Water Use Strategies of Two Co-occurring Tree Species in an Australian Semi-arid Karst Environment
Presented on Monday, April 29, 2013
Brooke A. Swaffer1, Kate L. Holland2, Tanya M. Doody2, Chris Li3 and John L. Hutson4, (1)South Australian Water Corporation, Adelaide, Australia, (2)CSIRO Land and Water, Adelaide, Australia, (3)South Australia Department of Environment, Water and Natural Resources, Adelaide, Australia, (4)School of Environment, Flinders University, Adelaide, Australia
Regional communities are often reliant on groundwater to sustain social, economic and environmental uses, with concern arising over substantial water level decline in many aquifers. In recognition of this, water use strategies of
Eucalyptus diversifolia and
Allocasuarina verticillata were investigated using a water balance, in conjunction with the stable isotopes of water, leaf and soil water potentials to test whether 1) groundwater recharge occurs in the presence of these species, and 2) groundwater is being used by the trees to sustain transpiration during drier months.
Overall, actual evapotranspiration (ET) exceeded rainfall (RF) received (E diversifolia ET = 560 and 504 mm year-1; A. verticillata ET = 501 and 560 mm year-1 vs. RF = 461 and 422 mm year-1), but was similar to the estimated long term average rainfall (502 mm year-1), suggesting convergence between evapotranspiration and water supply during typical years. Subsurface soil water was a better isotopic match to twig water than either surface soil or groundwater, and contained regions of low bulk density (1.02 g cm-3) and substantial water holding capacity (0.38 g g-1). However, geological variability makes it difficult to extrapolate this to the landscape level. Transpiration was greater for E. diversifolia than A. verticillata over the study period (341 mm vs. 184 mm), corresponding with higher midday leaf water potentials for E. diversifolia (average – 2.06MPa) than for A. verticillata (average – 2.86MPa), suggesting extraction at different locations within the soil profile.
These findings suggest it is unlikely groundwater resources are being used to sustain transpiration, despite the water balance indicating losses from the system during the study period. We conclude that the water holding capacity of the porous karst substrate plays an important role in moderating the effect of rainfall variability, and should be considered when assessing ecohydrological characteristics of karst systems.
Brooke A. Swaffer
South Australian Water Corporation, Adelaide, Australia
Brooke A. Swaffer undertook this research as part of a Ph.D. begun in 2008, in recognition of considerable knowledge gaps concerning a regionally significant karst groundwater system in southern Australia. Graduating with first class honors in 2005, Swaffer has been employed with the state water utility since, and tasked with providing scientifically underpinned evidence of water quality and quantity impacts in groundwater and surface water supplies.
Kate L. Holland
CSIRO Land and Water, Adelaide, Australia
NA
Tanya M. Doody
CSIRO Land and Water, Adelaide, Australia
NA
Chris Li
South Australia Department of Environment, Water and Natural Resources, Adelaide, Australia
NA
John L. Hutson
School of Environment, Flinders University, Adelaide, Australia
A Senior Lecturer in hydrology in Earth Sciences at Flinders University, John Hutson is a soil scientist with worldwide experience in the transport and fate of chemicals in soils, soil physical characterisation, plant-water relationships, salinity issues, and the impact of land-use on water quality at field and catchment scales. He is co-author of LEACHM, a widely-used model for predicting the water regime and chemical fate and transport in unsaturated soils.
