Effects of forestry on stream water chemistry during autumn : A before and after comparison between a reference and two streams with clear-cut watershed areas

Forestry is a large-scale business in many countries, and in northern Sweden a large portion of the Boreal forests is cut. Yet very few studies have investigated the impacts of forestry on the vast number of receiving stream waters. This study has therefore investigated the impacts of forestry, through clear-cutting, on stream water chemistry during autumn conditions in northern Sweden. The study compares the parameters water height, absorbance, dissolved organic carbon, total dissolved nitrogen and total phosphorus in two inlet streams in recently deforested sites, <1 year ago, and an undisturbed reference inlet stream. The disturbed inlet streams are compared to the reference inlet stream the year before and after clear-cutting. This study shows that during a 15- day period from late August to the beginning of September, water height was increased in both disturbed inlet streams, indicative of a higher run-off post-harvest. Absorbance showed a large decrease post-harvest in the disturbed inlet streams. Total dissolved nitrogen and total phosphorus concentrations decreased slightly after clear-cut in both disturbed inlet streams. The effect was probably larger for phosphorus, since the seasonal variation in the reference was larger in 2013. DOC concentrations increased slightly in one of the disturbed inlet streams in 2013, but decreased slightly in the other disturbed inlet stream. The increased run-off was therefore not followed by a higher DOC and nutrient leakage. Results suggest that during a short period in the autumn, harvest does not seem to lead to increased DOC and nutrient losses to receiving stream waters