Geochemical evolution of groundwater in the unsaturated zone of a karstic massif, using the relationship

Peyraube, Nicolas; Lastennet, Roland; Denis, A.

doi:10.1016/j.jhydrol.2012.01.033

Cited by 47 publications

(36 citation statements)

References 27 publications

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“…Most CO 2 in cave air is believed to originate from the soil and vadose zones and enter caves as gas (Breecker et al ., ; Faimon et al ., ; Peyraube et al ., ). Our data, however, cannot rule out the possibility that CO 2 could also be generated by the oxidation of DOC within the phreatic zone at Briar Cave.…”

Section: Discussionmentioning

confidence: 97%

Vadose CO₂ gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Gulley

Martin

Moore

2014

Earth Surf Processes Landf

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Most models of cave formation in limestone that remains near its depositional environment and has not been deeply buried (i.e. eogenetic limestone) invoke dissolution from mixing of waters that have different ionic strengths or have equilibrated with calcite at different pCO2 values. In eogenetic karst aquifers lacking saline water, mixing of vadose and phreatic waters is thought to form caves. We show here calcite dissolution in a cave in eogenetic limestone occurred due to increases in vadose CO2 gas concentrations and subsequent dissolution of CO2 into groundwater, not by mixing dissolution. We collected high‐resolution time series measurements (1 year) of specific conductivity (SpC), temperature, meteorological data, and synoptic water chemical composition from a water table cave in central Florida (Briar Cave). We found SpC, pCO2 and calcite undersaturation increased through late summer, when Briar Cave experienced little ventilation by outside air, and decreased through winter, when increased ventilation lowered cave CO2(g) concentrations. We hypothesize dissolution occurred when water flowed from aquifer regions with low pCO2 into the cave, which had elevated pCO2. Elevated pCO2 would be promoted by fractures connecting the soil to the water table. Simple geochemical models demonstrate that changes in pCO2 of less than 1% along flow paths are an order of magnitude more efficient at dissolving limestone than mixing of vadose and phreatic water. We conclude that spatially or temporally variable vadose CO2(g) concentrations are responsible for cave formation because mixing is too slow to generate observed cave sizes in the time available for formation. While this study emphasized dissolution, gas exchange between the atmosphere and karst aquifer vadose zones that is facilitated by conduits likely exerts important controls on other geochemical processes in limestone critical zones by transporting oxygen deep into vadose zones, creating redox boundaries that would not exist in the absence of caves. Copyright © 2014 John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 97%

Vadose CO₂ gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Gulley

Martin

Moore

2014

Earth Surf Processes Landf

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“…This is demonstrated in the models of geochemical evolution of dripwater in Fig. 5 (Peyraube et al 2012;Milanolo and Gabrovšek 2015). Projected data of the regular drip are aligned along the degassing line pointing to unique value of P CO 2 ðHÞ regardless of the season when the data point was measured, although the winter samples are usually more degassed.…”

Section: Hypothetical P Co 2 In Epikarstmentioning

confidence: 77%

“…In the caves of Moravian Karst, the hypothetical partial pressure of CO 2 varies in the range of 1-11 vol% (Faimon et al 2012). Other studies indicate similarly high CO 2 concentrations (3-10 vol%) (Peyraube et al 2012(Peyraube et al , 2013Milanolo and Gabrovšek 2015). This is contradictory to low concentrations of soil CO 2 with seasonal character (Faimon and Ličbinská 2010;SanchezCañete et al 2011;Plestenjak et al 2012;Blecha and Faimon 2014a), although supported by some measurements in vadose zone and caves (Otava 1995;Benavente et al 2010).…”

Section: Hypothetical P Co 2 In Epikarstmentioning

confidence: 78%

“…Even though soils are widely accepted as a main source of carbon dioxide in karst systems, much higher CO 2 concentrations were measured in vadose zone (2-6 %, see Benavente et al 2010). This contradiction is confirmed by results of inverse modeling of karst water composition (Faimon et al 2012;Peyraube et al 2012Peyraube et al , 2013Milanolo and Gabrovšek 2015) that indicates similar CO 2 concentrations (3-10 vol%). The aim of this study is to show the long-term variations in (i) cave air P CO 2 , and (ii) P CO 2 deduced from dripwater chemistry based on oneyear monitoring campaign in the Punkva Caves (Moravian Karst, Czech Republic).…”

