Eutrophication of Coastal Waters – Gulf of Trieste

Abstract

In this paper, ‘eutrophication' is defined as ‘undesirable degradation of the aquatic environment (caused by an excessive algal biomass) resulting in a deterioration of water quality which interferes with most of the beneficial uses of water; it is causing, in many cases, significant economic losses' (OECD, 1982). In other words, eutrophication is seen as a form of pollution. To achieve an evaluation of the relevance of this problem in the Gulf of Trieste, the main results of extensive chemical and biological monitoring carried out both by the Yugoslav and Italian sides in the last decade are briefly reviewed. The large amount of data on dissolved oxygen, transparency, chlorophyll, and on the obnoxious occurrence of coloured waters, indicate that the great majority of the Gulf waters are not affected by eutrophication (according the above definition); rather, the major part of the eastern (Yugoslav) waters appears to be essentially oligotrophic. Strong eutrophication, however, sometimes affects the inner part of semi-enclosed bays where large quantities of organic matter and nutrients are discharged. Such areas, such as the inner part of the Bay of Muggia, are severely polluted in many respects. A better form of treatment and disposal of sewage from Trieste (which is severely polluting the Bay of Muggia) would be advisable, and would also achieve amelioration of the trophic levels in areas laying outside the bay. The examination of numerous data concerning nutrient concentrations leads to some conclusions of significance, essentially consistent with the conclusions given above. The ƩNinorg./PO43− atomic ratio often exceeds 20. More difficult, and somewhat debatable, appears to be the assessment of the more subtle impacts of nutrients on the marine environment, given the uncertainties about the ‘natural' and/or ‘optimal' conditions to be assumed, the large variations of the ‘natural' conditions themselves, and the reaction of the environment to superimposed natural and anthropogenic impacts. This paper can be viewed as a preliminary to a more extensive review concerning, in addition, the more subtle effects induced by ‘non optimal' trophic conditions.