Chemical weathering and CO2 consumption in a multi-lithological karstic critical zone: Long term hydrochemical trends and isotopic survey

F. Ulloa-Cedamanos; A. Probst; I. Moussa; J. L. Probst

doi:10.1016/j.chemgeo.2021.120567

Chemical weathering and CO₂ consumption in a multi-lithological karstic critical zone: Long term hydrochemical trends and isotopic survey

F. Ulloa-Cedamanos, A. Probst, I. Moussa, J. L. Probst

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Abstract

The chemical weathering (CW) of rocks at the Earth's surface plays a key role in the global carbon cycle along multiple pathways. Although karst systems are hotspot carbonated areas, they are not always monolithological. It is therefore challenging to estimate the CW of these complex areas. The interannual, seasonal, and spatial variations of CW rates and CO₂ consumption were investigated using a long-term hydrogeochemical database (1994–2019) from a mountainous karstic catchment in southwestern France (Baget Catchment). A geochemical and isotopic spatial sampling allowed the identification of the main mineral or lithological sources in the catchment, which controlled the water chemistry. The CW budget showed that the (Ca²⁺ + Mg²⁺) fluxes originated from carbonate dissolution (1.14 mol·m⁻²·yr⁻¹ equivalent to 74%) and silicate weathering (18%) by carbonic acid solutions. Gypsum dissolution and carbonate weathering by sulphuric acid from pyrite oxidation contribute equally to 4%, although the former accounts for 66% of the dissolved sulphate fluxes. During a summer sampling survey, an innovative sulphur isotopic approach based on δ³⁴S_SO4, allowed us to demonstrate that the ore-nature sulphuric acid drove 9.0% of total carbonate dissolution and represented only 16.8% of the dissolved sulphate stream fluxes. Hydrological conditions, temperature, vegetation, the epikarst (quasi-permanent shallow and discontinuous saturated layer under the soil), and the water dynamics were the key factors influencing the inter-annual and inter-seasonal variations of the CW rates and CO₂ consumption. In addition, the carbon isotopic signature evidenced geochemical processes such as CO₂ outgassing and calcite precipitation processes. The latter could remove up to 74% of HCO₃⁻ from streamwaters, depending on the hydrological conditions at the outlet between 2016 and 2019. Finally, this study highlights that CW rates and CO₂ consumption may vary over inter-annual and inter-seasonal scales, and spatially even for a small catchment. Furthermore, the global CO₂ consumption appears to be mainly driven by the runoff intensity in karst hydrosystems, where carbonate dissolution was found to consume 71% of the total weathering CO₂ uptake.

Original language	English
Article number	120567
Pages (from-to)	1-16
Number of pages	16
Journal	Chemical Geology
Volume	585
DOIs	https://doi.org/10.1016/j.chemgeo.2021.120567
Publication status	Published - 20 Dec 2021
Externally published	Yes

Bibliographical note

Funding Information:
This research was supported by the CNRS-INSU within the framework of the SNO Karst and IR OZCAR and by the CNRS-INEE within the framework of the LTSER Zone Atelier Pyrénées-Garonne, which is part of the IR RZA.

Funding Information:
This research was supported by the CNRS-INSU within the framework of the SNO Karst and IR OZCAR and by the CNRS-INEE within the framework of the LTSER Zone Atelier Pyr?n?es-Garonne, which is part of the IR RZA.The BC belongs to the French Karst Network (SNO Karst, Jourde et al. 2018; www.sokarst.org) initiative of the INSU/CNRS, which aims to strengthen knowledge-sharing and to promote cross-disciplinary research on karst systems. It is one of the observatories of the French Research Infrastructure called OZCAR (the French network of Critical Zone Observatories, Gaillardet et al. 2018) and also a LTSER (Long-Term Socio-Ecological Reasearch) research site of the CNRS (National Center for Scientific Research) collaborative research platform called ?Zone Atelier Pyr?n?es-Garonne (ZA PYGAR)?, which belongs to a French Research Infrastructure called RZA (R?seau des Zones Ateliers, Bretagnolle et al. 2019). RZA grouped with OZCAR is the French contribution to the European Research Infrastructure eLTER (Long-Term Ecosystem in Europe, Mirtl et al. 2018). The authors specially thank the support from CNRS INEE and INSU, SNO KARST, OZCAR and Zone Atelier Pyr?n?es-Garonne (LTSER ZA PYGAR). The analytical platforms, PAPC (F. Julien, V. Payre-Suc, D. Lambrigot, and W. Amblas) and SHIVA (I. Moussa and D. Dalger) at Laboratoire ?cologie fonctionnelle et environnement, and the chemical lab service from the GET (C. Causserand and P. Besson) are thanked for their contribution to the analytical work during the more recent years. F. Ulloa-Cedamanos's PhD was supported by a fellowship from the French Ministry of Higher Education, Research and Innovation. Special thanks are given to Thierry Camboulive, Virginie Payre-Suc, Corinne Pautot, Franck Granouillac, Betty Chaumet and Vanessa Dos-Santos for their help in the field samplings and/or lab works.

