Effects of clear-cutting on streamwater quality in forest catchments in central Sweden

Hydrochemical studies were conducted in three forested catchments in central Sweden during a 12-year period (1977-1989). During this period, 50% and 95% of the surface of two of the areas were clear - felled. The third area was left untouched as a control for reference. A qualitative analysis of clear-cut effects was conducted to investigate changes in streamwater quality by use of Principal Component and SIMCA analyses. During the 8 years of clear-cutting, with reference to the control period, the average runoff increased by 85% and 110% (220 mm and 274 mm year(-1)), respectively, in the two areas felled to 50% and 95%. Significant changes in the status of the streamwater were detected for the two clear-felled catchments, whereas the changes detected in the control catchment were not significant, and within the limits of natural variation. In relation to the reference period, the changes in the clear-felled catchments were identified as dependent mainly on increased concentrations of K+, NH4+, NO3-, org-N, and tot-N. Concentrations of H+ decreased, while changes in concentrations of Ca2+, Mg2+, Na+, SO42-, and Cl- were less distinct. At the end of the 8 year investigation period, run-off and chemical composition of the streamwater successively returned to pre-cut conditions.