The impact of Vistula river discharge on spatial and temporal variability of the euphotic zone depth in the Gdansk Bay

Discharge from Vistula river is a major factor which determines the bio-optical properties of waters in the Bay of Gdansk. The limit for vertical light penetration, defined as an euphotic zone depth is one of the primary parameters that control aquatic life and is often used to asses the condition of marine environment.
The variability in the euphotic zone depth in Bay of Gdansk has been observed during the last 15 years during field surveys on over seventy research cruises organized by Institute of Oceanology in Sopot. That long period of observations covers typical seasonal patterns and also episodic events as floods and extensive spring discharges that significantly affect the optical properties of waters in the Gdansk Bay.
An extensive bio-optical data set from field measurements was used to investigate the wide range of variability of the optical properties in the area. Satellite ocean color remote sensing data from SeaWiFS and MODIS scanners have been used to map their spatial variability. The new, site specific algorithm for retrieving the euphotic zone depth has been developed and applied in the study. Seasonal patterns in the variability as well the long term trends were presented and discussed.