22/Pollution in the Ocean - Washingtonville · PDF fileWhen you have ﬁnished this chapter, ... pollution can produce harmful effects in living things, ... Pollution in the Ocean

When you have finished this chapter, you should be able to:

DISCUSS the impact of sewage pollution on aquatic ecosystems.

DESCRIBE the effects of toxic chemicals on marine organisms.

EXPLAIN the importance of clean waters to aquatic life-forms.

DISCUSS the problem of solid wastes in marine ecosystems.

For years the ocean has been used as a dumping ground for thedisposal of human wastes and garbage. We now find wastes pro-duced by industrial societies washing up on remote tropical islands.Toxic chemicals have been found in the bodies of ocean animals.Many people are now aware of the hazards of polluting the waterand are becoming involved in both local and large-scale efforts toclean up the marine environment.

This change in attitude and behavior occurred when peoplerealized that marine pollution can produce harmful effects in livingthings, including humans. Although the ocean is vast and seemscapable of absorbing great quantities of wastes, it is not unaffectedby the activities of humans. Fortunately, the ocean is important topeople—as a source of food, as a place for recreation, and for itsnatural beauty. How polluted is the ocean? In this chapter, you willlearn about different kinds of pollution in the marine environment,and about attempts to protect the ocean and improve its waterquality.

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22.1Sewage Pollution

22.2Toxic Chemicals

22.3Clean, Clear Waters

22.4Litter in the Water

Pollution in the Ocean

MARINE ECOLOGY

2222

22.1 SEWAGE POLLUTION

Tens of thousands of years ago, people lived in small groups thattraveled from one site to another as they hunted and gathered food.Garbage and wastes rarely accumulated, since populations weresmall and people never settled in one place for too long (and theirwastes were from natural materials that degraded easily). Peoplewere able to move away from the messes they made. As they settledin more permanent communities, and populations grew, wastesbegan to accumulate.

Pollution of Water

Most human populations lived along rivers and coasts. In theseareas, there is access to water, food resources, and trade. Bodies ofwater have always been convenient places for people to dispose ofwastes. In pre-industrial times, the water could dilute and washaway most of the wastes that were dumped into it. However, humanpopulations along the world’s coasts have increased dramatically.In the United States, about three-fourths of the population liveswithin 80 km of a coast. As a result, there is a greater concentrationof wastes along the coasts, and these wastes may be dumped intothe sea. The quantity and quality of these wastes can, in someinstances, exceed the ocean’s capacity to store or dispose of themwithout being damaged.

The natural by-products of living systems are wastes. Marineorganisms certainly produce their share of natural wastes; and,as you learned in Chapter 21, ecosystems handle these wastesthrough the processes of decomposition and nutrient recycling.However, when people introduce substances into the environ-ment that harm living things and damage water quality, it resultsin the condition known as pollution. The substances that have aharmful effect are called pollutants. Pollution not only threat-ens the well-being of other living things but also endangershuman health, since we depend on Earth’s natural resources forour survival.

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Sewage and Sewage Treatment

Unlike the pristine tropical beach shown in Figure 22-1, many U.S.beaches are closed periodically because they are contaminated, orpolluted, with sewage. Sewage is made up of the human intestinal(fecal) wastes that are discharged into our waterways. Water that iscontaminated with sewage poses a serious public health problem.Such water may contain a variety of harmful microorganisms, orpathogens, that can cause life-threatening diseases such as typhoidfever, cholera, dysentery, and hepatitis.

How do we know if the water is contaminated with sewage?Public health scientists routinely test water samples for fecal coli-form bacteria. Fecal coliform bacteria, which are present in the largeintestine of humans and normally do not cause disease, are used asindicators of sewage pollution. The presence of coliform bacteria ina water sample means that the water has been contaminated bysewage. If coliform bacteria are present, there is a good chance thatdisease-causing bacteria are also present. Usually, water from a har-bor area has the highest bacterial count because raw sewage isdumped into many harbors in industrialized or urban areas. Muchless raw sewage is dumped into the waters near public beaches andfishing areas. (Raw sewage is waste material that has not beentreated; that is, the pollutants have not been removed from it.)

Pollution in the Ocean 543

Figure 22-1 An unpol-luted tropical beach.

Escherichia coli (E. coli) is one species of coliform bacteria foundin water samples contaminated with sewage. This rod-shaped uni-cellular organism, only 1 micron (µm) in length, is too small to beidentified in a water sample. In order to be seen, the E. coli bacteriahave to be grown under suitable conditions until they produceenough cells to form masses called colonies. A special procedure isused to culture the coliform bacteria for easy identification. Bacter-ial growth begins with the division of a single bacterium into twocells. During a 24-hour incubation period, the cells multiply, pro-ducing millions of bacteria that form raised colonies. The coloniesare counted and compared with EPA contamination standards todetermine if the water sample is, or is not, in compliance with thestandards.

Contamination of water by sewage can be reduced or even elim-inated by sewage treatment, a process that helps kill bacteria andother harmful microorganisms. Sewage is treated in facilities calledsewage-treatment plants. (See Figure 22-2.) Solid litter such as sticks,rags, and other debris are separated from sewage and trucked to alandfill or incinerator. Notice the large tanks that treat the incomingsewage. In some tanks, bacteria are added to digest the fecal wastes.(Remember, in nature, bacteria help break down organic wastes,including those produced by people. But the great volume ofhuman waste that may be poured into an area can overload the nat-ural ability of the area to deal with it. That is why sewage treatmentis so important.)

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Figure 22-2 A sewage-treatment plant.

