Jean-Sébastien Moquet
email: jean-sebastien.moquet@ird.fr

Jean-Loup Guyot

Alain Crave

Jérôme Viers

Naziano Filizola

Tereza Jean-Michel Martinez

Cristina Oliveira

Liz Stefanny

Hidalgo Sánchez

Christelle Lagane

Waldo Sven

Lavado Casimiro

Jean-Michel Martinez Tereza

Luis Noriega

Rodrigo Pombosa

Calle Reyes Senamhi

Ortiz

Piso

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

Keywords:

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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 HCO 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.

Introduction

AQ4

Solutes in large rivers are the main tracers of the element cycles of the Earth's critical zone at the continental scale. The estimation of their annual fluxes and the description of their concentration variability in response to the hydrology allow the determination of the weathering budget of contrasted environments and their responses to climate forcing. Because of its geological and climate heterogeneity, the Amazon basin can be considered as a "natural laboratory" allowing, for example, for the evaluation of the role of these environmental factors in matter exportation budgets. Moreover, the riverine solute exports are also an important source of nutrients for the oceans. At the global scale, the tropical basins are the main source of dissolved matter for the oceans [START_REF] Gaillardet | Geochemistry of large river suspended sediments: silicate weathering or recycling tracer?[END_REF][START_REF] Meybeck | Global occurence of major elements in rivers[END_REF]. Among these tropical basins, the Amazon River is a major source of dissolved solids (e.g. [START_REF] Milliman | River discharge to the coastal ocean-a global synthesis[END_REF].

Historically, the waters of the Amazon streams were classified based on their colour, which is related to their hydrochemical characteristics (transparency, pH, conductivity, organic matter content and suspended matter) and to their ecological properties (e.g., [START_REF] Sioli | General features of the limnology of Amazonia[END_REF][START_REF] Junk | Plant life in the floodplain with special reference to herbaceous plants[END_REF][START_REF] Rios-Villamizar | Chemistry of different Amazonian water types for river classification: a preliminary review[END_REF] ). These characteristics are in turn linked to the geological, geomorphological and biological properties of each sub-basin. The chemical composition of the main tributaries of the Amazon has allowed for the discrimination of the lithological sources of the dissolved load [START_REF] Stallard | River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco Basins[END_REF]Edmond 1983 , 1987 ;Edmond et al. 19956;[START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF][START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF][START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF]. From these studies, it appears that the source of the dissolved load is mainly associated with silicate and carbonate weathering processes in the Andes. Nevertheless, [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF] and [START_REF] Bouchez | Floodplains of large rivers: weathering reactors or simple silos?[END_REF]Bouchez et al. ( , 2014 ) ) suggested that the lowland sedimentary areas contribute to dissolved load production and that the CO consumption associated with the weathering of floodplain sediments is significant for the Amazon basin budget. From these studies, it also appears that the Andes silicate weathering flux is nearly proportional to the water flux, at least at the annual timescale (Moquet et al. 2014a ).

AQ5

However, the methods used to discriminate the sources of dissolved load are associated with significant uncertainties that might obscure the variability of the dissolved load along the hydrological cycle. These uncertainties are mainly associated with the definitions of the silicate end member compositions [START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF]Bouchez et al.and Gailladet 2014 ;[START_REF] Moon | New estimates of silicate weathering rates and their uncertainties in global rivers[END_REF] ) and with the identification of the SO sources [START_REF] Calmels | Sustained sulfide oxidation by physical erosion processes in the Mackenzie River basin: climatic perspectives[END_REF][START_REF] Beaulieu | Modeling water-rock interaction in the Mackenzie basin: competition between sulfuric and carbonic acids[END_REF], especially in the case of the Andean basins [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF] ). In the present study, we explore the major element concentrations and fluxes without applying any correction/discrimination, and we focus on (1) the relationships between solute production and water flux at a timescale shorter than 1 year and on (2) the identification of the geographical areas producing each major solute.

AQ6

Although the total suspended solids (TSS) dynamics and budget in the Amazon have largely been documented in the literature, both at the scale of the whole Amazon basin (e.g. [START_REF] Meade | Storage and remobilization of suspended sediment in the lower Amazon River of Brazil[END_REF][START_REF] Dunne | Exchanges of sediment between the flood plain and channel of the Amazon River in Brazil[END_REF][START_REF] Filizola | 46 basin: an assessment using the Brazilian national data set[END_REF][START_REF] Martinez | Increase in suspended sediment discharge of the Amazon River assessed by monitoring network and satellite data[END_REF]Filizola et al. 2011 ) and of the Andes [START_REF] Guyot | Dissolved solids and suspended sediment yields in the Rio Madeira basin, from the Bolivian Andes to the Amazon[END_REF]Armijos et al. 2013a , b ;[START_REF] Pepin | Climatic control on eastern Andean denudation rates (Central Cordillera from Ecuador to Bolivia)[END_REF][START_REF] Santini | Sediment budget in the drainage basin of the Ucayali River, an Andean tributary of the Amazon[END_REF], the total dissolved solid (TDS) variability in response to the hydrological cycle has been less examined. Some local studies have been performed in the shields [START_REF] Markewitz | Control of cation concentrations in stream waters by surface soil processes in an Amazonian watershed[END_REF] ), in the central plain area [START_REF] Devol | Seasonal variation in chemical distributions in the Amazon (Solimões) river: a multiyear time series[END_REF], at the outlet of the Amazon [START_REF] Oltman | Amazon River investigations reconnaissance measurements of July 1963[END_REF][START_REF] Oltman | Reconnaissance investigations of the discharge and water quality of the Amazon[END_REF]Gibbs 1967a , b ) and on Andean rivers [START_REF] Roche | Water resources, salinity and salt yields of the rivers of the Bolivian Amazon[END_REF][START_REF] Guyot | Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie bolivienne), en période de crue[END_REF][START_REF] Townsend-Small | Suspended sediments and organic matter in mountain headwaters of the Amazon River: results from a 1-year time series study in the central Peruvian Andes[END_REF][START_REF] Aufdenkampe | Organic matter in the Peruvian headwaters of the Amazon: compositional evolution from the Andes to the lowland Amazon mainstem[END_REF][START_REF] Wilcke | Change in water quality during the passage through a tropical montane rain forest in Ecuador[END_REF][START_REF] Wilcke | Soil properties on a chronosequence of landslides in montane rain forest, Ecuador[END_REF][START_REF] Boy | Water flow paths in soil control element exports in an Andean tropical montane forest[END_REF]Armijos et al. 2013b ;[START_REF] Torres | Geomorphic regime modulates hydrologic control of chemical weathering in the Andes-Amazon[END_REF]. Some studies provide a general overview of the temporal variability of TDS (e.g. [START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF][START_REF] Tardy | The Amazon. Bio-geochemistry applied to river basin management: part I. Hydro-climatology, hydrograph separation, mass transfer balances, stable isotopes, and modelling[END_REF][START_REF] Bustillo | Biogeochemistry of the Amazonian floodplains: insights from six end-member mixing models[END_REF][START_REF] Bustillo | Factors driving the biogeochemical budget of the Amazon River and its statistical modelling[END_REF][START_REF] Sanchez | Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica[END_REF], but these results are restricted to a limited number of hydrological stations, and the Andean rivers are not specifically considered. To date, no study has presented an integrated view of the TDS variation as a function of discharge from the Andean basins to the outlet.

AQ7

The present paper is a complementary study of [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF] and [START_REF] Sanchez | Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica[END_REF] and includes the database previously used by these authors. These studies estimate the weathering budget of the Andean basins [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF] ) and report estimates of dissolved load exports at the scale of the main tributaries [START_REF] Sanchez | Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica[END_REF]. In the present study, we expanded our analysis to all the available contents of the Geodynamical, hydrological and biogeochemical control of erosion/alteration and material transport in the Amazon, Orinoco and Congo basins-Environmental Research Observatory ( HYBAM observatory) and Programa Climatologico y Hidrologico de la Cuenca Amazonica de Bolivia (PHICAB) databases (>3,000 samples analysed for major elements over 34 gauging stations) at the outlet of the main geomorphological domains of the Amazon basin. We exploited this database following three main objectives. The first objective is to discuss the spatial variability of major element concentrations as a function of lithological, geomorphological and climate parameters. The second objective is to show the role of intra-annual hydro-climatological variability in the variability of TDS concentrations. The third objective is to determine the dissolved load fluxes exported by the Amazon basin and to identify their main geographical origin at the basin scale.

AQ8

Study area

The Amazon basin covers 5.9 million km [START_REF] Callède | Les apports en eau de l'Amazone à l'océan Atlantique[END_REF]. It is located between 5° 16′ N and 20° 28′ S, between 79° 36′ W and 50° 15′ W and across five main countries: Brazil (63 % of the surface area), Peru (16 %), Bolivia (12 %), Colombia (6 %) and Ecuador (2 %). Negligible portions of the basin are also included in Venezuela and Guyana. With an annual discharge of 6.5-6.6 × 10 m year [START_REF] Dai | Estimates of freshwater discharge from continents: latitudinal and seasonal variations[END_REF][START_REF] Callède | Les apports en eau de l'Amazone à l'océan Atlantique[END_REF], the Amazon River contributes 16-18 % of the continental discharge to the oceans according to the global estimates of [START_REF] Dai | Estimates of freshwater discharge from continents: latitudinal and seasonal variations[END_REF] and GRDC ( 2014 ). In the present work, the study area corresponds to the Amazon basin at the Óbidos station (Amazon River), Itaituba station (Tapajós River) and Altamira station (Xingu River) and covers 5.6 million km , representing 94 % of the entire Amazon basin (Fig. 1 ).

