Carbon dioxide in the soils and adjacent caves of the Moravian Karst

Variations of soil/cave CO2 concentrations and further vari­ables suchas temperature, humidity, and cave visitor atten­dance were studied in two sites of the Moravian Karst (CzechRepublic). All the variables showed the same seasonality; they were strongly correlated witheachother. The dependence of soil CO2 levels on soil air temperature and absolute humidity was confirmed. Individual effects could not be distinguished because of multicollinearity. The effect of vegetation on soil CO2 production was not recognized. Cave attendance was identified as the most significant predictor of cave CO2 levels. Other variables, soil CO2 and temperature gradients, were less significant. A spurious relationship was alternatively consid­ered, in whichexternal temperature was the universal predic­tor of cave CO2 levels

Spatiotemporal distribution of CO2 concentrations in the soils of karst sinkhole and its vicinity (Harbechy Plateau; Moravian Karst)

Soil CO2 is an important part of the global carbon cycle. In karst, it controls fundamental processes as limestone dissolution and calcite speleothem growth. A spatiotemporal distribution of soil CO2 concentrations was studied at the site of Společňák sinkhole and its close vicinity (Harbechy Plateau, Moravian Karst). The aim of the study was testing an effect of subterranean ventilation of the CO2 concentrations in soil profile. At this site, 25 soil boreholes were drilled: each 2 cm in diameter and 60 cm deep. A central drill-hole was situated at the bottom of the sinkhole. Six identical drill-holes, six meters of each other, were in the direction of NE, SW, NW, and SE. As result, 3 drill-holes were placed in sinkhole body and 3 drill-holes outside in the field in every direction. CO2 concentrations were measured directly in the atmosphere of soil drill-holes at a depth of about 10 cm below the surface. Soils were identified as haplic Luvisols. The found CO2 concentrations varied spatially and temporally between 1 188 ppmv and 6 039 ppmv. Statistical analysis showed that the differences between CO2 concentrations in sinkhole and its vicinity are not significant at α = 0.05. The only exception from these results seems to be inconclusive. The differences between the sinkhole CO2 concentrations in summer and winter were found also insignificant. Therefore, we have concluded that the study did not confirm any impact of subterranean ventilation on soil CO2. However, for a definitive confirmation or rejection of the hypotheses about subterranean ventilation, it is needed more comprehensive survey under tighter spatial and temporal sampling at multiple locations.Soil CO2 is an important part of the global carbon cycle. In karst, it controls fundamental processes as limestone dissolution and calcite speleothem growth. A spatiotemporal distribution of soil CO2 concentrations was studied at the site of Společňák sinkhole and its close vicinity (Harbechy Plateau, Moravian Karst). The aim of the study was testing an effect of subterranean ventilation of the CO2 concentrations in soil profile. At this site, 25 soil boreholes were drilled: each 2 cm in diameter and 60 cm deep. A central drill-hole was situated at the bottom of the sinkhole. Six identical drill-holes, six meters of each other, were in the direction of NE, SW, NW, and SE. As result, 3 drill-holes were placed in sinkhole body and 3 drill-holes outside in the field in every direction. CO2 concentrations were measured directly in the atmosphere of soil drill-holes at a depth of about 10 cm below the surface. Soils were identified as haplic Luvisols. The found CO2 concentrations varied spatially and temporally between 1 188 ppmv and 6 039 ppmv. Statistical analysis showed that the differences between CO2 concentrations in sinkhole and its vicinity are not significant at α = 0.05. The only exception from these results seems to be inconclusive. The differences between the sinkhole CO2 concentrations in summer and winter were found also insignificant. Therefore, we have concluded that the study did not confirm any impact of subterranean ventilation on soil CO2. However, for a definitive confirmation or rejection of the hypotheses about subterranean ventilation, it is needed more comprehensive survey under tighter spatial and temporal sampling at multiple locations

STUDIUM SAMOVOLNÉ DESTRUKCE "JEMNÝCH SINTROVÝCH FOREM"

A spontaneous destruction (a corrosion followed by falling) of fine speleothems was studied in the Punkevní Cave (the Moravian Karst) from geochemical point of view. During eight months of the year 2000, the cave atmosphere and dripping waters were monitored. All inner waters (waters from limestone fissures as far as to "mouth of hollow sinters") were found to be close to equilibrium with calcite (SI ~ 0.08 to 0.15). Not being undersaturated, these waters cannot dissolve calcite sinters. The same waters become supersaturated with respect to calcite (SI ~ 0.85 to 2.20) at a contact with cave atmosphere (pCO2 ~ 3,0.10-4 to 4,1.10-3 atm). Thus, during the monitored period, there was not proved any corrosion of the sinters by dripping waters

