16.5: Ocean Pollution Issues

Petroleum

If asked to identify the sources of serious pollution in the oceans, most people would name oil spills at, or near, the top of their list. This is not surprising, since oil spills, unlike any other form of ocean pollution, provide spectacular images and video of leaking tankers (Fig. 16-5a), oiled marine animals and birds being rescued or dead on a beach (Fig. 16-5b), and towering flames and smoke from burning oil rigs (Fig. 16-6). As a result, media coverage of oil spills is always extensive, and since bad news sells better than good news, the media tends to emphasize and often exaggerate the extent of the environmental harm. In contrast, most other ocean pollution is almost impossible to photograph or video so gets little or no media attention. The net result of this is that the public perception is that oil spills are the most serious form of ocean pollution and that huge sums of money must be spent to monitor the impacts of each spill and to provide absolute assurance that spills “never occur again.” Many marine oil spills have been extensively studied over more than the past half century and the findings of such studies support a different conclusion. While spill prevention is important and oil spills do have adverse impacts on the area in which they occur, the adverse effects are geographically limited and the affected marine ecosystems recover to a natural state (not to the same state as before since ecosystems are naturally always changing and a previous state can never be restored exactly) within a few years. 

Figure 16-5. Oil spills provide spectacular images that ensure media coverage. (a) The Exxon Valdez tanker 48 h after it ran aground on Bligh Reef in Prince William Sound, Alaska, in 1989. In this photograph, the tanker is seen still leaking some oil, and it is surrounded by a boom that has been placed on the water surface in an attempt to contain this oil so that it can be collected. (b) A rescuer tries to capture an oiled Pelican after the 2010 Deepwater Horizon spill in the Gulf of Mexico. Rarely do heavily oiled birds survive even when cleaned up.

Figure 16-6. Major oil spills from the offshore oil industry are rare but dramatic events such as the Deepwater Horizon rig which is shown burning before it sank in the Gulf of Mexico, April 2010.

Oil spills are discussed in more detail in Online Box 16B1, but some of the more important findings are summarized here.

1. Oil is a natural substance that is consumed by microbial decomposers.
2. Oil spills have short-term adverse effects in the spill area including, deaths of birds and some marine animals due to oiled fur or feathers, oiled beaches, and disruption of plankton communities. Long-term effects are uncertain but may include some reduction in reproductive success of some marine species.
3. Ecosystems subject to spilled oil recover to a natural state within years in most areas to a decade or more in cold regions.
4. The use of dispersants or aggressive cleanup techniques such as hot water washing of rocky coastline or beaches generally leads to greater harm to the ecosystem than simply skimming off as much oil as can be done easily and allowing the microbial community to remove the remainder (adding nutrients to aid these microbial organisms may be appropriate in some cases).
5. Efforts to rescue and clean oiled marine animals and birds are often very expensive but result in very low survival rates for the cleaned animals.
6. Measures taken over the past several decades to minimize oil spills from tanker accidents and other accidental spills have been largely successful in reducing the frequency of large spills.
7. Chronic inputs of petroleum products from dispersed sources such as runoff from highways are still large and may have chronic adverse effects in some locations, especially rivers and estuaries where such inputs are large. 

Sewage 

Some human waste has been disposed in oceans, estuaries, and rivers for millennia. However, once sewers systems were introduced, they acted as a public health tool to ensure that human wastes were carried easily and efficiently for disposal in nearby bodies of water. Sewers are historically so important that human wastes are now called sewage. Sewage is a combination of liquid and solid natural materials that was disposed of in rivers, estuaries and oceans for centuries after sewers were introduced, generally without causing adverse effects on the discharge ecosystem. Most cities were, and still are, located next to or near rivers, estuaries or a coastline for reasons that included the availability of these bodies of water into which sewage could be discharged. As the human population grew and cities became ever larger, the quantities of sewage discharged increased as did the concentrations of sewage waste in bodies of water near these cities. By the mid 20th century, many rivers and estuaries worldwide were anoxic. This anoxia was caused by microbial decomposition of sewage organic matter that consumed oxygen faster than it could be replaced from the atmosphere. The ecosystems of many rivers, estuaries, and even some coastal ocean areas were severely damaged and waterside locations in many areas became undesirable places to live or work because of the smell of sulfide and partially decomposed organic matter. This was one of the primary driving reasons for the environmental revolution of the 1960s and 1970s. 

The problems caused by sewage waste discharges prior to the 1970s were primarily due to the high organic matter loading of untreated sewage. Sewage treatment was developed and designed to address this problem by collecting sewage wastes in treatment plants where the larger particle solids could be filtered or precipitated out (primary treatment) and then treated with bacteria to decompose the organic matter that remains after primary treatment (secondary treatment). Both steps generate sludge (mostly particulate solids with enough water to allow them to flow as a thick slurry). Secondary treatment of sewage is now required in the U.S. and in most nations and large cities, and has proved to be effective in alleviating the anoxia problems. Most river, estuary and ocean ecosystems that were damaged by overloading of organic matter from sewage have now recovered. 

