Naslov
Rogozničko jezero, jedinstveni krški fenomen na jadranskoj obali: Zaštita i upravljanje priobaljem
(Rogoznica Lake as a unique karstic phenomenon of Adriatic coast: Protection and Coastal management)

Autori
Ciglenečki, Irena ; Ćosović, Božena

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, neobjavljeni rad, stručni

Skup
Training course on Integrated Coastal Zone Management

Mjesto i datum
Split, Hrvatska, 25.11.2002. - 29.11.2002

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
Rogoznica Lake; anthropogenic influence; protection; coastal zone management

Sažetak
Rogoznica Lake is a small (15 m deep), naturally intensely eutrophicated and intermittently anoxic sea-lake situated on the eastern coast of the Adriatic Sea. Anoxic conditions appear in the lake mostly in summer months as the result of increased stratification of the water column in spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline and benthic decay of organic detritus accumulated from plankton blooms which occurred during the previous spring and summer. Owing to mentioned characteristics the lake is unique and a very interesting model system in the Adriatic Sea to study biogeochemical and natural eutrophication processes. Eutrophication in the lake is strongly influenced by nutrient recycling under anaerobic conditions. Since 1994 seasonal variations of temperature, salinity and oxygen, as well as vertical distribution of nutrients, dissolved organic matter, surface active substances, phyto- and zoo-plankton and reduced sulfur compounds have been investigated in the Rogoznica Lake. The stratification and mixing of lake waters are greatly affected by rainfall. During the termohaline stratification the surface water is well-oxygenated (oxygen saturation up to 300%), while hypoxia/anoxia occurring in the bottom layer. Anoxic deep water (below 10 m) is characterised by high concentrations of sulfur compounds and nutrients indicating the pronounced remineralization of organic matter in this water layer. In September 1997 total anoxia occurred in the Rogoznica Lake with the presence of hydrogen sulfide in the whole water column, succeeded by massive death of planktonic and benthic organisms. Due to the decomposition of dead organisms, concentrations of nutritous salts tremendously increased along the entire water column and high concentrations were maintained in the lake during several months after disastrous anoxia, which points out to a very complex and slow lake regeneration processes. Due to extreme ecological conditions which prevail in this lake phyto- and zoo-plankton populations are represented by a small number of species, but some in denser population than in the surrounding sea. After the period of total anoxia the number of species and their abundance were significantly reduced in comparison with the pre-anoxia values. Diatoms were found to be the dominant microphytoplankton group, while copepods, the heterotrophic zoo-plankton organisms, play an important role and control the biochemical processes in the lake, especially in the post-anoxic period. The turnover of the Lake water are probably affected by the recorded hyperproduction of dense phyto- and zoo-plankton populations as well as the high activity of sulfur bacteria. These populations could have consumed the dissolved oxygen in the water and therefore caused the occurance of the anoxic conditions throughout the whole lake of Rogoznica. On the other side it could be not ruled out the anthropogenic influences on the events in the Rogoznica Lake. Namely during the spring and summer months in 1997 series of construction works in the framework of nautical centre building which occurred close to the Lake undergone their maximum. Mine and deep drilling in karstic rocks could caused the vertical vibration of water column and led to the overturn of water layers. Concluding, due to special beauty and natural singularity Rogoznica Lake represents a unique karstic phenomenon of Croatian Adriatic coast. Due to its natural and scientific significance (it is natural bioreactor with numerous and intensive biogeochemical processes sensitive on the external influences) the Lake deserves to be put in one of the natural protection categories.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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