EFFECTS OF RESTORATION MEASURES ON NUTRIENT AVAILABILITY IN A FORMERLY NUTRIENT-POOR FLOATING FEN AFTER ACIDIFICATION AND EUTROPHICATION

Acidification and eutrophication have caused great changes in fen ecos ystems in The Netherlands. The main problems are the surplus of acid r ainwater, forming a lens above the calcareous groundwater, and the bla nket effect of the Sphagnum cover which results in a loss of rare spec ies and species-rich plant communities. Research on effects of restora tion measures was carried out in a floating fen with a vegetation type at present dominated by Sphagnum squarrosum, S. fallax and Polytrichu m commune. The nutrient dynamics were compared in 64 experimental plot s which received foul different treatments: control, drainage, sod rem oval and combined drainage plus sod removal. The amounts of extractabl e and mineralisable N and P were significantly reduced after both sod removal treatments. There was a significant negative correlation (p < 0.001) between pH and nutrient availability. After two years the mosse s had again become dominant (> 90% cover) in the plots that had only t he sod removal. they remained dominant in the control and drainage tre atments. In the drainage plus son removal plots, however, these bryoph ytes were still absent and the coverage of many characteristic fen spe cies had increased considerably. These conditions have persisted for a further three years (to 1995). Copyright (C) 1996 Elsevier Science Li mited