Assessing marine ecosystem response to nutrient inputs

The response of the Pagasitikos Gulf to enrichment caused by run-off fertil izers and the development and evolution of harmful algal blooms is investig ated through ecosystem modelling. A standard generic complex model has been developed to describe the ecosystem processes of Pagasitikos and has been validated with in situ data. Additionally external nutrient fluxes have bee n assimilated and incorporated into the ecosystem dynamics. The investigati on of spatial effects due to nutrient enrichment is investigated along a No rth-South transect. When externally forced the model successfully assimilat es the external river inputs producing nutrient and chlorophyll-a concentra tions, which are in good agreement with the in situ data. The nutrient inpu ts result in a more stable ecosystem at the north part of the Gulf and in t he development of eutrophic conditions. The changes in the ecosystem functi oning with emphasis on the nutrient cycling, the increase of primary produc tion, and the modes of operation are investigated and discussed. (C) 2001 E lsevier Science Ltd. All rights reserved.