Modulation of Riverine Concentration‐Discharge Relationships by Changes in the Shape of the Water Transit Time Distribution

Torres, Mark A.; Baronas, J. Jotautas

Abstract

The concentrations of weathering-derived solutes in rivers and their covariance with discharge are thought to reflect reactive-transport processes in hillslopes and to reveal the sensitivity of solute fluxes to climatic change. It is expected that discharge-driven changes in water transit times play some role in setting concentration-discharge (C-Q) relationships, but knowledge gaps remain. To explore the specific role of changes in the shape of the transit time distribution with discharge, we combine models to simulate C-Q relationships for major cations and Si as example solutes with contrasting affinities to partition into secondary phases. The model results are compared with an analysis of C-Q relationships using the Global River Chemistry Database. We find that changes in the shape of the transit time distribution with discharge can produce a range of cation-Q and Si-Q relationships that encompasses most of the range observed in real catchments, including positive Si-Q relationships and variable cation to Si ratios. We find that C-Q relationships (characterized by power law exponents) can remain approximately constant, even as the Damköhler Number (ratio of transport time scale to reaction time scale) is varied over 3 orders of magnitude. So, in our model analysis, C-Q relationships are as sensitive to hydrologic variability as they are to reaction rates. Additionally we find that, depending on the storage-discharge relationship, changes in rainfall patterns can influence C-Q relationships. Altogether, our results suggest ways in which C-Q relationships may be nonstationary in response to climatic change and/or vary in space and time due to catchment hydrologic properties.

Citation

Torres, M. A., & Baronas, J. J. (2021). Modulation of Riverine Concentration‐Discharge Relationships by Changes in the Shape of the Water Transit Time Distribution. Global Biogeochemical Cycles, 35(1), Article e2020GB006694. https://doi.org/10.1029/2020gb006694

• Journal Article Type: Article
• Acceptance Date: Nov 29, 2020
• Online Publication Date: Jan 6, 2021
• Publication Date: 2021-01
• Deposit Date: Dec 21, 2023
• Journal: Global Biogeochemical Cycles
• Print ISSN: 0886-6236
• Electronic ISSN: 1944-9224
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 35
• Issue: 1
• Article Number: e2020GB006694
• DOI: https://doi.org/10.1029/2020gb006694
• Public URL: https://durham-repository.worktribe.com/output/2048476