What is Land-based Pollution?
When we hear about ocean pollution, we often think of oil tanker spills. In fact, only 10 percent of pollution in the seas comes from this type of accident. A whopping 80 percent of ocean pollution comes from human activities on land and poses risks to human health and the environment. These land-based human activities pollute lakes, rivers, streams — and eventually oceans:
Municipal Wastewater and Stormwater Run-off
In Canada, approximately 25 percent of the population is without some form of sewage treatment. This situation has led to sewage discharges that range from major cities to leaks from home septic systems. As a result, about 500 billion litres of untreated wastewater flow into Canadian waters (both fresh and marine). Municipal wastewater can be a source of a number of pollutants, including: nutrients (phosphates and nitrates), oxygen-demanding material, suspended matter, bacteria and viruses, and a variety of toxic substances.
The primary concern is human health. Sewage treatment continues to be important to public health because it controls the spread of disease. Today, areas polluted with sewage are closed to swimming. Contaminated shellfish harvesting areas are also closed because eating shellfish from these locations is unsafe.
Other problems related to discharges of untreated sewage can include: algal blooms that consume excess oxygen and can produce toxins; water that becomes cloudy with silt; disruptions in habitat; and impacts on the normal growth of aquatic creatures. Two other sources of marine pollution are non-point (widely spread) sources, such as landwash from agricultural areas (including manure, fertilizers, and pesticides) and run-off from industrial or commercial areas.
Hazardous Household Wastes
Canadians dump 30 million litres of used motor oil into the environment annually. In fact, almost half the oil that ends up in oceans comes from land.
- Toxicants in this oil can cause health problems like liver disease in fish and cancer in humans.
- Other hazardous wastes poured into our waters include paints, solvents, and corrosive chemicals from household cleaners. Sometimes these chemicals wash into storm sewers or end up in landfill sites, where they can leach into the soil and contaminate groundwater and nearby streams.
Factories and mines discharge toxic chemicals, such as dioxins, furans, and more harmful polycyclic aromatic hydrocarbons (PAHs). They also release heavy metals like mercury and lead, plus airborne pollutants, including sulphur dioxide and nitrogen oxides, which cause acid rain.
- Some toxic chemicals, such as dioxins and furans, build up in the environment and persist for a long time. Removing them can be difficult, if not impossible. These persistent chemicals come from many sources, including combustion and chemical processes used in industry. They can cause cancer, liver damage, reproductive problems, and birth defects in animals and humans.
- Some persistent pollutants build up in the fatty tissue of plants, animals, and humans. This process is called bioaccumulation. When plants or animals are eaten, the contaminants in their fat enter the body of the consumer. This process is called bioconcentration because the consumer gets higher concentrations of contaminants through its food. Bioaccumulation of contaminants is especially high in the Arctic, where many species have a lot of fatty tissue. Airborne PAHs fall to the earth in Arctic snow after blowing on air currents and jet streams from industrial areas thousands of kilometres away.
- Imagine an enormous tank the size of a football field, 4.5 metres deep, full of healthy fish. If you poured just a tablespoon of mercury into the tank, the fish would become unsafe to eat. Mercury compounds contaminate water, often through pulp and paper plant discharges.
- Industrial smokestacks spew sulphur dioxide and nitrogen oxides into the atmosphere, causing acid rain. When water becomes too acidic, plants and animals can die.
- Many industries and power generating plants cause thermal pollution by using water as a cooling agent. Heated water is returned to rivers and lakes, creating a warm zone that attracts more creatures than the surrounding colder water. When the flow of heated water stops, the site's temperature suddenly drops and may cause these creatures to die.
How Many Oceans Are There?
Usually, we think in terms of seven oceans: the North Atlantic, South Atlantic, North Pacific, South Pacific, Arctic, Antarctic, and Indian oceans. Some other large bodies of salt water are the Mediterranean Sea, the Gulf of Mexico, and Hudson Bay. There's no telling where one ocean merges into another. Countries have borders between them, but not oceans. All these watery bodies really add up to a single huge ocean, interconnected by currents and tides, covering the whole planet. The continents are like huge islands dotting the global sea.
You wouldn't believe all the garbage that ends up in our oceans and along beaches everywhere.
- Marine debris can be anything we throw away daily — from fast food containers and pop cans to motor oil, bottles, rope, and fishing line.
- Most debris cannot break down for three to five years, and as it continues to be released year after year, it accumulates in the marine environment.
- Debris gets into the marine ecosystem through waste disposal or loss of materials from tourists, boaters, commercial shipping and fishing operations, and construction along shores and at sea.
- Tides and currents carry debris to even the most remote locations, such as B.C.'s Queen Charlotte Islands.
- Marine creatures get tangled and trapped in plastic fishing lines, nets, ropes, and six-pack rings. Sea turtles can choke on plastic bags and balloons they mistake for jellyfish.