Despite the success of sewage treatment, several issues still remain because secondary sewage treatment is not designed to remove trace metals, many soluble organic compounds, human pathogens, or dissolved inorganic nitrogen and phosphorus, although it does partially remove most of these. In most areas, sewage entering sewage treatment plants is a mixture of: human waste water, water used for washing and cleaning that often contains potentially toxic chemicals, wastewaters from some industries, and in some areas storm drain runoff. These are all mixed in one waste stream. In the U.S. and many other nations, industrial pretreatment programs have been highly effective in drastically reducing inputs to sewage of trace metals and potentially toxic organic compounds from industry before they reach the treatment plant. Street cleaning and other measures have somewhat reduced storm runoff of metals and potentially toxic organics. Efforts to improve the removal of remaining non industrial continue to make slow progress. 

Most pathogens in sewage are killed quickly in estuaries and ocean water but extensive monitoring programs are still required to assure that pathogen concentrations on swimming beaches are safe. Beach closures due to sewage discharges still occur infrequently when treatment plants have technical problems or when those sewage treatment plants that must treat storm water runoff combined with the sewage waste stream are overwhelmed by large rainfalls. 

Sewage treatment has been perhaps the greatest success story in environmental management since the environmental movement began. Nevertheless, some issues remain, and a new one is increasingly becoming apparent. This issue is the nutrient loading due to treated sewage wastes. Recall, that secondary treatment was not designed to reduce the concentrations of nutrients like nitrogen and phosphorus and does not do so effectively. Recall also from earlier chapters that anoxia and dead zones driven by discharges of nutrients from rivers are a major and growing problem worldwide (Chaps. 1, 12, 13). Treated sewage discharges to rivers are a major contributor to the nutrient inputs that cause coastal dead zones and likely also cause an increase in total primary production in the surface oceans that contributes to the problem of deoxygenation of the deep oceans discussed in Chapter 1 and later in this chapter. Tertiary treatment technologies do exist to reduce nutrient concentrations in sewage but they are not widely used. These tertiary treatment technologies are costly to perform and require large capital expenditures to upgrade and expand existing sewage treatment plants.

A more detailed discussion of sewage and sewage treatment can be found in Online Box 16B2.

Urban and Agricultural Runoff 

Many chemicals are used in urban and agricultural communities. Fertilizers and pesticides are applied in large quantities to fields and gardens. Oil and rubber dust (containing toxic contaminants such as cadmium) are left on road surfaces by vehicles. Hydrocarbons and other chemicals are released from road-paving and other building materials. Particulates injected to the atmosphere from the burning of fossil fuels settle everywhere. Paints, solvents, acids, and other chemicals are spilled or released in many different ways, and toxic chemicals are still deliberately dumped to avoid costs of proper disposal. There are also many other ways for toxic contaminants and nutrients to be deposited on the land.

When it rains, contaminants are either absorbed into the soil or washed off into storm drains, streams, rivers, and eventually estuaries and the ocean. Many contaminants are carried by runoff in dissolved form, but most are carried on small organic-rich particles. These particles are carried by streams and rivers to estuaries and coastal ocean, where they can become trapped in the estuarine circulation and sediments (Chap. 13). Contaminants from urban and agricultural runoff reach estuaries through numerous drainage channels spread throughout the watershed. Consequently, their sources are often referred to as nonpoint sources. Nonpoint source inputs are highly variable. Such inputs are greatest during the first few hours of a rainfall, especially if it follows a prolonged dry period. Thus, contaminants that are carried into the estuarine and marine environment generally are diluted by large quantities of freshwater. These factors make the identification and control of nonpoint sources of contaminants extremely difficult and make the cost of possible treatment in most instances prohibitively high.

Urban and agricultural runoff contributes a major proportion of the nutrients and contaminants that enter many estuaries and coastal embayments. Substantial efforts have been made to control nonpoint sources. However, success has been limited, and nonpoint sources are still much greater than industrial and sewage inputs in most estuaries. Consequently, where such substances cause pollution problems, further controls on industrial and sewage inputs will have only a minor effect. The difficult task of controlling nonpoint source inputs must be addressed successfully if estuarine and coastal ecosystems are to be fully protected and restored. 

Pollution problems caused by urban and agricultural runoff are many and varied. Two examples illustrate the complexity of such problems. First, in Chesapeake Bay, nutrient-induced eutrophication has led to widespread, persistent anoxia. Although sewage discharges contribute some nutrients, the predominant sources are fertilizer and animal waste in runoff from surrounding agricultural land, as well as atmospheric inputs. Extensive efforts have been made to reduce these nonpoint source inputs—for example, by reducing fertilizer use and avoiding its application near streams. These efforts have resulted in some improvement, but the problem remains a difficult one.