During treatment, the solid part of the sewage settles to the bot-tom of the tanks, forming what is called sludge (a mixture of waterand solid wastes). The sludge is pumped into tankers and deliveredto other sites for further treatment. For many years, sewage sludgewas dumped at sea, without additional treatment. The sludge oftenhad a harmful effect on local marine life. Besides organic substances,sludge may contain harmful chemicals from industry and agricul-ture. Finally, in 1991, the federal government required that sludgebe recycled. For many centuries, people in rural societies have usedhuman wastes to fertilize their fields. Today, some sludge, which ishigh in organic matter, is converted into fertilizer and sold to farm-ers for commercial use. The liquid part of the sewage in the tanks isfurther treated with chlorine to kill the harmful microorganismsbefore it is discharged into waterways. As a result, the liquid dis-charge, or effluent, contains far fewer pathogens than the rawsewage that comes into the plant. (See Figure 22-3.)

In big cities, such as New York, there has been an upgrading ofsewage-treatment plants and an improvement in the local water qual-ity. Yet, from time to time there is a sharp rise in coliform bacteria inwater samples from New York City harbors. The sudden increase infecal coliforms coincides with periods of heavy rain. When it rainsheavily, the sewage-treatment plants cannot handle the excess waterthat comes in from storm drains in the streets. (In cities, much of the


Figure 22-3 A sewageeffluent pipe along theshore.

ground is paved over, so much less water can be absorbed by theground.) This runoff water and the wastes it contains are diverted anddumped untreated into local waterways. (See Figure 22-4.)

In southern California, an area prone to water shortages, onefacility has a productive and profitable way of treating sewage. Thepurified sewage water is used for irrigation and to grow aquaticplants and animals, and the leftover sludge is used for landfill. Wet-lands, such as salt marshes, have the ability to purify polluted water.As a result, marshes are being explored for their potential to natu-rally treat sewage. Unfortunately, in many parts of the world,untreated sewage is dumped directly into the sea—so sewage is stilla major source of pollution in the ocean.

22.1 SECTION REVIEW

1. Why are some waters more polluted than others?

2. How do we determine if water is contaminated with sewage?

3. Describe how a sewage-treatment plant works.

22.2 TOXIC CHEMICALS

In 1962, the American biologist Rachel Carson (1907–1964) pub-lished a book called Silent Spring, in which she warned about theincreasing dangers of chemical pollutants in our environment. Car-

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1970 1975 1980 1985 1990100

1,000

10,000

100,000

Tot

al c

olifo

rm b

acte

ria (

per

mL)

Figure 22-4 Coliformtrends in New York Citywaters.

son, who was a respected marine scientist and writer, is generallycredited as being the first person to make the public aware of thedangers of chemical contaminants to wildlife and, ultimately, toourselves. Chemicals that are harmful to living things are known astoxic chemicals. Wastes or by-products from industrial, agricul-tural, and domestic activities often contain toxic chemicals, whichare pollutants that harm the environment. Carson warned thatunless we cut back on the use of toxic chemicals—especially pesti-cides, which can poison living things besides insects—we couldwake up to a “silent spring” in which no more birds would be left tosing. Fortunately, many readers listened to her warning, and thereare ongoing efforts to protect the environment. One chemicalRachel Carson warned about was DDT. The use of this chemical pro-vides an important case study about the dangers presented by toxicchemicals to the environment.

DDT

The toxic chemical DDT (dichlorodiphenyltrichloroethane) is aninsecticide. For more than 20 years in the United States, it wassprayed on farms, in swamps, and in coastal areas to kill insects such as mosquitoes. DDT belongs to a group of compounds calledchlorinated hydrocarbons. When DDT enters the marine environ-ment, the chemical passes through the food chain where it accu-mulates in ever-greater concentrations, from mosquito larvae to fishto marine birds.

One marine bird, the California brown pelican, almost becameextinct in the mid-1960s as a result of DDT spraying. Scientists dis-covered that DDT interfered with the birds’ use of calcium, animportant element in eggshells. DDT caused the pelicans to producethin-shelled eggs. Many of the eggs cracked during incubation. As aresult, the pelican population declined. DDT had similarly harmedother predatory birds, such as the bald eagle, peregrine falcon, andosprey. Since 1971, however, the U.S. government has banned theuse of DDT, and in recent years we have seen a gradual increase inthe populations of brown pelicans, ospreys, peregrine falcons, andeagles. (See Figure 22-5.) Unfortunately, the use of DDT is notbanned worldwide, and its effects are seen far from the areas inwhich it is sprayed. DDT has been found in the fatty tissues of


Figure 22-5 Brown peli-cans have made a come-back since DDT wasbanned.

seabirds and marine mammals in the Arctic and the Antarctic, prov-ing that the chemical can be carried quite far by air and water.

PCBs

Factory sites are usually located near bodies of water. The water is aconvenient place to dispose of chemical wastes produced by the fac-tories. From 1950 to 1975, a company located along the HudsonRiver in upstate New York dumped hundreds of thousands of kilo-grams of another type of chlorinated hydrocarbon, called PCBs(polychlorinated biphenyls), into the river. PCBs are used in a vari-ety of consumer products, including paints and electrical compo-nents. PCBs were found to cause cancer in laboratory animals andare suspected of causing cancer and birth defects in humans. Thedangers of PCB contamination are now well documented.

After being discharged into the Hudson River, the PCBs sank tothe bottom, where they remained in the sediment for a long time.Here they contaminated bottom-dwelling invertebrates. When fishate these animals, the PCBs in them entered the food chain. As thePCBs moved up the food chain, their concentration increased.Remember that this had also occurred with DDT. The increase inconcentration of a chemical substance, particularly a toxic one, as itmoves up a food chain is called biological magnification, or bio-magnification for short.