Funding Information:
The analytical platforms, PAPC (F. Julien, V. Payre-Suc, D. Lambrigot, and W. Amblas) and SHIVA (I. Moussa and D. Dalger) at Laboratoire écologie fonctionnelle et environnement, and the chemical lab service from the GET (C. Causserand and P. Besson) are thanked for their contribution to the analytical work during the more recent years. F. Ulloa-Cedamanos's PhD was supported by a fellowship from the French Ministry of Higher Education, Research and Innovation . Special thanks are given to Thierry Camboulive, Virginie Payre-Suc, Corinne Pautot, Franck Granouillac, Betty Chaumet and Vanessa Dos-Santos for their help in the field samplings and/or lab works.

Funding Information:
The BC belongs to the French Karst Network (SNO Karst, Jourde et al., 2018 ; www.sokarst.org ) initiative of the INSU/CNRS, which aims to strengthen knowledge-sharing and to promote cross-disciplinary research on karst systems. It is one of the observatories of the French Research Infrastructure called OZCAR (the French network of Critical Zone Observatories, Gaillardet et al., 2018 ) and also a LTSER (Long-Term Socio-Ecological Reasearch) research site of the CNRS (National Center for Scientific Research) collaborative research platform called “Zone Atelier Pyrénées-Garonne (ZA PYGAR)”, which belongs to a French Research Infrastructure called RZA (Réseau des Zones Ateliers, Bretagnolle et al., 2019 ). RZA grouped with OZCAR is the French contribution to the European Research Infrastructure eLTER (Long-Term Ecosystem in Europe, Mirtl et al., 2018 ). The authors specially thank the support from CNRS INEE and INSU , SNO KARST , OZCAR and Zone Atelier Pyrénées-Garonne (LTSER ZA PYGAR) .

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© 2021 The Authors

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10.1016/j.chemgeo.2021.120567

72669343-oaFinal published version, 9.4 MBLicence: CC BY-NC-ND

Cite this

@article{1edc2369cf544418986e77263c45d0aa,

title = "Chemical weathering and CO2 consumption in a multi-lithological karstic critical zone: Long term hydrochemical trends and isotopic survey",

abstract = "The chemical weathering (CW) of rocks at the Earth's surface plays a key role in the global carbon cycle along multiple pathways. Although karst systems are hotspot carbonated areas, they are not always monolithological. It is therefore challenging to estimate the CW of these complex areas. The interannual, seasonal, and spatial variations of CW rates and CO2 consumption were investigated using a long-term hydrogeochemical database (1994–2019) from a mountainous karstic catchment in southwestern France (Baget Catchment). A geochemical and isotopic spatial sampling allowed the identification of the main mineral or lithological sources in the catchment, which controlled the water chemistry. The CW budget showed that the (Ca2+ + Mg2+) fluxes originated from carbonate dissolution (1.14 mol·m−2·yr−1 equivalent to 74%) and silicate weathering (18%) by carbonic acid solutions. Gypsum dissolution and carbonate weathering by sulphuric acid from pyrite oxidation contribute equally to 4%, although the former accounts for 66% of the dissolved sulphate fluxes. During a summer sampling survey, an innovative sulphur isotopic approach based on δ34SSO4, allowed us to demonstrate that the ore-nature sulphuric acid drove 9.0% of total carbonate dissolution and represented only 16.8% of the dissolved sulphate stream fluxes. Hydrological conditions, temperature, vegetation, the epikarst (quasi-permanent shallow and discontinuous saturated layer under the soil), and the water dynamics were the key factors influencing the inter-annual and inter-seasonal variations of the CW rates and CO2 consumption. In addition, the carbon isotopic signature evidenced geochemical processes such as CO2 outgassing and calcite precipitation processes. The latter could remove up to 74% of HCO3− from streamwaters, depending on the hydrological conditions at the outlet between 2016 and 2019. Finally, this study highlights that CW rates and CO2 consumption may vary over inter-annual and inter-seasonal scales, and spatially even for a small catchment. Furthermore, the global CO2 consumption appears to be mainly driven by the runoff intensity in karst hydrosystems, where carbonate dissolution was found to consume 71% of the total weathering CO2 uptake.",

