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

Abstract

Clear-cutting of forests have pronounced effects on chemistry of soils and runoff water. The major effects are increased water yield, changes in nutrient cycles and increased leakage of the nutrients nitrate and potassium in runoff. As part of the national monitoring programme for long-range transported air pollutants, administered by the Norwegian Pollution Control Authority (SFT), four groundwater aquifers in southern Norway were monitored for acidification trends during the period 1980-1995. For the monitoring station, Langvasslia in southeastern Norway, samling was continued until the end of 1999. This groundwater aquifer is located about 3 km north-east of the calibrated catchment Lake Langtjern. The catchment of the groundwater aquifer, covered completely by Norway spruce, was totally clear-cut in September 1986 and was treated with glyphosate in summer 1991. The effects on the groundwater are generally similar to those observed in stream-water from clear-cut areas: increases in water runoff, water temperature, concentrations of K, NO3 and organic carbon (TOC) and decrease in SO4-concentration. In the groundwater aquifer also inorganic aluminum decreased and ANC increased more than would have been expected without clear-cutting. NO3 concentrations are now almost back to the levels prior to clear-cutting, whereas K still shows elevated concentrations.