Affiliations: School of Science and Engineering, University of
Ballarat Mount Helen, University Drive, Ballarat, Victoria 3353, Australia.
[email protected]
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.
Keywords: Rainwater, major cations, individual rain events, seasonal changes, Australia