keywords = "Carbonate dissolution, Karst, Long-term hydrochemical survey, Mixing diagrams, Mountainous forested catchment, Seasonal patterns, Weathering, δC and δS",

author = "F. Ulloa-Cedamanos and A. Probst and I. Moussa and Probst, {J. L.}",

note = "Funding Information: This research was supported by the CNRS-INSU within the framework of the SNO Karst and IR OZCAR and by the CNRS-INEE within the framework of the LTSER Zone Atelier Pyr{\'e}n{\'e}es-Garonne, which is part of the IR RZA. Funding Information: This research was supported by the CNRS-INSU within the framework of the SNO Karst and IR OZCAR and by the CNRS-INEE within the framework of the LTSER Zone Atelier Pyr?n?es-Garonne, which is part of the IR RZA.The BC belongs to the French Karst Network (SNO Karst, Jourde et al. 2018; www.sokarst.org) initiative of the INSU/CNRS, which aims to strengthen knowledge-sharing and to promote cross-disciplinary research on karst systems. It is one of the observatories of the French Research Infrastructure called OZCAR (the French network of Critical Zone Observatories, Gaillardet et al. 2018) and also a LTSER (Long-Term Socio-Ecological Reasearch) research site of the CNRS (National Center for Scientific Research) collaborative research platform called ?Zone Atelier Pyr?n?es-Garonne (ZA PYGAR)?, which belongs to a French Research Infrastructure called RZA (R?seau des Zones Ateliers, Bretagnolle et al. 2019). RZA grouped with OZCAR is the French contribution to the European Research Infrastructure eLTER (Long-Term Ecosystem in Europe, Mirtl et al. 2018). The authors specially thank the support from CNRS INEE and INSU, SNO KARST, OZCAR and Zone Atelier Pyr?n?es-Garonne (LTSER ZA PYGAR). The analytical platforms, PAPC (F. Julien, V. Payre-Suc, D. Lambrigot, and W. Amblas) and SHIVA (I. Moussa and D. Dalger) at Laboratoire ?cologie fonctionnelle et environnement, and the chemical lab service from the GET (C. Causserand and P. Besson) are thanked for their contribution to the analytical work during the more recent years. F. Ulloa-Cedamanos's PhD was supported by a fellowship from the French Ministry of Higher Education, Research and Innovation. Special thanks are given to Thierry Camboulive, Virginie Payre-Suc, Corinne Pautot, Franck Granouillac, Betty Chaumet and Vanessa Dos-Santos for their help in the field samplings and/or lab works. Funding Information: The analytical platforms, PAPC (F. Julien, V. Payre-Suc, D. Lambrigot, and W. Amblas) and SHIVA (I. Moussa and D. Dalger) at Laboratoire {\'e}cologie fonctionnelle et environnement, and the chemical lab service from the GET (C. Causserand and P. Besson) are thanked for their contribution to the analytical work during the more recent years. F. Ulloa-Cedamanos's PhD was supported by a fellowship from the French Ministry of Higher Education, Research and Innovation . Special thanks are given to Thierry Camboulive, Virginie Payre-Suc, Corinne Pautot, Franck Granouillac, Betty Chaumet and Vanessa Dos-Santos for their help in the field samplings and/or lab works. Funding Information: The BC belongs to the French Karst Network (SNO Karst, Jourde et al., 2018 ; www.sokarst.org ) initiative of the INSU/CNRS, which aims to strengthen knowledge-sharing and to promote cross-disciplinary research on karst systems. It is one of the observatories of the French Research Infrastructure called OZCAR (the French network of Critical Zone Observatories, Gaillardet et al., 2018 ) and also a LTSER (Long-Term Socio-Ecological Reasearch) research site of the CNRS (National Center for Scientific Research) collaborative research platform called “Zone Atelier Pyr{\'e}n{\'e}es-Garonne (ZA PYGAR)”, which belongs to a French Research Infrastructure called RZA (R{\'e}seau des Zones Ateliers, Bretagnolle et al., 2019 ). RZA grouped with OZCAR is the French contribution to the European Research Infrastructure eLTER (Long-Term Ecosystem in Europe, Mirtl et al., 2018 ). The authors specially thank the support from CNRS INEE and INSU , SNO KARST , OZCAR and Zone Atelier Pyr{\'e}n{\'e}es-Garonne (LTSER ZA PYGAR) . Publisher Copyright: {\textcopyright} 2021 The Authors",

year = "2021",

month = dec,

day = "20",

doi = "10.1016/j.chemgeo.2021.120567",

language = "English",

volume = "585",

pages = "1--16",

journal = "Chemical Geology",

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TY - JOUR

T1 - Chemical weathering and CO2 consumption in a multi-lithological karstic critical zone

T2 - Long term hydrochemical trends and isotopic survey

AU - Ulloa-Cedamanos, F.

