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The cause of two of the four most serious problems from land-based activities

Marine scientists say sewage and 'nutrification' – the effects of excessive nutrients – reaching marine systems are among the four most serious problems for the oceans associated with land-based activities. In January 2001 the UN experts declared:

At the global level, the most serious problems associated with land-based activities are:

• sewage;

• the physical alteration and destruction of habitat;

• excessive nutrient inputs; and

• sediment mobilization.