The Stable Isotope Chemistry of a Native and Irrigated Typic Natrargid in the San Joaquin Valley of California1
- Ronald G. Amundson and
- L. J. Lund2
The stable C and O isotope chemistry of native and irrigated Typic Natrargids was examined in order to determine the relationship between the climate and vegetation and the δ13C and δ18O of the native pedogenic carbonates (CaCO3) and the effect of irrigation on the CaCO3 in the cultivated soils. The native soil had a sparse vegetative cover consisting of grasses and salt tolerant shrubs, especially Atriplex polycarpa (Torr.), S. Wats. The δ13C of the CaCO3 reflected the mixture of C3 and C4 vegetation and the δ18O of the CaCO3 suggested that it had formed from soil H2O that had undergone extensive amounts of evaporation. At the time of sampling, alfalfa (Medicago sativa L.) was being grown on the irrigated soils. These soils had CO2 partial pressures of up to 7 KPa, nearly 20 times that of the native soil. The δ13C of the CaCO3 in the irrigated soils was not significantly different than that of the native soils which was due, in part, to the relatively small isotopic difference between the newly formed CaCO3 in the irrigated soil and much of that which occurred naturally. However, the δ18O of CaCO3 in the irrigated soils appeared to be shifted to more negative values than the δ18O of the native CaCO3. Based on the differences in the δ18O of the CaCO3 in the irrigated and native soils, it was semiquantitatively estimated that between 10 to 40% of the carbonate in the irrigated soils was newly formed or had dissolved and reprecipitated as a result of irrigation, increased biological activity, and the application of chemical amendments.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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