The second example is the “dead zone,” of the nearshore continental shelf of the Gulf of Mexico in which the bottom waters are seasonally hypoxic (Chap 13). The Gulf dead zone is located in the middle of one of the most important commercial and recreational fisheries in the U.S. The Mississippi River basin drains about 41% of the Lower 48 states of the U.S.—a total of over 3.2 million km2. The drainage basin encompasses all or part of 30 states, a population of about 70 million people, and extensive agriculture. The Mississippi River discharge contains a high nutrient level, some of which is natural but much of which comes from runoff of fertilizers applied to farmlands and from treated sewage. In the last four decades of the twentieth century, the discharge of nitrogen by the Mississippi River basin tripled. It is this excess nutrient load that is believed to have created the dead zone, which was first documented in 1972. Efforts to reduce the nutrient loads of the Mississippi River are under way, but, as in the Chesapeake Bay region, these efforts are difficult and will take many years if the dead zone is to be eliminated.

Industrial Effluents 

Most industries produce solid or liquid wastes that differ widely in composition among industries and even among factories within an industry. Most of these wastes contain various potentially toxic chemicals. A few decades ago, most industrial wastes were discharged to sewers or a local waterway or dumped in a nearby landfill.

The U.S. and most other nations have had laws for several decades to control contaminant discharges to aquatic environments. Enforcement of most of these laws has focused on industrial discharges and sewage treatment. Industries have been required to reduce drastically the concentrations of contaminants in their liquid effluents before discharge. Most industries have changed technologies to reduce the amount of wastes they generate and avoid or reduce the expense of treating effluents.

As a result of decades-long efforts to reduce toxic substances, nutrients, and other contaminants in industrial effluents, industry is now only a minor contributor to the contamination of estuaries and coastal oceans in most areas. Problems remain with some older industrial plants, with industrial discharges that are poorly located where residence time is long, and with the enforcement of discharge permits at a few plants whose unscrupulous owners or operators find ways to discharge wastes illegally. Nevertheless, the general public mistakenly still believes that industry is the principal polluter of the marine environment. There are several reasons for this misunderstanding. The most important is probably that it is easier for the media, politicians, and the public to blame industry for pollution problems than to face the difficult problems of cleaning up individual actions, homes, public utilities, and farms. Another reason is that the only demonstrated and confirmed incident in which the discharge of toxic chemicals to the oceans caused human deaths involved industrial effluents.

For many years, Chiso Chemical Corporation in Minamata, Japan, generated an organic form of mercury, methylmercury, as a by-product of its manufacture of acetaldehyde using mercury as a catalyst. A small portion of the methylmercury was discharged continuously to Minamata Bay in wastewater. Mercury, a toxic metal, accumulated in water, sediments, and fishes. Because methylmercury is more fat-soluble than elemental mercury and is biomagnified (CC18) in marine food webs, its concentration in fishes rose to very high levels.

The discharge of methylmercury to Minamata Bay started in 1952. By 1953, many cats were becoming ill, behaving erratically, and dying. Dead fishes were periodically found floating throughout the region (Fig. 16-7a). At the same time, some of the human population contracted a puzzling “disease” that produced numbness, disturbances in vision and hearing, and loss of the control of motor functions, similar to drunkenness. The “disease” quickly assumed epidemic proportions, and between 1953 and 1962 more than 40 people died and as many as 2000 other victims suffered what has later proven to be a persistent disability (Fig. 16-7b). In 1957, it was found that “Minamata disease” could be induced in cats by feeding them fishes taken from near the Chiso plant outfall. Although fishing was quickly banned, the discharge of methylmercury was not stopped until 1968, because Chiso denied that methylmercury caused the disease until it was overwhelmed by the weight of scientific evidence.

 

Figure 16-7. Methylmercury, discharged by a chemical factory at Minamata, Japan, and concentrated in fish and shellfish tissues, caused a major pollution problem in the 1950s. (a) Map of the locations around Minamata where diseased cats and dead fishes were reported many kilometers away from the discharge point. (b) Detailed map of the Minamata city area identifying the locations where humans lived who were confirmed to have contracted the “disease.” (c) Forty-six people died of mercury poisoning, and many more suffered lasting effects. Even after the early poisonings, the Chiso Chemical Corporation continued to increase its production of acetaldehyde and its waste byproduct, methylmercury. Poisonings continued for years after the release of mercury from the plant was eventually curtailed.

Minamata is apparently the only documented case of human deaths caused by industrial inputs to the marine environment, but a number of cases of deaths of fishes and other marine organisms caused by industrial effluents have been documented. For example, in 1970, the Montrose Chemical Corporation in Los Angeles produced about two-thirds of the world’s DDT. Starting in 1953, the plant discharged effluent containing DDT through a sewer to Santa Monica Bay. By 1970, this and other sources of DDT, which is fat-soluble and biomagnified, had caused the total collapse of many species at the top of the food web. It particularly affected pelicans, whose eggshells were so thinned by the DDT that they broke before hatching, and sea lions, which produced large numbers of stillborn offspring. DDT discharge was stopped, and the use of DDT was banned in the U.S. and Europe early in the 1970s.