Destruction of calcite speleothem in the Moravian Karst caves

Speleothem extensive damage was observed in the Moravian Karst caves during the last 20–30 years. It covers corrosion and falling of straw stalactites especially. Both the processes were studied in the Amatérská Cave and the Punkevní Caves, the sites where the damage is most extensive. The results indicate that corrosion dominates in the Amatérská Cave whereas speleothem falling seems more extensive in the Punkevní Caves. Based on fissile cracks in calcite wall, the falling was interpreted as result of a mechanical damage. As the corrosion impact was found only on the outer site of stalactite wall, it was interpreted as consequence of calcite dissolution by condensed water (condensation corrosion). An anthropogenic impact is ambiguous.Speleothem extensive damage was observed in the Moravian Karst caves during the last 20–30 years. It covers corrosion and falling of straw stalactites especially. Both the processes were studied in the Amatérská Cave and the Punkevní Caves, the sites where the damage is most extensive. The results indicate that corrosion dominates in the Amatérská Cave whereas speleothem falling seems more extensive in the Punkevní Caves. Based on fissile cracks in calcite wall, the falling was interpreted as result of a mechanical damage. As the corrosion impact was found only on the outer site of stalactite wall, it was interpreted as consequence of calcite dissolution by condensed water (condensation corrosion). An anthropogenic impact is ambiguous

Impact of hydrodynamic conditions on gypsum growth

The interaction of gypsum (CaSO4.2H2O) with water is controlled by mixed transport-surface reaction kinetics. Therefore, the rate of gypsum growth/precipitation should depend on hydrodynamic conditions. Gypsum nucleation and crystal growth were studied in a batch reactor under ambient conditions in dependence on varying hydrodynamic conditions (advection of solution). The statistically significant dependence (R2 = 0.875), u = 4.10-7 v+0.0007 (where u is crystal growth rate in mol/min and v is stirring rate in rpm) was found for gypsum growth rate and stirring rate of solution. In contrast, induction times at gypsum nucleation were slightly increasing, i.e., nucleation rates decreased with increasing stirring rate. However, no statistically significant dependence (R2 = 0.115) was found.The interaction of gypsum (CaSO4.2H2O) with water is controlled by mixed transport-surface reaction kinetics. Therefore, the rate of gypsum growth/precipitation should depend on hydrodynamic conditions. Gypsum nucleation and crystal growth were studied in a batch reactor under ambient conditions in dependence on varying hydrodynamic conditions (advection of solution). The statistically significant dependence (R2 = 0.875), u = 4.10-7 v+0.0007 (where u is crystal growth rate in mol/min and v is stirring rate in rpm) was found for gypsum growth rate and stirring rate of solution. In contrast, induction times at gypsum nucleation were slightly increasing, i.e., nucleation rates decreased with increasing stirring rate. However, no statistically significant dependence (R2 = 0.115) was found

Partial pressures of CO2 in epikarstic zone deduced from hydrogeochemistry of permanent drips, the Moravian Karst, Czech Republic

Permanent drips from straw stalactites of selected caves of the Moravian Karst were studied during one-year period. A hypothetical partial pressure of CO2 that has participated in limestone dissolution, PCO2(H)=10-1.53±0.04, was calculated from the dripwater chemistry. The value significantly exceeds the partial pressures generally measured in relevant shallow karst soils, PCO2(soil)=10-2.72±0.02. This finding may have important implications for karst/cave conservation and paleoenvironmental reconstructions.Keywords: cave, carbon dioxide, dripwater, hydrogeochemistry,hypothetical partial pressure, karst processes, karstification model

Acid-base properties of the soils in Koňský Spád site (Moravian Karst)

Soils generally produce humic substances that are a source of percolating water acidity. The acidity is believed to be associated with the type of vegetation cover. The karst soils formed under coniferous in the Koňský Spád site (Moravian Karst) were studied to deduce a risk for karst/cave environment. The soils were classified as strongly acidic, based on the minimum of pH values of soil leachates (pH ~ 2.99 in KCl solution; pH ~ 3.82 in water). It was found that the soil acidity markedly exceeds the soil alkalinity and that the acidity of upper soils horizons exceeds the acidity of the lower horizons. The very low variability in the spatial distribution of acid-base parameters (pH, acidity, and alkalinity) indicates that a uniform type of vegetation produces nearly identical acid-base properties. The results showed that acidity of the soil under coniferous vegetation is responsible for a strong aggressiveness to underlying rocks. However, it seems evident that (i) the acidity is neutralized on the base of soil profile by reaction with limestone clasts and that (ii) the acidic solutions do not permeate deeper into vadose zone/caves.Soils generally produce humic substances that are a source of percolating water acidity. The acidity is believed to be associated with the type of vegetation cover. The karst soils formed under coniferous in the Koňský Spád site (Moravian Karst) were studied to deduce a risk for karst/cave environment. The soils were classified as strongly acidic, based on the minimum of pH values of soil leachates (pH ~ 2.99 in KCl solution; pH ~ 3.82 in water). It was found that the soil acidity markedly exceeds the soil alkalinity and that the acidity of upper soils horizons exceeds the acidity of the lower horizons. The very low variability in the spatial distribution of acid-base parameters (pH, acidity, and alkalinity) indicates that a uniform type of vegetation produces nearly identical acid-base properties. The results showed that acidity of the soil under coniferous vegetation is responsible for a strong aggressiveness to underlying rocks. However, it seems evident that (i) the acidity is neutralized on the base of soil profile by reaction with limestone clasts and that (ii) the acidic solutions do not permeate deeper into vadose zone/caves