Fig. 1

Topographic map of the Amazon basin and locations of the monitored gauging stations of the PHICAB program and SO-HYBAM programsobservatory (Gauging stations are detailed in Table 2 ). (M.d.D. Madre de Dios)

AQ9

The Amazon basin can be separated into three geomorphological domains (Fig. 1 and Table 1 ):

1. The Andes (25 % of the basin) is the active orogenic zone and the major source of dissolved matter (due to the abundance of evaporite and carbonate outcrops ;Gibbs 1967b ;[START_REF] Stallard | Geochemistry of the Amazon. 3. Weathering chemistry and limits to dissolved inputs[END_REF] ) and of suspended solids (e.g. [START_REF] Guyot | Dissolved solids and suspended sediment yields in the Rio Madeira basin, from the Bolivian Andes to the Amazon[END_REF]Armijos et al. 2013a , b ). In the present study, this domain includes the Andean forelands (approximately half of this area), corresponding to Cenozoic back-arc basins [START_REF] Roddaz | Sediment provenances and drainage evolution of the Neogene Amazonian foreland basin[END_REF], which make up the transition zone between the Andes and the central plain. This domain can behave as a sediment trap or as an erosional surface, according to the regional structural dynamics [START_REF] Guyot | Hydrogéochimie des fleuves de l'Amazonie Bolivienne[END_REF][START_REF] Laraque | Sediment budget of the Napo River, Amazon basin, Ecuador and Peru[END_REF][START_REF] Baby | Tectonic control of erosion and sedimentation in the Amazon Basin of Bolivia[END_REF]Armijos et al. 2013a , b ;[START_REF] Santini | Sediment budget in the drainage basin of the Ucayali River, an Andean tributary of the Amazon[END_REF].

forms a sedimentary basin for inputs coming from the Andes and, in much lower proportions, from the shields. It corresponds to the zone occupied by the main outflow channel of the Amazon toward the ocean (Filizola et al. 2011 ). This area is punctuated by floodplain lakes (várzeas) along the main channel of the Solimões and Amazon Rivers, which respond to the seasonal regime of inundation. These areas can play a significant role in the geochemical cycle of the Amazon sedimentary plain [START_REF] Viers | The influence of the Amazonian floodplain ecosystems on the trace element dynamics of the Amazon River mainstem (Brazil)[END_REF][START_REF] Cullmann | The impact of seepage influx on cation content of a Central Amazonian floodplain lake[END_REF].

3. The Guiana and Brazilian shields (51 % of the basin) lie to the north and south of the Amazon corridor. They consist of two extensively eroded Precambrian terrains and have little influence on the inorganic dissolved and solid fluxes carried by the Amazon (Furch et al. 1982 ;[START_REF] Konhauser | Multi-element chemistry of some Amazonian waters and soils[END_REF]. The hydrological network of the Amazon basin is organized according to five main tributaries: the Negro, Solimões, Madeira, Tapajós and Xingu Rivers.

The following water budget and areas are compared with the corresponding number after the confluence of the Amazon, Tapajos and Xingu Rivers. It is based on the 2003-2012 discharge at the HYBAM observatory database at the outlet stations of these rivers reported in Table 2 and by [START_REF] Getirana | Hydrological modelling and water balance of the Negro River basin: evaluation based on in situ and spatial altimetry data[END_REF] for the Negro River budget (1997-2006 period). The Negro River, near Manaus City (~17 % of the Amazon discharge and 13 % of its area; Southern American Monsoon System (SAMS). It depends on the seasonal variation of continent-ocean contrast in temperature and the seasonal migration of the intertropical convergence zone (ITCZ) southward (northward) during austral summer (winter) [START_REF] Marengo | Interdecadal variability and trends of rainfall across the Amazon basin[END_REF][START_REF] Marengo | Review-recent developments on the South American monsoon system[END_REF]. The ITCZ causes deep atmospheric convection with high rainfall and contributes a constant supply of moisture from the Atlantic Ocean to the Amazon Basin (Nogués [START_REF] Paegle | Progress in Pan American CLIVAR research: understanding the South American monsoon[END_REF][START_REF] Vera | Toward a unified view of the American monsoon systems[END_REF] ). The Andean mountain chain acts as an orographic barrier and affects the atmospheric circulation and rainfall patterns at the continental scale [START_REF] Insel | Influence of the Andes Mountains on South American moisture transport, convection, and precipitation[END_REF][START_REF] Garreaud | Present-day South American climate[END_REF] ). This orographic effect also induces a high heterogeneity of the rainfall distribution and intensity over the Andes and can favour either extremely humid (hotspots) or extremely dry (semi-arid) conditions in this region [START_REF] Vera | Toward a unified view of the American monsoon systems[END_REF][START_REF] Garreaud | Present-day South American climate[END_REF]Espinoza et al. 2009a ).

AQ12

At the scale of the basin, a north-south gradient is observed in the precipitation amount and seasonality (Espinoza et al. 2009a , b ). Northern and northwestern Amazonia are exposed to high rainfall associated with a low seasonality, whereas southwestern and southern Amazonia experience lower rainfall associated with high seasonality and a dry (humid) season during austral winter (summer). This affects the hydrographs [START_REF] Guimberteau | Discharge simulation in the sub-basins of the Amazon using ORCHIDEE forced by new datasets[END_REF] ) (Fig. 2 ). The maximum monthly discharges of the Tapajós, Madeira, Solimões and Negro Rivers occur in March, April, June and July, respectively. This temporarilytime lag in maximum discharge reflects the south-north displacement of the ITCZ throughout the year (Fig. 2a ). Moreover, this time lag in the maximum dischargeand is is accompanied by a south-north gradient in the intensity of seasonality (the relative difference between the higher and lower monthly discharges) and in the specific discharge (Fig. 2b ). Indeed, the Tapajós River experiences the highest seasonality and the lowest annual specific discharge, whereas the Negro River has the lowest seasonality but the highest specific discharge. The Amazon River at the Óbidos station displays the highest discharge between April and June. This maximum in discharge reflects the inputs of the Solimões River, but the seasonal variability of discharge of the Amazon at the Óbidos station is smoothed by the lag in time of the maximum discharge in the tributaries (the Madeira, Solimões and Negro Rivers) over the years (Fig. 2 ) and by the storage in the floodplains [START_REF] Guimberteau | Discharge simulation in the sub-basins of the Amazon using ORCHIDEE forced by new datasets[END_REF].

Fig. 2 a Monthly discharge of the Amazon River (right axis) and its main tributaries (left axis) and b monthly specific discharge of these rivers. Data are averaged for the 1983-2013 period (source: SO-HYBAM website)

The mean transit times of overland flow, shallow subsurface flow and groundwater have been estimated at the scale of the main Amazon tributaries based on the hydrograph separation using water-stable isotopes [START_REF] Mortatti | Hydrograph separation of the Amazon River: a methodological study[END_REF][START_REF] Tardy | The Amazon. Bio-geochemistry applied to river basin management: part I. Hydro-climatology, hydrograph separation, mass transfer balances, stable isotopes, and modelling[END_REF][START_REF] Bustillo | Factors driving the biogeochemical budget of the Amazon River and its statistical modelling[END_REF]. For example, [START_REF] Tardy | The Amazon. Bio-geochemistry applied to river basin management: part I. Hydro-climatology, hydrograph separation, mass transfer balances, stable isotopes, and modelling[END_REF] showed that the mean half-lives of water in the Amazon basin are approximately 22.2, 32.6 and 60.5 days for superficial runoff, hypodermic and groundwater reservoirs which annually contribute 29.5, 47.8 and 22.7 % of the Amazon discharge, respectively. Recently, based on hydrological models, [START_REF] Paiva | Large-scale hydrologic and hydrodynamic modeling of the Amazon River Water[END_REF] showed that surface waters govern most of the monthly terrestrial water storage changes (56 %), followed by soil water (27 %) and ground water (8 %). In the channel, as the velocity of surface water ranges between 1 and 2 m s (SO-HYBAM gauging database), the mean transit time from the Andes to the outlet of the basin (approximately 6,000 km) can be morehigher than 1 month.

Material and methods

In this study, we used the available data of the PHICAB (Programa Climatologico y Hidrologico de la Cuenca Amazonica de Bolivia) and HYBAM observatory (Geodynamical, hydrological and biogeochemical control of erosion/alteration and material transport in the Amazon, Orinoco and Congo basins-Environmental Research Observatory) frameworks (the HYBAM data are freely available at the HYBAM observatory website, http://www.ore-hybam.org , and the PHICAB database is available in [START_REF] Guyot | Hydrogéochimie des fleuves de l'Amazonie Bolivienne[END_REF]. The PHICAB framework collected hydrochemical data at various gauging stations of the Upper Madeira basin between 1983 and 1992. The HYBAM framework has collected hydrochemical data since 2000. In the present study, we use the available data corresponding to the 2000-2012 period in the Solimões basin, at three stations in the Madeira basin and at Brazilian stations on the Negro, Amazon and Tapajós Rivers (Table 2 ). Importantly, the studied stations are not homogenously distributed throughout the Amazon basin. Among the 34 studied stations, 26 are located at the outlet of the Andean and foreland basins, seven stations record the inputs of the main Amazon tributaries, and Óbidos (OBI) is the main station recording the Amazon outputs. Each gauging station is hereafter named according to a three-letter code listed in Table 2 .

Hydrological data

Water levels were collected daily or twice daily using a conventional hydrologic method. During the PHICAB period (1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992), gauging was accomplished using punctual velocity measurements with a mechanical current metre over the whole river section [START_REF] Guyot | Hydrogéochimie des fleuves de l'Amazonie Bolivienne[END_REF]. For the 2000-2012 period, within the framework of the HYBAM programobservatory ( http://www.ore-hybam.org ), gauging was accomplished using a 600-kHz (Peru, Bolivia and Brazil) or 1,200-kHz (Ecuador) acoustic Doppler current profiler (ADCP). The daily discharge series was then calculated from rating curves (discharge-water level relationship) using the Hydraccess software [START_REF] Vauchel | HYDRACCESS: software for management and processing of hydro-meteorological data[END_REF] ; free download at the SO-HYBAM website).

Sampling method and water chemistry analysis

Conductivity and pH were measured every 10 days at a set of stations of the HYBAM framework, named the 'SO-HYBAM framework' and following a 3-month frequency at the other stations of the HYBAM network (named the Remarkably, a conductivity time series is available at a frequency of 10 days since October 1994 at the Óbidos station.

Regarding the hydrochemical data, a sample of 650 ml was collected monthly at each gauging station, with the exception of the ALT station (Xingu River), where we use only two sample analyses. The samples were filtered on site using a 0.45-or 0.2-µm porosity filter. Major element concentrations (Ca, Mg, Na, K, Cl, SO , HCO and Si) were determined at the Instituto de Investigacion en Quimica, Universidad Mayor de San Andres (IIQ-UMSA) laboratory (La Paz, Bolivia) for the 19801983-1992 sampling period, at the Géoscience Environnement Toulouse laboratory (GET, France) for the 20002000-2012 sampling period for Ecuadorian, Peruvian and Bolivian samples and at the Laboratory of Geochronology, Universidade de Brasilia (UnB) for the 20002003-2012 sampling period for Brazilian samples. The samples collected during the PHICAB program were analysed according to the analytical procedure described in [START_REF] Guyot | Hydrogéochimie des fleuves de l'Amazonie Bolivienne[END_REF]: alkalinity was measured by acid titration, Cl by mercuric thiocyanate colorimetry, SO by barium sulfate nephelometry, Ca and Mg by atomic absorption, Na and K by flame spectrometry and Si by ammonium molybdate colourimetry. The samples collected during the HYBAM program were analysed according to the procedure described in [START_REF] Cochonneau | L'Observatoire de Recherche en Environnement, ORE HYBAM sur les grands fleuves amazoniens = The Environmental Observation and Research project, ORE HYBAM, and the rivers of the Amazon basin[END_REF]. Cl and SO concentrations were measured by ion chromatography, and Na , Ca , Mg , K and Si were analysed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Alkalinity was determined by acid titration. The TDS concentration corresponds to the sum of the cations (Ca, Mg, Na and K), the anions (HCO , SO and Cl) and SiO concentrations, all expressed in milligram per litre. Based on the analyses of geostandards, the analytical error is less than 10 % for both sampling periods.

