Effects of restoration measures on nutrient availability in a formerly nutrient-poor floating fen after acidification and eutrophication

Abstract Acidification and eutrophication have caused great changes in fen ecosystems in The Netherlands. The main problems are the surplus of acid rainwater, forming a lens above the calcareous groundwater, and the blanket effect of the Sphagnum cover which results in a loss of rare species and species-rich plant communities. Research on effects of restoration measures was carried out in a floating fen with a vegetation type at present dominated by Sphagnum squarrosum, S. fallax and Polytrichum commune . The nutrient dynamics were compared in 64 experimental plots which received four different treatments: control, drainage, sod removal and combined drainage plus sod removal. The amounts of extractable and mineralisable N and P were significantly reduced after both sod removal treatments. There was a significant negative correlation ( p 90% cover) in the plots that had only the sod removal: they remained dominant in the control and drainage treatments. In the drainage plus sod removal plots, however, these bryophytes were still absent and the coverage of many characteristic fen species had increased considerably. These conditions have persisted for a further three years (to 1995).