In 1976, the Environmental Protection Agency (EPA) tested theHudson’s striped bass for PCBs, and found the concentration to be 5parts per million (ppm)—more than twice the permissible limit. As aresult, the commercial fishing of striped bass in the Hudson Riverwas stopped. Like many other marine organisms that hatch anddevelop in brackish water or freshwater, striped bass migrate betweenthe river (an estuary) and the ocean, forming a link with the marineecosystem. This connection is important, because PCBs have beendetected in the tissues of seals, porpoises, and beluga whales.

How has PCB contamination fared in recent years? There is somegood news. First, PCBs are no longer being dumped into the HudsonRiver. As a result, PCB levels in striped bass have dropped to less than2 ppm. Second, now that the level of contamination has dropped,the striped bass fishing industry can start again in New York. (See thefeature about striped bass and the Hudson River on page 549.)

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ENVIRONMENTSwimming with the Fishes

1. Why was commercial fishing for striped bass banned in the Hudson?

2. Explain why it is now safe for people to swim in the Hudson River again.

3. Why is a cleaner Hudson River important for the survival of the striped bass?

QUESTIONS


Who would have thought that New Yorkerswould ever be able to have locally caughtstriped bass for dinner again? Well, the tide isfinally turning against water pollution in theHudson River. For more than two decades, com-mercial fishing for striped bass has been forbid-den due to the high levels of cancer-causingPCBs in river sediments. The latest tests showthat, as result of cleanup efforts, PCB levels arenow low enough to again permit commercialfishing for “stripers” in the lower Hudson River.

There is more to this success story—you cannow “swim with the fishes” in the Hudson River.The construction of new sewage-treatmentplants and the upgrading of other plants havegreatly reduced the levels of pathogenic bacte-ria in the river. Marathon swims around theisland of Manhattan are now regular eventseach summer because the water quality hasimproved so dramatically. Also, when you swim,you will have lots of company. Fishermen havereported record numbers of striped bass insome parts of Lower New York Bay. During thespring, huge numbers of the adult bass swim up the Hudson River to spawn. The fish are sonumerous in some areas that they bump againstthe fishing boats!

With stripers thriving, water qualityimproving, and New Yorkers discovering first-hand that Manhattan is indeed an islandcity, we are reminded that success stories in the battle against water pollution are possiblewhen stewardship of the environment is takenseriously.

Mercury

Another toxic substance that has been dumped into the marineenvironment is the element mercury (Hg). In Minimata Bay, Japan,from the early 1950s to 1960, more than 100 people developedtremors, fell into comas, and died. Many more were stricken with avariety of nervous system ailments that included blindness, loss ofhearing, insanity, and paralysis. Doctors discovered that all victimshad consumed large amounts of local fish and shellfish, so they sus-pected that the seafood was contaminated. When the seafood wasexamined, high levels of mercury were found. The mercury wastraced to a nearby industrial plant that manufactured plastics andchemicals. The factory’s liquid wastes, which contained mercury,were being discharged into the bay.

How does mercury get into humans from a contaminated envi-ronment? Like DDT and PCB, mercury enters the food chain. Wastesthat contain mercury compounds enter the water from industrialsources. The mercury settles to the ocean bottom, where it is actedon by bacteria and changed into a form that can be absorbed byother organisms. First, plankton take up the mercury; then it movesalong the food chain to humans, increasing in concentration (bio-magnifying) at each step. In the so-called Minamata disease thatoccurred in Japan, small fish contained 24 ppm of mercury, whilepeople had 144 ppm. Doctors found that mercury binds to the pro-teins in nerve cells. This explains why victims suffered from variousnervous system disorders.

In the 1970s, the chemical plant in Minamata finally stoppeddischarging mercury. Unfortunately, as in the Hudson with itsPCBs, the sediments in Minamata Bay were still contaminated withmercury. The events in Minamata spurred a global investigationinto mercury contamination. Findings showed that fish eaten inother countries—including the United States—were contaminatedwith mercury. In 1972, Congress passed the Clean Water Act,which required industrial plants to install equipment that preventsmercury from being released directly into the water. However, mer-cury can also enter the ocean from factories (such as coal-burningplants and paint and chemical factories) located inland. Mercuryin their smoke emissions is absorbed by moisture in the atmos-phere. Winds carry the tainted air over bodies of water, such as

550 Marine Ecology

lakes and oceans. Then rain and snow deposit the mercury intothe ocean.

The U.S. government’s Food and Drug Administration (FDA) seta limit of no more than 0.5 ppm of mercury in fish. As a result, theoccurrence of mercury poisoning from marine sources has declinedsignificantly in this country. (By contrast, in the 1960s, some fishin the Great Lakes had mercury levels between 1 ppm and 2 ppm.)Not all countries have strict environmental laws, so the mercury lev-els in some food fish, such as swordfish, often exceeds the maxi-mum level. Accordingly, the FDA has forbidden the importation ofswordfish from other countries. Swordfish that is sold in this coun-try comes from U.S. waters. The FDA has also recommended that, inthe case of tuna, consumption be limited to no more than 400grams (about four servings) per week. Tuna and swordfish are bothlarge, predatory fish. Since these fish are high on the food chain,mercury concentrations are biomagnified in their tissues.

