Nutrient dynamics of forested catchments in Southeastern Australia and changes in water quality and nutrient exports following clearing

Abstract

Nutrient inputs in rainfall, and streamwater chemistry and quality, were measured from May 1976 to April 1982 at three forested catchments in Victoria. Streamwater chemistry was influenced by the strong seasonal fluctuations in streamflow. Yearly input-export balances for Na, K, Ca, Mg and Cl varied substantially and were highly correlated with runoff. This underlines the importance of sampling a wide range of climatic variation to derive meaningful balances. Calibration relationships between catchments were used to evaluate the impact of clearing native eucalypt forest for the establishment of P. radiata on streamwater chemistry and quality and on nutrient exports. Clearing was found to have little effect on streamwater quality, thus demonstrating the effectiveness of a 30-m wide buffer strip retained on both sides of the stream channel. Only minor changes in streamwater chemistry were observed; however, exports of nutrients and suspended solids were significantly higher because of increased discharge following clearing. Exports of most nutrients returned to pre-treatment levels within 18 months after clearing. Nutrient losses in streamwater were small when compared with losses due to burning the cleared vegetation. Balances for Na were used to estimate nutrient inputs from geological weathering. It was concluded that inputs of Ca are probably too low to ensure adequate supply of Ca for successive rotations of P. radiata, and future management practices should aim at conserving this nutrient.