Chemistry of rainfall, throughfall and stemflow in a eucalypt forest and a pine plantation in south-eastern Australia: 2. Throughfall

A rainfall event-based study allowed the examination of factors affecting the amounts and chemical concentrations of throughfall. The amount and frequency of antecedent rainfall was of influence in both forests, in that concentrations were higher with dry antecedent conditions. The debarking season influenced throughfall in the eucalypt forest. Potassium was the dominant cation in the throughfall of both forests, being 50% of the sum of the major cations (Ca, Mg, Na and K) for the pines and 70% for the eucalypts. The largest difference was in sodium, being 29% of the combined cations for the pines and 10% for the eucalypts. There was net uptake of hydrogen ions from rainfall for both forests, i.e. throughfall was less acid than rainfall, but release occurred for a significant proportion of events and was associated with higher rainfall pH. There was a small net input of NH4-N and NO3-N by the eucalypts. A more substantial input of both ions occurred in the pines. However, uptake and release of both ions occurred for different events in both forests. Throughfall samples taken during events showed that the chemical concentration was related to variations in the intensity and continuity of the rainfall, particularly for the major cations. NH4-N and NO3-N did not always follow the cation trends through time.