| Summary: | The concentration of suspended solids in a meso-eutrophic basin remained unchanged in the years following clear felling (1983–85). The amount of suspended solids increased upon ditching, ploughing and mounting to a mean level of 81.8 mg l–1 in 1986–88, decreased to a level of 7.8 mg l–1 for 1989–91 and 4.5 mg l–1 for 1992–94. Total phosphorus concentration increased four-fold (142 µg l–1) in 1983–85 following clear felling, and remained at three times the reference concentration (95.4 µg l–1) in 1986–88 following ditching and site preparation. Phosphate phosphorus concentration increased more than five-fold after clear felling (97.8 µg l–1) in 1983–85 and was more than two-fold the reference (39.5 µg l–1) following ditching and site preparation in 1986–88. The concentrations of total phosphorus and phosphate phosphorus returned to the level recorded in a natural state by 1989 onwards. Total nitrogen concentrations doubled (965 µg l–1) upon clear felling, and remained the same after ditching and site preparation in 1986–88. Where a protective strip of forest was left between the felling site and the brook, suspended solid did not increase in response to either clear felling or ploughing of the felled area, nor were any changes observed in total phosphorus, phosphate phosphorus or nitrogen componds.The ditching of peatland down to the level of the mineral soil led to an increase in the suspended solid concentration (17.8 mg l–1) by a factor of more than 12 in the first three years (1983–85) and by a factor of more than four (5.7 mg l–1) in the following three years (1986–88) compared with the reference period. Total nitrogen, nitrate and nitrite concentrations of ground water were markedly low all the time the forests remained in their natural state, but began to rise gradually following clear felling. A high increase was recorded as a consequence of ditching and site preparation.
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