Geomorphic regime modulates hydrologic control of chemical weathering in the Andes–Amazon

Abstract

The interplay between the hydrologic processes that supply, store, and route water in catchment systems and the chemical weathering reactions that add and remove solutes acts as an important control on chemical weathering fluxes. In this study, we use paired measurements of solute chemistry and runoff in four nested catchments that span the transition from the Andes Mountains to the Amazonian foreland floodplain in Peru in order to investigate the links between hydrology and weathering processes and to determine how these links change across a geomorphic gradient. All of the sites show variation in elemental concentrations and ratios with runoff consistent with hydrologically driven changes in lithologic sources, the extent of secondary mineral precipitation, and, potentially, fluid flow paths. In the Andean sites, solute concentrations are relatively constant despite large changes in runoff. This is in direct contrast to the foreland floodplain site, where solute concentrations are diluted as runoff increases. In the Andes-Amazon, the concentration-runoff behavior is correlated with the mean catchment slope angle, which suggests that erosional processes, by modulating the timescales over which weathering reactions occur within the critical zone, can be an underlying control on solute production and therefore on chemical weathering. Due to the co-variation between the geomorphic and hydrologic controls on chemical weathering, weathering fluxes in Andean sites are more sensitive to seasonal changes in runoff than in the foreland floodplain site.

Oxidation of sulfides and rapid weathering in recent landslides

“…Therefore, we expect that although the period when we sampled was relatively dry, our measurements are a fair first-order representation of solute concentrations and ratios during the majority of the year. This is consistent with observations from other mountain belts, including the Southern Alps of New Zealand, the Himalayas, and the Andes, where rivers exhibit near-chemostatic behaviour over a range of discharge conditions (Lyons et al, 2005;West et al, 2005;Torres et al, 2015;Tipper et al, 2006).…”

Erosion of organic carbon from the Andes and its effects on ecosystem carbon dioxide balance

“…The sediment yield is therefore lower in this upstream subcatchment compared to the larger catchment at San Pedro, which is consistent with the lower rates of landsliding occurring upstream of the Wayqecha gauging station [ Clark et al ., ], since landslides often supply a large amount of sediment to mountain rivers [ Hovius et al ., ]. The lower SS yield at Wayqecha in comparison to San Pedro is also consistent with a lower average catchment slope [ Clark et al ., ; Torres et al ., ; Clark et al ., ]. The Wayqecha POC biosphere yield was estimated to be 5.3 ± 2.7 t C km −2 yr −1 and the POC petro yield 3.5 ± 1.8 t C km −2 yr −1 .…”

Temporal Variations in Water Chemistry of the (Lower) Brahmaputra River: Implications to Seasonality in Mineral Weathering

“…These two parameters in river basins often follow an empirical power law: C = a × Q b , where a and b are constant values. In large river systems, the b values show large spatial variations with chemostatic (b~0) behavior in their upper reaches and dominancy of dilution (b~−1) effect toward the lowland regions (Bouchez et al, 2017;Torres et al, 2015). In large river systems, the b values show large spatial variations with chemostatic (b~0) behavior in their upper reaches and dominancy of dilution (b~−1) effect toward the lowland regions (Bouchez et al, 2017;Torres et al, 2015).…”

“…have been recognized, surface runoff plays a dominant role in regulating intensity of this land surface process in river basins (Dalai et al, 2002;Gaillardet et al, 1999;Riebe et al, 2004;Singh et al, 2005;Torres et al, 2015;West et al, 2005;White & Blum, 1995). Although several controlling factors (temperature, physical erosion, basin relief, lithology, etc.)…”