Hydrology and Nutrient Enrichment at Two Coastal Lagoon Systems in Northern Greece

Abstract

The lagoons of N.E. Greece, located on the western side of Nestos River, and of N.W. Greece, located at the lower reaches of Kalamas River, are among the most important shallow, semi-enclosed ecosystems in Northern Greece. The temporal variability of nutrients at both lagoonal systems shows the strong influence of fresh water discharge on water quality. Nutrient enrichment factors showed that nitrites and ammonium were six times higher at the lagoons of N.W. Greece than those observed at N.E. Greece, while phosphates were forty times higher at Nestos River lagoons. The flushing half-life was calculated based on a combination of hydrological and tidal processes, for each lagoon of these two systems, allowing for the assessment of water quality changes. Proper management measures for both systems should focus on the control of fresh water quality entering the lagoons, the reduction of phosphoric fertilizers used by agriculture and the better oxygenation of the water column. One way to eliminate massive fish deaths during the winter in N.E. Greece is also the transfer of fresh, warm groundwater, while bathymetric modifications and channel widening are needed at the lagoons of N.W. Greece.