We observed that TDS and conductivity are significantly correlated (r = 0.86; p values < 0.01; N = 1,782), considering the whole database, with the exception of one outlier (when conductivity or TDS > average + 3σ; ABA station):

Here, the error is defined as the mean averagebsolute error (MAE) of the relationship. In the present study, we use the conductivity as a proxy for TDS concentration to describe the concentration (C) vs discharge (Q) relationship because of the higher frequency of conductivity acquisition (10 days), allowing a precise characterization of the total solute dynamics throughout the hydrological year.

Annual flux calculation

The Amazon TDS flux corresponds to the sum of the inputs of the Amazon River at the OBI station, the Tapajós River at the ITA station and the Xingu River at the ALT station. To calculate the annual flux of each solute at each station, we first estimated the monthly flux based on the multiplication of the instantaneous concentrations obtained at a monthly period by the monthly discharge calculated from the sum of daily discharges (method M1C in Table S1 of the supplementary material). We then calculated the interannual average of monthly fluxes. We finally added the 12 monthly flux averages to evaluate the mean annual flux.

At two stations (the OBI and ITA stations), we also performed three other annual flux calculations for TDS (Table S1 ) to compare the effect of the flux calculation methods based on the same dataset in the period 2003-2012. The results are presented in Table S2 . The method M1A corresponds to the mean concentration of the overall data multiplied by the mean monthly discharge; then, we added the 12 monthly flux averages to evaluate the mean annual flux.

The method M1B corresponds to the monthly concentration interannual average multiplied by the mean monthly discharge interannual average; then, we added the 12 monthly flux averages to evaluate the mean annual flux. The method M2A corresponds to the application of the C = aQ relationship (see the following section) based on the daily discharge database. The daily flux is then calculated based on the multiplication of Cj and Qj, and the annual flux corresponds to the sum of the daily fluxes.

The error associated with these estimates corresponds to the sum of the analytical error (<10 %) and the error associated with the discharge measurements. The discharge measurement errors at OBI, ITA and ALT were estimated to be ±3, ±10.7 and ±9.8 %, respectively, by [START_REF] Callède | Les apports en eau de l'Amazone à l'océan Atlantique[END_REF].

The weighted discharge measurement error of the sum of the discharge at these three stations was therefore ±4 %. A maximum of error of 14 % is estimated. Indeed, regardless of the calculation method performed, if we compare the sum of the annual solute fluxes calculated upstream of the OBI station (at the MAN, FAZ, CAI and SER stations) with the solute fluxes 1 calculated at the OBI station, the upstream flux is equal to the OBI fluxes within 10 % ((flux OBI - flux upstream) / flux OBI) for TDS, Cl, SO , HCO , Ca, Mg and Na. Only the upstream annual fluxes of K and Si are 11 and 26 % lower than those at the flux measured at OBI station most likely due to significant K and Si inputs by the surface basin included between these stations.

AQ13

C vs Q relationships

Water discharge is an important factor affecting the variation of riverine material fluxes. The time series of dissolved concentrations allows us to derive the relationships between major element concentrations and river discharge. These relationships are functionally described using:

where C is the instantaneous (daily) concentration of the studied major element, Q is the daily discharge corresponding to the sampling date and a and b are the regression coefficients. Such relationships have been reported for several rivers to characterize the variation of the solute concentration in response to discharge variability (e.g. [START_REF] Walling | Patterns of sediment yield[END_REF][START_REF] Nkounkou | Hydrology and geochemistry of the Congo river system[END_REF][START_REF] Roy | Geochemistry of dissolved and suspended loads of the Seine River, France: anthropogenic impact, carbonate and silicate weathering[END_REF][START_REF] Chen | Major element chemistry of the Changjiang (Yangtze River)[END_REF][START_REF] Godsey | Concentration-discharge relationships reflect chemostatic characteristics of US catchments[END_REF][START_REF] Gislason | Direct evidence of the feedback between climate and weathering[END_REF][START_REF] Clow | Mechanisms for chemostatic behavior in catchments: implications for CO2 consumption by mineral weathering[END_REF][START_REF] Li | Variations in suspended and dissolved matter fluxes from glacial and non-glacial catchments during a melt season at Urumqi River, eastern Tianshan, central Asia[END_REF][START_REF] Laraque | Seasonal variability of total dissolved fluxes and origin of major dissolved elements within a large tropical river: the Orinoco, Venezuela[END_REF][START_REF] Moon | New estimates of silicate weathering rates and their uncertainties in global rivers[END_REF] ). These relationships between flow and load have important implications for predicting the fluxes of chemical constituents to receiving water bodies due to variable environmental conditions [START_REF] Godsey | Concentration-discharge relationships reflect chemostatic characteristics of US catchments[END_REF][START_REF] Jawitz | Temporal inequality in catchment discharge and solute export[END_REF]. In this paper, we used the slope b of the C-Q regression as an index, allowing for the characterization of the first-order response of the production of Amazonian solutes to changes in discharge. Indeed, the slope is a measure of the first-order degree to which concentration responds to a change in discharge. The larger the slope, the less sensitive is the concentration. When b ∼ 0, the concentration variability is low and independent of discharge. This behaviour, called 'chemostatic' [START_REF] Godsey | Concentration-discharge relationships reflect chemostatic characteristics of US catchments[END_REF], reflects a constant solute concentration despite variations in discharge.

When b ∼ -1, concentration decreases with increasing discharge, corresponding to a total dilution pattern and reflecting a constant solute flux despite variations in discharge. When b > 0, concentration increases with increasing discharge, as generally observed for suspended load concentrations (e.g. Armijos et al. 2013b ).

Based on a global compilation that included HYBAM for the Amazon at the OBI station, [START_REF] Moon | New estimates of silicate weathering rates and their uncertainties in global rivers[END_REF] suggested that at least 40 paired concentration-discharge measurements are needed to calculate unbiased weathering rates. Following this criterion, the data from the PUN, PCH and ALT stations are excluded for the analysis. Moreover, the C-Q relationship at NYO station is not significant (Moquet et al. 2014b ). In the supplementary material S3 , we reported the regression parameters with their related standard errors (SE) on a and b values and the mean absolute percentage error ( MAE%) of each regression. Because of the occurrence of hysteresis behaviour at the OBI station (see below), we did not use this method to calculate the annual Amazon fluxes.

Results

Hydrochemical characteristics

The description presented hereafter is based on the PHICAB and HYBAM monitoring networks and partly summarizes results already reported in [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF], for the Andean tributaries, and in [START_REF] Sanchez | Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica[END_REF], for some of the downstream stations. Even if slight differences in the mean concentration values are observed between the present study and the previous ones due to the actualization of the database, the values measured in both studies are commensurate. Hydrochemical characteristics are reported in Table 3 and are illustrated in Fig. 3 . The pH of the river water samples ranges between 4.8 and 7.9 (median value for each gauging stations). The highest value is recorded in the semi-arid basin of the Grande River (ABA station, Upper Madeira River), which is characterized by significant carbonates and Neogene evaporites [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF]. The lowest pH values are recorded in the Upper Negro River at the SER station, which is characterized by a high abundance of arenosol/podzol soils and is known to release waters with high organic matter concentrations (e.g. [START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF][START_REF] Moreira-Turcq | Exportation of organic carbon from the Amazon River and its main tributaries[END_REF]. At the other stations, the pH is closer to neutral conditions, with slightly alkaline water in the Andean tributaries and slightly acid water in the rivers of the central plain and shield. These values are coherent with previous observations [START_REF] Sioli | General features of the limnology of Amazonia[END_REF][START_REF] Junk | Plant life in the floodplain with special reference to herbaceous plants[END_REF][START_REF] Rios-Villamizar | Chemistry of different Amazonian water types for river classification: a preliminary review[END_REF].

The TDS concentration (and conductivity) is contrasted throughout the basin (Fig. 3 and Table 3 ).

AQ14

With the exception of some specific contexts, Ca , Mg , Na , SO , Cl and HCO concentrations follow the same hierarchy as the conductivity and

-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 2+ 2+ + 4 2- -
TDS. However, high relative chlorine and sodium contents are recorded in the Marañon sub-basin in the Huallaga River (CHA station), which drains large evaporitic domes [START_REF] Benavides | Saline deposits of South America[END_REF] ) and in the El Tigre River (NYO station), which was characterized by formation water released from oil extraction activity until February 2009 (Moquet et al. 2014b ) (Fig. 3 ). These two basins exhibit high Cl and Na concentrations (Cl and Na ≥800 µmol L ) and a 1:1 Cl/Na ratio characteristic of halite dissolution. SO concentrations are generally higher than 50 µmol L in all Andean sub-basins. This element is released by dissolution of evaporites (gypsum) and by pyrite oxidation [START_REF] Berner | The global water cycle: geochemistry and environment[END_REF][START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF] ).

In contrast with TDS and the Ca , Mg , Na , SO , Cl and HCO concentrations, K and Si do not follow the same trend. The highest concentrations of dissolved Si are measured in the basins draining volcanic areas (the Upper Napo and the PUN and SAN stations of the Marañon basin), and the lowest values are measured in the Upper Negro River. Despite the high geographical diversity (lithology, geomorphology, climate, etc.), all the other basins exhibit a low spatial variability of dissolved Si concentration. High K concentrations are measured in the El Grande River (ABA station), probably due to the high inputs of evaporite dissolution [START_REF] Guyot | Hydrogéochimie des fleuves de l'Amazonie Bolivienne[END_REF] ). In the other rivers, the K concentration has low spatial variability. These elements can both reflect silicate weathering and vegetation inputs [START_REF] Berner | The global water cycle: geochemistry and environment[END_REF][START_REF] Lucas | The role of plants in controlling rates and products of weathering: importance of biological pumping[END_REF][START_REF] Chaudhuri | Plant decay as a major control of river dissolved potassium: a first estimate[END_REF]. With the exception of some specific contexts (volcanic area and upper Negro River for Si and Grande River for K ), the Si and K concentrations are relatively homogenous over areas characterized by high heterogeneity in lithology, geomorphology or climate. This difference in the spatial variability in concentration between K and Si and the other major elements was also observed by [START_REF] Guyot | Regional characteristics of the hydrochemistry in the humid tropics of Bolivian Amazonia[END_REF] in the Madeira basin.

