Abstract
Rainfall events (n = 120, representing 702.7 mm rain) were collected at the Mount Helen site in Ballarat, Central Victoria (Australia) from November 2002 to November 2003 and analysed for rainfall amount, pH, electric conductivity (EC), temperature and major cation (Ca, Na, Mg and K) composition. The pH exhibited large variations, from 4.2 (in winter) to 7.7 (in summer) with an average value of 6.0. Twenty-one percent of the recorded rain events were acidic (pH < 5.5) and 29% were neutral to alkaline (pH > 6.5). The mean dissolved concentrations of major cations varied in the order: Na>>Ca>K>Mg. All major cations varied significantly (Na and K >50-fold, Ca >100- fold and Mg >450-fold) in the individual rain events. While Na and Mg were the most and least abundant cations in all seasons, respectively, Ca recorded the second dominant cation in spring and winter, and K in summer and autumn seasons. About 3-fold higher K concentration in summer (average ∼65μeq/L) as compared to the winter season (average ∼21μeq/L), pointed to possible biogenic emissions and forest burnings in the area. The rainwater chemistry appeared to be controlled mainly by terrestrial sources; however, the higher value of Na (upto 434.9 μeq/L in summer season) pointed to the influence of marine sources in few rain events. More than 15% of rain events recorded >300 μeq/L of Na, which could be significant from the agricultural and environmental point of view for both quality and quantity.
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