Nutrient movement due to overland flow in managed native Eucalyptus forests, southeastern Australia.

A rainfall simulator study of total nutrient movement due to overland flow on forest skid trails and general harvesting areas (GHA) in the native euca lypt forests of southeastern Australia, confirmed that the disturbed and co mpacted areas were the dominant sources of sediment-bound pollutants. Low r unoff production and low sediment availability on the rough surfaces of the Gl-IA reduced total nutrient yields. On the more recently disturbed and bu rnt sites, the solution pathway may have been more dominant due to runoff c oming in contact with surface ash and charcoal. We also recorded significan t reductions in the total nutrient yields as runoff from the skid trail was delivered to the adjacent hillslope via a cross bank (water bar). This was due primarily to coarse-grained sediment deposition at the base of the ban ks. Nutrient concentrations in the eroded sediment at the cross bank outlet s, however, remained 9 times higher than the in-situ surface soils, due to the preferential delivery of fine aggregate material to the adjacent hillsl ope. Further reductions in total nutrient yields occurred as overland flow passed through the GHA, illustrating the effectiveness of vegetative filter ing in reducing runoff volumes and sediment fluxes. Temporal trends in the data highlighted significant reductions in total nutrient movement on both areas of disturbance as sites regenerated over a period of similar to 5 yea rs. Water pollution abatement practices in these environments should aim to locate skid trails to maximise the redistribution of runoff and sediment f rom highly disturbed areas to more vegetated parts of the hillslope, and by appropriate cross bank spacing, reduce the volume of overland flow carryin g sediment and nutrients.