C-Q relationships

Regression parameters of Eq. 1 were determined for TDS concentration, conductivity and all elements over all gauging stations (Fig. 4 ). The slope b of the C-Q relationship varies from station to station and from element to element, but b value is usually between 0 and -1 in the Amazon basin, indicating that concentrations remain nearly constant or respond inversely to changes in discharge, consistently with observations at a global scale [START_REF] Meybeck | Evaluation des flux polluants dans les eaux superficielles Etude inter-Agence de l'eau[END_REF].

The definition of a C-Q log relationship is not adapted for all elements in all contexts to reproduce the measured concentration. A MAE greater than 50 % is generally measured for Cl and/or SO in the Solimões upper basin at the SRE and BEL stations and in the upper Madeira basin and for most of the elements at the SER station, indicating that the observed C-Q relationships are non-linear in log-log space (Fig. 4 ). At the SER station, this observation can be explained by the very low concentrations and high relative error. At the other stations with high MAE, the C-Q relationships are simply not univocal.

AQ15

As TDS and conductivity are correlated, they generally exhibit similar b values under the ±1 SE (standard error) uncertainties (Figs. 4 and5 ). Throughout the basin, the TDS b value varies between -0.42 ± 0.07 and 0.02 ± 0.04 but is generally close to -0.20. This implies that the TDS variability is lower than the discharge variability and that, at first order and as observed in other contexts (e.g. [START_REF] Markewitz | Dissolved rainfall inputs and streamwater outputs in an undisturbed watershed on highly weathered soils in the Brazilian cerrado[END_REF][START_REF] Yuan | Changes in major element hydrochemistry of the Pecos River in the American Southwest since 1935[END_REF] ), the TDS flux variability is controlled by discharge along the hydrological cycle.

Fig. 5

Ten-day frequency conductivity measurements (small symbols) and monthly averages (large symbols and lines) plotted against discharge for nine selected gauging stations. Simple dilution curves (concentration variability of a constant flux) are added for reference e.Proofing http://eproofing.springer.com/journals/printpage.php?token=GXEh0Z...

Figure 5 shows conductivity vs discharge at nine selected stations representative of the main geomorphological contexts of the Amazon basin.

The Solimões River (BOR, TAB and MAN stations) exhibits the highest conductivity values. In its Andean part (BOR station), the conductivity is highly variable. This behaviour can reflect the spatial and temporal heterogeneity of rainfall and solute sources. Downstream at the TAB and MAN stations, lower conductivity values can reflect the dilution effect due to the contribution of tributaries draining sedimentary areas. Nevertheless, in response to the hydrological cycle at all these stations, the variability of conductivity remains low in comparison with discharge variability, and b value is lower than -0.2.

AQ16

In the Madeira sub-basins, the conductivity-Q slope b is nearly zero at the RUR station, representing the Andean part of the sub-basin, and decreases to -0.2 in the central plain. At the RUR station, even if the slope b is close to zero, concentration is variable, as previously observed by [START_REF] Guyot | Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie bolivienne), en période de crue[END_REF], and two regimes can be distinguished. For discharge lower than 1,800 m s , the conductivity is close to the simple dilution curve. For discharge higher than 1,800 m s , conductivity is more variable and in some cases increases with discharge. The hypothesis considered here is that, as observed in other Amazonian contexts [START_REF] Markewitz | Control of cation concentrations in stream waters by surface soil processes in an Amazonian watershed[END_REF] ), the highest concentration during the rainy period (November-May), when discharge is higher than 1,800 m s , can reflect inputs from the mobilization of elements by surface runoff from the upper layer of the soils. Such a contribution might vary in the Andes from one rain event to another due to the spatial and temporal rainfall heterogeneity [START_REF] Roche | Hétérogénéité des précipitations sur la cordillère des Andes boliviennes[END_REF][START_REF] Guyot | Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie bolivienne), en période de crue[END_REF]. During the dry period, the variability in concentration would be mainly controlled by the dilution effect associated with groundwater inputs. Downstream, on the Madeira basins at the PVE and FAZ stations, the conductivity is less variable for a given discharge range. The conductivity decreases with discharge, but b value remains high (b ∼ -0.2) and the flux variability is therefore mainly controlled by discharge variability. This dilution effect has been previously reported by [START_REF] Roche | Water resources, salinity and salt yields of the rivers of the Bolivian Amazon[END_REF] in plain basins of the Madeira.

AQ17

In the basins of the shields (SER, CAI and ITA), the conductivity remains relatively constant (with b value higher than -0.1 and lower than 0.1) in response to the hydrological cycle.

The b values for Ca, Mg, SO and HCO are higher than -0.5 but are generally lower than 0. For Ca, Mg, HCO and TDS, the Solimões stations exhibit generally higher b values than the Madeira stations, as previously shown by [START_REF] Sanchez | Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica[END_REF]. This implies that the Solimões basins are more responsive to rainfall events in term of solute delivery than the Madeira basins, which tend to dilute to a limited extent. decrease of b from the Andean stations to the foreland station (BEL). This implies that the foreland area of this basin contributes more to diluting the Andean inputs than it contributes to solute inputs. Among the solutes, the b values of Si and K are close to 0 in most cases. With the exception of Cl and Na, these results imply that, at first order, discharge variability is the main factor controlling the variability of solute and TDS fluxes throughout the year.

These C-Q regressions must be considered as indexes that allow characterizing the first-order relationship between the variability of solutes and their respective daily discharge using a large amount of data from 310 stations of the Amazon basin. In specific cases, these relationships are not significant (e.g. NYO station, Moquet et al. 2014b ), and in other cases, other functional relationships can better explain the temporal variability in concentration. This is the case in particular when a significant hysteresis is observed. We illustrate this latter case through the description of hysteresis behaviour observed at the OBI station.

At the OBI station, the C-Q regressions defined for conductivity and TDS concentration allow estimating the measured values with a mean average error of ±8 µS cm and ±7.5 mg L , respectively. Nevertheless, examining closely the TDS/ and the conductivity as a function of discharge, a non-univocal C-Q relationship is observed (Fig. 6a ). The relationship between conductivity and discharge of the Amazon at the OBI station follows a clockwise hysteresis and concave curvature behaviour ('C1' type hysteresis of Evans and Davies 1998 classification) (Fig. 6a ). The highest conductivity values (>70 µS cm ) are recorded during the low water stage (November-December), whereas lower values are recorded during the high water stage (June-August period). For a given discharge value, higher conductivities associated with the increasing water stage (January-May) compared with the decreasing water stage (September-October) are recorded. Here, this absence of a univocal relationship between TDS and discharge is clearly due to a mass water mixing phenomenon that is the combined effect of (1) the contrast of the mean TDS concentration/conductivity between the three main tributaries (Negro, Solimões and Madeira Rivers) and (2) the lag of their relative discharge contribution over the course of the year. The monthly TDS flux at the OBI station corresponds to the sum of the inputs of the Solimões River at the MAN station, the Madeira River at the FAZ station and the Negro River at the CAI and SER stations within a range of ±11 % (relative difference between the monthly OBI fluxes and the upstream tributary fluxes) (Fig. 6b ). Following 2 this calculation, the Solimões controls between 77 and 89 % of the monthly TDS inputs in February and September, respectively. In contrast, the Madeira River controls between 8 and 22 % of the TDS inputs in September and February, respectively. The Negro River inputs at the CAI and SER stations control less than 5 % of the monthly TDS flux over the course of the year. The hysteresis behaviour is also explained by the variation in the relative discharge contribution of the Solimões, the Madeira and the Negro Rivers (Fig. 2 ). During the November-January period, when TDS concentration is at a maximum at the Óbidos station, the Solimões at the MAN station controls more than 60 % of the Amazon discharge at the OBI station. During the February-June period, the relative contribution of the Solimões discharge decreases as the discharge of the Madeira continues to contribute more than 20 % of the Amazon discharge at the OBI station. The TDS flux of the Solimões River is consequently partly diluted by that of the Madeira River.

During the July-October period, the discharge inputs of the Negro River and the discharge produced by the remaining area between the Negro, Solimões and Madeira River stations and the OBI station are maximal and represent more than 30 % of the Óbidos discharge. These highly diluted water inputs would consequently dilute the mineralized Solimões and Madeira River water inputs. To confirm this behaviour, we calculated the TDS concentration at the OBI station following Eq. 2 :

where C is the mean monthly concentration (mg L ), F is the mean monthly flux at the MAN, FAZ, SER and CAI stations (mg month ) and Q is the mean monthly discharge at the OBI station (L month ). Not all individual solutes show hysteresis. As Ca and HCO are the main species contributing to the TDS content (Fig. 3 ), they control the hysteresis behaviour observed for TDS and conductivity and also individually show hysteresis (TableFigure S31 ). Hysteresis phenomena are also observed for Mg, SO and K. Cl and Na exhibit dilution behaviour because these elements are mainly produced by the Solimões basin. Consequently, the Negro and Madeira Rivers mainly dilute these waters. Si exhibits a low variability in response to the hydrological cycle because of the low contrast in concentration between the contributing tributaries (Fig. S1 ). A slight hysteresis for Ca and HCO is observed upstream at the TAM, TAB and MAN stations (Solimões River), and a clear hysteresis is observed for SO at the FAZ station (Madeira River). The variability in the Ca, HCO and TDS concentrations remains low and does not explain the observed hysteresis for these solutes at the OBI station. Indeed, considering a constant concentration of Ca, HCO and TDS throughout the year (mean values in Table 3 ) at the upstream stations, we are able to reproduce the variability in concentration observed at the OBI station based on Eq. 2 (we considered a constant concentration and the monthly discharge at each station) with a maximum monthly error of +9 mg L for TDS (Fig. 6 ), +48 µmol L for Ca and +88 µmol L for HCO . The Si and K concentrations remain relatively constant at the upstream stations. The high hysteresis of SO observed at the FAZ station explains a significant part of the SO variability observed at the OBI station. Indeed, considering a constant SO concentration upstream of the OBI station, the monthly SO concentration is reproduced with a maximal error of 16 µmol L in July. Nevertheless, SO contributes only to 4-9 % of the Amazon TDS over the course of the year. In consequence, the dynamics of this solute do not contribute significantly to the observed TDS/conductivity hysteresis.