Other Heavy Metals

Mercury is classified among a group of elements known as heavymetals. Other heavy metals, such as lead, cadmium, arsenic,chromium, copper, nickel, zinc, and tin, are also discharged into theworld’s waterways as a result of industrial processes. Some of thesemetals are discharged along with sewage sludge. Although thesemetals may occur naturally in the ocean, they pose a problem whenthey are present in large amounts. Like mercury, when these metalsaccumulate in fish and shellfish, they can harm marine organismsand present a health risk to people who eat them. The FDA moni-tors the concentration of such toxic elements in seafood and offerssuggestions about safe levels of consumption.

Oil Pollution

On March 24, 1989, the oil tanker Exxon Valdez hit a reef in PrinceWilliam Sound near Valdez, Alaska, and spilled about 50,000 tons ofcrude oil. The oil spill affected marine life in the area. The crude oilsank to the bottom, covering innumerable shellfish. Seabirds were


coated with oil. The birds could not remove the sticky oil from theirfeathers, so their feathers could neither insulate them from the coldnor be used for flight. Thousands of birds froze to death, drowned,or were poisoned by the oil as they tried to clean themselves. Fish,too, were covered with oil, which coated their gills and caused thefish to suffocate. Countless microscopic plankton, on which allother marine life depends, were killed by the oil.

This oil spill was only one of many spills that have occurredover the years. The biggest spill occurred in 1978 when the tankerAmoco Cadiz broke up in stormy weather off the coast of France andspilled about 200,000 tons of oil into the sea. The oil continued toleak from the tanker and washed ashore for weeks following theaccident. The damage the spill caused to marine life along a 300-km stretch of coastline was enormous. As in the case of the ExxonValdez, thousands of fish, seabirds, plankton, and bottom-dwellinginvertebrates died. The effect on the marine environment lasted forseveral years. Oil remained in the water and sediment, and the catchof fish in commercial fisheries declined. For millions of years, oilhas been naturally seeping from sediments in parts of the marineenvironment. However, the effects of natural seepage are small com-pared to the impact of a major crude oil spill from a tanker.

In early 1996, the oil tanker Sea Empress ran aground off thecoast of Wales and leaked more than 70,000 tons of oil. Nearly 200km of coastline were affected, and hundreds of square kilometers ofthe sea were declared off-limits to the local fishing industry. InNovember 2002, the oil tanker Prestige split in half and sank off thecoast of Spain, spilling at least 10,000 tons of toxic fuel oil into thestormy North Atlantic. The oil slicks that resulted from the spilldamaged the region’s fishing industry, killed countless seabirds,soiled more than 250 km of beaches, and harmed the fragile marineecosystem. Unfortunately, since more than 1 billion metric tons ofcrude oil are transported by tankers each year, other large oil spills atsea still may occur in the future.

As devastating as these oil spills are to the environment, theyaccount for only about 20 percent of all oceanic oil pollution. Mostoil pollution originates from what are called nonpoint sources. Unlikea spill from a tanker, which is a specific point of origin for oil pol-lution, nonpoint source pollution includes many diffuse sourcesof pollution. For example, the discharge of consumer products thatcontain oil into sewer systems from homes, businesses, and motor

552 Marine Ecology

vehicles is a major form of nonpoint source oil pollution. Such oil isnot removed during sewage treatment, so it is discharged with theeffluent into our waterways. Nonpoint source pollution is difficultto correct because it occurs everywhere along the shore, especially inharbors. Oil leaks out when ships dock and handle oil supplies, andwhen ships flush their tanks at sea. The practice of flushing tanksat sea is illegal, but it still occurs—often at night—because the sea-water is readily available.

Efforts are underway to reduce oil contamination in the marineenvironment. Regulations have been issued that call for the con-struction of stronger, double-hulled tankers, which are less likely tospill oil in the event of a collision. The occurrence of oil spills hasbeen decreasing. Yet slicks and globs of oil still float over the ocean’ssurface. In time, the oil dissipates in the environment because bac-teria and wave action break it down. In addition, scientists haveidentified certain bacteria that break down crude oil. These oil-eat-ing bacteria are sprayed onto oil spills to try to clean them up beforethey damage the marine environment. Scientists found these bacte-ria to be effective in cleaning up the major oil spills that were causedduring the Persian Gulf War. In spite of those efforts, marine lifestill suffered. The large amounts of oil that suddenly enter the oceanfrom such spills are usually more than natural processes can handle.

Radioactive Wastes

Another type of pollutant that poses a risk to the health of the marineenvironment is radioactive wastes. Radioactive wastes, also callednuclear wastes, consist of radioactive isotopes, which are atoms of thesame element that differ in their atomic mass. Isotopes are unstable;that is, they break down, or decay, into smaller atoms of other ele-ments and emit high-energy rays and particles in the process. Eachelement has its own half-life, which is the time it takes for half theradioactive atoms present to decay into a stable nonradioactive sub-stance. For some elements, the half-life is very short—less than a day.For others, it is thousands of years. This means that the radioactivematerial will be present for a very long time until it is completelydecayed. Such materials can threaten the well-being of living things.

The high-energy rays and particles that are emitted during decaycan pass through the tissues of organisms. As they do so, they can


damage DNA and other molecules. This damage can cause cancerand genetic mutations. Energy from radioactive reactions is used formilitary purposes and to run power plants that produce electricity;radioactive elements are also used in medical procedures. Theabove-ground testing of atomic weapons, which put radioactivewastes into the atmosphere, has now been banned. However, theother processes still generate large amounts of radioactive wastes.

