In Mediterranean ecosystems vegetation overlying shallow, transient aquifers is often dominated by woody phreatophytes, trees and shrubs that have been shown to be dependent on groundwater for their water requirements. Natural and anthropogenic alterations of groundwater tables (abstraction) are of clear importance to phreatophytic vegetation as reduction of water tables may sever these plants from their natural water sources. Seasonal water sources were determined for species growing on a coastal dune system that overlies a shallow sandy aquifer in south-western Australia. The plants studied grew over groundwater that ranged in depth from 2.5 to 30 m. The naturally occurring stable isotope of hydrogen (deuterium, δH) was used to distinguish potential water sources. Isotopic ratios from vascular water of the dominant species of the study area (Banksia ilicifolia R. Br. and Banksia attenuata R. Br. trees) were compared with those of potential sources of precipitation, soil moisture and groundwater. A relatively shallow-rooted perennial shrub, Hibbertia hypericoides Benth., was also included as an isotopic reference. The results suggest that both B. attenuata and B. ilicifolia are phreatophytic as they derived some of their water from groundwater throughout the dry-wet cycle, with the exception of B. attenuata at the site of greatest depth to groundwater (30 m) which did not use groundwater. A high proportion (>50%) of groundwater use was not maintained throughout all seasons. With the onset of the hot Mediterranean summer, progressive drying of the surface soils resulted in increased use of groundwater and deep soil moisture. During the wet winter plants used proportionately more water from the upper layers of the soil profile. The degree to which groundwater was utilised by the study species was dependent on the proximity of groundwater, availability of moisture in shallower horizons of the soil profile, root system distribution and maximum root depth.

The amounts of Na+, Mg2 +, K+, Ca2 +, C1-, SO42-, HCO3- and dust precipitated in rainfall and as dry fallout into continuously open collection funnels are reported for 59 centres throughout Western Australia. Ionic accessions for 1973 were in the following ranges; Na+, 2-98 kg ha-1; Mg2+, 0.3-15 kg ha-1; Ca2+, 0.8-35 kg ha-1; K+, 0.3-14 kg ha-1; SO42-, 2-57 kg ha-1; C1-, 2-180 kg ha-1; HCO3-, 1-105 kg ha-1. Chloride deposition at the coast is approximately an order of magnitude greater in the south-west of the state than in the north. In each region the amount of chloride precipitated exhibited the usual decrease with distance inland. There were regional differences in rainwater salt composition. Excess of ions over the amounts attributed to oceanic aerosols are explained by the locations of sampling centres relative to other source areas. Perth, the largest city, had the highest excess sulphur and above average values were obtained at the larger mining and country centres. Industry and domestic fires are the probable sources of this sulphur. Excesses of all ions from terrestrial sources were indicated at many inland centres, and were greatest in the zone of salt lakes and occluded drainage in the south-west.

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The amount of calcium in Eucalyptus diversicolor (karri) ecosystems is high in comparison with other eucalypt forest ecosystems in Australia. A large proportion of this calcium is present as crystalline Ca oxalate. Whewellite (CaCO·HO) accumulates in leaf tissue of the over- and understorey species. Up to 70% of the calcium in the leaves of karri is stored as whewellite, the highest concentrations occurring in the oldest leaves. Synthesis of Ca oxalate by karri may be related in part to the high levels of exchangeable soil calcium. Oxalate of plant origin is rapidly metabolized on the forest floor during decomposition of leaf litter. About 70% of the whewellite in fresh karri leaf litter is degraded during the first wet season following leaf fall. However, additional oxalate is formed in the soil and litter layer from microbial production of oxalic acid. These crystals are of the dihydrate calcium salt, weddelite (CaCCO· 2HO). Microbial production of oxalate, particularly by ectomycorrhizal fungi, may be an important mechanism for mobilizing of phosphate from the strongly phosphateadsorbing soils on which these forests grow.