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Hypoxic Zone in the Gulf of Mexico
Excessive amounts of nitrogen lead to ecosystem takeover by certain species
such as the notorious red and brown tides caused by excessive algal blooms in
coastal areas. The recently reported hypoxic zone at the mouth of the
Mississippi River is an example where excessive surface algal growth leads to
oxygen depletion at lower levels when these organisms die, sink, and decay. The
algal blooms are produced by excess nutrients (nitrogen) from sewage and
fertilizer runoff, perhaps as far away as the US Midwest. Depleted oxygen
supplies at low levels disrupts populations of deep-dwelling fish. This zone
has area of about 18,000 square kilometers and may threaten fisheries in the
area.