AU - Probst, A.

AU - Moussa, I.

AU - Probst, J. L.

N1 - Funding Information: This research was supported by the CNRS-INSU within the framework of the SNO Karst and IR OZCAR and by the CNRS-INEE within the framework of the LTSER Zone Atelier Pyrénées-Garonne, which is part of the IR RZA. Funding Information: This research was supported by the CNRS-INSU within the framework of the SNO Karst and IR OZCAR and by the CNRS-INEE within the framework of the LTSER Zone Atelier Pyr?n?es-Garonne, which is part of the IR RZA.The BC belongs to the French Karst Network (SNO Karst, Jourde et al. 2018; www.sokarst.org) initiative of the INSU/CNRS, which aims to strengthen knowledge-sharing and to promote cross-disciplinary research on karst systems. It is one of the observatories of the French Research Infrastructure called OZCAR (the French network of Critical Zone Observatories, Gaillardet et al. 2018) and also a LTSER (Long-Term Socio-Ecological Reasearch) research site of the CNRS (National Center for Scientific Research) collaborative research platform called ?Zone Atelier Pyr?n?es-Garonne (ZA PYGAR)?, which belongs to a French Research Infrastructure called RZA (R?seau des Zones Ateliers, Bretagnolle et al. 2019). RZA grouped with OZCAR is the French contribution to the European Research Infrastructure eLTER (Long-Term Ecosystem in Europe, Mirtl et al. 2018). The authors specially thank the support from CNRS INEE and INSU, SNO KARST, OZCAR and Zone Atelier Pyr?n?es-Garonne (LTSER ZA PYGAR). The analytical platforms, PAPC (F. Julien, V. Payre-Suc, D. Lambrigot, and W. Amblas) and SHIVA (I. Moussa and D. Dalger) at Laboratoire ?cologie fonctionnelle et environnement, and the chemical lab service from the GET (C. Causserand and P. Besson) are thanked for their contribution to the analytical work during the more recent years. F. Ulloa-Cedamanos's PhD was supported by a fellowship from the French Ministry of Higher Education, Research and Innovation. Special thanks are given to Thierry Camboulive, Virginie Payre-Suc, Corinne Pautot, Franck Granouillac, Betty Chaumet and Vanessa Dos-Santos for their help in the field samplings and/or lab works. Funding Information: The analytical platforms, PAPC (F. Julien, V. Payre-Suc, D. Lambrigot, and W. Amblas) and SHIVA (I. Moussa and D. Dalger) at Laboratoire écologie fonctionnelle et environnement, and the chemical lab service from the GET (C. Causserand and P. Besson) are thanked for their contribution to the analytical work during the more recent years. F. Ulloa-Cedamanos's PhD was supported by a fellowship from the French Ministry of Higher Education, Research and Innovation . Special thanks are given to Thierry Camboulive, Virginie Payre-Suc, Corinne Pautot, Franck Granouillac, Betty Chaumet and Vanessa Dos-Santos for their help in the field samplings and/or lab works. Funding Information: The BC belongs to the French Karst Network (SNO Karst, Jourde et al., 2018 ; www.sokarst.org ) initiative of the INSU/CNRS, which aims to strengthen knowledge-sharing and to promote cross-disciplinary research on karst systems. It is one of the observatories of the French Research Infrastructure called OZCAR (the French network of Critical Zone Observatories, Gaillardet et al., 2018 ) and also a LTSER (Long-Term Socio-Ecological Reasearch) research site of the CNRS (National Center for Scientific Research) collaborative research platform called “Zone Atelier Pyrénées-Garonne (ZA PYGAR)”, which belongs to a French Research Infrastructure called RZA (Réseau des Zones Ateliers, Bretagnolle et al., 2019 ). RZA grouped with OZCAR is the French contribution to the European Research Infrastructure eLTER (Long-Term Ecosystem in Europe, Mirtl et al., 2018 ). The authors specially thank the support from CNRS INEE and INSU , SNO KARST , OZCAR and Zone Atelier Pyrénées-Garonne (LTSER ZA PYGAR) . Publisher Copyright: © 2021 The Authors

