Abstract

Measurements of naturally occurring stable isotopes of hydrogen (²H) and oxygen (¹⁸O) were used to determine the importance of creek waters to river red gums (Eucalyptus camaldulensis Dehnh., Myrtaceae) on the banks of creeks in the semi-arid and saline Chowilla floodplain region of South Australia. The ²H and ¹⁸O concentrations of water sampled from trees were significantly different from those of the creek water, indicating that, generally, trees were not obtaining all their water from the creek. This was found even in trees overlying highly saline groundwater. Thus, saline groundwater and/or soil water were important water sources for the trees studied. The results indicated that the water relations of these trees are complex, and the trees may be less affected by changes in creek flow and/or salinity than was previously anticipated.