Alteration of stream nutrient discharge with increased sedimentation due to thinning of a deciduous forest in Istanbul

Abstract

The effects of 11% thinning on the nutrient outflux of a deciduous forest ecosystem in Belgrad forest is investigated with a paired watershed study. The treatment was a selective cutting to remove 11% of the standing volume uniformly throughout the watershed. Skidding was done by horse dragging and residues were left on site. Regression equations for selected water quality parameters were computed for calibration period (1980–1985) and calculated output values for the first year of post-treatment period was compared with observed ones. All linear regression equations were strong enough to be used in this procedure. Suspended sediment, total N, HCO 3 −, PO 4-P, Cl −, Ca 2+, Mg 2+, K + and Na + were the parameters in consideration. Most of them increased in the following winter months soon after precipitation reached to a considerable amount. Increase in suspended sediment, Cl −, Ca 2+, Mg 2+, and K + loads were statistically detectable ( p < 0.05) while total nitrogen and PO 4-P outputs remained almost unchanged after the treatment. Twenty percent, 23%, and 31% increases in annual suspended sediment, Cl −, and Ca 2+ discharges, respectively, due to a slight thinning treatment emphasize the importance of harvesting methods and techniques for nutrient cycling of a forest ecosystem.