For a long time, it was thought that radioactive wastes could besafely stored on the ocean floor because it was thought to be calmand barren. We now know that parts of the seafloor are actually veryactive—geologically and biologically. Up until 1972, low-levelradioactive wastes were, in fact, placed in metal drums and dumpedhundreds of kilometers off the Atlantic and Pacific coasts. Some ofthese drums have since washed ashore on the West Coast, whileothers have been pulled up in trawl nets from the Atlantic. Perhapseven more frightening, other drums have rusted, causing the releaseof their radioactive elements into the water. Radioactive fish andinvertebrates have been caught in the Pacific Ocean. Obviously,there is a risk to marine organisms and to the people who eat them.

One radioactive isotope of particular concern is strontium-90,which competes with calcium for a place in the bones. This elementcan enter the marine environment as fallout from weapons tests, ineffluent from industrial wastes, or from leaking drums of wastes inthe ocean. Although we absorb some strontium-90 from normalbackground radiation, exposure to it from tainted marine foodscould be dangerous. At present, much less than 1 percent of theradioactive particles humans receive comes from marine resources.

Fortunately, in 1972, U.S. laws and an international agreementwere passed that prohibited the dumping of high-level radioactivewastes into the ocean. In addition, clay in the ocean’s sedimentscan absorb radioactive particles that are dispersed through the water.However, there is still a chance that the ocean floor will be used as adumpsite for radioactive wastes, if they can be placed far below theseafloor in geologically stable regions.

Thermal Pollution

Factories and power plants are often located along estuaries so theycan use seawater as a coolant for their machinery. Some plants dis-

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charge the heated water back into the estuary. This creates a ther-mal plume, a flow of water with temperatures that are significantlyhigher than those of the water it enters. The release into naturalwaterways of very warm water—which can adversely affect marinelife—is called thermal pollution. At higher temperatures, the pop-ulations of microscopic phytoplankton such as diatoms and greenalgae decline significantly, while the blue-green bacteria (algae)greatly increase their population. (See Figure 22-6.)

Large numbers of blue-green bacteria produce foul odors andtoxic substances that are harmful to marine life. Fish avoid the hightemperatures and low oxygen levels of thermal plumes, resulting inthe decline of fish species in such areas. In shallow waters, benthicinvertebrates are not able to escape the thermal shock produced byhigher water temperatures.

Some communities have solved the problem of thermal pollu-tion by constructing cooling towers at power plants. Others havebuilt shallow pools on the land to cool the heated water before it isdischarged into an estuary. Recently, some power-plant operatorshave used the cooling pools to commercially raise fish and lobsters.

22.2 SECTION REVIEW

1. Explain how mercury in the marine environment is a potentialpublic health problem.

2. Why is dumping of radioactive wastes on the seafloor generallyconsidered an unsafe practice?

3. Why is thermal pollution damaging to estuarine ecosystems?


20 25 30 35 40

Temperature (°C)

Phy

topl

ankt

on p

opul

atio

ns

Diatoms

Greenalgae

Blue-greenbacteria (algae)

Figure 22-6 Theeffects of thermalpollution onalgae popula-tions.

22.3 CLEAN, CLEAR WATERS

As you already learned, plants and algae need light in order to carryon photosynthesis. The amount of light aquatic plants receivedepends on the clarity of the water they are in and the depth ofpenetration of the sun’s rays. Clear waters that are not clouded bysuspended particles such as sand or silt, or fouled by an oil slick,enable greater penetration of light, which marine plants can thenabsorb. Likewise, polluted or murky waters decrease the light avail-able for plants. The measure of the level of clarity or murkiness ofwater is called turbidity.

Turbidity

How is water turbidity measured? A simple device called a Secchidisk, named after the Italian scientist Father Pietro Secchi(1818–1878), is used to measure the distance light penetrates intothe water. The disk, which has four alternating sections of black andwhite, is gradually lowered into the water from a pier or a boat untilthe disk can no longer be seen. The depth at which the disk is nolonger visible is defined as the turbidity. A reading of less than 2meters indicates that the water is very turbid. (See Figure 22-7.)

Cloudy or turbid water can be caused by natural conditions. Inthe northern latitudes, where light is less intense and high planktonpopulations cloud the waters, visibility is low and turbidity is high.In the tropics, where light is much more intense but there are fewerplankton, you can see more than 30 meters underwater, so turbidityis low. Other natural conditions, such as stormy weather and strongocean currents, can stir up bottom sediments and reduce visibility.

Human activities can also cloud the waters. Sometimes, pooragricultural practices lead to soil erosion. When soil is blown orwashed off the land, it can enter rivers and streams and eventuallybe carried out to sea. Great quantities of eroded soil cloud coastalwaters and choke aquatic communities such as estuaries and coralreefs.

During several summers in the late 1980s, the coastal waters offLong Island, New York, turned so cloudy that the condition becameknown as brown tide. Marine biologists discovered that the cloudy

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Secchidisk

Rope isknotted at1-meterintervals

Figure 22-7 How to use aSecchi disk to measurewater turbidity.

water was caused by an overpopulation of algae, called an algalbloom. Water turbidity was so high that bathers could hardly seetheir hands in front of them while swimming along the beach. Thesituation became so bad that, in the summer of 1987, a fish killoccurred in Hempstead Harbor, Long Island. (See Chapter 4 toreview information on algal blooms, brown tides, and fish kills.)

