A model for evaluating continental chemical weathering from riverine transports of dissolved major elements at a global scale

Abstract

This study presents a process-based-empirical model for the assessment of ionic fluxes derived from chemical weathering of rocks (ICWR) at a global scale. The equations are designed and the parameters fitted using riverine transport of dissolved major ions Ca 2+ , Mg 2+ , K + , Na + , Cl − , SO 4 2− , and alkalinity at a global scale by combining point sampling analysis with spatial descriptions of hydrology, climate, topography, lithology and soil variables such as mineral composition and regolith thickness. Different configurations of the model are considered and the results show that the previously reported "soil shielding" effect on chemical weathering (CW) of rocks presents different values for each of the ions considered. Overall, there is good agreement between median and ranges in observed and simulated data, but further analysis is required to downscale the model to catchment scale. Application to the global scale provides the first global ICWR map, resulting in an average cationic flux derived from chemical weathering of 734•10 6 Mg•y −1 , where 58% is Ca 2+ , 15% is Mg 2+ , 24% is Na + and 3% is K + , and an average anionic flux derived from chemical weathering of 2640•10 6 Mg•y −1 , where 74% is alkalinity, 18% is SO 4 2− , and 8% is Cl −. Hyperactive and hotspot areas are elucidated and compared between ions.

Global carbon sequestration through continental chemical weathering in a climatic change context

“…Third, draining area characteristics are summarized for each river basin by considering the relative abundance of lithological classes contained in the Global Lithological Map 47 (GLIM), the soil classes as de ned by the Harmonized World Soil Database 48 (HWSD), and the climatic zones present according to the Köppen-Geiger classi cation presented by Beck et al 33 . The modelling approach consists of two models in cascade; the ux of ions derived from the chemical weathering of rocks is computed using the ICWR 49 model daily for each river basin under each discharge time series. Then, the Major Element Geochemical Approach 35 (MEGA) model uses these loadings to estimate the CO 2 consumed through chemical weathering.…”

“…The ICWR model is an empirical model that was developed to estimate major ion riverine uxes released by chemical weathering of rocks at the global scale, based on Equation 2, and it has been validated at the global scale under static conditions 49 and at the local scale under dynamic evolution 52 . Computing it requires a description of the draining area of each river basin in terms of soil coverture and lithological distribution.…”

Stream Hydrochemical Response to Flood Events in a Multi-Lithological Karstic Catchment from the Pyrenees Mountains (SW France)

“…The streamwater chemical signature is derived from atmospheric, biological, and anthropogenic inputs and rock weathering [62,63], with the carbonate dissolution as the dominant process controlling BC streamwater chemistry [17]. The C-Q (Figure 4) and flux- The hydrograph separation of flood event 2 (Figures 2A and 6A) exhibited three distinct recession coefficients (α), respectively, for the quick-response flow (α q : 0.64 to 0.66), the subsurface flow (α s : 0.19), and the baseflow (α b : 0.11 to 0.12).…”

“…The streamwater chemical signature is derived from atmospheric, biological, and anthropogenic inputs and rock weathering [62,63], with the carbonate dissolution as the dominant process controlling BC streamwater chemistry [17]. The C-Q (Figure 4) and flux-Q (Figure 7) relationships can be used to identify changes in sources and to assess the sensitivity of the solute concentrations and fluxes to runoff during changing hydrological conditions [64].…”

Global carbon sequestration through continental chemical weathering in a climatic change context

“…However, higher air temperatures may decrease CO 2 dissolution in water, as carbonate weathering follows a boomerang-shaped evolution with increasing temperature 16 . Hydrology is the dominant driver of matter transport at large scale 17 . Nevertheless, the potential implication of respiration and temperature in the global balance remains poorly understood 13 .…”