CHEMISTRY OF RAINFALL, THROUGHFALL AND STEMFLOW IN A EUCALYPT FOREST AND A PINE PLANTATION IN SOUTH-EASTERN AUSTRALIA .1. RAINFALL

Rainfall samples were collected from several hundred rainfall events. Up to nine samples per event were collected fi om sites 3-500m apart. They differed substantially in both concentration and composition, eve n though great care was taken to wash all collectors beforehand. Dryfa ll, storage and analytical procedures could not explain the variation. When data for rainfall events of similar size (but very different cat ion inputs) were examined, the major differences were associated with the prevailing wind direction. Events leading to high concentrations w ere associated with easterly winds and showed the influence of a marin e source. Chemical concentration and composition were not altered by t he occurrence of a drought year followed by a very wet year. The mean pH was 5.3 and ranged from 4.6 to 5.8. For a given event, a difference of 0.5 often occurred between collection sites. Regular seasonal vari ations in the concentration of NO3-N and the NO3/NH4 ratio occurred, w ith the ratio being higher in summer due primarily to bush fires. Orga nic nitrogen comprised 14% of total nitrogen.