Pelican, sea lion, and other affected populations have slowly recovered in the decades since the DDT ban. However, DDT and its persistent and toxic decomposition products can still be found in elevated concentrations in sediments and the biota of the southern California coastal zone. Unfortunately, despite its ban in the U.S. and many other countries, estimates suggest that more DDT is produced and used today than in 1970. Most of it is used for mosquito and malaria control in developing tropical countries that cannot afford more costly and less effective alternatives to DDT, especially since the resurgence of malaria since the 1990s.

Dredged Material

With the exception of a few deep-water ports, most ports and harbors do not have sufficient natural depth for vessels to navigate safely and berth. Consequently, most ports and harbors must be dredged to increase navigable depth. Once sediments have been removed to deepen a channel or basin, suspended sediments tend to settle in the new topographic depression. Therefore, all dredged channels and harbors must be re-dredged periodically to remove newly accumulated sediment. In some high-energy regimes where the new channels are regularly swept by currents, or areas where very little suspended sediment is transported to refill the channel, dredging may be necessary only once every several years. However, other channels must be dredged more often, and some require almost continuous dredging.

Dredging is done either by scooping up buckets of sediment or by sucking sediment from the seafloor through a pipe lowered from a surface vessel. In most cases, the dredged material is loaded onto barges and transported to another location before being dumped into an estuary or the ocean.

Dredging destroys the benthos, causes increased turbidity, and, if the dredged material is contaminated, releases toxic substances into the water and suspended sediment at both dredging and dumping sites. These effects may be serious at some dredging sites, but they are generally more damaging at the disposal site. The U.S. has more than 150 aquatic disposal sites for dredged material. Most are in bays or coastal waters very close to the mouth of the estuary from which the material is dredged.

When dredged material is dumped, it descends quickly until it strikes the seafloor. Upon impact, it spreads rapidly across the seafloor as a suspended sediment cloud. Coarse-grained materials settle out quickly. Some smaller particles are partially buried with the coarse-grained material, and others are carried off by currents and deposited elsewhere where current speed is slower. Most or all benthos in the area buried by the dredged material are killed. The area is recolonized over the next few weeks or months except where the dredged material is badly contaminated with toxic substances or if dumping is frequent or continuous.

Because most dredged material consists of sediment taken from channels close to industrial and urban areas, it is usually contaminated with toxic substances from urban runoff, industrial discharges, sewage, and spills. Dumping at most dredged-material dump sites is continuous or is done several times each year. Consequently, the bottom at almost all such dump sites is covered with contaminated sediment, and the benthos is severely damaged on a continuing basis.

A proportion of the fine-grained contaminated dredged material is released as suspended sediment during dumping. Because the contaminants associated with these particles will be at least partially bioavailable, dredged material can contribute substantial quantities of toxic substances to the marine environment. For example, until the 1990s the amount of several toxic contaminants dumped annually at the dredged-material dump site near Alcatraz Island in San Francisco Bay (Fig. 16-8) exceeded the combined total annual input of these toxic substances to San Francisco Bay from more than 100 industrial and treated sewage discharges. Some of the dredged material previously dumped at the Alcatraz site has now been diverted to disposal on land or at a deep-ocean dump site.

 

Figure 16-8. Dumping of dredged material in San Francisco Bay. (a) The Alcatraz dredged-material dump site in San Francisco Bay is located close to the estuary mouth and to the city of San Francisco. (b) The dump site, which is located between Alcatraz Island and the shoreline in this photograph, is only a few hundred meters from one of the famed tourist attractions of San Francisco, Fisherman’s Wharf, and it is within easy view from much of the city.

At some dump sites, very heavily contaminated dredged material is covered within a few days by a cap of clean, sandy dredged material several tens of centimeters deep. Once under this cap, contaminants are effectively removed from the biosphere, but it is not clear what fraction of the contaminants, especially those associated with fine-grained materials, escape before being capped or whether erosion caused by waves and currents eventually breaches the cap.

Most dredged-material dump sites are located in low-current areas to ensure that as much of the dumped material as possible is retained at the site. However, at some sites, such as the Alcatraz dump site in San Francisco Bay (Fig. 16-8), with its fast tidal currents, all but the largest dredged particles are resuspended and swept away soon after their disposal. Alcatraz and other similar dump sites were originally selected near estuary mouths because it was asserted that the dumped material would be quickly swept to sea by the river flow. Unfortunately, the dredged material dumped at many such sites, including the Alcatraz dump site, is instead transported back into the estuary by estuarine circulation (Chap. 13).

The practice of dredging and dumping the dredged material within estuaries has two important effects. First, the material is partially transported back to, and deposited at, dredging sites within the estuary, thereby increasing the frequency and cost of dredging. Approximately 40% to 50% of the dredged material dumped at the Alcatraz site returns to dredging sites and must be re-dredged. Second, contaminants that were discharged to estuarine sediments decades ago, when waste discharges were largely uncontrolled, are continuously re-dredged, dumped, and resuspended within the estuary, where they come into contact with the biota. The Alcatraz site has been used for dumping dredged material since the 1890s. Since that time, the once extremely valuable commercial fish and shellfish populations of San Francisco Bay have been largely destroyed. Dredged material dumping has undoubtedly contributed to their decline.