PY - 2021/12/20

Y1 - 2021/12/20

N2 - The chemical weathering (CW) of rocks at the Earth's surface plays a key role in the global carbon cycle along multiple pathways. Although karst systems are hotspot carbonated areas, they are not always monolithological. It is therefore challenging to estimate the CW of these complex areas. The interannual, seasonal, and spatial variations of CW rates and CO2 consumption were investigated using a long-term hydrogeochemical database (1994–2019) from a mountainous karstic catchment in southwestern France (Baget Catchment). A geochemical and isotopic spatial sampling allowed the identification of the main mineral or lithological sources in the catchment, which controlled the water chemistry. The CW budget showed that the (Ca2+ + Mg2+) fluxes originated from carbonate dissolution (1.14 mol·m−2·yr−1 equivalent to 74%) and silicate weathering (18%) by carbonic acid solutions. Gypsum dissolution and carbonate weathering by sulphuric acid from pyrite oxidation contribute equally to 4%, although the former accounts for 66% of the dissolved sulphate fluxes. During a summer sampling survey, an innovative sulphur isotopic approach based on δ34SSO4, allowed us to demonstrate that the ore-nature sulphuric acid drove 9.0% of total carbonate dissolution and represented only 16.8% of the dissolved sulphate stream fluxes. Hydrological conditions, temperature, vegetation, the epikarst (quasi-permanent shallow and discontinuous saturated layer under the soil), and the water dynamics were the key factors influencing the inter-annual and inter-seasonal variations of the CW rates and CO2 consumption. In addition, the carbon isotopic signature evidenced geochemical processes such as CO2 outgassing and calcite precipitation processes. The latter could remove up to 74% of HCO3− from streamwaters, depending on the hydrological conditions at the outlet between 2016 and 2019. Finally, this study highlights that CW rates and CO2 consumption may vary over inter-annual and inter-seasonal scales, and spatially even for a small catchment. Furthermore, the global CO2 consumption appears to be mainly driven by the runoff intensity in karst hydrosystems, where carbonate dissolution was found to consume 71% of the total weathering CO2 uptake.

AB - The chemical weathering (CW) of rocks at the Earth's surface plays a key role in the global carbon cycle along multiple pathways. Although karst systems are hotspot carbonated areas, they are not always monolithological. It is therefore challenging to estimate the CW of these complex areas. The interannual, seasonal, and spatial variations of CW rates and CO2 consumption were investigated using a long-term hydrogeochemical database (1994–2019) from a mountainous karstic catchment in southwestern France (Baget Catchment). A geochemical and isotopic spatial sampling allowed the identification of the main mineral or lithological sources in the catchment, which controlled the water chemistry. The CW budget showed that the (Ca2+ + Mg2+) fluxes originated from carbonate dissolution (1.14 mol·m−2·yr−1 equivalent to 74%) and silicate weathering (18%) by carbonic acid solutions. Gypsum dissolution and carbonate weathering by sulphuric acid from pyrite oxidation contribute equally to 4%, although the former accounts for 66% of the dissolved sulphate fluxes. During a summer sampling survey, an innovative sulphur isotopic approach based on δ34SSO4, allowed us to demonstrate that the ore-nature sulphuric acid drove 9.0% of total carbonate dissolution and represented only 16.8% of the dissolved sulphate stream fluxes. Hydrological conditions, temperature, vegetation, the epikarst (quasi-permanent shallow and discontinuous saturated layer under the soil), and the water dynamics were the key factors influencing the inter-annual and inter-seasonal variations of the CW rates and CO2 consumption. In addition, the carbon isotopic signature evidenced geochemical processes such as CO2 outgassing and calcite precipitation processes. The latter could remove up to 74% of HCO3− from streamwaters, depending on the hydrological conditions at the outlet between 2016 and 2019. Finally, this study highlights that CW rates and CO2 consumption may vary over inter-annual and inter-seasonal scales, and spatially even for a small catchment. Furthermore, the global CO2 consumption appears to be mainly driven by the runoff intensity in karst hydrosystems, where carbonate dissolution was found to consume 71% of the total weathering CO2 uptake.

KW - Carbonate dissolution

KW - Karst

KW - Long-term hydrochemical survey

KW - Mixing diagrams

KW - Mountainous forested catchment

KW - Seasonal patterns

KW - Weathering

KW - δC and δS

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U2 - 10.1016/j.chemgeo.2021.120567

DO - 10.1016/j.chemgeo.2021.120567

M3 - Article

AN - SCOPUS:85110003026

SN - 0009-2541

VL - 585

SP - 1

EP - 16

JO - Chemical Geology

JF - Chemical Geology

M1 - 120567

ER -

Chemical weathering and CO₂ consumption in a multi-lithological karstic critical zone: Long term hydrochemical trends and isotopic survey

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