Primary weathering rates, water transit times, and concentration-discharge relations: A theoretical analysis for the critical zone

Ameli, Ali A. and Beven, Keith and Erlandsson, Martin and Creed, Irena F. and McDonnell, Jeffrey J. and Bishop, Kevin (2017) Primary weathering rates, water transit times, and concentration-discharge relations: A theoretical analysis for the critical zone. Water Resources Research, 53 (1). pp. 942-960. ISSN 1944-7973

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Official URL: http://dx.doi.org/10.1002/2016WR019448

Abstract

The permeability architecture of the critical zone exerts a major influence on the hydrogeochemistry of the critical zone. Water flow path dynamics drive the spatiotemporal pattern of geochemical evolution and resulting streamflow concentration-discharge (C-Q) relation, but these flow paths are complex and difficult to map quantitatively. Here we couple a new integrated flow and particle tracking transport model with a general reversible Transition State Theory style dissolution rate law to explore theoretically how C-Q relations and concentration in the critical zone respond to decline in saturated hydraulic conductivity (Ks) with soil depth. We do this for a range of flow rates and mineral reaction kinetics. Our results show that for minerals with a high ratio of equilibrium concentration ( Ceq) to intrinsic weathering rate ( Rmax), vertical heterogeneity in Ks enhances the gradient of weathering-derived solute concentration in the critical zone and strengthens the inverse stream C-Q relation. As CeqRmax decreases, the spatial distribution of concentration in the critical zone becomes more uniform for a wide range of flow rates, and stream C-Q relation approaches chemostatic behavior, regardless of the degree of vertical heterogeneity in Ks. These findings suggest that the transport-controlled mechanisms in the hillslope can lead to chemostatic C-Q relations in the stream while the hillslope surface reaction-controlled mechanisms are associated with an inverse stream C-Q relation. In addition, as CeqRmax decreases, the concentration in the critical zone and stream become less dependent on groundwater age (or transit time).

Item Type: Article
Language: English
Uncontrolled Keywords: chemical weathering, 1832 Groundwater transport , 1886 Weathering , 1829 Groundwater hydrology , 1830 Groundwater/surface water interaction
Future Forest Subject: Skogsbruk i klimatförändringens tid > Natur
Depositing User: Christer Enkvist
Date Deposited: 03 Apr 2017 09:48
Last Modified: 03 Apr 2017 09:48
URI: https://ffpdb.slu.se/id/eprint/4111

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