Streamwater chemistry of mountain forest watersheds in the Bavarian alps : changes induced by forest harvesting and natural disturbances

Abstract. The streamwater chemistry in two mountain forest watersheds in the Bavarian Alps is described. A close correlation was found to exist between precipitation and runoff. However, the rainwater was to a great part first stored in the ecosystem, to be exchanged by new rainwater after each rainfall event, thus enabling system buffering. An almost complete buffering of aeidity could be identified due to the strong watershed Output of alkali and alkaline earth cations and silicic acid. On the other hand, protons, organic carbon. nitrogen, organic and inorganic pollutants were aecumulated in the ecosystem.

40% of tree stem volume was removed from one of the watersheds after a monitoring period of about two years (patch cutting method) in order to make observations on the stability of these ecosystems in situations of natural or man-made disturbances. Runoff and export rates strongly increased in the first year after the disturbance due to enhanced mineralisation, aeidification, and a reduced uptake of nutrients and waler. Except for nitrate, the changes returned to pre-event conditions about a year after the disturbance.Thus, the extent and manner of forest use tested in this study is in terms of ecological consequences an acceptable forest management tool.