engleski

Is a marine lake at the Adriatic coast the natural model of progressive water column anoxia?

Nowadays, the anthropogenic influence is observed even in large water masses, yet minor, fragile ecosystems are particularly prone to environmental change. One such biome is the marine lake at the eastern Adriatic coast, near the settlement of Rogoznica (Croatia). The lake is highly eutrophic and has a small average depth and area ; it is surrounded by steep karstic cliffs, while the weak connection to the adjacent Adriatic Sea is maintained through the pores in the karst. Meromictic conditions prevail in the lake, with deeper parts being permanently euxinic. However, in certain physicochemical situations, the stratification disrupts abruptly, and a sudden mixing of the layers leaves the whole vertical water column deoxygenized. Since the 1990s, anoxic water volume has increased, along with the frequency of the sudden layers overturn, with two out of five anoxic holomixis ever recorded in the lake taking place in 2020 and 2021. Recurrent mixing has caused a reduction in both the diversity and number of the organisms inhabiting the lake, which indicates that this ecosystem is slowly dying off. Alarmingly, the lake's stratified conditions resemble ones found in some shallow bays, estuaries, and coastal seas around the world, with the Black Sea as a prominent example. The question that naturally imposes is whether this lake represents an amplified model of what could happen to other similar ecosystems in a changing environment. With the scope of better understanding the preconditioning of the anoxic holomixis, an analysis of the physicochemical parameters has been conducted, implying that the sea-lake water exchange has slowed down in the last 20 years. Moreover, additional study of the available climatological and meteorological data could help predict future holomixis events in the Rogoznica Lake, and possible atmospheric effects on kindred marine environments. Financial support of MARRES project IP-2018-01- 1717 is highly acknowledged.

Rogoznica Lake ; anoxia ; holomixis ; marine lake

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