|CHAPTER 06: THE SEAS - INTRODUCTION|
Europe's seas, as part of the world's oceans, play a key role in maintaining the natural balance of the Earth's biosphere. Covering over two thirds of the Earth's surface, the oceans contain about 97 per cent of the world's water. Interaction between the atmosphere and the oceans and seas has a large influence on climate and weather patterns. Furthermore, plant life in the oceans is an important part of the 'lungs' of the planet, and photosynthesis in the seas and oceans is responsible for the removal of a large amount of carbon dioxide from the atmosphere.
The sea regions covered in this report are: the Mediterranean Sea, Black Sea and Sea of Azov, Caspian Sea, White Sea, Barents Sea, Norwegian Sea, Baltic Sea, North Sea and North Atlantic Ocean. Map 6.1 shows Europe's seas with the main subsidiary seas and bays, and their respective catchment and drainage areas.
Of the countries included in this report all except Austria, Belarus, the Czech Republic, Hungary, Luxembourg, Moldova, the Slovak Republic and Switzerland share coastlines of at least one of these European sea regions. Countries such as Germany, France, the UK, Denmark and Norway have coastlines with at least two major seas while the Russian Federation shares the shores of five European seas.
How human activities affect a given sea area depends very much on the sea's ability to dilute, disperse and assimilate pollutants or other influences. The characteristics which determine this include the circulation of the water, the strength and movement of the currents, the 'flushing' or retention time of waterbodies and the geological diversity of the sea floor. A comparison of some of these characteristics and physical features is shown in Figures 6.1a to 6.1e.
The open oceans, such as the North Atlantic Ocean, due to their vast areas, great depth and efficient water circulation, are still relatively unaffected by human activities compared with coastal areas and enclosed or semi-enclosed seas. The smaller, shallower seas can be classified into those which are nearly completely enclosed by landmasses and those which have a large water exchange with the oceans. The state of the seas which have only limited exchange of water with adjacent oceans is strongly influenced by their water circulation, which reflects the local dominant wind patterns (eg, the Black Sea).
The general nature of the enclosed and semi-enclosed seas is essentially dependent on whether or not the freshwater lost through evaporation is more or less than the amount of freshwater input from precipitation and direct runoff from land. In the case where evaporation is higher than the freshwater input, the surface waters become denser and sink, resulting in considerable vertical mixing of the waters. The oxygen acquired from the atmosphere thus becomes available in deeper waters to foster life. An example of this type of sea is the Mediterranean. In the reverse situation where the freshwater inflow exceeds evaporation the lighter freshwater remains on the surface. When such a sea is also isolated from the ocean, for example by a sill, oxygen becomes depleted and even absent in the deeper water. Often oxygen cannot be replenished and the variety of life-forms becomes much reduced. This is the case for the Black Sea and to some extent the Caspian Sea and the Baltic Sea.
In all seas, estuaries exist where freshwater runoff and sea water mix. They are smaller and shallower than seas, and are more influenced by the neighbouring landmass. Areas of exceptionally rich biological production, they are especially sensitive to the activities of local human populations such as excavation, construction and the discharge of domestic, industrial and agricultural pollutants.
Another important physical feature is the retention or turnover time within the seas. This is more relevant to the enclosed and semi-enclosed seas (eg, the Mediterranean and the Baltic), rather than the more open 'oceanic' seas, for example, the Barents and Norwegian seas and the North Atlantic Ocean. Retention time has a direct influence on how contaminants are retained or accumulated in the marine ecosystem. Values range from 0.1 to 3.9 years in the North Sea to 140 years in the Black Sea (Figure 6.1c). The Caspian Sea is completely land-locked and would largely retain non-degradable contaminants.
The environmental quality and status of a sea is also influenced by the amount or load of contaminants entering the sea and their degradability, persistence and toxicity to aquatic organisms. Total loads entering a sea are not only a function of the population size and industrialisation within its catchment but also on the level of treatment or control, of contaminants in discharges. The type of human activity for example, agricultural or industrial within the catchment is also important in determining the type as well as the quantity of load. The Black Sea and the Sea of Azov have not only the largest catchment of Europe's seas but also the largest population within the catchment (Figures 6.1d and 6.1e): contaminant loads would therefore be potentially higher than in other seas. Europe's northern seas, the White, Barents and Norwegian seas, have by far the smallest populations living in their catchments, relatively small catchment areas, and, in the case of the latter two, relatively large surface areas: these features contribute to the relatively uncontaminated nature of these seas.
An attempt to compare loads of contaminants entering each sea has been made in this report: this should be considered as only approximate as there are likely to be variations in data collection methodology, and for some seas data were not available for all of the different sources or do not exist at all. It should also be noted that the data do not necessarily relate to the same year for all seas; in all cases the most recent available data were used. Figure 6.2 compares the riverine loads of selected contaminants into Europe's seas this source has the most complete dataset. Where riverine data were not available, land-based (riverine and direct discharges) load data have been used. It should also be noted that for some seas, and for the various contaminants, riverine and land-based sources may not necessarily be the most important. For most seas, it has not been possible to differentiate between the contaminant load associated with particulate material and that in the dissolved phase, or to take account of non-conservative estuarine processes that may add to or decrease loads entering the sea. Total gross loads have therefore generally been used. An example of how allowance for contaminant form and estuarine processes may affect total or gross loads entering seas is given for the Mediterranean in terms of mercury, lead and zinc (Figures 6.2b, 6.2d and 6.2e, respectively).
Within Europe there are examples of regional conventions which deal with pollution at a regional or individual sea basis. These will be treated in the sections on individual seas. In addition, there are two global conventions that address marine pollution (Nauke and Holland, 1992). The two conventions are the London Dumping Convention (now the London Convention) and the MARPOL Convention: the former deals with direct disposal of waste into the sea and the latter with ship-borne operations. Both are administered by the International Maritime Organisation. Compared with the other sources of pollution (such as land-based and the atmosphere) these two are generally relatively small. The London Dumping Convention came into force in 1975; enforcement is undertaken through national legislation by the contracting parties. Sixty-seven countries have signed and ratified the convention. MARPOL is now known as the International Convention for the Prevention of Pollution from Ships 1973, as modified by the protocol of 1978 (MARPOL 73/78). The regulations contained in Annexes I (oil) and II (bulk liquid chemicals) are mandatory and must be applied by all parties, while those contained in Annexes III (packaged goods), IV (sewage) and V (garbage) are optional. By June 1992, 72 states, representing 90 per cent of total ship tonnage, had accepted Annexes I and II of the Convention.
When reading the text on the individual seas it will become apparent that there are problems which are recurrent or common to many of the seas in Europe. These problems, briefly outlined here, not only arise from the direct or indirect consequence of human activities but may also be compounded by the natural variability and changes within the marine environment itself. Most of the problems are associated with, or manifest themselves more noticeably within, the coastal zone of each sea (which is closest to humankind's direct influence). The degradation of the coastal zone has, therefore, been identified as a prominent environmental problem of concern to Europe to be treated in more detail in Chapter 35.