Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Water Resources Research 8660-8685 concentration-discharge (C-Q) relationships Amazon River C-Q hysteresis loops tributary mixing spectral analysis AMAZONE BASSIN 2017 fdi:010071962 ENG Water Resources Research 0043-1397 ISI:000418736700002 11 10.1002/2017wr020591 https://www.documentation.ird.fr/hor/fdi:010071962 https://www.documentation.ird.fr/intranet/publi/2018/01/010071962.pdf 53 Horizon (IRD) Large hydrological systems aggregate compositionally different waters derived from a variety of pathways. In the case of continental-scale rivers, such aggregation occurs noticeably at confluences between tributaries. Here we explore how such aggregation can affect solute concentration-discharge (C-Q) relationships and thus obscure the message carried by these relationships in terms of weathering properties of the Critical Zone. We build up a simple model for tributary mixing to predict the behavior of C-Q relationships during aggregation. We test a set of predictions made in the context of the largest world's river, the Amazon. In particular, we predict that the C-Q relationships of the rivers draining heterogeneous catchments should be the most "dilutional" and should display the widest hysteresis loops. To check these predictions, we compute 10 day-periodicity time series of Q and major solute (Si, Ca2+, Mg2+, K+, Na+, Cl-, SO42-) C and fluxes (F) for 13 gauging stations located throughout the Amazon basin. In agreement with the model predictions, C-Q relationships of most solutes shift from a fairly "chemostatic" behavior (nearly constant C) at the Andean mountain front and in pure lowland areas, to more "dilutional" patterns (negative C-Q relationship) toward the system mouth. More prominent C-Q hysteresis loops are also observed at the most downstream stations. Altogether, this study suggests that mixing of water and solutes between different flowpaths exerts a strong control on C-Q relationships of large-scale hydrological systems. 062 ; 020 UR234 Bolivie / Brésil / Équateur / Pérou