Section: Introductionmentioning

confidence: 88%

“…The simplified relation between SI calcite , P CO 2 ðWÞ , and Ca 2? activity (Peyraube et al 2012;Milanolo and Gabrovšek 2015) is:…”

Section: Hydrogeochemical Model Of Co 2 Degassing and Calcite Precipimentioning

confidence: 99%

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Variations of carbon dioxide in the air and dripwaters of Punkva Caves (Moravian Karst, Czech Republic)

Pracný

Faimon

Kabelka

et al. 2015

Carbonates Evaporites

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Carbon dioxide (CO 2 ) was studied in Punkva Caves in the Moravian Karst (Czech Republic) during a one-year period from February 2012 to March 2013. Partial pressures of the CO 2 corresponding to aqueous carbonates, P CO 2 ðWÞ (10 -2.91 -10 -2.35 , i.e., 0.12-0.45 vol%), and those participating in the initial dripwater formation, P CO 2 ðHÞ (10 -1.77 -10 -1.49 , i.e., 1.7-3.2 vol%), were calculated from dripwater hydrogeochemistry, and compared with the partial pressure in cave air, P CO 2 ðairÞ (10 -3.31 -10 -2.49 , i.e., 0.06-0.32 vol%). Both the P CO 2 ðairÞ and P CO 2 ðWÞ showed clear seasonal variations with maxima in summer and minima in winter. In contrast, the P CO 2 ðHÞ was very stable without any significant seasonality, which could indicate its independence on surface conditions. As an exception, one anomalous drip with significantly lower and varying P CO 2 ðWÞ , P CO 2 ðHÞ , and SI calcite was recognized as a result of prior calcite precipitation. Evolution of dripwater during CO 2 degassing and calcite precipitation is demonstrated in detail in a geochemical model. The study presents new data indicating that the CO 2 source might be deployed in deeper parts of karst profile (epikarst) in addition to karst soils.

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Heterogeneous distributions of CO₂ may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution

Gulley

Martin

Moore

et al. 2015

Earth Surf Processes Landf

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Mixing dissolution, a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals, is commonly considered to form cavernous macroporosity (e.g. flank margin caves and banana holes) in eogenetic karst aquifers. On small islands, macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface, suggesting that dissolution processes are decoupled from surface hydrology. Mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pCO2 was assumed to be homogeneously distributed within the phreatic zone. Here, we report data from two abandoned well fields in an eogenetic karst aquifer on San Salvador Island, Bahamas, that demonstrate pCO2 in the phreatic zone is distributed heterogeneously. The pCO2 varied from less than log −2.0 to more than log −1.0 atm over distances of less than 30 m, generating dissolution in the subsurface where water flows from regions of low to high pCO2 and cementation where water flows from regions of high to low pCO2. Using simple geochemical models, we show dissolution caused by heterogeneously distributed pCO2 can dissolve 2.5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater. Dissolution resulting from spatial variability in pCO2 forms isolated, globular chambers lacking initial entrances to the surface, a morphology that is characteristic of flank margin caves and banana holes, both of which have entrances that form by erosion or collapse after cave formation. Our results indicate that heterogeneous pCO2, rather than mixing dissolution, may be the dominant mechanism for observed spatial distribution of dissolution, cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings. Copyright © 2015 John Wiley & Sons, Ltd.

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Geochemical evolution of groundwater in the unsaturated zone of a karstic massif, using the relationship

Cited by 47 publications

References 27 publications

Vadose CO₂ gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Vadose CO₂ gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Variations of carbon dioxide in the air and dripwaters of Punkva Caves (Moravian Karst, Czech Republic)

Heterogeneous distributions of CO₂ may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution

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Geochemical evolution of groundwater in the unsaturated zone of a karstic massif, using the relationship

Cited by 47 publications

References 27 publications

Vadose CO2 gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Vadose CO2 gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Variations of carbon dioxide in the air and dripwaters of Punkva Caves (Moravian Karst, Czech Republic)

Heterogeneous distributions of CO2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution

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Vadose CO₂ gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Vadose CO₂ gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Heterogeneous distributions of CO₂ may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution