Environmental Problems, Their Causes, and Sustainability 1

veloped countries. Two causes of these problems areaccidental or deliberate releases of toxic inorganic andorganic chemicals by industries or mines and malfunctioningsewage treatment plants. A third cause is nonpointrunoff of pesticides and excess plant nutrientsfrom cropland and animal feedlots.What Have Developing Countries Done to ReduceStream Pollution? Little ProgressStream pollution in most developing countries is a seriousand growing problem.Available data indicate that stream pollution from dischargesof untreated sewage and industrial wastes is aserious and growing problem in most developingcountries. According to a 2003 report by the WorldCommission on Water in the 21st Century, half of theworld’s 500 major rivers are heavily polluted, most ofthem running through developing countries. Most ofthese countries cannot afford to build waste treatmentplants and do not have or do not enforce laws for controllingwater pollution.Industrial wastes and sewage pollute more thantwo-thirds of India’s water resources (Case Study, below)and 54 of the 78 streams monitored in China.Only about 10% of the sewage produced in Chinesecities is treated. In Latin America and Africa, moststreams passing through urban or industrial areas sufferfrom severe pollution.Case Study: India’s Ganges River: Religion,Poverty, and HealthReligious beliefs, cultural traditions, poverty, littleeconomic development, and a large populationinteract to cause severe pollution of the Ganges Riverin India.To India’s Hindu people, the Ganges is a holy river.Each day more than 1 million Hindus bathe or take a“holy dip” in the river. Many people also drink its waterand use it to wash their clothes.Bad news. The Ganges is highly polluted. About350 million people—one-third of the country’s population—livein the Ganges River basin. Very little of thesewage produced by these people and by the industriesand 29 large cities in the basin is treated.This situation is complicated by the Hindu beliefin cremating the dead to free the soul and throwing theashes in the holy Ganges to increase the chances of thesoul getting into heaven. Traditionally, wood firesburn most bodies in the open air. This creates air pollutionand helps deplete India’s forests.It also causes water pollution because many peoplecannot afford enough wood for cremation. As a result,many bodies are dumped into the river withoutcremation or are only partially burned. Decompositionof these bodies depletes dissolved oxygen and addsdisease-carrying bacteria and viruses to the water. Thisproblem is expected to get worse because about 19million people are added to India’s population eachyear—about a third of them to the Ganges River basin.Good news. The Indian government has launched aplan to help clean up the river. It involves buildingwaste treatment plants in the basin’s 29 large cities andconstructing 32 electric crematoriums along the banksof the river that can burn bodies more efficiently and at alower cost than wood cremation. The government alsointroduced 25,000 snapping turtles to devour corpses.Bad news. Most of the sewage treatment plants arenot completed or do not work very well and only afew of the crematoriums have been completed. Thereis also concern that many Hindus will not abandon thetraditional ritual of wood cremation or will not be ableto afford any type of cremation.This situation shows how religious and culturalconditions and poverty can affect environmental problemsand solutions to such problems.22-3 POLLUTION OF FRESHWATERLAKESWhy Are Lakes and Reservoirs More Vulnerableto Pollution than Most Streams? Too LittleFlow and MixingDilution of pollutants in lakes is less effective than inmost streams because most lake water is not mixedwell and has little flow.In lakes and reservoirs, dilution of pollutants often isless effective than in streams for two reasons. One isthat lakes and reservoirs often contain stratified layersthat undergo little vertical mixing. The other is thatthey have little flow. The flushing and changing of waterin lakes and large artificial reservoirs can take from1 to 100 years, compared with several days to severalweeks for streams.This means that lakes and reservoirs are more vulnerablethan streams to contamination by runoff ordischarge of plant nutrients, oil, pesticides, and toxicsubstances such as lead, mercury, and selenium. Thesecontaminants can kill bottom life and fish and birdsthat feed on contaminated aquatic organisms. Manytoxic chemicals and acids also enter lakes and reservoirsfrom the atmosphere.As they pass through food webs in lakes, the concentrationsof some chemicals can be biologically magnified.Examples include DDT (Figure 19-4, p. 411),PCBs (Figure 22-6, p. 498), some radioactive isotopes,and some mercury compounds.http://biology.brookscole.com/miller14497