to July. A signature enriched in Cl- is present at the Saut Maripa station on the Oyapock River indicating a more marked influence of the trade winds in this basin. The computation of atmospheric contributions to ions budget indicated a weak contribution for Ca2+ and Mg2+, which originates mainly from water-rock interactions in both stations, while more than half of Na+ is derived from atmospheric inputs

Climatic control on eastern Andean denudation rates (Central Cordillera from Ecuador to Bolivia)

The suspended sediment yield and associated current denudation rates of eight large catchments located along the eastern range of the central Andes have been determined. The catchments have been chosen as mountainous and mainly denudational basins to avoid sediment sinks that could bias our analysis. Discharge data and suspended sediment concentrations measured at each catchment outlet have been combined to produce average annual sediment fluxes and thus yields and current denudation rates over time spans of 2–43 years. Denudation rates range between 0.25 and 1.20 mm yr−1 with a north to south gradient. Maximum values are observed in Bolivian catchments. A correlation analysis has been carried out to determine the main controlling factors of current denudation rates at the catchments spatial scale. Climatic, topographic and lithologic parameters have been studied. Our results suggest that denudation rate is mainly controlled by the climate and especially its variability. A strong negative correlation between mean average runoff and denudation rate is detectable whereas topography and lithology are playing no significant role. A multiple regression analysis is suggesting that large Andean catchment denudation rate could be efficiently estimated by the variability of the climate. Combining both slope and lithologic secondary parameters improves the estimation. Finally, the important effect of climate variability on erosion and sediment transport seems to be enhanced by the potential protection of the vegetation cover that is directly controlled by the climate regime

Temporal variability and annual budget of inorganic dissolved matter in Andean Pacific Rivers located along a climate gradient from northern Ecuador to southern Peru

In Ecuador and Peru, geochemical information from Pacific coastal rivers is limited and scarce. Here, we present an unedited database of major element concentrations from five HYBAM observatory stations monitored monthly between 4 and 10 years, and the discrete sampling of 23 Andean rivers distributed along the climate gradient of the Ecuadorian and Peruvian Pacific coasts. Concentration (C) vs. discharge (Q) relationships of the five monitored basins exhibit a clear dilution behavior for evaporites and/or pyrite solutes, while the solute concentrations delivered by other endmembers are less variable. Spatially, the annual specific fluxes for total dissolved solids (TDS), Ca2+, HCO3 −, K+, Mg2+, and SiO2 are controlled on the first order by runoff variability, while Cl−, Na+ and SO4 2− are controlled by the occurrence of evaporites and/or pyrite. The entire Pacific basin in Ecuador and Peru exported 30 Mt TDS·yr−1, according to a specific flux of ∼70 t·km−2·yr−1. This show that, even under low rainfall conditions, this orogenic context is more active, in terms of solute production, than the global average

Temporal variability and annual budget of inorganic dissolved matter in Andean Pacific Rivers located along a climate gradient from northern Ecuador to southern Peru

In Ecuador and Peru, geochemical information from Pacific coastal rivers is limited and scarce. Here, we present an unedited database of major element concentrations from five HYBAM observatory stations monitored monthly between 4 and 10 years, and the discrete sampling of 23 Andean rivers distributed along the climate gradient of the Ecuadorian and Peruvian Pacific coasts. Concentration (C) vs. discharge (Q) relationships of the five monitored basins exhibit a clear dilution behavior for evaporites and/or pyrite solutes, while the solute concentrations delivered by other endmembers are less variable. Spatially, the annual specific fluxes for total dissolved solids (TDS), Ca2+, HCO3 −, K+, Mg2+, and SiO2 are controlled on the first order by runoff variability, while Cl−, Na+ and SO4 2− are controlled by the occurrence of evaporites and/or pyrite. The entire Pacific basin in Ecuador and Peru exported 30 Mt TDS·yr−1, according to a specific flux of ∼70 t·km−2·yr−1. This show that, even under low rainfall conditions, this orogenic context is more active, in terms of solute production, than the global average

Sediment budget in the Ucayali River basin, an Andean tributary of the Amazon River

Formation of mountain ranges results from complex coupling between lithospheric deformation, mechanisms linked to subduction and surface processes: weathering, erosion, and climate. Today, erosion of the eastern Andean cordillera and sub-Andean foothills supplies over 99% of the sediment load passing through the Amazon Basin. Denudation rates in the upper Ucayali basin are rapid, favoured by a marked seasonality in this region and extreme precipitation cells above sedimentary strata, uplifted during Neogene times by a still active sub-Andean tectonic thrust. Around 40% of those sediments are trapped in the Ucayali retro-foreland basin system. Recent advances in remote sensing for Amazonian large rivers now allow us to complete the ground hydrological data. In this work, we propose a first estimation of the erosion and sedimentation budget of the Ucayali River catchment, based on spatial and conventional HYBAM Observatory network. Copyrigh