The effects of clearcutting of Eucalyptus plantation on the water balance, water quality and soil and nutrient losses in a small catchment

Abstract

Streamflow and water quality parameters were measured continuosly for a period of 7 years in a small catchment, which was planted with Eucalyptus saligna Smith at the begining of the study period. After this period, the eucalypts plantation was clearfelled and the measurement continued throughout the first year after the cut, so that comparison could be made between the two periods in order to evaluate the effects of clearcutting on catchment water balance and water quality parameters. Streamflow showed a general downward trend in the first period, but increased about 115 mm during the first year after clearcutting. Taking the entire 8 years of measurements, the average catchment water balance showed the following values: Precipitation = 1327 mm, Streamflow = 141 mm, Evapotranspiration = 1186 mm. In comparison with the average values of the initial 7-year period, the data from the first year after felling showed an increase in streamwater turbidity, color, conductivity and sediment concentration. In terms of flux density of sediments, the increase was from 19.8 to 41.5 Kg.ha-1. yr-1, as a result of the clearcutting. The increase in conductivity was mostly a result of increases in the concentration of nitrate, calcium, iron and sodium in streamwater. These increases, on the other hand, were most pronounced during the rainy period of November through April. Streamwater concentrations of potassium and magnesium were not affected. In terms of flux density of the studied nutrients, there were slight increases in nitrate, calcium, potassium, magnesium and iron after clearcutting.