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The unique, highly eutrophic, and euxinic (anoxic water with free hydrogen sulphide in the water column) marine lake, Rogoznica Lake (RL) in the central Dalmatia (Middle Adriatic, 43o32’N 15o58’E) is selected as one of the important study site on the Adriatic Coast in the frame of the Croatian Science Foundation project MARRES-1717. This lake is considered as an extreme, naturally eutrophic system which senses all effects of the Adriatic atmospheric and sea conditions. Influence of these conditions due to the lake semi-closed nature might be several times stronger than in rest of the Adriatic. Our results show that RL is an ideal site to study processes that control the biogeochemistry of coastal potentially hypoxic- anoxic environment. Stratification and mixing of the water layers are directly influenced by the meteorological conditions i.e. balance between precipitation and evaporation, heat flux, as well as frequency of extreme weather events which are directly consequence of environmental, climate change. Such events strongly impact biogeochemistry and food-web interactions in the RL. In general, enclosed marine basins are exposed to the increased human activities from the coastal areas. Today eutrophication-related phenomena are closely related to environmental/climate changes. The integration of the long-term (from 1994 up to the present) data on physico-chemical conditions and ecological status, indicate that RL, in addition to its meromictic and holomictic characteristics, can potentially serve as a valuable sentinel of the environmental/climate change. The Lake has proven to be an ideal test-bed to track changes in the environment that reflect in the warming, and accumulation of toxic sulphide and ammonium in the bottom layer of the lake. Those changes are congruent with the reports for the Adriatic, and represent a potential trigger for further, even more severe changes, which can ultimately lead to degradation of this lake ecosystem. On the other side the Lake may be considered as a natural laboratory for the studies of marine redox chemistry since it provides sites with several redox conditions, etc. the redox cline is situated in the sediment and in the water column (euxinic conditions). Comparison between those sites is a unique situation as both sites are situated in the same water body. The small size and physically stable nature of the Lake allows research on small scale spatial and temporal variability as well as longer term processes. In RL’s water column a large range of reduced sulfur species (RSS) concentration (nM – mM) can be found, and a variety of organic and inorganic sulfur species, from organosulfur i.e. mercapto compounds to colloidal sulfur and polysulfides, thus RL environment is an ideal site for testing and development of methodology for RSS characterization and speciation. In the same time, the Lake offers a great possibility for studying microbial diversity that control biogeochemical cycling of sulfur. It is apparently that the Lake's extreme environment severely curtails the ecological and metabolic diversity (food-web interactions) relying on dominant taxa, some of which could be easily lost as a result of environmental perturbations. |
