Date of Award
Bachelor of Science Honours
Faculty of Computing, Health and Science
Dr Ray Froend
Lake Toolibin is one of a few remaining freshwater lakes in the central wheatbelt of Western Australia. Since monitoring began at Lake Toolibin in the early 1970's groundwater levels have risen to within 1-2 m of the lakebed with an accompanying migration of salt. The site-specific nature of water uptake in Casuarina obesa Miq. (the dominant lakebed tree species) and rhizosphere salinity were explored spatially through analyses of soil properties (groundwater depth and salinity, particle size and components of soil water potential ψ1). Plant water sources (using δ2H signatures) and water availability (based on ψleaf and ψt) were measured to define water uptake within the rhizosphere. Plant response to these conditions was determined using critical indicators of plant water relations such as stomatal conductance (gs) and water use. This investigation was conducted over a drying period (October 2002 - February 2003) on the lakebed. The drying period coincided with a maximum in soil water potential (ψ1) and sites with shallower depths to groundwater had soil profiles dominated by osmotic potentials (ψ0) due to the accumulation of salts near the soil surface. At some sites groundwater was transmitted above the water table along films of coarse textured sands, forming perched systems of thin saturated soil (0.l - 0.2 m). These were important mechanisms in the transport of saline groundwater to the rhizosphere. Patterns of water uptake for C. obesa across the lake appeared to be closely related to seasonal effects of the drying period and soil water and salt movement from the capillary fringe. Pre-dawn leaf water potentials (ψpd), stomatal conductance and water use decreased during summer at all sites, especially where salt accumulation had occurred, but this species exhibited substantial tolerance to moisture deficits caused by salt accumulation. C. obesa obtains its summer moisture from relatively shallow depths (< 0.9 m) and regulates water loss through stomatal control during this period, allowing it to persist under these conditions.
Mitchell, P. J. (2003). Patterns of water uptake and rhizosphere salinity in Casuarina Obesa Miq. during a drying period at Lake Toolibin, Western Australia. https://ro.ecu.edu.au/theses_hons/337