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| Titel |
Rogoznica Lake (Croatia), a unique anoxic seawater system on the Adriatic coast under the anthropogenic pressures |
| VerfasserIn |
Irena Ciglenečki, Elvira Bura-Nakić, Marija Marguš, Milan Čanković, Marina Carić, Damir Viličić, Zrinka Ljubešić, Frano Krsinic, Mirna Batistić, Ivica Janeković, Filip Plavčić |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093312
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| Publikation (Nr.) |
 EGU/EGU2014-7925.pdf |
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| Zusammenfassung |
| Rogoznica Lake is a typical example of euxinic saline lake, situated on the eastern Adriatic
coast (43o32’N 15o58’E). It is a karstic depression filled with seawater, with an area of 10276
m2 and a maximum depth of 15m The lake has circular shape and is surrounded with sheer,
karstic cliffs (4-23 m high), which completely protect the lake from the influence of the
wind.
During the year the lake is thermally, densely and chemically stratified into oxic and
anoxic layers. The surface water is well oxygenated, while hypoxia/anoxia occurs in the
bottom layer. The mixolimnion varies seasonally and it is greatly influenced by
meteorological conditions (temperature, wind, rainfall) which also influence the water
layer mixing. Vertical mixing usually occurs during autumn/winter when cold,
oxygen-rich water from the surface sinks downwards. Depending on the intensity of the
mixing process anoxic conditions in the entire water column could appear. At the
boundary oxia-anoxia usually a pinky colored chemocline layer, cca 50 cm thick
develops.
Anoxic deep water is characterized by high concentrations of reduced sulfur compounds
(RSS up to 1mM, mainly in the form of sulfide), and nutrients (NH4+, up to 150 μM; PO43-,
up to 22 μM; SiO44-, up to 400 μM) as well as dissolved organic carbon (DOC up to 6 mg
l-1) indicating the pronounced remineralization of allochthonous organic matter produced in
the surface water The eutrophication of the lake is strongly influenced by nutrient recycling
under anaerobic conditions.
Due to the extreme ecological conditions which prevail in this lake, phyto- and
zooplankton populations are represented by a relatively small number of species, some of
them, however, in the populations denser than those in the surrounding sea. After the period
of total anoxia appearance, the number of species and their abundance are significantly
reduced in comparison with the pre-anoxia values. Diatoms were found to be the
dominant microphytoplankton group while copepods, the heterotrophic zooplankton
organisms, play an important role and control the biochemical processes in the lake,
especially in the post-anoxic period. The calanoid copepod Acartia italica is the only
metazoan plankton species surviving and reaching high abundance in the Rogoznica
Lake.
Results of recent investigations (since 2001 up to now) have showed significant change of
organic matter properties what most probably is a consequence of changes in phytoplankton
abundance and composition in relation with significant change in hydrographic conditions,
i.e. temperature and salinity that highly influence stratification process what we believe is
closely related with global climate changes.
All our data show how particular sequences of meteorological events, some of which
can be regarded as extreme, have affected the internal processes in the Lake. An
integration of all results (since 1994 up to now) reveals an interesting possibility that this
environment may well potentially serve as valuable sentinels of climate change. |
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