Even if treatment techniques were available, treating estuarine sediments to remove historical contamination would not be possible because the sediment volumes are too large. In addition, land disposal of the dredged material is practical only in a few locations, and then only if the material is not contaminated. However, if dredged material disposal sites were moved offshore, beyond the biologically critical coastal zone, the contaminated material, especially if properly capped, would have less environmental impact on the limited benthic communities of the outer continental shelf and continental slope. In addition, if dredged material were dumped in the ocean, and if contaminant source control continued in the estuaries, contaminant concentrations in the estuaries would decrease, and dredged material eventually would be clean enough to be used for beneficial purposes on land.

Plastics and Trash

Although plastics are now known to be decomposed by bacteria in the oceans, they decompose very slowly in the environment. However, some plastic debris first breaks down into smaller particles that can be mistaken for food and eaten by marine organisms. Many species can neither digest the particles nor pass them through the gut, and plastic particles can accumulate in the gut until it is blocked, leading to starvation and death. Larger fragments of plastics are ingested by large animals, especially turtles, which mistake plastic bags and other plastic debris for their favorite food, jellies. Plastic fishing line, six-pack rings, plastic fishing nets, and all kinds of other plastic debris act as drifting traps that entangle and kill turtles, birds, and marine mammals (Fig. 16-9a).

Figure 16-9. Plastics can cause more than just aesthetic problems in the marine environment. (a) This northern fur seal pup is entangled by a section of lost or discarded gill net and would not have survived long without human intervention. (b) The remains of a dead Laysan Albatross chick (Phoebastria immutabilis) show the large variety and quantity of plastics that it had ingested. The ingested plastics were likely at least a contributing cause to the chick's death.

It has been found that microscopically small plastic fragments are ubiquitous in recent marine sediments and seawater. These fragments have been found in preserved plankton samples from the 1960s, and examination of more recent samples shows that their concentration has increased significantly since then. Adverse effects of plastic ingestion have been observed in larger animals that ingest relatively large particles of plastic (Fig. 16-9b), and there is substantial evidence that the ubiquitous microscopic fragments have adverse effects on zooplankton and benthic animals.

International law now prohibits the disposal of plastics in the oceans, but enforcement of this prohibition is virtually impossible, and violations are common. Plastic also reaches the oceans from many sources other than direct disposal, including storm-drain runoff and helium-filled balloons released at sporting events and other festive occasions.

In the 1980s, it was discovered that there was a large area at the center of the North Pacific subtropical gyre where floating plastic debris collects, carried into the center of the gyre by the Ekman transport processes described in Chapter 8. Subsequently, similar concentrations of plastic debris have been found in the centers of each of the five subtropical gyres (Fig. 16-10a). The area of greatest plastic debris concentration has been referred to as the North Pacific garbage patch, and the media have portrayed this area as being a huge visible debris field. However, this is a significant mischaracterization since the debris in most of the affected region (and affected regions in the four other subtropical gyres) primarily consists of particles that are generally invisible to the naked eye, with usually widely scattered larger plastic pieces or items. Nevertheless, the accumulation of plastic debris in these mid-ocean regions poses a threat to at least some marine organisms and birds. Since 1980, substantial efforts have been made in most countries to reduce the amount of plastics that enter the oceans, but these have only had modest success. There are also ongoing studies investigating how plastic debris might be collected and removed from the centers of the gyres. However, the amount of plastics is very large, and most of it is widely dispersed, so any removal efforts will be extremely costly and difficult.

 

Figure 16-10. (a) Plastic debris collects in the subtropical convergence zones at the center of each of the subtropical gyres. The largest concentration is apparently in the center of the North Pacific gyre and has been dubbed the “Pacific Garbage Patch.” (b) Plastic debris also washes up on the beaches of islands, such as the Hawaiian Islands, that are located within the subtropical gyres.

Metal, paper, and other trash items cause fewer problems in the ocean than plastics because they eventually corrode or decompose. Nevertheless, these discarded materials, including plastics, cause aesthetic problems when they wash up on beaches and shores or litter the seafloor that divers visit (Fig. 16-10b). Included among the floatable wastes are medical wastes, such as syringes, illegally discarded from vessels and into rivers and storm drains. These wastes have led to precautionary beach closures when they wash ashore. Storm drains are considered to be the primary source of most types of floatable wastes present in the oceans. 

Antifouling Paints 

Unless protected, almost any surface introduced into the ocean is quickly covered, or fouled, with a wide variety of marine animals and algae. Barnacles have an especially strong natural adhesive that enables them to attach and hold on to surfaces even in swift currents that can sweep off other fouling organisms. Hence, barnacles dominate the fouling community on vessel hulls and on structures in strong currents.

When a normally smooth vessel hull or other moving surface is fouled, friction between the hull and water increases, causing the vessel to either lose speed or use more fuel to maintain speed. Consequently, vessel hulls, turbines of tidal power plants, and water intakes and drainpipes must be protected from fouling.

