Fred Leaney

Unsaturated zone tritium and chlorine 36 profiles from southern Australia: Their use as tracers of soil water movement

In this paper we present seven unsaturated zone profiles of 36Cl and three 3H profiles from southern Australia. All profiles show single peaks corresponding to high radionuclide fallout from nuclear testing in the 1950s and 1960s. The profiles are used to estimate rates of water movement leading to recharge of the groundwater. Among these profiles is the first profile on which high concentrations of 36Cl have been found below a 2-m depth. In this profile, 3H and 36Cl peaks coincide. In six of the seven profiles, total 36Cl fallout was found to be between 1.2 and 2.4 × 1012 atoms m−2, and is of similar magnitude to that found at similar latitudes in the northern hemisphere. Comparisons of soil water fluxes estimated with 3H, 36Cl, and chloride are briefly discussed.

The Use of Stable Isotopes of Water for Determining Sources of Water for Plant Transpiration

Over the last ten years, there has been a large increase in the number of vegetation studies that have incorporated measurements of the stable isotopic composition of water. There are many methods for measuring the amount of water being used by plants, but until recently it has been difficult to determine from where plants obtained their water. This has been particularly difficult where there is more than one available water source (e.g. where groundwater is shallow or streams are nearby).

IMPROVED PREDICTIONS OF GROUNDWATER SALINISATION IN THE SE OF SOUTH AUSTRALIA - A CASE STUDY ON THE COMBINED ROLE OF GEOLOGICAL UNDERSTANDING, GEOPHYSICS AND MODELLING.

In many areas of South Eastern Australia, saline soil-water in the unsaturated zone overlies fresher groundwater. In areas where remnant vegetation has been removed and has been replaced with pasture or cropping, enhanced drainage has resulted, which after a lag time, flushes the saline soilwater down into deeper unconfined aquifer systems that contain fresh groundwater. For an area near Tintinara in south-eastern South Australia, spatial simulations of groundwater salinization under dryland and irrigation scenarios were developed for a 200 year timeframe using a distributed parameter recharge model. Inputs to the model include spatial patterns of near surface clay materials determined from the constrained inversion of helicopter frequency domain EM data. The AEM data were used to define the spatial distribution and thickness of a near surface clay-rich sedimentary unit. The presence of clay coupled with its thickness significantly affects the lag time for the downward movement of saline soil water and the salt flux to the aquifer. Under dryland agriculture leaching of the salt to the aquifer takes between 50 and 200 years, whereas under irrigation, leaching takes between 20 and 50 years. Under irrigation the salinity of the groundwater is expected to increase from 1000 – 6000mg/L over the next 25-40 years. While there are no obvious economic measures available to prevent groundwater salinization, the modelling suggests that efficient irrigation on appropriate soils could slow the process.