De Jong, F., Bakker, J., van Berkel, C.
, Dahl, K., Dankers, N., Gätje, C., Marencic, H. & Potel, P. (Ed.) (1999).
1999 Wadden Sea Quality Status Report. Common Wadden Sea Secretariat, Trilateral Monitoring and Assessment Group. Wadden Sea Ecosystem Vol. 9