The effects of episodic rainfall events to the dynamics of coastal marine ecosystems: applications to a semi-enclosed gulf in the Meditteranean Sea

A modelling procedure of hourly time discretisation is developed in order to study the effects of episodic rainfall events to the dynamics of coastal marine environments. This methodology was applied on the gulf of Gera, Island of Lesvos, Greece, a semi-enclosed and shallow ecosystem surrounded by an intensively cultivated watershed. The simulation of biological and chemical processes in the water column was focused on the interactions of inorganic nutrients, primary producers and organic matter. The hydrodynamic behaviour of the area was estimated by the combination of the Princeton Ocean Model and a multiple-box mass balance approach in order to describe the tidal hydraulic regime. The estimation of nutrient fluxes due to non-point sources was based on a modification of the unit-mass response functions. The results have shown that nutrient loading from agricultural runoff could be considerable after episodic rainfall events, resulting in an increase of the nutrient stock from 40% to 60%. The responses of the primary producers are regulated from weather conditions of the following period and the residence time of excessive nutrient loads within the gulf that ranges from a time span of less than 10 days to 1 month period. The good fit between simulated and experimental data supports the view that this integrated modelling approach should be considered as a realistic reproduction of the dynamics of coastal marine ecosystems and be used for testing various scenarios concerning their sustainability.