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 affect ing 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. T he debarking season influenced throughfall in the eucalypt forest. Pot assium was the dominant cation in the throughfall of both forests, bei ng 50% of the sum of the major cations (Ca, Mg, Na and K) for the pine s and 70% for the eucalypts. The largest difference was in sodium, bei ng 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 f or a significant proportion of events and was associated with higher r ainfall pH. There was a small net input of NH4-N and NO3-N by the euca lypts. A more substantial input of both ions occurred in the pines. Ho wever, uptake and release of both ions occurred for different events i n both forests. Throughfall samples taken during events showed that th e chemical concentration was related to variations in the intensity an d continuity of the rainfall, particularly for the major cations. NH4- N and NO3-N did not always follow the cation trends through time.