Soil CO2 sources above a subterranean cave—Pisani rov (Postojna Cave, Slovenia)
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The objective of this research is to detect abiotic sources of soil CO2 above a subterranean cave in the Slovenian karst region.
Materials and methods
The research was performed in the forest above Pisani rov (Postojna Cave) near the town of Postojna (SW Slovenia) and also in the cave. Soil gas, atmospheric air and cave air carbon stable isotope composition (δ13CCO2) and CO2 concentration were measured. Sampling and measurements were performed bi-monthly at the test and control sites above the cave. The abiotic source of soil CO2 was estimated using a stable isotope mass balance calculation.
Results and discussion
Similar seasonal patterns of soil CO2 and δ13CCO2 values were observed at both the test and control sites until spring, with higher levels of CO2 observed in summer and lower in winter. The δ13CCO2 showed the opposite trend, i.e. lower values (−26 to −20 ‰) in summer and higher values (up to −17 ‰) in winter and early spring. In spring, the soil CO2 concentration decreases and the δ13CCO2 value increases only at the control site. A time series of a modelled “isotopically light” endmember revealed large shifts in the data values, due to the presence of an abiotic CO2 source. Results suggest that the subterranean CO2 pool and its ventilation is the main source of soil CO2, accounting for up to 80 % of the soil gas during cold periods.
Ventilation from subterranean cavities is an important source of soil CO2 in karstic areas and should be taken into account during carbon cycling studies.
KeywordsAbiotic sources Karst region Soil CO2 Stable isotopes Ventilation
The study is a part of the PhD thesis of B. Krajnc supported by the Innovative scheme for co-financing of doctoral studies financed by the European Union through the European Social Fund and by the scholarship granted by the World Federation of Scientists. We are grateful to Iztok J. Košir from the Slovenian Institute for Hop Research and Brewing for the pedologic analyses and the Farmland and Forest Fund of the Republic of Slovenia for the permission to do research in the forest. We would also like to thank the Regional Forest Service Postojna of the Slovenian Forest Service and Maksimilijan Gorup for providing information regarding sanitation forest cutting. We appreciate the support of cave guides Stanislav Glažar, Janez Margon and Erik Rebec for their dedication during fieldwork. We would also like to acknowledge the managers of Postojna Jama d.d. and Ministry of Agriculture and Environment of Slovenia for the permission to access and work in the cave.
- ARSO (2015) ARSO. Available from: http://www.arso.gov.siGoogle Scholar
- Barnet I, Neznal M, Neznal M, Pacherová P (2008) Radon in geological environment—Czech experience. Czech Geological Survey, PragueGoogle Scholar
- Čater M, Ogrinc N (2011) Soil respiration rates and δ13CCO2 in natural beech forest (Fagus sylvatica L.) in relation to stand structure. Isot Environ Healt S 47:221–237Google Scholar
- Cerling TE, Quade J (1993) Stable carbon and oxygen isotopes in soil carbonates. Climate change in continental isotopic records pp:217–231Google Scholar
- Cuezva S, Fernandez-Cortes A, Benavente D, Serrano-Ortiz P, Kowalski AS, Sanchez-Moral S (2011) Short-term CO2(g) exchange between a shallow karstic cavity and the external atmosphere during summer: role of the surface soil layer. Atmos Environ 7:1418–1427Google Scholar
- Davidson GR (1995) The stable isotopic composition and measurement of carbon in soil CO2. Geochimica et Cosmochimica Acta 59(12):2485–2489Google Scholar
- Doerr H, Münnich KO (1986) Annual variations of the 14C content of soil CO2. Radiocarbon 2A:338–345Google Scholar
- Doran JW, Mielke LN, Power JF (eds) (1990) Microbial activity as regulated by soil water-filled pore space. Transactions 14th International Congress of Soil Science. Symposium III-3; Ecology of soil microorganisms in microhabital environments. Kyoto, Japan, pp 94–99Google Scholar
- GLOBALVIEW-CO2C13 (2009) GLOBALVIEW-CO2C13: cooperative atmospheric data integration project—δ13C of carbon dioxide. Available from: http://www.esrl.noaa.gov/gmd/ccgg/globalview/co2c13/co2c13_intro.html
- Guntiñas ME, Gil-Sotres F, Leirós MC, Trasar-Cepeda C (2013) Sensitivity of soil respiration to moisture and temperature. J Soil Sci Plant Nutr 2:445–461Google Scholar
- ISO 11464 (2006) Soil quality—pretreatment of samples for physio-chemical analysis. ISO, GenevaGoogle Scholar
- Jin L, Ogrinc N, Hamilton SK, Szramek K, Kanduč T, Walter LM (2009) Inorganic carbon isotope systematics in soil profiles undergoing silicate and carbonate weathering (southern Michigan, USA). Chem Geol 1:139–153Google Scholar
- Knohl A, Werner RA, Geilmann H, Brand WA (2004) Kel-F discs improve storage time of canopy air samples in 10-mL vials for CO2-δ13C analysis. Rapid Commun Mass Spectrom 14:1663–1665Google Scholar
- Kowalski AS, Serrano-Ortiz P, Janssens IA, Sánchez-Moral S, Cuezva S, Domingo F, Were A, Alados-Arboledas L (2008) Can flux tower research neglect geochemical CO2 exchange? Agric For Meteorol 6–7:1045–1054Google Scholar
- Kuzyakov Y (2006) Sources of CO2 efflux from soil and review of partitioning methods. Soil Biol Biochem 3:425–448Google Scholar
- Plestenjak G, Eler K, Vodnik D, Ferlan M, Čater M, Kanduč T, Simončič P, Ogrinc N (2012) Sources of soil CO2 in calcareous grassland with woody plant encroachment. J Soils Sediments 9:1327–1338Google Scholar
- Salomons W, Mook WG (1986) Isotope geochemistry of carbonates in the weathering zone. handbook of environmental isotope geochemistry. Elsevier, Amsterdam, pp. 239–269Google Scholar
- Schindlbacher A, Borken W, Djukic I, Brandstätter C, Spötl C, Wanek W (2015) Contribution of carbonate weathering to the CO2 efflux from temperate forest soils. Biogeochemistry 1-3:273–290Google Scholar
- Šebela S (2010) Accesses from the surface to the Postojna Cave system. Annales Series historia naturalis 1:55–64Google Scholar
- Šebela S, Čar J (2000) Velika Jeršanova doline—a former collapse doline: Velika Jeršanova dolina—nekdanja udornica. Acta carsologica 2:201–212Google Scholar
- Serrano-Ortiz P, Roland M, Sanchez-Moral S, Janssens IA, Domingo F, Godderis Y, Kowalski AS (2010) Hidden, abiotic CO2 flows and gaseous reservoirs in the terrestrial carbon cycle: review and perspectives. Agric For Meteorol 3:321–329Google Scholar
- Zhang J, Quay PD, Wilbur DO (1995) Carbon isotope fractionation during gas-water exchange and dissolution of CO2. Geochim Cosmochim Acta 1:107–114Google Scholar