The nutrient pollution of marine waters through losses from agricultural systems of nitrogen (N) and phosphorus (P), is primarily not a problem of the wide, deep open seas and oceans, but one mainly concerning estuaries, coastal waters and continental shelves (329). Naturally, it needs to be recognized that these coastal areas or coastal waters are part of a larger ecosystem.

In such coastal regions the degree of pollution (eutrophication / hypoxia through N and / or P over-feeding or hyper-feeding) depends on the urbanization at the coastlines, the concentration of industries and traffic there, on the intensity of agriculture at the coasts as well as in the hinterland, and on the number and size of rivers and streams discharging to the estuaries and coastal waters.

As can be concluded from the literature search, eutrophication / hypoxia are a specific problem of more-or-less closed seas like the Baltic Sea, Black Sea and Adriatic Sea, which suffer from an increase in primary production due to over- or hyper-feeding either with nitrogen (N) or with phosphorus (P). Furthermore, various Bays or Bights are polluted.

There is no general picture for future trends, because the trends discussed are all based on the past (60, 166, 294). While in some areas it has been possible to reduce the N and especially the P - loads (272), in other regions there has been an increase in nutrient emissions (173), and no positive reaction to implemented measures to reduce nitrogen (N) and phosphorus (P) loads (154) has been shown yet. However, in this respect it has to be recognized that it may take years or even decades until reductions in nutrient loads, especially reductions in nitrogen (N) loads, may become effective (147, 198).

A carefully considered conclusion may be, that in those areas which are identified as being seriously affected by (N) and phosphorus (P) loads, a reduction of nutrient emissions will be achieved with the different measures adopted (Baltic Sea, North Sea, North Atlantic Ocean, Mediterranean Sea, Adriatic Sea, Gulf of Mexico, some Australian estuaries and Bays), as has been the case with the successful programme for Chesapeake Bay. Stricter adoption of these measures may, however, be necessary in the future.

No estimation of future development can be given for African and South American rivers, estuaries and continental shelves. In the densely populated regions of Asia the problem may become more serious in the future. In these regions agriculture will have to further significantly intensify food production which will have the likely consequence of an increase of nutrient emissions (nitrogen (N) and phosphorus (P) loads) from the intensified agricultural systems to rivers, estuaries, marine waters.

The pathways / fluxes of nitrogen (N) and phosphorus (P) from agriculture are well known (leaching, runoff and erosion losses of nitrogen (N) and phosphorus (P), ammonia volatilisation). Also well known are possibilities to reduce such nutrient emissions effectively. Here, the further intensification of agriculture should and can be linked with the environmental protection experience of agriculture e.g. in Northern America, Europe, Australia, New Zealand.

This transfer of data, knowledge and experience does not seem to be possible in the case of already polluted estuaries, coastal waters, seas and oceans due to the complexity of this problem. Here a lack of standard methods for estimating nutrient inputs to marine waters (153) still exists. Despite the awareness of large-scale long-term changes in river estuarine watersheds, the consequences to estuarine ecosystems are not fully understood (228). The effect of reduced nitrogen (N) and phosphorus (P) loads on primary production / phytoplankton and algal biomass is also not as clear as would be expected (132), because the control on primary production in both coastal, and open ocean, ecosystems is dependent on a complex and poorly understood N and P mobilization and availability (227). Generally, this is also the case regarding the main causes of this problem, as well as the consequences of great seasonal variations in coastal and open waters of seas and oceans.

Therefore, the way for the successful restoration of nutrient polluted maritime ecosystems, and for their future protection, must be to study, explore and investigate each case individually. To be successful, possible solutions should be developed and adopted individually as well.

However, the challenge of all engagement should be sustainable development, i.e. development that meets the need of the present without compromising the ability of future generations to meet their own needs (World Commission on Environment and Development 1987).

FAO Home Page