Environmental Problems, Their Causes, and Sustainability 1

22-5 OCEAN POLLUTIONHow Much Pollution Can the Oceans Tolerate?We Do Not KnowOceans can disperse and break down large quantitiesof degradable pollutants if they are not overloaded.The oceans can dilute, disperse, and degrade largeamounts of raw sewage, sewage sludge, oil, and sometypes of degradable industrial waste, especially indeep-water areas. Also, some forms of marine life havebeen affected less by some pollutants than expected.This has led some scientists to suggest it is safer todump sewage sludge and most other harmful wastesinto the deep ocean than to bury them on land or burnthem in incinerators. Other scientists disagree, pointingout we know less about the deep ocean than we doabout the moon. They add that dumping harmfulwastes in the ocean would delay urgently needed pollutionprevention and promote further degradation ofthis vital part of the earth’s life-support system.How Do Pollutants Affect Coastal Areas?More People and Development Equal MorePollutionPollution of coastal waters near heavily populatedareas is a serious problem.Coastal areas—especially wetlands and estuaries, coralreefs, and mangrove swamps—bear the brunt of ourenormous inputs of pollutants and wastes into theocean (Figure 22-11). This is not surprising becauseabout 40% of the world’s population lives on or withinIndustryNitrogen oxides from autosand smokestacks, toxicchemicals, and heavymetals in effluents flowinto bays and estuaries.ClosedbeachCitiesToxic metals andoil from streets andparking lots pollutewaters; sewageadds nitrogen andphosphorus.Urban sprawlBacteria andviruses from sewersand septic tankscontaminate shellfishbeds and closebeaches; runoffof fertilizer fromlawns adds nitrogenand phosphorus.Closedshellfish bedsOxygen-depletedzoneContruction sitesSediments are washed into waterways,choking fish and plants, cloudingwaters, and blocking sunlight.FarmsRunoff of pesticides, manure, andfertilizers adds toxins and excessnitrogen and phosphorus.Red tidesExcess nitrogen causes explosivegrowth of toxic microscopic algae,poisoning fish and marine mammals.Toxic sedimentsChemicals and toxic metalscontaminate shellfish beds,kill spawning fish, andaccumulate in the tissuesof bottom feeders.Oxygen-depleted zoneSedimentation and algaeovergrowth reduce sunlight,kill beneficial sea grasses,use up oxygen, and degrade habitat.Healthy zoneClear, oxygen-rich waterspromote growth of planktonand sea grasses, and support fish.Figure 22-11 Natural capital degradation: how residential areas, factories, and farms contribute to thepollution of coastal waters and bays. According to the UN Environment Programme, coastal water pollutioncosts the world $16 billion annually—$731,000 a minute—due to ill health and premature death.504 CHAPTER 22 Water Pollution