AQ18 AQ19

This result highlights the need for a monthly sampling frequency to accurately calculate the dissolved flux of the Amazon basin.

Annual flux calculation

The database allows us to estimate the solute fluxes from the different domains of the Amazon basin. The Amazon basin (Amazon flux at OBI + Tapajós Basin at ITA + Xingu basin at ALT) produced approximately 272 (±54) × 10 t TDS year during the period 2003-2012. Using out four calculation methods (Table S1 ) based on the same database, results range between 263 and 278 × 10 t TDS year (Supplementary material S2 ).

The Andean tributaries (Napo, Marañon, Ucayali, Madre de Dios, Beni and Mamoré Rivers) contribute approximately 64 % of the Amazon TDS flux for only 26 % of the discharge and 25 % of the basin area (Fig. 7 ). The central plain (37 % of the basin area) and the shield tributaries (37 % of the basin area) contribute approximately 25 and 11 % of the TDS flux, respectively (Table 4 and Fig. 7 ). The Marañon-Ucayali basins largely dominate the Andean TDS fluxes. These basins contribute approximately 50 % of the Amazon TDS flux for only 14 % of the Amazon discharge and 13 % of the Amazon basin area (Fig. 7 ). Nevertheless, this spatial flux distribution is not homogenous for all the elements (Table 4 and Fig. 7 ). The Marañon-Ucayali Rivers contribute 60-70 % of the Na, Ca and HCO exports of the Amazon. Approximately 21 and 9 % of the Amazon HCO flux are produced by the central plain area and the tributaries in the shields, respectively, whereas 70 % of this budget is produced by the Andean and foreland tributaries. Cl and SO are mainly produced by the Andean and foreland sub-basins (83 and 88 % of the Amazon flux, respectively). Even if the Andean basins dominate the Mg flux, the contribution from the Solimões central plain and the shields is significant (37 % of the Amazon flux). In contrast with the other elements, the Amazon central plain and the shields are the main sources of K and Si (Table 4 and Fig. 7 ).

F + F + F
The formula used for the flux calculation is also reported F annual flux of the considered major element at gauging station x

Discussion

Relationships between concentration and discharge

Solutes delivered by evaporite dissolution

Cl, Na and SO are mainly produced by the Andean and foreland Solimões sub-basins. In these contexts, the main sources of these elements are the dissolution of evaporites (Cl, Na and SO ) [START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF][START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF], the anthropogenic inputs in the El Tigre basin before February 2009 (Cl) (Moquet et al. 2014b ) and pyrite oxidation (SO ) [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF]. The remaining Cl, Na and SO produced by the central plain and the shields are mainly derived from atmospheric inputs (Cl, Na and SO ), silicate weathering (Na) and, in the shields, from pyrite oxidation (SO ) as evaporite are nearly absent their [START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF]. However, in the Solimões Andean and foreland basins, these elements can be considered as After February 2009 (when anthropogenic inputs stopped), b value is close to -1 for these elements controlled by evaporites inputs (Moquet et al. 2014b ). This implies that the dissolved flux released by evaporite dissolution is relatively constant and insensitive to discharge variability, as also observed in the Southern Andes (Leons et al. 2015). A possible mechanism is that these inputs can be associated either with a constant groundwater flux after interaction with diapir domes or with constant flux from local resurgences of deep water. These deep saline waters would then be diluted by surface water during hydrological cycle.

AQ20

Other sources

For Cl, SO and Na in all other basins and for all elements in all contexts, the C-Q relationship is shallow (-0.1 > b > -0.5) or nearly chemostatic (0.1 > b > -0.1). This implies that dilute rainfall water does not act as a simple diluter. Low dilution and chemostatic C-Q relationships are observed in catchments of diverse sizes (10 -10 km ) (e.g. [START_REF] Kirchner | A double paradox in catchment hydrology and geochemistry[END_REF][START_REF] Godsey | Concentration-discharge relationships reflect chemostatic characteristics of US catchments[END_REF][START_REF] Clow | Mechanisms for chemostatic behavior in catchments: implications for CO2 consumption by mineral weathering[END_REF][START_REF] Maher | The role of fluid residence time and topographic scales in determining chemical fluxes from landscapes[END_REF][START_REF] Basu | Hydrologic and biogeochemical functioning of intensively managed catchments: a synthesis of top-down analyses[END_REF][START_REF] Guan | Spatiotemporal scaling of hydrological and agrochemical export dynamics in a tile-drained midwestern watershed[END_REF][START_REF] Moon | New estimates of silicate weathering rates and their uncertainties in global rivers[END_REF]Stallard and Herndon et al. 2015 ). These relationships are the result of hydrological (mixing reservoirs, mixing tributaries) or chemical (kinetic or thermodynamic equilibrium) processes [START_REF] Clow | Mechanisms for chemostatic behavior in catchments: implications for CO2 consumption by mineral weathering[END_REF][START_REF] Maher | The role of fluid residence time and topographic scales in determining chemical fluxes from landscapes[END_REF][START_REF] Eiriksdottir | Does temperature or runoff control the feedback between chemical denudation and climate? Insights from NE Iceland[END_REF] ) that influence the way solutes are produced and exported by watersheds. It has been suggested that an important control of the chemostatic or nearly chemostatic C-Q response of a is the residence time of water [START_REF] Maher | The dependence of chemical weathering rates on fluid residence time[END_REF][START_REF] Maher | The role of fluid residence time and topographic scales in determining chemical fluxes from landscapes[END_REF][START_REF] Maher | Relationships between the transit time of water and the fluxes of weathered elements through the critical zone[END_REF][START_REF] Li | A reactive transport model for examining tectonic and climatic controls on chemical weathering and atmospheric CO2 consumption in granitic regolith[END_REF][START_REF] Maher | Hydrologic Regulation of Chemical Weathering and the Geologic Carbon Cycle[END_REF]. A chemostatic behaviour in rivers would be observed when the water has sufficient time to reach equilibrium with minerals. Various models have been able to reproduce the chemostatic behaviour observed in most settings (e.g. [START_REF] Godsey | Concentration-discharge relationships reflect chemostatic characteristics of US catchments[END_REF][START_REF] Jawitz | Temporal inequality in catchment discharge and solute export[END_REF]. Based on catchments in the Colorado Rocky Mountains, [START_REF] Clow | Mechanisms for chemostatic behavior in catchments: implications for CO2 consumption by mineral weathering[END_REF] indicated that cation exchange and seasonal precipitation and dissolution of amorphous or poorly crystalline aluminosilicates are important processes that regulate the concentration in a stream. At the scale of large rivers, the observed chemostatic behaviour can also be explained by the contribution of hydrological reservoirs and tributary inputs with different concentrations induced by different processes. The mix of these waters would result in a buffered signal with nearly constant concentration with increasing stream order [START_REF] Creed | The river as a chemostat: fresh perspectives on dissolved organic matter flowing down the river continuum[END_REF].

AQ21 AQ22

For Ca, HCO and TDS in the Andes, the chemostatic behaviour of the Maranon and Ucayali would therefore reflect more reactive mineralogy than that of the Napo and Madeira basins, where low dilution is observed (Figs. 4 and5 ). This is consistent, at first order, with the fact that the carbonates, which are mainly restricted to the Maranon-Ucayali basins, are more reactive silicates, which are the main sources of these elements in the Napo and the Upper Madeira [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF]. Indeed, far from equilibrium, carbonates are highly reactive to weathering compared to silicate minerals [START_REF] Lasaga | Fundamental aspects of quantitative models for geochemical cycles[END_REF], and waters are able to rapidly reach equilibrium with respect to carbonate minerals.

In all Amazonian contexts, K and Si generally exhibit chemostatic behaviour. [START_REF] Godsey | Concentration-discharge relationships reflect chemostatic characteristics of US catchments[END_REF] observe the same phenomenon for Si in small catchments in the USA. They highlighted that the rates of reaction including these elements are very slow, implying that stream water should always be far from equilibrium with respect to the weathered material. The mechanism controlling chemostasis in this case may consequently be due to a ubiquitous source homogeneously distributed throughout the subsurface in the Amazon basin (clays or phytolytesphytoliths for example) or to preferential contribution of the flushing of old water to the rivers.

Hysteresis behaviour at the OBI station

In the context of a river, pPrevious studies on hysteresis of C-Q relationships observed in rivers mainly focused on solid suspended matter (e.g. Wood 1977; [START_REF] Walling | Sediment availability and the prediction of storm-period sediment yields[END_REF][START_REF] Richey | Water discharge and suspended sediment concentrations in the Amazon River[END_REF]Williams 1989;[START_REF] Meade | Suspended sediments of the modern Amazon and Orinoco Rivers[END_REF][START_REF] Jansson | Determining sediment source areas in a tropical river basin, Costa Rica[END_REF][START_REF] Guyot | The suspended sediment flux of the River Amazon at Obidos, Brazil, 1995-2003[END_REF][START_REF] Filizola | 46 basin: an assessment using the Brazilian national data set[END_REF][START_REF] Martinez | Increase in suspended sediment discharge of the Amazon River assessed by monitoring network and satellite data[END_REF]Filizola et al. 2011 ;Armijos et al. 2013), but this behaviour remains less documented for solutes.

AQ23 AQ24

AQ25

AQ26

AQ27

Hysteresis for solutes C-Q relationships is generally observed during storm events (e.g. [START_REF] House | Hysteresis of solute concentration/discharge relationship in rivers during storms[END_REF][START_REF] Bowes | Phosphorus -discharge hysteresis during storm events along a river catchment: the River Swale, UK[END_REF] and is more rarely reported at the scale of large basins [START_REF] Coynel | Spatial and seasonal dynamics of total suspended sediment and organic carbon species in the Congo River[END_REF][START_REF] Ollivier | Unusual variations of dissolved As, Sb and Ni in the Rhône River during flood events[END_REF]. Hysteresis trends for dissolved solid concentrations are induced by time lags between dissolved solid and water contributions of reservoirs or tributaries (e.g. [START_REF] Ollivier | Unusual variations of dissolved As, Sb and Ni in the Rhône River during flood events[END_REF] ). These time lags arise when different dissolution kinetics occur in the reservoirs and/or when the water transit times between reservoirs are different (e.g. [START_REF] House | Hysteresis of solute concentration/discharge relationship in rivers during storms[END_REF][START_REF] Rose | Comparative solute-discharge hysteresis analysis for an urbanized and a "control basin[END_REF]. Solid suspended matter in rivers can also be a significant source or sink of some dissolved elements and can control the concentrations of those elements [START_REF] Bowes | Phosphorus -discharge hysteresis during storm events along a river catchment: the River Swale, UK[END_REF]. This last case is especially observed for bioreactive solutes, like phosphorus [START_REF] Bowes | Phosphorus -discharge hysteresis during storm events along a river catchment: the River Swale, UK[END_REF][START_REF] O'connor | Estimation of total phosphorus loads for a large, flashy river of a highly developed watershed-seasonal and hysteresis effects[END_REF], dissolved organic nitrates and dissolved organic carbon [START_REF] Edokpa | High fluvial export of dissolved organic nitrogen from a peatland catchment with elevated inorganic nitrogen deposition[END_REF].

