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Much of the richest soils vital to meet food production needs worldwide are contained in low-lying coastal zones and fertile river valleys. 60 percent of the world's people live on such lands. In fact 25 per cent of biological production comes from these areas.

Two billion people live in low lying coastal areas. If present urban expansionary trends continue, this number will increase to 4.2 billion, or 70 per cent of total world population by 2005 AD, with the loss of precious food producing soils.

The interaction between land and sea through discharges from rivers of about 35,000 cubic kilometres of fresh water and 15 billion tonnes of sediment into the world's oceans each year, involves the transfer of huge quantities of nutrients and trace elements to the world's oceans, seas and lakes. Dams and modifications to river channels now regulate river flows, further affecting natural cycles.

The loss of nutrients and trace elements that are vital for human food needs is reducing Earth's capacity to produce food and is a permanent loss of natural resources which is limiting overall biomass production.

The deposits of these nutrients and the eroded soil from upriver catchments are polluting traditional fishing grounds and generally upsetting the marine ecology.

The land-sea interface is particularly sensitive to climate change and sea-level variation. The land is under threat from rising sea levels as a result of rising temperatures caused by climate disturbance due to atmospheric pollution. Already, many coastal regions are being affected by rises in sea levels, making them increasingly subject to storms and floods. Chemical pollution from major industries adds to the problems.

These major changes to the natural process of the ecosphere may prove crucial in determining climate change. They are certainly crucial in protecting vital natural resources necessary for maintaining world food supplies.

And we should not ignore the fact that coastal wetlands are feeding and nesting grounds for many species of birds and other wildlife and the spawning grounds for marine life.

Internationally, two action streams are urgently needed. One is to direct further urban and industrial development to land of low productive value. The other is to reverse the negative flow of minerals and nutrients.

Research has shown that recycling nutrients is possible in low-lying coastal zones by growing suitable plants that draw off substances from the sea[Ambio, Vol. 22, No. 1, February 1993].

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