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Images: Red Tides and Dead Zones

RIVER PLUMES ON THE GULF COAST—On Nov. 7, 2004, a satellite captured the outflow of river sediments and dissolved nutrients into the Gulf of Mexico, as well as the abundance of algae and phytoplankton in the water. Dark green or black patches near the shore indicate blooms of marine plants. White spots are clouds. Each summer, a stagnant, oxygen-depleted “dead zone” forms in the middle of the Gulf, likely caused by a surplus of nutrients from inland sources. (SeaWiFS Project, NASA Goddard, and ORBIMAGE.)

Overabundance of nutrients can cause certain marine plants to grow like weeds, choking off food sources for fish and shellfish, or literally asphyxiating the creatures from lack of oxygen. ( ©DigitalVision. )

NEXT STOP, COASTAL WATERS—Pesticides and fertilizers sprayed far from the coast still find their way to the ocean, running off farmlands into rivers, streams, and groundwater. Minor changes in agricultural practices could save money for farmers and reduce nutrient pollution in the sea. ( ©DigitalVision.)