Effects of clear-cutting of forest on the chemistry of a shallow groundwater aquifer in southern Norway

As part of the national monitoring programme for long-range transported air pollutants, four groundwater aquifers in southern Norway were monitored fo r acidification trends during the period 1980-1995. For the monitoring stat ion, Langvasslia in south eastern Norway sampling continued until the end o f 1999. This groundwater aquifer is about 3 km north east of the calibrated catchment Lake Langtjern. The catchment of the groundwater aquifer, covere d completely by Norway spruce, was clear-cut in September 1986 and was trea ted with glyphosate in the summer, 1991. The chemical effects on the chemis try of the groundwater are generally similar to those observed in stream-wa ter from clear-cut areas: increases in water runoff, water temperature, con centrations of K, NO3, and organic carbon (TOC), and decrease in SO4 concen tration. In the groundwater aquifer, inorganic Al and ANC increased more th an would have been expected without clear-cutting. By 1999 NO3 concentratio ns were nearly the same as prior to clear-cutting, whereas K still was elev ated.