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.