The predominant and most effective means of reducing fouling is to coat the substrate with paint containing a toxic substance that will kill any organism that settles. The toxic substance must be bioavailable to perform its function, so the paint must release its toxic substance slowly into solution. Consequently, vessels and other structures release these toxic substances to the marine environment, causing an especially serious problem in harbors where boats are concentrated and water residence times are long.

For many years, most antifouling paints contained copper as their active toxic ingredient. Copper is highly toxic at moderate concentrations in its ionic form. However, at lower concentrations, it is nontoxic and readily complexes with organic matter, reducing its toxicity. Thus, as copper is released from an antifouling paint, it has the desired antifouling action, but it is quickly diluted and complexed with natural organic matter as it diffuses away from the treated surface. Copper does accumulate in the water of harbors and marinas, but adverse impacts on biota other than those fouling the painted surface have been extremely rare.

Although copper-based antifouling paints are effective, their effectiveness diminishes as the copper progressively dissolves. To reduce the frequency with which ships’ hulls must be cleaned and repainted, a more effective antifouling paint was developed in which tributyltin replaced copper. Tributyltin is much more toxic than copper and is released more slowly from antifouling paints. Hence, each application of tributyltin-based paint was effective for a longer period than an application of copper-based paint.

Unfortunately, once released into the water, tributyltin is degraded only slowly into a less toxic chemical form. Consequently, it retains its toxicity and tends to concentrate in the water in areas where many boats have such paints. Tributyltin has caused serious marine pollution problems in some areas. Many ports and marinas where tributyltin paint was used extensively were essentially denuded of all animal life. Because tributyltin is particularly toxic to mollusks, it destroyed populations of oysters and other species over a wide area far from its source in some estuaries. There has been a worldwide ban on the use of tributyltin-based paints since 2008. Fortunately, unlike DDT, tributyltin does not persist in the environment for decades. Rapid recolonization and recovery have occurred in many areas previously affected by tributyltin.

Radionuclides 

Among the most feared words in the English language are nuclear, radioactive, and radionuclide. This is, of course, because most people associate these terms with nuclear bombs. As a result, during the nuclear testing era from 1945 to about 1990, there was considerable attention, both by the public and among environmental researchers, to the introduction of radioactive materials to the environment, including the oceans, of radioactive fallout from nuclear tests. Dumping of radioactive wastes and discharges or accidental releases from nuclear industrial facilities. Some of the radionuclides from these sources do not occur naturally on Earth. Public fears of radioactive materials in the environment were heightened by a nuclear power plant accident in Chernobyl, Ukraine in 1986 and further exacerbated by the severe damage of several nuclear reactors near Fukushima Japan in 2011 following a massive earthquake and tsunami.

There has been extensive research on the effects of radioactive material from nuclear bomb test fallout, and radioactive materials discharged or dumped, either deliberately or as a result of accidents. The results of this research are summarized in Online Box 16B3, and the principal findings are summarized here.

1. In the marine environment, radionuclides enter biogeochemical cycles and behave in the same way as the stable isotopes of their elements (if stable forms exist). 
2. Each element and its radioisotope(s) have their own distinct behavior in the oceans. For example:
   1. Tritium (hydrogen-3), released in nuclear explosions, quickly combines with oxygen to form water molecules that join the ocean circulation system, where they behave almost exactly as other water molecules do. 
   2. An iodine radioisotope, iodine-131, enters solution in ocean water and is concentrated by marine biota, particularly certain species of algae. 
   3. Plutonium does not occur naturally but is rapidly attached to particles in the ocean environment. Most plutonium is carried to sediments by these particles, where it remains until it decays to other elements.
3. Radioisotope concentrations are easily measured even in environmental samples that contain only a few atoms of the isotope. For this reason, radioactive isotopes are used as tracers to study geochemical, biological, and physical processes in the oceans (Chap. 8). They are also commonly used as tracers in biological systems, including human medical scans. 
4. Radioactivity can have adverse effects on marine ecosystems and on human health, primarily because some anthropogenic radioisotopes concentrate in seafood and increase the risk of cancer in consumers.
5. Except for very limited areas surrounding some nuclear bomb testing sites, concentrations of anthropogenic radioisotopes in seafood are well below background levels of naturally occurring radioactive elements. 
6. The accepted theory of carcinogenicity is that any increase in radioisotope intake will increase the risk of cancer. The oceans’ assimilative capacity for anthropogenic radioactive materials may therefore be zero. In reality, a very small increase in radioactivity above natural background levels will not produce a measurable or significant increase in cancers. 
7. Because the ocean’s assimilative capacity for radioactive materials is so small, international agreements require that anthropogenic inputs be eliminated. Almost all nations adhere to these agreements. 
8. A very small amount of liquid radioactive waste continues to leak from the Sellafield nuclear industrial complex in Sellafield, Northern England. 
9. The former Soviet Union routinely dumped and discharged large quantities of solid and liquid radioactive waste into the Arctic Ocean, the Sea of Japan, and rivers that empty into the Arctic Ocean, until 2005, when Russia agreed to the global treaty that bans these practices.
10. In 2011, the Fukushima Daiichi nuclear power reactors in Japan were damaged by an earthquake of magnitude 9.0 (a once in a century occurrence) and the more than 40  m-high tsunami it caused (a once in a thousand years occurrence). Large quantities of water containing radioactive elements were eventually released into the oceans. 
    1. Studies showed that radioactivity levels rapidly reduced with distance from the reactors. 
    2. Within five years, levels were too low for any adverse effects to be found in any marine organisms studied (ranging from microalgae to mollusks and fishes), even in ocean areas close to the accident site. 
    3. The major impact on the oceans appears to have been the precautionary closure of the area to fisheries. 

