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Modelling chemical weathering in contrasted watersheds : new implementations and application at the global scale

Lechuga-Crespo, Juan-Luis. Modelling chemical weathering in contrasted watersheds : new implementations and application at the global scale. PhD, Sciences de l'univers, de l'environnement et de l'espace, Institut National Polytechnique de Toulouse, 2020

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Abstract

The biogeochemical cycles will suffer impacts derived from global change hazards. Understanding and assessing the processes controlling the matter movement between reservoirs is critical to help on natural resource management. Rock weathering controls the amount of inorganic matter released to aquatic environments, which is eventually routed through rivers to oceans or lakes. However, the evaluation of these fluxes across spatial and temporal scales is challenging because of the number of factors involved. In this sense, the objective of this PhD thesis is to evaluate the role of chemical weathering on biogeochemical cycling at different spatial and temporal scales. Mainly, we have aimed at a) identifying the main drivers of chemical weathering at the global scale, b) developing a simple tool to estimate ionic fluxes derived from chemical weathering of rocks, c) evaluate downscaling capabilities of the model at the river basin scale, and d) estimate the impact of chemical weathering on the global carbon cycle. In the present PhD thesis, we have assessed the riverine exports of 1751 rivers to measure the role of hydrology, lithology, and soil on the different ionic fluxes released through chemical weathering of rocks. Such assessment allowed us to develop a simple model and apply it at the global scale to estimate a snapshot of the total amount (3374·106 Mg·y-1) of matter released by rocks, and characterise it among the major ion constituents, being 58% Ca2+, 24% Na+, 15% Mg2+, and 3% K+ of the total cation flux, and 74% alkalinity, 18% SO42-, and 8% Cl- for the total anion flux. Besides, an assessment of the geochemical processes governing the water major ion composition and dissolved loadings at a local case study (Deba river basin, Gipuzkoa, North Spain) has provided a framework to test the local performance of the model. The application of the model at the local scale has let the coupling of this simple equation to the SWAT model, which permitted the study of the capabilities and limitations of the model in estimating the daily geochemical loadings in a heterogeneous geological context affected by evaporitic springs. Once evaluated at the local scale, a dynamic application of the model at the global scale has allowed the assessment of the role of chemical weathering in the carbon sequestration under two climate change scenarios (RCP2.6 and RCP8.5). According to our simulations, the potential shifts in the global hydrological balance will increase C uptake by chemical weathering in an 8 to 13% by the 2069-2099 period, depending on the scenario studied. The results from this PhD thesis have allowed us to evaluate the role of chemical weathering on the carbon cycle at the global scale. Future research should be focused on the configuration of the model, by including physical weathering in its configuration and assessing the local effect of variables such as temperature and land-use change.

Item Type:PhD Thesis
Uncontrolled Keywords:
Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Laboratory name:
Research Director:
Sanchez-Pérez, José Miguel and Ruiz-Romera, Estilita
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Deposited On:25 Mar 2021 11:04

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