What caused the algal bloom and the fish kill? Scientists thinkthat pollution set into motion the chain of events that led to thefish kill. Effluent that contained sewage and chemical fertilizersfrom lawns and farms entered the harbor from the land. Organicmatter in the sewage and fertilizers contained high levels of phos-phates and nitrates, which caused an algal bloom. The large algaepopulation used up oxygen and clouded the waters, reducing lightpenetration. Other microscopic algae suspended in the water andeel grass growing on the bottom died from lack of light. Dead plantmatter accumulated on the bottom, where it decayed. During theprocess of decay, aerobic bacteria extracted still more oxygen fromthe water. The result was a fish kill. Fish breathe by taking oxygenout of the water through their gills. The fish suffocated becausethere wasn’t enough oxygen dissolved in the water.

The discharge of sewage and chemical fertilizers into localwaterways are major factors that contribute to the poor water qual-ity off Long Island and elsewhere around the country. Greaterefforts are needed to reduce the runoff of nutrient-rich wastes andfertilizers into rivers and estuaries.

Dissolved Oxygen

In 1976, a major fish kill occurred in the waters between New Jerseyand New York. Scientific tests found that the amount of oxygen dis-solved in the water was very low. The amount, or concentration, ofoxygen dissolved in water is called the dissolved oxygen (DO).Depending on its temperature, ocean water has a DO concentrationthat ranges from 1 to 12 ppm. On the day of the fish kill, the waterhad a DO concentration of only 2 ppm. Scientists concluded thatthe fish died of suffocation, because the DO level was below the crit-ical threshold of 4 ppm, the minimum level of oxygen required forfish to breathe. This aquatic condition is known as hypoxia, mean-ing “low oxygen.”


What caused hypoxia in these waters? The low DO levels werefound in an offshore area where the dumping of sludge had occurredfor a number of years. As in the case of the Hempstead Harbor fishkill mentioned above, bacteria in the sludge were using up oxygenduring the process of decay. The DO levels declined over time andthen fell to 2 ppm. In light of these findings, the U.S. governmentand the state of New York agreed to dump sludge farther offshoreand to eliminate ocean dumping entirely by 1993—which they did.

The reduction and elimination of sludge dumping in the oceanhas had a beneficial effect on DO levels in coastal cities such as NewYork. Notice, in Figure 22-8, the overall rise in DO mean levels inthe Hudson River since 1925. There is still room for improvement,and other cities around the country have not fared as well. How-ever, the construction of new sewage-treatment plants and theupgrading of older treatment plants will greatly improve the qualityof our local waterways. In addition, projects are being undertaken inmany cities to recycle some of the organically rich sludge for use asfertilizer.

22.3 SECTION REVIEW

1. What is turbidity? How is it measured?

2. Explain how pollution can cause an algal bloom.

3. Describe how an algal bloom lowers DO levels and leads to afish kill.

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1925 1935 1945 1955 1965 1975 1985 199510

20

30

40

50

60

70

80

90Top mean, during summer

Bottom mean, during summer

Dis

solv

ed o

xyge

n (%

sat

urat

ion)

Figure 22-8 The DO levelshave been increasing inthe Hudson River.

22.4 LITTER IN THE WATER

During the summer of 1988, a tide of solid wastes washed up on theshore, from Massachusetts to Maryland. Much of the debris con-sisted of medical wastes, including hypodermic syringes and otherproducts made of plastic. There was so much garbage in the waterthat many beaches had to be closed. The public was frightened andoutraged.

No spot is too remote for seagoing trash. On Ducie Island, anuninhabited spot in the middle of the South Pacific nearly 500 kmfrom the nearest inhabited island, scientists have discovered litterwashed up on its beaches. On one occasion, a scientist counted 953pieces of trash, most of it plastic, along a 2.5-km stretch of beach.Much of the garbage came from ships, such as cruise ships, that hadroutinely dumped their trash overboard.

Litter is solid waste or garbage. Most litter consists of plastic,glass, and metal—materials that do not undergo natural decay. Lit-ter that cannot be broken down by natural processes is called non-biodegradable. A nonbiodegradable waste such as plastic mayremain in the environment for hundreds of years.

Plastic wastes not only are unsightly but often pose a threat tomarine life. Some animals, particularly sea turtles that eat jellyfish,mistake plastic bags for food. The turtles then die—either of starva-tion (with plastic bags filling their stomachs) or of suffocation (afterchoking on the plastic bags). Carelessly discarded plastic rings frombeverage six-packs trap and choke fish, birds, and other marine lifewhen the animals swim, or put their heads in, through the ringsand are unable to get them off their bodies. And each year, thou-sands of fish, seabirds, turtles, and marine mammals die when theybecome entangled in plastic gill nets, fishing line, and huge driftnets that are discarded or lost at sea by fishing vessels.

The United States throws away more trash than does any othernation in the world. More than 150 million tons of solid wastes, orrefuse, are thrown out each year—nearly 10 million tons of it intooffshore waters. Among the items dumped into the sea are millionsof old cars, along with old boats and military weapons. In addition,millions of glass, metal, paper, plastic, and plastic foam items arethrown into the ocean each year. Whereas many of these items maybe harmful to marine life and the environment, sunken cars and


ships sometimes serve as artificial reefs that attract fish, which isgood for ocean life and for recreational activities. (See Figure 22-9.)

Approximately 75 percent of all garbage is buried in landfillsites. But many U.S. cities and states are running out of such spacesto dump their solid wastes. Landfills are supposed to be constructedso that waste substances do not leach into the ground and contam-inate groundwater. In spite of this, some landfills contain hazardouschemicals that seep through the ground into drinking water sourcesand into nearby waterways that are used for swimming and fishing.The proper disposal of solid wastes is a serious problem because asthe U.S. population increases so too will the amount of garbage itgenerates.