Fears of radioactivity releases fueled by media accounts of the Fukushima and Chernobyl, Ukraine (1986) power plant accidents, and a 1979 accident at Three Mile Island in Pennsylvania (that released small amounts of radioactivity to the atmosphere) have caused public perception to conclude that nuclear power plants are unsafe and nuclear power should not be used in the future. While these fears are understandable, they are not based on scientific facts.

1. At present, there are about 420 nuclear power plants operating worldwide, and these provide about 9% of the world’s electrical power generation capacity and needs. 
2. Nuclear power is the only electricity-generating technology that is 
   1. Free from carbon dioxide emissions to the atmosphere, 
   2. Operates 24 h per day and can be operated at variable levels to meet hourly demand fluctuations, and 
   3. can provide city-scale amounts of power from a single plant with a small land-use footprint.
   4. Has a long history (since the 1950’s) of safe operations. The Chernobyl accident occurred at a poorly designed Soviet reactor with no safety containment vessel. The Fukushima accident was caused by one of the most powerful earthquakes, plus one of the largest tsunamis in human history. No other major accidents have occurred that have caused deaths or significant radioactivity exposure beyond a small number of plant employees. 
3. Waste disposal is a significant issue with nuclear power. However, there are breeder reactors that reduce the radioactivity of waste from other nuclear power plants, or wastes could be placed in safe storage and disposal sites. Disposal sites must be located where wastes will remain undisturbed until radioactivity is reduced to background levels. The best such geologically stable long-term storage locations may be beneath the sediments in the center of oceanic tectonic plates. Technologies to emplace radioactive waste deep within ocean sediments were extensively researched and developed in the U.S. in the 1970s. This research was abandoned after the London Dumping Convention adopted a ban on all disposal of wastes in the oceans in 1975.  

Noise 

The ocean environment has always been noisy, with sounds generated by many marine species that use sound for communication or other purposes (Chap. 14) and by rain, waves, and earthquakes. However, the oceans are becoming progressively noisier due to sound from ships, offshore resource extraction, including offshore oil and gas development, from military and civilian use of sonar, and from seismic surveying. Very little is known about the individual sources of sound in the oceans or about how anthropogenic noise may affect marine species. However, there is concern that anthropogenic noise may adversely affect some species, especially marine mammals that communicate and navigate by using sound. 

In March 2000, 14 beaked whales and two minke whales became stranded on beaches in the Bahamas after they were exposed to sound emitted by the U.S. Navy in testing of a new high-intensity, mid-frequency sonar. Six of the beaked whales died and were found to have internal bleeding that apparently resulted from close-range exposure to the high-intensity, mid-frequency sonar. As a result, use of this sonar, which uses higher intensity than other anthropogenic sound sources and a frequency not used in other sonar applications, has now been severely restricted. Precautions are now taken to ensure that no marine mammals are within a wide exclusion zone whenever this sonar, which is believed to be essential for national security, is tested. Also, as a result of the finding that excessive sound can harm marine mammals, ongoing research aims to study the effects of all anthropogenic sounds in the oceans.

Nonindigenous Species

Marine species are transported around the world in ships’ ballast water, attached to ships’ hulls, and in other unintended ways. Species are also deliberately transported from one location to another to be used in aquariums or for aquaculture, and many of these are inadvertently or deliberately released to marine ecosystems in which they do not occur naturally. Once in their new environment, these species may die if they are unable to tolerate the new conditions or avoid their new predators, or they may survive and reproduce with little effect on the rest of the ecosystem. However, some nonindigenous species not only survive but also reproduce, spread rapidly, and out-compete native species. Estimates suggest that approximately 15% of introduced species cause severe harm to their new environment.

Many examples can be given of nonindigenous species that have severely damaged terrestrial and freshwater ecosystems. Fewer examples of damage are known in the marine environment, probably for several reasons. First, marine biota are not as easily observed as freshwater and land biota; thus, adverse changes due to nonindigenous species may not be noticed. In addition, because the ecology of marine ecosystems is poorly known, declines of important species and other ecological changes may be attributed to other factors, even if caused by nonindigenous species. Open-ocean ecosystems are generally well connected with each other and more uniform than terrestrial or freshwater ecosystems. However, coastal marine ecosystems, especially estuaries, are more isolated from one another and therefore more vulnerable to the introduction of nonindigenous species.

