Modelling the annual cycles of nutrients and phytoplankton in a Mediterranean lagoon (Gialova, Greece) G. Petihakis a , G. Triantafyllou a, *, D. Koutsoubas a , I. Allen b , C. Dounas a Institute of Marine Biology of Crete, PO Box 2214, 71003 Iraklio, Crete, Greece Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PL1 3DH, UK Abstract Nutrient dynamics for phosphate, nitrate, ammonium and silicate have been simulated with the European Regional Seas Ecosystem Model in a Mediterranean lagoon. This generic model designed for the open sea can be usefully applied also to coastal lagoon ecosystems with minimum modi®cations. The annual cycles of the nutrients phosphate and silicate compare quite well with the observed ranges of variability. This does not hold for ammonium and nitrate where the increased concentrations could be attributed to external inputs from the land. Nutrient budgets calculated from the model results indicate some competition between phytoplankton and bacteria for nutrients, a common characteristic of lagoons. To further develop the model, an adaptation of the phytoplankton submodel to represent benthic pri- mary production, as well as the modi®cation of the benthic nutrient model to cope with anoxic events, are suggested. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Numerical models; Nutrients; Primary production; Lagoons 1. Introduction Coastal lagoons are a very common feature of coastal environments occupying 13% of the world coastline (Barnes, 1980). They are autonomous dynamic systems with a high productivity potential and a number of common geomorphological and ecological features (Nixon, 1982). Characteristic features of these systems are fre- quent ¯uctuations in the environmental parameters (temperature and salinity) causing severe changes in the abundance and distribution of organisms (Lasserre, 1981). 0141-1136/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0141-1136(99)00031-8 Marine Environmental Research 48 (1999) 37±58 * Corresponding author. E-mail address: gt@imbc.gr (G. Triantafyllou)