Solutions to Pollution

What can communities do to dispose of garbage properly, withoutdumping it directly into the ground or the ocean? One method isincineration, the disposal of solid wastes by combustion. There aresome 200 large incinerators now operating in the United States.Although the burning of wastes can be used to generate energy, it isnot a perfect solution to waste disposal. Many towns cannot affordto build an incinerator. In addition, incineration of garbage can pro-duce air pollutants, especially when plastics are burned.

There are valid environmental and economic concerns aboutthe disposal of solid wastes in landfills and by incineration. A moreecologically sound method of handling solid wastes is recycling—the

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Figure 22-9 An old tirehas become part of thisbarracuda’s environ-ment.

disposal of garbage by reusing it or by converting it into useful prod-ucts. Some of the most commonly recycled items are paper, plastics,glass, and metal. The incentive of deposit payments for beveragecans and bottles has greatly diminished the number of such con-tainers that are discarded. Billions of glass food jars and aluminumcans are recycled in the United States each year. Incentives for therecycling of paper have spawned about 2000 wastepaper dealers andbrokers nationwide. Out of an estimated 27 million tons of wastepaper, about 5 million tons have been recycled into packaging prod-ucts and exported abroad. However, experts believe that recyclingat best will involve only 25 percent of our trash. Hopefully, compa-nies will use more biodegradable products, and the government willprovide more economic incentives for companies and consumers torecycle. In Japan, 50 percent of solid wastes are recycled. Citizenparticipation in recycling programs is essential if we are to reducethe amount of litter we produce and discard.

There Ought to Be a Law!

Pollution affects everyone. At best, it is an eyesore; at worst, it pre-sents a hazard to the environment and to the health of all livingthings. Knowing this, many governments, organizations, and indi-viduals are working to develop solutions to pollution. These effortsoften specifically concern the marine environment.

What have governments done to prevent or reduce marinelitter? In 1973, the International Maritime Organization, an agencyof the United Nations, formed an agreement called MARPOL(Marine Pollution) that regulates the disposal of hazardous chemi-cals, sewage, and trash from ships at sea. As of 1992, fifty nationshad signed the MARPOL Treaty, which prohibits the dumping ofplastic trash overboard from ships at sea.

Groups and Organizations Against Pollution

Private industry, nonprofit research groups, environmental groups,and government organizations are all working to find ways toprevent and reduce debris in the marine environment. Plasticsmanufacturers have introduced photodegradable plastics in some


consumer items. These plastics break down over time from theaction of sunlight on the product. Additional work has been done toincrease the feasibility of plastic recycling. The Society of PlasticsIndustry, a trade organization of more than 1900 members, is tryingto solve the problem of plastic discarded at sea that breaks downinto pellets. These small pieces of plastic disperse throughout theocean and can be harmful to marine animals that eat them.

Federal agencies are also engaged in efforts to reduce marinedebris. The Environmental Protection Agency, National Oceano-graphic and Atmospheric Administration, U.S. Coast Guard, Depart-ment of the Interior, and U.S. Navy have undertaken a cooperativeeffort to deal with the problem of garbage in the marine environ-ment. The EPA and NOAA are cosponsors of the Center for MarineConservation. One of their initiatives is the national Beach CleanupCampaign, during which volunteers record the types and quanti-ties of solid wastes that they collect along the shore. Clearly, it isbetter to keep a beach free of litter than to risk the health hazards,damage to wildlife, and high cleanup costs of pollution.

Individuals can make a difference in tackling ocean pollution,too. By becoming informed about the problem, people can chooseto do a number of constructive things to help protect the marineenvironment. They can actively clean up local beaches (or at leastnot leave any debris on them that may damage the environment orthreaten marine life); request and purchase products that have less,or recyclable, packaging on them; and lobby for the passage andongoing enforcement of environmental laws. Consumers must bewilling to assume the extra costs that may be involved in more envi-ronmentally sound manufacturing and recycling processes, becausethe costs involved in environmental degradation are much higher.

22.4 SECTION REVIEW

1. Explain why plastic debris is dangerous to marine life.

2. Which method of solid waste disposal is best for protecting theenvironment?

3. What products can be reused through recycling of materials?

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Laboratory Investigation 22

PROBLEM: How can the pH of various water samples be determined? What isthe pH of ocean water?

SKILL: Using chemical indicators to measure pH levels.

MATERIALS: Tray, loose-leaf paper, red litmus paper, blue litmus paper, pHhydrion paper (wide range), medicine dropper, ocean water, rainwater, tapwater, pond water.

PROCEDURE

1. Place a piece of loose-leaf paper on your tray. Open the vials containing redlitmus paper and blue litmus paper. Remove four strips of red litmus paperand four strips of blue litmus paper. Place them on the loose-leaf paper, infour sets of one blue and one red each. Label each set with the type of waterbeing tested: ocean, rain, tap, and pond water.

2. Use the medicine dropper to place one drop of each water sample on thered litmus paper and one drop on the blue litmus paper. Do one water sam-ple at a time. Observe if there is a color change. Write the color in your copyof Table 22-1. Repeat for each of the samples.

3. To determine if the water sample is acidic, basic, or neutral, you can use thefollowing scheme: Red litmus paper stays red in acid, but turns blue in base;blue litmus paper stays blue in base, but turns red in acid.

TABLE 22-1 TESTING THE pH OF WATER SAMPLES

Sample Red Litmus Blue Litmus Acidic, Basic, or Neutral pH level

Ocean water

Rainwater

Tap water

Pond water

Determining the pH of Water Samples


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4. Litmus paper is useful only for determining whether your water sample isacidic, basic, or neutral. To find the pH level, you need to use pH hydrionpaper, which comes in a container with a color scale that indicates pH values.

