Environmental Problems, Their Causes, and Sustainability 1

Types oforganismsDissolvedoxygen(ppm)Normal clean water organisms(Trout, perch, bass,mayfly, stonefly)Trash fish(carp, gar,leeches)Fish absent,fungi, sludgeworms,bacteria(anaerobic)Trash fish(carp, gar,leeches)Normal clean water organisms(Trout, perch, bass,mayfly, stonefly)8 ppm 8 ppmBiologicaloxygendemandDecomposition Septic Zone RecoveryZoneZoneClean Zone Clean ZoneFigure 22-5 Natural capital: dilution and decay of degradable, oxygen-demanding wastes and heat in astream, showing the oxygen sag curve (blue) and the curve of oxygen demand (red). Depending on flow ratesand the amount of pollutants, streams recover from oxygen-demanding wastes and heat if they are givenenough time and are not overloaded.The depth and width of the oxygen sag curve andthus the time and distance needed for a stream to recoverdepend on several factors. They include the volumeof incoming degradable wastes and the stream’svolume, flow rate, temperature, and pH level. Similaroxygen sag curves can be plotted when heated waterfrom industrial and power plants is discharged intostreams.What Have Developed Countries Doneto Reduce Stream Pollution? Good andBad NewsMost developed countries have sharply reducedpoint-source pollution, but toxic chemicals andpollution from nonpoint sources are still problems.Water pollution control laws enacted in the 1970s havegreatly increased the number and quality of wastewatertreatment plants in the United States and mostother developed countries. Such laws also require industriesto reduce or eliminate point-source dischargesinto surface waters.These efforts have enabled the United States tohold the line against increased pollution by diseasecausingagents and oxygen-demanding wastes in mostof its streams. This is an impressive accomplishmentgiven the rise in the country’s economic activity, resourceconsumption, and population since passage ofthese laws.One success story is the cleanup of Ohio’s CuyahogaRiver. It was so polluted that in 1959 and again in1969 it caught fire and burned for several days as itflowed through Cleveland. The highly publicized imageof this burning river prompted elected officials toenact laws limiting the discharge of industrial wastesinto the river and sewage systems and provide funds toupgrade sewage treatment facilities. Today the river iscleaner and is widely used by boaters and anglers. Thisaccomplishment illustrates the power of bottom-uppressure by citizens to spur elected officials to change aseverely polluted river into an economically and ecologicallyvaluable public resource. Individuals matter!Another spectacular cleanup occurred in GreatBritain. In the 1950s, the Thames River was little morethan a flowing anaerobic sewer. Now, after more than45 years of effort and hundreds of millions of dollarsspent by British taxpayers and private industry, theThames has made a remarkable recovery. Commercialfishing is thriving and the number of fish species hasincreased 20-fold since 1960. In addition, many speciesof waterfowl and wading birds have returned to theirformer feeding grounds.There is also some bad news. Large fish kills anddrinking water contamination still occur in parts of de-496 CHAPTER 22 Water Pollution