Natural fertilisation of the marine environment - Modelling of the Glomma flood 1995

The flood in the Norwegian river Glomma in May-June 1995 was among the larg est ones during this century. Besides bring devastating for man and buildin gs, it implied an extra supply of nutrients to the Skagerrak. This paper wi ll focus on the possible effects this natural fertilisation could have had on the primary production in the receiving water. The NORWegian ECOlogical Model system (NORWECOM) has been used to quantify this effect, The model has been run three times with different runoff scena rios to isolate the effects of the flood. To investigate the dispersion and dilution of the water from Glomma, this water has been labelled in the mod el. The model results have also been compared with a set of field data obta ined during the period. During the flood the model gives a significant change in primary production over large areas of the Skagerrak, and all extra nutrients added from the flooded rivers were consumed by the algae. However, the flood seems to have only a small impact on the annual production.