Nutrients and phytoplankton biomass in the Ombla River estuary, Southern Adriatic

The Ombla River estuary, only 4 km long, is a region influenced by karstic fresh and marine waters. The sea penetrates deeply into the estuary. Maximal nutrient values were found in the surface layer. The nutrient concentrations in the surface layer oscillated far more than in the bottom layer. The concentration of all nutrients decreased from the upper to the lower reaches of the estuary. The Redfield ratio values were 27-38, from April to August. The ratio values were far greater, 78-103, in the remaining months. Two peaks of phytoplankton, both microphytoplankton (MICRO) and nanophytoplankton (NANO), occurred in May and August. The phytoplankton population density, as with nutrients, decreased towards the lower reaches of the estuary.