Although, in the Amazon, the hysteresis behaviour between TSS concentrations and discharge at the OBI station is well established (e.g. [START_REF] Richey | Water discharge and suspended sediment concentrations in the Amazon River[END_REF][START_REF] Meade | Suspended sediments of the modern Amazon and Orinoco Rivers[END_REF][START_REF] Filizola | 46 basin: an assessment using the Brazilian national data set[END_REF]Filizola et al. 2011 ;[START_REF] Martinez | Increase in suspended sediment discharge of the Amazon River assessed by monitoring network and satellite data[END_REF], it is less well characterized for TDS concentration [START_REF] Tardy | The Amazon. Bio-geochemistry applied to river basin management: part I. Hydro-climatology, hydrograph separation, mass transfer balances, stable isotopes, and modelling[END_REF][START_REF] Bustillo | Biogeochemistry of the Amazonian floodplains: insights from six end-member mixing models[END_REF] ) and never with a high frequency conductivity allowing a precise characterization of the phenomena.

Both TDS and TSS hysteresis phenomena are clockwise, but their relative variability in response to the hydrological cycle is different (Fig. 8a,b ). Indeed, the relative amplitude of TSS (9.8 to 255 mg L ) is higher than that of conductivity (26 to 99 µS cm ), whereas the daily discharge (over the days of sampling) varies from 52,500 to 259,600 m s . In response to the hydrological cycle, during the decreasing and low water stages, high variability in conductivity is recorded when TSS is almost constant and minimal. During the increasing water stage, the TDS concentration remains high because of the high input of the Solimões River, whereas TSS increases. In the March-April-May (MAM) periods, during the second half of the increasing water stage, TDS and TSS decrease together because of the dilution effect of the Negro inputs for both TSS and TDS concentrations (Fig. 8c ).

Fig. 8

Ten-day frequency conductivity values (a) and TSS concentration (b) as a function of discharge at the Óbidos station (September 1994 to December 2012 period). c Conductivity as a function of TSS concentration -1 -1 3 -1 e.Proofing http://eproofing.springer.com/journals/printpage.php?token=GXEh0Z... TSS and TDS concentrations respond to different mobilization processes (as generally observed in most rivers; e.g. [START_REF] Négrel | Long-term fluxes of dissolved and suspended matter in the Ebro River Basin (Spain)[END_REF][START_REF] Sondag | Suspended sediment and dissolved load budgets of two Amazonian rivers from French Guiana: Maroni and Oyapock rivers[END_REF], and they are not produced in equivalent proportion by the Amazon tributaries. In the Amazon, the TSS dynamics has been explained by the combination of various processes such as the 'depletion' or 'exhaustion' effect (e.g. [START_REF] Meade | Suspended sediments of the modern Amazon and Orinoco Rivers[END_REF], the lag in time of tributary inputs [START_REF] Filizola | 46 basin: an assessment using the Brazilian national data set[END_REF]Filizola et al. 2011 ) and the backwater effect [START_REF] Meade | Backwater effects in the Amazon River basin of Brazil[END_REF][START_REF] Espinoza | A study of sediment transport in the Madeira River, Brazil, using MODIS remote-sensing images[END_REF], but this behaviour remains debated.

In contrast with TSS, the hysteresis observed for TDS is explained by a simple mixing model. The three main tributaries (Solimões, Madeira and Rio Negro) show different average TDS concentrations with low fluctuation during the hydrological cycle. Consequently, hysteresis of TDS concentration at OBI arises mainly because of offsets between the contributions of the main tributaries during the hydrologic cycle (Fig. 6 ).

Origin of the dissolved load throughout the Amazon basin

The Andean inputs

The Andean (including foreland) basins produce approximately 172 × 10 t TDS year and contribute approximately 64 % of the TDS of the Amazon basin (Figs. 7 and9 ). Even though the Andean TDS contribution to the Amazon exports was identified early on as the main solute source of the Amazon River (Gibbs 1967a , b ;Stallard et al. 1988Stallard and[START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF], estimates of its relative contribution to TDS and solutes fluxes have rarely been reported (MacClain et al.and Naiman 2008;[START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF]. Based on eight samples along the hydrological cycle on the main tributaries of the Solimões-Amazon River, [START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF] estimated that the Andean basins contributed up to 80 % (201 t TDS year ) of the Amazon TDS production. Our estimates are lower than these estimates. The difference can be attributed to both differences in sampling frequency and to the spatial distribution of the sampled stations. The high sampling frequency and the distribution of the SO-HYBAM framework stations allow for precise quantification of TDS and solute fluxes and of the relative contribution of the Andes and central plain. The TDS-specific flux from the Andes (118 × 10 t km year ) is larger than that from the plain (33 × 10 t km year ) and the shields (14 × 10 t km year ) for similar runoff values (1,070, 1,375 and 790 mm year for the Andes, central plain and shields, respectively) (Fig. 9b ). Specific fluxes are a function of concentration and of runoff. We previously showed that the temporal variability of most of the solute fluxes is mainly controlled by discharge variability. Nevertheless, as the mean runoff across these three geomorphological domains is similar, the Andes-sedimentary areas-shield TDS-specific flux (and flux) gradient observed throughout the basin is controlled by the contrast in TDS concentration values rather than by runoff (and discharge) variability. This observation shows that the total weathering flux of the Amazon is primarily controlled by the geomorphological/geological setting rather than by the spatial variability of the water supply (Figs. 7 and9 ). This result confirms the high sensitivity of the Andean environment to weathering processes compared with sedimentary areas and shields. Indeed, in orogenic areas such as the Andes, high slopes and physical erosion favour the contact between minerals sensitive to weathering processes (carbonates, evaporites and primary silicate minerals) and water [START_REF] Stallard | River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco Basins[END_REF][START_REF] Raymo | Tectonic forcing of late Cenozoic mountain building on ocean geochemical cycles[END_REF][START_REF] Dupré | Rivers, chemical weathering and Earth's climate[END_REF][START_REF] Milliman | River discharge to the coastal ocean-a global synthesis[END_REF]. Furthermore, the TDS b value decreases from Andean basins to floodplain areas (Fig. 5 ). [START_REF] Torres | Geomorphic regime modulates hydrologic control of chemical weathering in the Andes-Amazon[END_REF] observed also this phenomenon for solutes derived from silicate weathering in the Andean and Andean foreland of the Madre de Dios basin (Madeira River). They explained this observation by the topography and/or erosional regime differences between Andes and Andean foreland contexts. In particular, in mountains, the high erosion would favour the abundance of reactive mineral and the fluid transit time in fractured bedrocks would be longer than in plain, while foreland floodplain is composed of thick soils depleted in reactive minerals and, possibly, shorter fluid transit time.

AQ31 AQ32

Role of the plains in the Amazon weathering budget

The central plain area is currently active in terms of the TDS, HCO , Ca, Mg, K and Si production of the Amazon basin (Fig. 7 ). Because of the absence of evaporites and carbonates, there silicate weathering and atmospheric inputs are the main sources of dissolved load in this area. The atmospheric inputs do not significantly influence the HCO and Si of rivers [START_REF] Berner | The global water cycle: geochemistry and environment[END_REF][START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF], and with the exception of the Negro River for Mg [START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF], they influence less than 10 % of the Ca, Mg and K production [START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF][START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF]. These elements are consequently released to the river from silicates directly by weathering processes (Ca, Mg, HCO , K and Si) or indirectly through plant uptake and decay (K and Si). This implies that the central plain area is currently active in terms of silicate weathering and has a significant influence on the production of dissolved load in the Amazon basin. This is well illustrated by the budget of HCO . In the Andean and foreland area, 75 (61-83) % of the annual HCO flux derives from carbonate weathering [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF]. Because the sub-basins of the central plain and shields are mainly underlain by silicate lithology and because rainfall inputs are negligible for HCO production in rivers, the HCO produced in this area is mainly derived from CO consumption associated with silicate weathering processes (CO sil). Thus, the Andean sub-basins, the central plain sub-basins and the shield sub-basins are, respectively, responsible for approximately 41 % (33-45), 41 % (33-45) and 18 % of the HCO flux derived from silicate weathering (HCO sil) (or CO sil consumption). Following this calculation, the relative contribution of Andean CO sil consumption appears much lower than previous estimates [START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF][START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF] ). Nevertheless, this first-order estimate needs to be confirmed by further mass balance calculations allowing discrimination of the solute sources (atmospheric, evaporites, silicates, carbonates, anthropogenic inputs) (e.g. [START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF][START_REF] Gaillardet | Geochemistry of large river suspended sediments: silicate weathering or recycling tracer?[END_REF][START_REF] Moon | New estimates of silicate weathering rates and their uncertainties in global rivers[END_REF].

Our number shows that silicate weathering processes occurring in the sedimentary areas of an active mountain range can be significant at the scale of the basin, as shown by previous studies in the Amazon basin [START_REF] Moquet | Chemical weathering and atmospheric/soil CO2 uptake in the Andean and Foreland Amazon basins[END_REF][START_REF] Bouchez | Floodplains of large rivers: weathering reactors or simple silos?[END_REF]Bouchez et al. , 2014 ) ) and the Brahmaputra basin [START_REF] Galy | Weathering processes in the Ganges-Brahmaputra basin and the riverine alkalinity budget[END_REF][START_REF] Lupker | Predominant floodplain over mountain weathering of Himalayan sediments (Ganga Basin)[END_REF]. The weathering budgets of these sedimentary area need to be taken into account for long-term carbon cycle modelling to estimate the long-term CO variability and the links between orogenesis, climates and chemical-physical erosion processes (e.g. GEOCARB, [START_REF] Berner | GEOCARB III: a revised model of atmospheric CO2 over phanerozoic time[END_REF]COPSE, Mills et al. 2014 ;WITCH, Godderis et al. 2006 ;CIDRE, Carretier et al. 2014 ).