5. Remove four strips of pH paper from the container. Put a drop of water fromthe first sample on one strip of pH paper. Compare the color on the stripwith the color scale on the container. Note the pH and record it in Table22-1. Repeat for the other water samples.

6. Check your results by referring to the following pH scale: 0 to 6 ranges fromvery to slightly acidic; 7 is neutral; 8 to 14 ranges from slightly to very basic(alkaline).

OBSERVATIONS AND ANALYSES

1. What is the pH of ocean water? Find its location on the pH scale.

2. Briefly describe how you would determine the pH of ocean water.

3. What is the advantage of using pH hydrion paper instead of, or in additionto, litmus paper?

Answer the following questions on a separate sheet of paper.

Vocabulary

The following list contains all the boldface terms in this chapter.

biological magnification, effluent, heavy metals, hypoxia,nonbiodegradable, nonpoint source pollution, pollutants,pollution, radioactive wastes, sludge, thermal plume, thermalpollution, toxic chemicals, turbidity

Fill In

Use one of the vocabulary terms listed above to complete each sentence.

1. Litter that cannot be broken down naturally is ____________________.

2. The solid part of the sewage that settles in tanks is ____________________.

3. The measure of water’s level of murkiness is called ____________________.

4. The liquid part of sewage that is discharged is the ____________________.

5. The condition called ____________________ describes a very low DO level.

Think and Write

Use the information in this chapter to respond to these items.

6. Explain why it might be dangerous to eat shellfish that weregathered near a harbor.

7. How does oil pollution affect marine life? What are some waysthat its effects can be lessened?

8. What conditions can produce a low DO? What is its effect onaquatic life?

Inquiry

Base your answers to questions 9 through 11 on the data below and onyour knowledge of marine science.

A group of marine science students wanted to know if the water attheir beach was clean enough to swim in. They decided to test thewater for the presence of fecal coliform bacteria to see if the level

Chapter 22 Review


was in compliance with EPA standards. (See the table below.) Thestudents used the membrane-filter technique to culture a 10-mLsample of ocean water. A tap water sample was cultured as a con-trol. After 24 hours, the Petri dishes were observed for the presenceof fecal coliform colonies. To compare to EPA standards, the stu-dents counted the number of bacterial colonies in the dish, andthen multiplied by 10 to obtain the number of coliforms that wouldbe present in 100 mL of ocean water. (See diagram below.)

Type of Water EPA Fecal Coliform Standards

Drinking water Zero coliforms allowed

Shellfish water Should not exceed 14 coliforms/100 mL

Swimming water Should not exceed 200 coliforms/100 mL

Harbor water Should not exceed 2000 coliforms/100 mL

9. How many colonies were found in the 10-mL sample? Howmany coliforms would be in a 100-mL water sample?

10. Based on the EPA standards, would this ocean water be suit-able for swimming in? Explain.

11. Would this ocean water be suitable for the harvesting of shell-fish? Explain why or why not.

Multiple Choice

Choose the response that best completes the statement or answers thequestion.

Base your answers to questions 12 and 13 on thegraph and on your knowledge of marine science.

12. What would be a suitable title for thisgraph? a. The effect of overcrowding onalgae populations. b. The effect of salinityon algae populations. c. The effect oftemperature change on algae populations.d. The effect of temperature change onzooplankton populations.

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Culture of fecal coliformbacteria from ocean water

Petri dishBacterialcolonies

20 25 30 35

Temperature (°C)

Diatoms

Greenalgae

Blue-greenbacteria (algae)

13. Based on the data in the graph, which is an accuratestatement? a. Green algae are best adapted to survive at thehighest temperatures. b. As water temperature increases, thenumber of blue-green bacteria decreases. c. As watertemperature increases, the number of diatoms decreases.d. Green algae are not affected by changes in temperature.

14. Which type of beach litter is biodegradeable? a. plasticbottles b. soda cans c. nylon fishing line d. pieces ofwood

15. A pollutant that has biomagnified in aquatic food chains isa. coliform bacteria b. PCBs c. crude oil d. hydrogensulfide.

16. A fish kill is most likely to occur in waters where there isa. a high DO level b. a low DO level c. low turbidityd. a high mercury content.

17. All of the following are examples of toxic substances excepta. PCBs b. mercury c. DDT d. manganese nodules.

18. The best explanation for why some swordfish have highmercury levels is that a. they take in water containingmercury b. they absorb mercury from bottom sedimentsc. the mercury moves up the food chain to them d. theyare exposed to atmospheric mercury.

19. Which is the greatest source of oil pollution in the ocean?a. oil well blow-outs b. nonpoint source pollution c. oilspills from tankers d. oil refinery accidents

20. The instrument used to measure water turbidity is thea. Secchi disk b. pH scale c. hydrometer d. barometer.

21. Acid rain is more of a problem in lakes than in the oceanbecause a. it rains more on land than at sea b. airpollution is greater inland than along the coasts c. thebuffering action of the ocean counteracts the acidityd. ocean currents carry the acids away.

22. The type of pathogen that is used to indicate human sewageas the source of water pollution is a. blue-green bacteriab. coliform bacteria c. dinoflagellates d. diatoms.


Research/Activity

■ Build a Secchi disk from household items. Work with a team ofclassmates to check water turbidity daily, weekly, or during thetidal cycle, from the safety of a local dock or pier. Record yourresults and prepare a graph. You can submit the completed proj-ect to your school science fair.

■ Identify the types of items you are recycling that may be foundin the marine environment as garbage. Report on their impactin the ocean in contrast to their use as recycled products.

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