Impacts of Groundwater Extraction on the Ecophysiology of Several Australian Tree Species of NSW

University of Technology Sydney. Faculty of Science.Groundwater extraction has increased seven-fold worldwide in the last century leading to extensive overexploitation of aquifers. A loss of groundwater involves considerable changes in the function of ecosystems that were previously dependent upon it. However, the significance of these changes due to extraction-induced increases depth-to-groundwater (DGW) is poorly understood in the mesic forests of Australia's East Coast, where water resources regulators require such information. The research presented in this thesis thus sought: (a) to investigate the initial changes in ecophysiological adaptations such stem diameter, leaf water relations, and foliar ¹³C to a short-term extraction-induced groundwater drawdown and (b) to identify any indication of stress in trees occupying the cone of depression in comparison with trees not affected by the groundwater drawdown. Three different bore-fields, located within the Hunter-Central Rivers area (New South Wales, Australia), were selected to conduct this research and where DGW fluctuates naturally from 0 m to 7 m. Twelve trees of two dominant species ( and ) were studied at each site, radiating out from an extraction bore at near, intermediate, and distant locations (plots 1, 2, and 3). Overall, the findings of this thesis highlight that vegetation responded positively to a DGW increase from 1 m to 4.2 m. This suggests that trees benefited from groundwater extraction and were well-watered across all levels of DGW. This can be explained as a lowered water table that still remains within the potential root zone opens up a temporary larger volume of soil water for the trees to access, suggesting that GW extraction is beneficial to trees by reducing waterlogging and anoxic conditions in soil and increasing the volume of soil with good aeration. Changes in DGW due to groundwater extraction were immediate but short-lived, with DGW in plot 1 nearest the extraction bore declining relative to DGW in bores of the more distant plots for only the first week of extraction, despite the timing to coincide with regional drought leading to widespread bushfires. This research provides insight into the initial physiological responses of groundwater-dependent vegetation to short-term groundwater drawdown in a highly dynamic mesic ecosystem assisting pumping companies and state regulatory agencies to manage water resources under the rapidly changing conditions to which they are exposed in this region