Geomorphology modification and its impact to anoxic lagoons

Abstract

Anoxia constitutes an important environmental problem, affecting coastal systems around the world. The physicochemical alterations on the water column of anoxic basins, caused by morphological modifications, were studied. Deepening on the connecting sill between the permanent anoxic Aitoliko lagoon and Messolonghi lagoon was accomplished on May 2006. Seasonal variations of parameters like temperature, salinity and dissolved oxygen along the lagoon's water column were recorded and studied in a net of 14 stations, after sill's dredging. Wind speed and wind direction time series were used to estimate the wind's contribution to the hydrographical changes. The water fluxes between the two environments increased, due to the sill's cross section increase. Salty water inflow into Aitoliko lagoon was recorded during the sampling period and was correlated with monimolimnion oxygenation throughout winter months. The meteorological conditions that prevailed during the sampling period could not create strong water inflows into the Aitoliko lagoon, and consequently it was not the reason for the recorded alterations in the lagoon's water body anoxia. The limited deepening of the sill created a mild increase of water flow into the anoxic lagoon. This inflow of the saltier water resulted in a weak mixing of the water column, introducing oxygen into the bottom water for the first time in 55 years, without destroying the stratification.