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Dynamics of Water Soil Storage in the Unsaturated Zone of a Sand Dune in a Semi-Arid Region Traced by Humidity and Carbon Isotopes: The Case of Ashdod, Israel

Published online by Cambridge University Press:  02 July 2018

Israel Carmi*
Affiliation:
Tel Aviv University, Tel Aviv, Israel Weizmann Institute of Science, Rehovot, Israel Geological Survey of Israel, Jerusalem, Israel
Mariana Stiller
Affiliation:
Geological Survey of Israel, Jerusalem, Israel
Joel Kronfeld
Affiliation:
Tel Aviv University, Tel Aviv, Israel
*
*Corresponding author. Email: carmiisr@post.tau.ac.il.

Abstract

A 22 m sediment core was collected from the unsaturated zone (USZ) in the dunes south of Ashdod, Israel, in a low rainfall year, following an even lower-rainfall year. The mineralogy of was quartz with some clay and carbonate. The local climate is semi-arid. The roots of the sparse vegetation can reach ~8 m. The porosity was ~40–55%. The DIC ranged from 2 to 13 mmole C/L. Large variability is noted in the soil moisture, with a maximum at the high clay region at ~8 m. Oxygen isotopes enter the USZ with rain falling on the surface. There is 18O enrichment in the top of the section due to evaporation during the summer. Below this depth δ18O values of ~ –5‰ prevail as in the local aquifer. CO2 and the carbon isotopes enter the USZ laterally by exhalation from roots. The δ13C varies from –5‰ to –23‰, representing stages in carbon isotopic fractionation: CO2gas becomes dissolved CO2aqueous which then forms carbonic acid and HCO3 . The high δ13C, Δ14C, and DIC are found at the 8 m depth. These values along with high humidity are replicated at ~22m depth. They most probably represent recharge water from the previous rainy season at 8 m depth subsequently pushed down 12.8±0.8 m during the last winter.

Type
Water, Sediment, Karst
Copyright
© 2018 by the Arizona Board of Regents on behalf of the University of Arizona 

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