Naslov
Eutrophication problems in the semi-enclosed bay of Kaštela (Adriatic Sea)

Autori
Marasović, Ivona

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

Skup
International Conference on Sustainable Development of the Mediterranean and Black Sea environment

Mjesto i datum
Solun, Grčka, 29.05.2003. - 01.06.2003

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
Adriatic Sea; eutrophication

Sažetak
The increase of eutrophication during the last four decades has been noticed in many estuarine and coastal areas, particularly those affected by riverine freshwater or domestic and industrial wastewater. One of these areas is also Kaštela Bay, semi-enclosed coastal bay in the Middle Adriatic, which receives a great amount of untreated wastewater, both domestic and industrial. The narrow coastal strip of the Bay is a highly developed area with various uses (habitable areas, industries, harbor, tourism, etc.). The towns of Split and Trogir, as well as several villages are located there with more than 350.000 inhabitants. The population of this area has increased sevenfold over last 50 years. Intensive urbanization and industrialization have not been followed by development of necessary urban structure and large quantities of urban and industrial wastewater are released untreated into the Bay. The trend of eutrophication of the Kaštela Bay has been paralleled by an increase in urbanization and industrialization of this region. Since the early fifties regular monthly observations of basic hydrographic, chemical and biological parameters have been carried out in the Bay. The measuring of primary production on the monthly bases started in 1962. The first changes in the Bay, such as a gradual increase in primary production and changes in the regular seasonal cycle of phytoplankton fluctuations were observed at the end of seventies. The structure of phytoplankton community also has been changed and dinoflagellate species have been dominant rather than diatoms. After the analysis of the diatom/dinoflagellate relationship to primary production, it was established that the positive peaks of primary production coincided with the negative peaks of diatom/dinoflagellate ratio that is higher presence of dinoflagellates. By the end of summer 1980, the occurrence of &laquo ; red tide&raquo ; in the Bay was observed for the first time. Since then &laquo ; red-tide&raquo ; bloom has been observed regularly every summer, always provoked by the dinoflagellate species Lyngulodinium polyedra Stein. Occasionally, the &laquo ; red tide&raquo ; bloom has caused mortality of shellfish and demersal fish (1980, 1985, 1987, 1989 and 1990). All these changes were accompanied by a steady increase in percent oxygen saturation in the surface layers and reduction in bottom layers. During the usual summer blooms a number of potentially toxic and suspect toxic phytoplankton species, such as Dinophysis fortii, D. acuminata, D. caudata, D. sacculus, D. acuta, Alexandrium minutum, Lyngulodinium polyedra, Prorocentrum micans, P. lima have been observed. The results of a systematic survey of the phytoplankton composition in the Kaštela Bay, available since the early thirties, provide enough evidence to verify an autochthonous origin of most organisms found in the Bay, however their abundance and frequency of occurrence has apparently increased. There was a continuous tendency of higher eutrophication in the Bay present until the mid nineties when significant changes occurred once again. By mid nineties has initiated decrease in the primary production what lasts up to now. The values of the primary production, especially during summer time, are considerably lower than in eighties when they were enormously high. Diatoms became once again dominating group of organisms in the phytoplankton community. Regularly, each summer the Lyngulodinium polyedra has caused high intensity red tide blooms (>107 cells dm3) during eighties, but recently very often is not present in the phytoplankton community in the Bay or it appears in neglecting quantity. The regular seasonal cycle of phytoplankton has been re-established, that is besides spring and autumn maximum appears the summer minimum of fitoplankton. That is to say by middle seventies in the Kaštela Bay disappeared the usual summer minimum, instead beyond the spring and autumn maximum appeared the third maximum, which was more noticeable than spring and autumn one. All these positive changes can be related to the closure of many industrial plants situated on the Bay coast during the last war in Croatia. At the beginning of the nineties many plants have stopped working such as brewery, dairy plant, slaughter house, plastic products plant, etc. Due to the same reasons tourist activities have been suspended and consequently the level of wastewater was lower that in the same period previously to nineties. Since the same changes have been observed in the Adriatic open waters, the question rises spontaneously: is eutrophication in the Kaštela Bay caused exlusively by antrophogenic influence or is it possibly the consequence of both negative antrophogenic impact and global climate changes? That is very difficult to clarify since the period of less intensive wastewater output collided with the period characterized by unusual climate conditions.

Izvorni jezik
Engleski

Znanstvena područja
Biologija

POVEZANOST RADA