1. Arts, G.H.P.: 1990.Deterioration of atlantic sofl-water systems and their flora, a historical account. PhD thesis, University of Nijmegen.
2. Arts, G.H.P., Van Der Velde, G., Roelofs, J.G.M. and Van Swaay, C.A.M.: 1990.Freshwater Biol. 24, 287?294.
3. Bobbink, R., Boxman, D., Fremstad, E., Heil, G., Houdijk, A. and Roelofs, J.: 1992. In:Critical loads for Nitrogen. Nord (Milj�rapport) 41, 111?159.
4. Bobbink, R. and Roelofs, J.G.M.: 1995. In:Mapping and modelling of critical loads for nitrogen ? a workshop report. Institute of Terrestrial Eoclogy, Peniciuik, 9?19.
5. Boxman, D., Van Dijk, H., Houdijk, A. and Roelofs, J.: 1988. In:Critical loads for sulphur and nitrogen. Milj�rapport 15, 295?323.