The geographic variation of salt precipitated over Western Australia

Abstract

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.