San Francisco Bay is an excellent example of an estuary that has been severely damaged by nonindigenous species. It is the only major estuary on a long stretch of coast, and as a result, it is isolated from other estuaries. Therefore, the Bay had many unique species when European settlers arrived. The settlers deliberately introduced nonindigenous species, such as the eastern oyster (Crassostrea virginica), in an attempt to populate the bay with valuable food species. The oyster did not survive, but a variety of other species brought in with the oyster, either attached to its shell or in the seawater in which it was transported, did become established. 

Eastern oysters were the first of many introductions. Among these introductions, one notable species was striped bass, which became a major anadromous sport fish. However, the striped bass competes for food and habitat with indigenous species, such as salmon and sturgeon. These and other introductions of nonindigenous species into San Francisco Bay have caused dramatic changes. Most original species in the Bay are now gone, and the majority of species present today were introduced. For example, almost half of the fish species in the critical wetland habitat are nonindigenous. Nearly all invertebrates that now inhabit shallow, nearshore parts of the Bay are also non-indigenous. Indigenous clams and other edible mollusks have been largely replaced by a small, economically valueless species of Asian clam.

Habitat Alteration 

Alteration or destruction of habitat is among the most damaging forms of pollution in estuaries and the coastal zone. The most serious habitat destruction is the filling of wetlands to create dry land. An estimated 450,000 km² (almost 50%) of the historical wetlands of the U.S., excluding those in Alaska, have been lost since European settlers arrived. In some areas, such as San Francisco Bay, less than 10% of the historical wetland area remains (Fig. 16-2). Many tens of thousands of acres of wetland habitat for aquatic birds, juvenile fishes, and other species have been lost. Other forms of adverse habitat alteration or loss include beach erosion or loss due to coastal structures (Chap. 11), dredging of channels through mudflats, burial of seafloor by dredged material, and damage to coral reefs by anchors.

Less obvious habitat alteration is caused by human activities that lead to changes in salinity, temperature, and turbidity. Soil erosion has increased in many watersheds because trees and other vegetation have been removed. Increased suspended sediment loads have altered sediment grain size in many rivers, making the sediments unsuitable as spawning habitat for anadromous fishes. Excess turbidity has reduced light penetration and thus rendered both benthic and pelagic habitats less suitable, or unsuitable, for algae growth, with resultant effects throughout the food web. For example, more than 90% of the historical sea grass cover has been lost in Galveston Bay, more than 75% in Mississippi Sound, and more than 50% in Tampa Bay.

Reduction of freshwater flow into estuaries is a particularly serious form of habitat alteration. In many estuaries, species zonation is based on the salinity distribution. For example, plants rooted in freshwater are replaced by saltwater species in the lower parts of the estuary, where salinity is higher. If freshwater inputs are drastically reduced, as when rivers are dammed, salinity ranges can be shifted many kilometers up an estuary, dramatically altering the balance between freshwater-dominated and seawater-dominated habitats.

In some estuaries, such as San Francisco Bay, freshwater input reductions have caused the critical brackish water zone, where much estuarine productivity occurs, to migrate from a wide wetland-fringed part of the estuary into a deeper, narrower, faster-flowing section. Primary productivity has been lowered because of the smaller area of suitably brackish water and the high turbidity. Such loss of primary productivity may have contributed to dramatic declines in anadromous fish species in this and other estuaries. Reduction of freshwater inflows also tends to increase residence times within the estuary. Consequently, contaminants have longer residence times and reach higher concentrations.

Fishing

Far from being the traditional environmentally friendly activity that it is often portrayed to be by the media and thought to be by the general public, fishing is acknowledged by most marine scientists to be the human activity that has caused more adverse impacts on the oceans than anything other than anthropogenic releases of carbon dioxide and nutrients. Fisheries and overfishing, their principal impact, are discussed in Chapter 2.

Fishing, particularly commercial fishing and subsistence fishing in some nations, contributes to ocean contamination or pollution in many ways beyond overfishing. The most significant impact of fishing on ocean environments is the habitat disturbances and destruction caused by trawl fishing for fish and shellfish that involve dragging nets across the seafloor. Trawling generally destroys or collects all epibenthos, including delicate and extremely slow-growing deep sea corals, which take centuries to regrow even if they can recolonize the altered seafloor sediments. 

Large quantities of fishing gear, including fishing line, fishing nets, and Styrofoam floats, much of which are made from plastics, are lost and can have adverse effects on marine organisms, as discussed earlier in this chapter. This lost or discarded fishing gear is so widespread and problematic that the media often refers to it as “ghost gear.” In addition, vessels intentionally or accidentally discharge oil and diesel fuel, oily bilge waters, sewage, and food and packaging wastes. Such discharges are regulated or banned by many nations, including the U.S. However, as is true of fishing regulations, anti-discharge laws are difficult to enforce on the high seas, and especially difficult in those areas that are not part of any nation’s exclusive economic zone (EEZ), where many of these laws do not even apply. Fishing vessels also have hull paints that contain toxic chemicals to combat fouling by organisms such as barnacles, and these toxic chemicals can damage fishery resources.