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 × 10(6) 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 c...

Large hydrological systems aggregate compositionally different waters derived from a variety of pathways. In the case of continental‐scale rivers, such aggregation occurs noticeably at confluences between tributaries. Here we explore how such aggregation can affect solute concentration‐discharge (C‐Q) relationships and thus obscure the message carried by these relationships in terms of weathering properties of the Critical Zone. We build up a simple model for tributary mixing to predict the behavior of C‐Q relationships during aggregation. We test a set of predictions made in the context of the largest world's river, the Amazon. In particular, we predict that the C‐Q relationships of the rivers draining heterogeneous catchments should be the most “dilutional” and should display the widest hysteresis loops. To check these predictions, we compute 10 day‐periodicity time series of Q and major solute (Si, Ca2+, Mg2+, K+, Na+, Cl‐, SO42−) C and fluxes (F) for 13 gauging stations located throughout the Amazon basin. In agreement with the model predictions, C‐Q relationships of most solutes shift from a fairly “chemostatic” behavior (nearly constant C) at the Andean mountain front and in pure lowland areas, to more “dilutional” patterns (negative C‐Q relationship) toward the system mouth. More prominent C‐Q hysteresis loops are also observed at the most downstream stations. Altogether, this study suggests that mixing of water and solutes between different flowpaths exerts a strong control on C‐Q relationships of large‐scale hydrological systems.

RESUMEN com, lstefanny@gmail.com, rennydaniel@gmail.com, btapia@gmail.com, apolex23@gmail.com La investigación, se realizó en el ámbito del altiplano Peruano, con el objetivo de evaluar los cambios en la disponibilidad del recurso hídrico bajo escenarios de emisiones de Modelos Climáticos Globales (MCG) del Proyecto de Intercomparación de Modelos Acoplados Fase 5 (CMIP5). La distribución espacio-temporal de la precipitación, se tomó como referencia la climatología 1971 -2000 y sus proyecciones para el horizonte 2071 -2100, así mismo para la simulación de caudales se utilizó el modelo hidrológico conceptual de Ingeniería Rural de 2 parámetros, cuyas evaluaciones estadísticas se midieron a través de la eficiencia de Nash y Sutcliffe. El Simulador del Sistema Terrestre y el Clima de la Comunidad Australiana versiones 1.0 y 1.3 (ACCESS1.0 y 1.3) y el Modelo para la Investigación Interdisciplinaria sobre el Clima versión 5 (MIROC5), simularon adecuadamente el ciclo estacional de la precipitación y en base a los resultados, los cambios de precipitaciones para los caminos de concentración representativas (RCP4.5 y 8.5) a finales del siglo XXI, indican un ligero incremento de la precipitación anual en la cuenca Ramis y una disminución para la cuenca Ilave. Es así que las variaciones de las precipitaciones son también reflejadas en los caudales, concluyéndose que las mayores disminuciones del recurso hídrico se darían para la cuenca Ilave, con incrementos ligeros en promedio anual para la cuenca Ramis..The research was conducted in the area of the Peruvian altiplano with the aim to assess changes in the availability of water resources under emission scenarios Global Climate Models (GCMs) of the Coupled Model Intercomparison Project phase 5 (CMIP5). The spatio-temporal precipitation distribution was taken as reference climatology 1971 -2000 and its projections for the horizon 2071 -2100, also for simulating flows conceptual hydrological model of Rural Engineering 2 parameters are used, whose evaluations statistics were measured through efficiency Nash and Sutcliffe. The Australian Community Climate and Earth System Simulator versions 1.0 and 1.3 (ACCESS1.0 and 1.3) and Model for Interdisciplinary Research on Climate version 5 (MIROC5), adequately simulated the seasonal cycle of precipitation and based results, changes in rainfall for Representative Concentration Pathways (RCP4.5 and 8.5) at the end of the XXI century, indicate a slight increase of annual rainfall of the basin Ramis and a decrease for the Ilave basin. Is thus that variations in rainfall are also reflected in the flows, concluding that the largest decreases of water resources would be given for the Ilave basin, with slight increases in annual average for the basin Ramis. ARTICLE INFO

A bacia do rio Amazonas é importante no aporte de material dissolvido para o oceano (4% a nível mundial apresentaram concentrações quase constantes ao longo dos anos e entre as estações, indicando que seus fluxos dependem da variação da vazão. Portanto, a variação temporal do fluxo de material inorgânico dissolvido no rio Solimões e Amazonas depende do fator hidroclimatológico e da heterogeneidade das fontes. Nos rios Madeira e Purus há menor influência desses fatores, o que evidencia maior aporte dos silicatos. Como a bacia do Solimões aporta aproximadamente 84% do fluxo total de material dissolvido na bacia e está sob influência, principalmente, do fator hidroclimático, pode-se concluir que a variabilidade temporal desse fator controla a temporalidade dos fluxos do material dissolvido na bacia Amazônica. PALAVRAS CHAVE: intemperismo, fluxos hidroquímicos, diluição teórica, hidroclimatologia. Spatial-temporal variation of dissolved inorganic material in the Amazon basin ABSTRACTThe Amazon River basin is important in the contribution of dissolved material to oceans (4% worldwide). The aim of this work was to study the spatial and the temporal variability of dissolved inorganic materials in the main rivers of the Amazon basin. Data from 2003 to 2011 from six gauging stations of the ORE-HYBAM localized in Solimões, Purus, Madeira and Amazon rivers were used for this study. , HCO 3 -and SO 4 -2 had heterogeneous distribution over the years and did not show seasonality. At the stations of Madeira river, the concentration of these ions had seasonality inversely proportional to water discharge (dilution-concentration effect). Similar behavior was observed for the concentrations of Cl -and Na + at the stations of the Solimões, Amazon and Madeira rivers, indicating almost constant release of Cl -and Na + fluxes during the hydrological cycle. K + and SiO 2 showed almost constant concentrations throughout the years and all the stations, indicating that their flows depend on the river discharge variation. Therefore, the temporal variability of the dissolved inorganic material fluxes in the Solimões and Amazon rivers depends on the hydro-climatic factor and on the heterogeneity of the sources. In the Madeira and Purus rivers there is less influence of these factors, indicating that dissolved load fluxes are mainly associated to silicates weathering. As the Solimões basin contributes approximately 84% of the total flux of dissolved materials in the basin and is mainly under the influence of a hydro-climatic factor, we conclude that the temporal variability of this factor controls the temporal variability of the dissolved material fluxes of the Amazon basin.