The shields

The Sshields rivers exhibit both the lowest TDS concentrations and the lowest TDS-specific fluxes observed of the studied stations (Fig. 9b ). This observation is consistent with the previous observations of [START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF] and [START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF]. Indeed, the formation of thick tropical soils would protect the bedrock from chemical weathering [START_REF] Stallard | River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco Basins[END_REF]. This effect is particularly marked in the Upper Negro basin (SER station), where very low TDS concentrations are recorded (∼6 mg L ) in comparison with the three other tributaries in the shields (the Branco, Tapajos and Xingu Rivers) (Table 3 ). The high runoff received by the upper Negro River partially compensates partially for the low concentration making TDS-specific fluxes relatively high. Indeed, the TDS-specific flux delivered by this area (∼13 × 10 t km year ) is similar with the TDS-specific flux measured in the Tapajos (19 × 10 km year ) and Xingu Rivers (13 × 10 t km year ) but is low compared with that of the Branco River (31 × 10 km year ).

The Upper Negro (SER station) is characterized by podzols/arenosols (more

3 3 2 2 2 -1 3 -2 -1 3 -2 -1 3 -2 -1 3 -2 -1
than 40 % of the area; [START_REF] Dijkshoorn | Update of the 1:5 million Soil and Terrain Database for Latin America and the Caribbean (SOTERLAC)[END_REF], which are mainly composed of quartz and have low sensitivity to weathering processes. In contrast, podzol/arenosol formations represent less than 3 % of the surface of the other shield basins. Even if the deep soils of the area are known to be poor in mobile elements [START_REF] Stallard | River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco Basins[END_REF]Edmond 1983 , 1987 ), these soils are currently submitted to weathering processes and are still able to produce dissolved mobile elements. Indeed, due to their surface area and their contribution of discharge to the Amazon, the shields contribute significantly to the TDS production (11 % of the Amazon flux), especially for Si and K production (20 and 25 % of the Amazon flux, respectively). This observation highlights that the main parts of the shield areas have a low impact on the total weathering budget of the Amazon basin, although they are chemically active environments.

Annual Amazon dissolved load export to the oceans

The Amazon basin (Amazon flux at OBI + Tapajós Basin at ITA + Xingu basin at ALT) produced approximately 272 × 10 t TDS year during the monitored period of 2003-2012 (Fig. 9 ). This value is close to previous estimates ranging from 251 to 292 × 10 t TDS year [START_REF] Gibbs | Water chemistry of the Amazon River[END_REF][START_REF] Berner | The global water cycle: geochemistry and environment[END_REF][START_REF] Gaillardet | Chemical and physical denudation in the Amazon River Basin[END_REF][START_REF] Gaillardet | Geochemistry of large river suspended sediments: silicate weathering or recycling tracer?[END_REF][START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF][START_REF] Milliman | River discharge to the coastal ocean-a global synthesis[END_REF][START_REF] Sanchez | Variação espaço-temporal do material inorgânico dissolvido na bacia Amazônica[END_REF]. The flux for each element is also generally commensurate with the estimates of [START_REF] Gibbs | Water chemistry of the Amazon River[END_REF] and [START_REF] Mortatti | Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations[END_REF]. The Amazon TDS solute production is dominated by HCO , Si and Ca, which represent 48, 21 and 12 % of the TDS, respectively (mass unit). Using the annually exported TSS (600-800 × 10 t year ; [START_REF] Guyot | The suspended sediment flux of the River Amazon at Obidos, Brazil, 1995-2003[END_REF][START_REF] Martinez | Increase in suspended sediment discharge of the Amazon River assessed by monitoring network and satellite data[END_REF]Filizola et al. 2011 ), the TDS flux corresponds to 25-31 % of the total solid material carried by the Amazon River.

Using the [START_REF] Berner | The global water cycle: geochemistry and environment[END_REF] and [START_REF] Milliman | River discharge to the coastal ocean-a global synthesis[END_REF] estimates of global continental TDS exportations (3,843 × 10 and 3,800 × 10 t TDS year , respectively), the Amazon River contributes approximately 7 % of the total dissolved load exported to the oceans. As highlighted by these authors, the Amazon River ranks as the most important basin in terms of dissolved load flux before the Changjiang (180 t TDS year ; Milliman and Farnsworth 2011 ) and has a dissolved yield (49 t TDS km year ) similar with the world average (∼40 t TDS km year ; [START_REF] Milliman | River discharge to the coastal ocean-a global synthesis[END_REF]. Individually, the Solimões, the Madeira and the rivers of the shields (Negro + Tapajós + Xingu) contribute up to 5.6 % (214 t TDS year ), 1.0 %

6 -1 6 -1 3 6 -1 6 6 -1 -1 -2 -1 -2 -1
-1 et al. ( 1999 ), the TDS flux of the Madeira River is similar with that of the Rhine (18th position), and the TDS fluxes delivered by the tributaries from the shields are together commensurate with those of the Don and Nelson River TDS fluxes (26th and 27th positions, respectively). The Solimões TDS-specific flux exhibits higher TDS specific flux values (97 t TDS km year ) than the global average and is similar with that of the Ganges Brahmaputra basin (which ranges as the third highest dissolved load of world rivers; Milliman and Farnsworth 2011 ), whereas the Madeira and the basins of the shields exhibit lower values than the world average (29 and 17 t TDS km year , respectively). The Ca, Mg, Na, Cl, SO and HCO carried by the Amazon River to the oceans correspond to 5-8 % of the world riverine fluxes, and the dissolved Si and K exports correspond to 10-12 %.

AQ33

In the 2003-2012 period, only the Cl concentration appears to show a slight decrease between the period before and after February 2009 due to the decrease in contamination by oil extraction activities identified throughout the northern foreland (Tigre River at NYO) (Moquet et al. 2014b ). The other elements do not show a significant interannual trend during the 10 years of monitoring at the Óbidos station.

Potential effects of further climate changes

During the last decades, the Amazon basin has been affected by climate changes in term of both the annual distribution of rainfall and increasing frequency of extreme events (Espinoza et al. 2009b ;[START_REF] Casimiro | Trends in rainfall and temperature in the Peruvian Amazon-Andes basin over the last 40 years (1965-2007)[END_REF]. From global and regional climate models, climate projections predict that these trends will intensify in the future (IPCC report: [START_REF] Magrin | Regional Aspects Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change e[END_REF]. Projections reported by the IPCC [START_REF] Magrin | Regional Aspects Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change e[END_REF] ) agree that the basin will experience a significant increase in temperature. The projections for rainfall are affected by large uncertainties, but some general trends can be extracted on a regional scale. The northwestern part of the basin would experience higher precipitation, whereas central, southern and eastern Amazonia would be subjected to drier conditions [START_REF] Giorgi | Developing regional climate change scenarios for use in assessment of effects on human health and disease[END_REF][START_REF] Bombardi | IPCC global coupled model simulations of the South America monsoon system[END_REF][START_REF] Marengo | Development of regional future climate change scenarios in South America using the Eta CPTEC/HadCM3 climate change projections: climatology and regional analyses for the Amazon, São Francisco and the Paraná River Basins[END_REF][START_REF] Magrin | Regional Aspects Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change e[END_REF]. Increases in the frequency and intensity of extreme events would accompany these general trends. Following these scenarios, if the observed

AQ34

Nevertheless, these predictions assume that the C-Q relationships are stationary through time. However, weathering rates depend not only on water availability but also on a number of other parameters such as lithology, temperature, erosion rates, abundance of organic acids and vegetation (Goudie and Viles 2012 and references within). Moreover, it is likely that the C-Q relationships determined for a given range of Q are not stable for extreme conditions [START_REF] Maher | The dependence of chemical weathering rates on fluid residence time[END_REF]. Further studies on small basins and on basins undergoing extreme climatic conditions need to be performed to better constrain these laws, to model chemical weathering processes and to better predict the future evolution of dissolved matter exportation from the Amazon basin.

Conclusion

In the period 2003-2012, the Amazon basin exported an average of 272 × 10 t year of dissolved load, which corresponds to nearly 7 % of the TDS flux annually exported from the continents to the oceans. The Amazon TDS exports are mainly composed of HCO , Si and Ca. Ca and HCO are mainly produced by carbonate weathering in the Andean basins and especially in the Marañon and Ucayali basins (representing approximately 50 % of their fluxes), whereas Si production is mainly controlled by the spatial distribution of rainfall throughout the basin. A TDS concentration gradient is observed according to the following geomorphologic hierarchy: Andean basins > 6 -1 3 3 sedimentary areas > non-podzolic shields > podzolic shields. Due to its surface and its relative contribution to the Amazon, the water flux from the central plain significantly contributes to the dissolved production of the basin, with an export of approximately 25 % of the total TDS flux. This result confirms that sedimentary areas are currently undergoing weathering processes. Further analysis needs to be performed to accurately discriminate the TDS sources.

Over the main Amazon tributaries, the variability of TDS fluxes is mainly controlled by discharge variability in response to the hydrological cycle.

Evaporite dissolution produces a nearly constant flux throughout the year, whereas the TDS fluxes released by other sources (carbonate weathering, silicate weathering, biosphere and atmospheric inputs) are mainly controlled by variability in discharge. For the first time, the hysteresis behaviour observed for TDS (conductivity) at the Óbidos station is described. This phenomenon is mainly explained by the time lag in discharge seasonality of the three main tributaries (Solimões, Madeira and Negro), which have contrasted TDS concentrations. If the C-Q relationships determined throughout the basin remain stable, further changes in rainfall distribution and intensity would consequently have a direct impact on the variability of TDS flux. In particular, an increase in rainfall over the western and northwestern sub-basins underlain by carbonates would increase the exportation of Ca and HCO , whereas the dissolved Si exportation would be nearly proportionally affected by the changes occurring over the Amazon basin surface. Nevertheless, the main processes controlling the C-Q relationships of solutes throughout the basin are not identified. Further studies are still required to identify the main physico-chemical processes controlling these empirical laws, to better constrain their limitations and to quantify the effect of extreme events on these solute export budgets.

