A numerical approach to simulate nutrient dynamics and primary production of a semi-enclosed coastal ecosystem (Pagassitikos Gulf, Western Aegean, Greece)

Abstract

Pagassitikos Gulf is a relatively shallow semi-enclosed bay at the western part of Aegean sea influenced by industrial, urban and agricultural activities concentrated mainly at the North part. Field measurements since 1975 on a number of physical (temperature, salinity), chemical (dissolved oxygen, nutrients) and biological (chlorophyll-a, phytoplankton, zooplankton, benthic fauna) parameters have produced a valuable data set. In this work a complex ecosystem model has been used in an attempt to study the ecosystem dynamics and the dominant processes underlying the functioning of the system. The model uses a functional group approach to describe the ecosystem, and its dynamics is simulated by a series of interacting complex physical, chemical and biological processes. Model results bring out the seasonal variation of nutrients, primary producers and secondary production in the water column and are validated with in situ data. The importance of external physical forcing on the pelagic system and its consequent effect in the ecosystem functioning is investigated and discussed. Simulations of nutrients and Chlorophyll-a are in good agreement with the validation data. The low primary production during summer as shown by the chlorophyll-a is investigated in respect to the operating limiting factors. Although the ecological model is forced with a simplistic atmospheric forcing it describes rather well the various ecosystem variables, indicating that it can be usefully applied as a management tool to the particular area providing essential information for the functioning of the ecosystem under investigation.