Is the cave airflow influenced by external wind?

Based on the case study in Císařská Cave (Moravian Karst), it was tested the impact of external wind on airflow dynamic. Time series of the cave airflow, external wind, and cave/external temperature (signals) were monitored at the lower entrance of the cave during an upward airflow ventilation mode. The periods of the oscillations in both signals (3.8 to 13.3 minutes in the cave airflow and 5.5 to 9.2 minutes in the external wind) were inconsistent. The correlation between both signals was statistically insignificant. The cross correlation did not show any time shift between both signals. These results rather question the generally presumed impact of external wind on cave airflow.Based on the case study in Císařská Cave (Moravian Karst), it was tested the impact of external wind on airflow dynamic. Time series of the cave airflow, external wind, and cave/external temperature (signals) were monitored at the lower entrance of the cave during an upward airflow ventilation mode. The periods of the oscillations in both signals (3.8 to 13.3 minutes in the cave airflow and 5.5 to 9.2 minutes in the external wind) were inconsistent. The correlation between both signals was statistically insignificant. The cross correlation did not show any time shift between both signals. These results rather question the generally presumed impact of external wind on cave airflow

NOVÉ POZNATKY Z VÝZKUMU SPELEOAEROSOLŮ VE VYBRANÝCH JESKYNÍCH MORAVSKÉHO KRASU

Speleo-aerosols were isolated by ultra-filtration from the atmospheres of some caves of the Moravian Karst. Significant differences in composition were found. The matter collected on ultra-filters in the Soupsko-oůvská Caves had high contents of sulfur (calcium sulfate) and were black colored. The ultra-filter matter from the Císařská Cave, on the other hand, was typically light-gray colored and contained only small quantities of sulfur. In the matter of both localities, heavy metals and chlorine were occasionally found. The resources of sulfur, chlorine, and heavy metals are unknown

INTERAKCE BAYERITU A KYSELINY KŘEMIČITÉ V SLABĚ KYSELÉM PROSTŘEDÍ ZA NORMÁLNÍCH PODMÍNEK

Interaction between bayerite, Al(OH)3, and silicic acid, H4SiO4, was studied in slightly acid solutions (pH ~ 4.2) at three Si/Al molar ratios (1:1, 1:3 and 1:5) under using of stirred batch reactors. The initial concentrations of H4SiO4 were 1.65x10-3 mol l-1 in all solutions. Two different concentrations of alkaline metals (K, Na), zero and 2x10-3 mol l-1, were adjusted in the solutions. At the initial stage of experiment (0-2 days), the H4SiO4 concentrations quickly decrease to the roughly limit values, between 1.55x10-3 and 1.60 x10-3 mol l-1. This decrease, relatively slight (from 5x10-5 to 1x10-4 mol) and rapid (from -8.10-6 to -7.10-5 mol l-1 day-1), was linearly dependent on the bayerite content; it was interpreted as a (chemi)sorption of H4SiO4 on bayerite surface. At the advanced stages of experiment (2 200 days), the concentrations of H4SiO4 stagnated (the slopes of kinetic curves range from -7.10-8 to +2.10-7 mol l-1 day-1). Therefore, despite the permanent supersaturation with respect to kaolinite (SIkaolinite < 3.60), K-mica (SI(K-mica) < 4.49 in the solutions containing K), and Na-beidellite (SINa-beidellite < 3.27 in the solutions containing Na), any expected reaction (some bayerite conversion into kaolinite, smectite or their precursors) was not proved. If such reaction runs, it is extremely slow under given conditions. Despite the limit values of aqueous Al in the majority of solutions, the bayerite saturation was not reached in any solution (the SIbayerite values ranged from -0.35 to -0.81 at the end of experiments). This phenomenon was interpreted as a modification of bayerite solubility product by the sorption of H4SiO4. Both the initial slopes of kinetics curves for aqueous Al and the times needed for reaching the limit values of aqueous Al show that the rate of bayrite dissolution increases in the solutions containing Na and K ions