Sondag, Nore Arevalo, the Servicio Nacional de Meteorología e Hidrología -Lima, Peru and La Paz, Bolivia (SENAMHI), the Instituto Nacional de Meteorología e Hidrología-Quito, Ecuador (INAMHI), Agência Nacional de Águas-Brasília, Brazil (ANA), the Universidad Nacional Agraria de La Molina-Lima, Peru (UNALM), the Universidad Mayor de San Andres-La Paz, Bolivia (UMSA), Universidade de Brasília-Brazil (UNB), Universidade do Estado de Amazonas-Manaus, Brazil (UEA) and all members of the SO-HYBAM (Hydrogeodynamics of the Amazon basin), for providing hydrological and water chemistry data.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Table S2

Calculation of annual fluxes at OBI and ITA stations following the flux calculation methods reported in Table S1 for the period 2003-2012. The TDS flux at ALT has been calculated from the average of the TDS concentration of the 2 samples collected at ALT multiplied by the yearly discharge the TDS flux at this station is 5.8 × 10 t year . The Amazon flux corresponds to the sum of OBI, ITA and ALT TDS fluxes. Even considering a 100 % error at ALT gauging station, it would not significantly influence the Amazon budget because this river contributes only to around 2 % to the Amazon TDS production.

(DOCX 16 kb)

Table S3 There is an error in the head of this table : There is an inversion between the column : "b ± SE" and the column "a ± SE".

Please, find in attached file the new version of this table (Table S3)

Linear regression parameters describing solutes concentration (mmol L ) and conductivity (µS cm ) as a function of the discharge (m s ) (Eq. 1 ). Errors indicate ±1 standard error (SE). The MAE% corresponds to the relative mean average standard errormean absolute percentage error. (DOCX 38 kb)

  [START_REF] Getirana | Hydrological modelling and water balance of the Negro River basin: evaluation based on in situ and spatial altimetry data[END_REF], in the north of the basin, drains a large part of the Guyana shield. The main tributaries are the Branco River to the east and the Upper Negro River to the west. The Solimões River (51 % of the Amazon annual discharge and 39 % of its area) drains the Northern and Central Andean sub-basins and the main part of the central plain. The main Andean Solimões tributaries are, from north to south, the Napo, Marañon and Ucayali Rivers. The Napo basin includes most of the active volcanoes of the basin. The Marañon and the Ucayali drain diverse lithologies and are especially marked by the occurrence of karstified carbonates and evaporite domes(Stallard and Edmond 19873 ). After the confluence of the Napo, Marañon and Ucayali, the main left bank tributaries of the Solimões are the Iça and Japura Rivers that drain the northern central plain and the small Colombian Andean basins. The main right bank tributaries are the Javarí, Jutaí, Juruá and Purus Rivers, which drain the centre part of the central plain. The Madeira River (13 % of the Amazon discharge and 23 % of its area) drains the southern Andes and the western part of the Brazilian shield. The main Andean tributaries of the Madeira River are, from north to south, the Madre de Dios, the Beni and the Mamoré,. Mamoré basin which includes the semi-arid basin of the Grande River. The Tapajós and Xingu Rivers (6 and 4 % of the Amazon discharge, respectively, and 8 and 8 % of its area) drain the remaining area of the Brazilian shield in the south-southeastern part of the basin. These five main Amazon tributaries (Negro, Solimões, Madeira, Tapajos and Xingu) connect with the Amazon River in the central Amazon plain between the cities of Manaus and Belem (Brazil) from ~1,200 to 150 km upstream from the estuary.

Fig. 4

 4 Fig. 4 Log-log slopes of concentration-discharge relationships (log(C ) = a + b log(Q )) for studied stations by site name for cations (a), anions (b), TDS, Si and conductivity (c). Error bars indicate ±1 standard error (SE). Large symbols indicate that the MAE of the C-Q relationship is >50 %

  Cl and Na exhibit very variable b values ranging from -0.78 ± 0.09 to 0.04 ± 0.06, and the lowest b values are generally recorded at some Napo stations, Maranon-Ucayali stations and downstream Solimões and Amazon stations (TAB, MAN and OBI), whereas b values closer to 0 are recorded in the plain (LAB) and in the tributaries in the shields (CAI and ITA). The Napo River exhibits an overall eproofing.springer.com/journals/printpage.php?token=GXEh0Z...

Fig. 6 a

 6 Fig. 6 a Ten-day frequency conductivity values (small symbols) and interannual monthly conductivity averages (large symbols and lines) at Óbidos as a function of discharge (September 1994 to December 2012 period). Simple dilution curves (concentration variability of a constant flux) are added for reference. b Comparison of the sum of the monthly TDS flux of the Solimões at the MAN station, Madeira at the FAZ station and Negro at the CAI and SER stations with the Amazon TDS flux at the OBI station (January 2003 to December 2012 period). c Comparison of the mean monthly TDS concentration at the OBI station, the calculated Amazon TDS using fluxes (sum of the monthly TDS flux at the MAN, FAZ, SER and CAI stations divided by the monthly discharge at the OBI station) and the calculated Amazon TDS considering constant TDS

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Fig. 7 a

 7 Fig. 7 a Contribution of each sub-basin of the Amazon basin to the surface area, the discharge and the dissolved load production. (TDS = Ca + Mg + Na + K + Cl + SO + HCO + SiO in mass unit). b Total flux of each major element from the Amazon

Fig. 9 a

 9 Fig. 9 a Specific flux of the dissolved load in the Amazon basin and TDS flux budget as a function of the main geomorphological contexts. b TDS flux, specific flux and mean concentration for the Andes, central plain and shields

  relationships at the scale of the hydrological year are valid for decadal evolution of discharge, the Amazon TDS fluxes would increase in the future because the main source of TDS is located in the northwestern part of the basin. In particular, the dissolved fluxes of the Amazon mainly associated with carbonate weathering in the Marañon and Ucayali basins would increase proportionally to the discharge, whereas the Madeira TDS fluxes would decrease. Cl and Na fluxes, controlled by evaporite inputs, would not be affected by projected climate changes. Si and K fluxes would vary proportionally with the mean rainfall variation of the Amazon basin. As a perspective and as performed by VonBlankenburg et al. (2015) for the Last Glacial Maximum based on Maher and Chamberlain (2014) C-Q model, further combination of derived C-Q relationships with climate model output projections of Amazon river discharge (and its tributaries) would allow to assess future changes in flux due to the anthropogenically altered climate state.

Fig. S1

 S1 Fig. S1Monthly frequency solutes measurements (small symbols) and monthly averages (large symbols and lines) plotted against discharge and averages discharge, respectively, at Obidos gauging station (the discharge of the sampled date is considered here). Simple dilution curves (concentration variability of a constant flux) are added for reference.(JPEG 276 kb)

Table 1

 1 Amazon

	AQ10

basin and geomorphological domains (% of the total Amazon basin area) See Fig.

1

for the definition of domain boundaries

Table 2

 2 Geographical and hydrological characteristics of gauging stations

	Solimões	Napo

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Table 3 Physico

 3

	NLO	7.1 (6-8.8) 92 ± 16	318 ± 55	57 ± 11	98 ± 30	38 ± 38	31 ± 64	48 ± 13
	DJI	7.2 (5-8.7) 88 ± 31	233 ± 133	52 ± 22	114 ± 47	41 ± 34	25 ± 19	49 ± 31
	FOR	7 (6.3-7.8) 63 ± 19	189 ± 41	49 ± 13	116 ± 48	36 ± 18	20 ± 12	29 ± 10

-chemical characteristics and average dissolved solid concentrations for the monitored stat station, the values for the two analysed samples are presented) e.Proofing http://eproofing.springer.com/journals/printpage.php?token=GXEh0Z... 0 sur 61 08/10/2015 21:46

  The highest mean value (TDS at ABA = 396 mg L ) is recorded in the semi-arid basin of the Grande River (Upper Madeira), and the lowest value (TDS at SER = 6.5 mg L ) is recorded in the podzolic/arenitic basin of the Upper Negro River. The other TDS values decrease as follows: Marañon-Ucayali (TDS = 63 to 222 mg L ) > Napo (TDS = 64 to 99 mg L )

	stations,
	respectively) are characterized by highly diluted waters. Even if all the basins
	of the shields exhibit low TDS concentrations (<35 mg L ), they can be
	separated into two groups: the Branco, Tapajós and Xingu Rivers (CAI, ITA
	and ALT stations, respectively; 22-35 mg L ) exhibit higher TDS
	concentrations than the Upper Negro River (SER station; 6 mg L ).

= Upper Madeira (TDS = 63 to 109 mg L ) > central plain tributaries (TDS of Purus at LAB = 52 mg L ) > shield tributaries (Negro, Branco, Tapajós and Xingu Rivers; TDS = 22 to 48 mg L ). This hierarchy reflects the lithological/geomorphological characteristics of the river basins. Importantly, this hierarchy is based only on the monitored tributaries that integrate the upstream sub-basins. Intra-basin concentration heterogeneities have previously been observed, especially in the Andes (e.g.

[START_REF] Stallard | Geochemistry of the Amazon. 2. The influence of geology and weathering environment on the dissolved load[END_REF][START_REF] Guyot | Regional characteristics of the hydrochemistry in the humid tropics of Bolivian Amazonia[END_REF]

. The Grande River (Madeira Andes) is characterized by significant evaporite deposits and a semi-arid climate. The Marañon and the Ucayali (Andean tributaries) drain large evaporite and carbonate outcrops. The Napo basin (Andean tributaries) includes the main active volcanoes of the basin. The central plain tributaries (e.g. Purus River) drain old deposits of silicate sediments, initially exported from the Andean area. These waters are fairly diluted. As a consequence, the Solimões (TAM, TAB and MAN) and Madeira (PVE and FAZ) stations are affected by dilution associated with the foreland and central plain inputs. The tributaries in the shields (Negro, Branco, Tapajós and Xingu Rivers at the SER, CAI, ITA and ALT

Table 4

 4 Dissolved load flux calculation by geomorphological setting e.Proofing http://eproofing.springer.com/journals/printpage.php?token=GXEh0Z...

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  TDS year ) and 0.6 % (22 t TDS year ) of the global TDS flux, respectively. The Solimões itself is the first world basin in terms of the flux of river dissolved load. Following the hierarchy of 62 largest rivers of Gaillardet

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Acknowledgments AQ35

We especially thank Daniel Ibarra (Stanford University) for his constructive recommendations under the review process. We also especially thank Dr. Julien Bouchez (CNRS-IPGP) for insightful discussions and his help to improve the manuscript. This work was funded by the French Institut de Recherche pour le Développement (IRD) and the French Institut des Sciences de l'Univers (INSU) through the SO-HYBAM Observatory. We especially thank Pascal Fraizy, Philippe Vauchel, William Santini, Elisa Armijos, Francis