Michael Karydis
Department of Marine Sciences
University of the Aegean
81100 Mytilini
Greece

Extended abstract

General

Eutrophication may be defined as the nutrient enrichment of the marine environment with nutrients primarily nitrogen and phosphorus that stimulate primary production and algal growth (Vollenweider, 1992). Although nitrogen and phosphorus are not themselves contaminants, they cause adverse effects in the marine ecosystem and the water quality. The excessive organic matter promotes growth of heterotrophic bacteria, sometimes leading to hypoxic or even anoxic conditions in bottom water and sediments, resulting in serious impacts on benthic or demersal food webs. In addition, eutrophic waters can lead to fish kills, reduction of fertility, fouling of fish nets, high turbidity of the seawater and increase in the number of pathogen microorganisms (UNEP, 1996). The development of algal blooms of toxic flagellates known as ‘red tides’ is widespread in the Mediterranean either on a seasonal basis or as site-specific. Dinoflagellate toxins may severely affect fish which ingest them, as well as human beings who may eat infected seafood, thus causing disorders and even diarrhoeic or paralytic shellfish poisoning.

Eutrophication scaling in the Mediterranean

Seawaters depending on nutrient loading and phytoplankton growth are classified according to their level of eutrophication. Low nutrient/ phytoplankton levels characterize oligotrophic areas, water enriched in nutrients is characterized as mesotrophic, whereas water rich in nutrients and algal biomass is characterized as eutrophic. The Mediterranean is one of the most oligotrophic seas in the world and most of its biological productivity takes place in the euphotic zone (UNEP, 1989). Although the development of nutrient / phytoplankton concentration scales seems to be a relatively simple approach, there are numerous difficulties mainly due to seasonal fluctuations. The development of nutrient / phytoplankton concentration scales has been a difficult task for marine scientists because of the seasonal fluctuations of nutrient and phytoplankton concentrations, phytoplankton patchiness and small-scale eutrophication phenomena. However, there are some attempts reported in the literature, mostly based on probabilistic methods. A preliminary classification of the trophic state of the sea was carried out within the framework of the OECD eutrophication programme. Total phosphorus, total nitrogen, chla, chla peak and secchi depths were used as the variables expressing eutrophication. Data sets were used from the Adriatic Sea and the geometric mean was calculated. Critical values of phosphate, nitrate, nitrite and ammonia were proposed by Ignatiades et al. (1992). The work was based on probabilistic procedures. Similar work used phosphate, nitrate, ammonia and phytoplankton cell number values to propose a classification scheme for coastal waters, using the following categories: oligotrophic, lower mesotrophic, upper mesotrophic and eutrophic water types (Kitsiou & Karydis 1998). The procedure was based on spatial analysis. Critical values of ecological indices for characterizing eutrophication and oligotrophy have also been published (Tsirtsis & Karydis 1999, Kitsiou & Karydis 2000).

Pollution sources in the Eastern Mediterranean

The Mediterranean coastal zone is important for human activities including habitation, industry, agriculture, fisheries, military facilities and tourist resorts. It is obvious that there is some conflict over the use of natural resources. Most of these activities contribute to coastal eutrophication in the Eastern Mediterranean. Urbanization and tourism result in sewage pollution along the coastal zone. The pressure from tourism activities is more serious because of the high number of tourists in the coastal zone and the highly accentuated seasonality.
Large-scale agriculture in the Eastern Mediterranean basin is limited by the topography in the Nile area. Northern countries such as Italy and Greece specialize in monocultures to achieve good yields. In the south and east of the Mediterranean, demographic pressure increases the cultivated surfaces at the expense of forests and grazing land. The fertilizer consumption (in 103 kg/ha/yr) for Albania is 143, Cyprus 425, Egypt 382, Greece 171, Israel 244, Italy 158, Lebanon 84, Libya 38, Malta 48, Syria 50, Turkey 64 and Ex-Yugoslavia 115 (UNEP, 1996).

Eutrophication assessment in Eastern Mediterranean

Eutrophication also occurs as point pollution events. Coastal sites and lagoon areas showing eutrophic trends in Eastern Mediterranean are given in Figure 1. There is a limited number of eutrophic sites along the eastern and southern part of the Mediterranean. However, eutrophication phenomena in these areas should not be underestimated. The limited number of sites is due to poorer monitoring of these areas and unavailability of nutrient data. In the Adriatic Sea that has been studied thoroughly over three decades it has been estimated that 250000 tones/year of nitrogen and 82000 tones/year of phosphorus are deposited in the Adriatic through riverine inputs. Good data records also exist for the Aegean as well as for the coastal waters of Cyprus. There is also a good record of algal blooms and related effects such as hypoxia, dystrophy, toxins, water discoloration and reduced transparency (UNEP, 1999).
Conversely, the open seawaters of the Mediterranean appear to be oligotrophic or even ultratrophic, except in areas where upwelling brings nutrient-rich waters to the surface. Eutrophication in the eastern Mediterranean is limited to the Adriatic and some urban / industrial areas of the coastal zone.

Figure 1 Areas in Eastern Mediterranean where eutrophication phenomena have been reported (Source UNEP/FAO/WHO, 1996, modified)

References

Ignatiades, L., Karydis, M. and Vounatsou, P., 1992 : A possible method for evaluating oligotrophy and eutrophication based on nutrient concentrations scales. Marine Pollution Bulletin, 24: 238-243.

Kitsiou, D. and Karydis, M., 1998: Development of categorical mapping for quantitative assessment of eutrophication. Journal of Coastal Conservation 4: 35-44.

Kitsiou, D. and Karydis, M.,, 2000: Categorical mapping of marine eutrophication based on ecological indices. The Science of the Total Environment 255: 113-127

Tsirtsis, G. and Karydis, M. 1999: Application of discriminant analysis for water quality assessment in the Aegean.

UNEP, 1989: State of the Mediterranean Marine Environment. MAP Technical Series No. 28, UNEP, Athens

UNEP/FAO/WHO, 1996: Assessment of the State of Eutrophication in the Mediterranean Sea. MAP Technical Series No. 106, UNEP, Athens

UNEP, 1996: The State of the Marine and Coastal Environment in the Mediterranean Region. MAP Technical Series No. 100, UNEP, Athens

UNEP, 1999: State and pressures of the marine and coastal Mediterranean environment. European Environment Agency, Environmental Assessment Series No.5, Copenhagen

Vollenweider, R.A., 1992: Coastal Marine Eutrophication. In: Vollenweider, R.A., Marchetti, R., Viviani, R. (ed.). Marine Coastal Eutrophication. London:Elsevier, pp1-20