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Variations in Soil CO2 Concentrations and Isotopic Values in a Semi-Arid Region Due to Biotic and Abiotic Processes in the Unsaturated Zone

Published online by Cambridge University Press:  09 February 2016

I Carmi*
Affiliation:
Weizmann Institute of Science, Rehovot, Israel Geological Survey of Israel, Jerusalem, Israel Tel Aviv University, Tel Aviv, Israel
D Yakir
Affiliation:
Weizmann Institute of Science, Rehovot, Israel
Y Yechieli
Affiliation:
Geological Survey of Israel, Jerusalem, Israel
J Kronfeld
Affiliation:
Tel Aviv University, Tel Aviv, Israel
M Stiller
Affiliation:
Geological Survey of Israel, Jerusalem, Israel
*
5Corresponding author. Email: carmiisr@post.tau.ac.il.

Abstract

A study of CO2 in soil gas was conducted in a bare plot in the unsaturated zone (USZ) of Yatir Forest, northern Negev, Israel. In 2006, 6 tubes for sampling of soil gas were inserted into the USZ to depths of 30, 60, 90, 120, 200, and 240 cm. Profiles of soil gas in the USZ were collected from the tubes 5 times between October 2007 and September 2008. Measurements of the collected profiles of soil gas were of CO2 (ppm), δ13C (′), and Δ14C (′). At all times, the concentration of CO2 in the soil gas was higher than in the air at the surface (CO2 ≃ 400 ppm; δ13C ≃ −9′). The main source of the CO2 in soil gas is from biotic activity released through roots of trees and of seasonal plants close to the surface. In the winter, the CO2 concentrations were lowest (6000 ppm) and the δ13C was −20′. In the spring and through the summer, the CO2 concentration increased. It was estimated that the major source of CO2 is at ≃240 cm depth (δ13C ≃ −22′; CO2 ≃ 9000 ppm) or below. Above this level, the concentrations decrease and the δ13C (′) become more positive. The 14C values in the measured profile are all less than atmospheric and biotic 14C. It was deduced that biotic CO2 dissolves in porewater to form carbonic acid, which then dissolves secondary carbonate (δ13C ≃ −8′; 14C ≃ −900′) from the sediments of the USZ. With the 14C data, the subsequent release of CO2 into the soil gas was then estimated. The 14C data, supported by the 13C and CO2 data, also indicate a biotic source at the root zone, at about 90 cm depth.

Type
Articles
Copyright
Copyright © 2013 by the Arizona Board of Regents on behalf of the University of Arizona 

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References

Carmi, I. 2007. Processes that affect the isotopic concentration of carbon in the unsaturated zone: implications for the improved dating of groundwater with 14C , Tel Aviv University. 66 p.Google Scholar
Carmi, I, Kronfeld, J, Yechieli, Y, Yakir, D, Boaretto, E, Stiller, M. 2009. Carbon isotopes in pore water of the unsaturated zone and their relevance for initial 14C activity in the coastal aquifer of Israel. Chemical Geology 268(3–4):189–96.Google Scholar
Cerling, TE. 1984. The stable isotopic composition of modern soil carbonate and its relationship to climate. Earth and Planetary Science Letters 72(2):229–40.Google Scholar
Clark, I, Fritz, P. 1997. Environmental Isotopes in Hydrogeology. Boca Raton: Lewis Publishers. 328 p.Google Scholar
Davidson, GR 1995. Geochemical and isotopic investigation of the rate and pathway of fluid flow in partially-welded fractured unsaturated tuff , University of Arizona.Google Scholar
Deines, P, Langmuir, D, Harmon, RS. 1974. Stable carbon isotope ratios and the existence of a gas phase in the evolution of carbonate groundwater. Geochimica et Cosmochimica Acta 38(7):1147–64.Google Scholar
Gorczyca, Z, Kuc, T, Rozanski, K. 2013. Concentration of radiocarbon in soil-respired CO2 flux: data-model comparison for three different ecosystems in southern Poland. Radiocarbon, these proceedings, doi: 10.2458/azu_js_rc.55.16321.Google Scholar
Grünzweig, JM, Lin, T, Rotenberg, E, Schwartz, A, Yakir, D. 2003. Carbon sequestration in arid-land forest. Global Change Biology 9(5):791–9.Google Scholar
Grünzweig, JM, Hemming, D, Maseyk, K, Lin, T, Rotenberg, E, Raz-Yaseef, N, Falloon, PD, Yakir, D. 2009. Water limitation to soil CO2 efflux in a pine forest at the semiarid “timberline.” Journal of Geophysical Research 114:G03008, doi:10.1029/2008JG00874.Google Scholar
Klein, T, Hemming, D, Tongbao, L, Grünzweig, JM, Maseyk, K Rotenberg, E, Yakir, D. 2005. Association between tree-ring and needle δ13C and leaf gas exchange in Pinus halpenesis under semi-arid conditions. Oecologia 144(1):4554.Google Scholar
Liu, W, Moriizumi, J, Yamazawa, H, Iida, T. 2006. Depth profiles of radiocarbon and carbon isotopic compositions of organic matter and CO2 in a forest soil. Journal Environmental Radioactivity 90(3):210–23.Google Scholar
Levin, I, Naegler, T, Kromer, B, Diehl, M, Francey, RJ, Gomez-Pelaez, AJ, Steele, PL, Wagenbach, D, Weller, R, Worthy, DE. 2010. Observations and modelling of the global distribution and long-term trend of atmospheric 14CO2 . Tellus B 62(1):2646.Google Scholar
Maseyk, K, Grünzweig, JM, Rotenberg, E, Yakir, D. 2008. Respiration acclimation contributes to high carbon-use efficiency in a seasonally dry pine forest. Global Change Biology 14(7):1553–67.Google Scholar
Parker, LW, Miller, J, Steinberger, Y, Whitford, WG. 1983. Soil respiration in Chihuahuan Desert rangeland. Soil Biology and Biochemistry 15:303–9.Google Scholar
Pumpanen, J, Ilvesniemi, H, Kulmala, L, Siivola, E, Laasko, H, Kolari, P, Helenelund, C, Laasko, M, Uusimaa, M, Hari, P. 2008. Respiration in boreal forest soil as determined from carbon dioxide concentration profile. Soil Science Society of America Journal 72(5):1187–2008.Google Scholar