Deoxygenation and stratification dynamics in a coastal marine lake

Abstract

Rogoznica Lake (RL; “Zmajevo oko”) is a shallow marine body of water that exhibits the physical characteristics of lakes (layer overturn and morphology), estuaries (distinct halocline), and seas (tidal regime). This study addresses the physicochemical stratification of the RL and its evolution over 27 years since the beginning of continuous RL research, in the context of regional climate variability. Stratification dynamics were evaluated from several aspects. First, reduced sulphur species accumulation was noted, which was associated with the anoxic water expansion from the bottom of the lake. Second, the connection of the lake with the sea and its attenuation was observed. These results are supported by the negative correlation between annual precipitation and water column salinity, which shows that the role of atmospheric variability in controlling the stability of the lake has increased. A change in the surface layer warming rate was noted, possibly related to unresolved quasi-decadal climate variability. At the same time, the enhancement of the chemocline is in favour of the reported stagnation of the bottom layer. All results suggest that there is a positive feedback mechanism leading to rapid ecosystem degradation.