- Ocean garbage also damages boat propellers, clogs up water intake pipes, and blocks pumping systems.
- Lost or discarded fishing nets, known as "ghost nets," continue to trap and kill sea creatures, depriving fishers of their catches.
- Tourism languishes when vile garbage washes up on shorelines.
We can no longer fish to our heart's content. Now, most countries monitor a zone of up to 200 nautical miles (370 kilometres) from shore, where they control who fishes and how much is caught. About 95 percent of the world's catch occurs in this zone. The other five percent is caught on the "high seas." High seas fishing is regulated by regional groups, such as the North Atlantic Fisheries Organization. Not all countries belong to these groups, however, and even those that do may break the rules, since there may be nobody to enforce them.
The government relies on scientific fish surveys and commercial harvest statistics to decide how many tonnes of fish can be caught each year. Nonetheless, Atlantic cod and other fish stocks worldwide continue to decline alarmingly.
- Fisherfolk worldwide catch 80 to 90 million tonnes of fish and shellfish a year. In 1992, the global fish catch was five times greater than in 1952 — mainly on account of our swelling human population. What's more, some trawler nets today are big enough to trap a dozen Boeing 747 planes.
- In 1968, 1.5 million metric tonnes of northern cod were caught in the Atlantic. By 1990, the catch had plummeted to about 200,000 tonnes. Cod fishing in most of Atlantic Canada was therefore banned in 1992, resulting in the loss of as many as 50,000 jobs.
- Sodium cyanide and dynamite, used to catch tropical fish, also kill aquatic wildlife, such as the tiny organisms that form coral reefs.
- "Ghost fishing" occurs when lost or discarded nets trap and kill sea creatures.
- Often fishing trawlers catch species they don't want. For example, for every tonne of wild shrimp harvested, four tonnes of "by-catch" fish are captured accidentally. Often, the unwanted catch is thrown away, dead or dying. Seventeen to 39 million tonnes of fish are discarded by trawlers each year.
- Nets are dragged over 30,000 square kilometres (almost 15 percent) of the Atlantic continental shelf, harming plants and animals on the ocean floor and stirring up silt that can smother bottom-dwellers.
- Fish caught too young may fail to reproduce in their lifetime. On the other hand, older fish lay more eggs, so catching them could also be bad news for their populations.
- Taking too much of any species from an ecosystem unbalances the food web. Many marine creatures depend on the same fish that people eat. For example, whales, eagles, seals, and white sturgeon rely on Pacific salmon. Atlantic cod depend heavily on capelin. So, when we catch too many salmon, we may be starving other species and putting fishers out of work. If we start catching more capelin to make up for fewer cod, we may disrupt the food supply that cod need to replenish their numbers.
How Does Pollution Affect Aquatic Ecosystems?
Pollution impacts on different parts of the ocean in different ways. Unfortunately, areas with a lot of productive sea life tend to be most affected.
- The ocean's surface, where air, water, and sunlight meet, is especially vulnerable to airborne contaminants and pollution from sources like oil spills. This layer teems with all-important plankton, which nourishes other ocean creatures and supplies oxygen to our planet.
- Tides, winds, and currents carry surface toxicants to bays and inlets, where they often build up. Enclosed waters, such as the Mediterranean, Baltic, and Yellow seas, plus the St. Lawrence Estuary and the mouth of the Mississippi River, suffer from an extraordinarily high accumulation of these pollutants.
- Estuaries (tidal river mouths where fresh and salt water merge, supporting an unusual diversity of plant and animal life) are particularly hard hit by marine pollution. Pollutants flowing through inland waterways are funnelled through estuaries on their way to the ocean. As well, nearby cities and communities dump sewage and other harmful wastes into estuaries.
Loss and Degradation of Coastal Habitat
Coastal lands and waters, such as estuaries, salt marshes, coral reefs, and mangrove swamps, provide some of the most important marine habitat of all. Salt marshes, for example, produce up to three times as much plant life as the richest farmland. About 70 percent of commercial fish species spend part of their life cycle in these spots. Loss and degradation of habitat is a huge problem for marine wildlife. Here's how humans, often unknowingly, damage and destroy coastal wildlife habitat:
- Over two-thirds of the world's human population lives within 80 kilometres of the ocean, and nearly half of our largest cities are built on or near estuaries. About 20 percent of Canadians reside within 50 kilometres of the coast. That number is growing in some areas. For instance, Victoria's population mushroomed by 32 percent and Vancouver's by 28 percent between 1971 and 1986. Since 1880, over 70 percent of shoreline habitat and half the wetlands in the Fraser River estuary have been diked, filled, drained, dredged, and developed out of existence.
- Construction too close to shorelines ruins nesting beaches for sea turtles, rocky nurseries for seals, and feeding grounds for resident and migratory birds.
- Dams interrupt water flow and disrupt fish migration and spawning, while changing ocean currents and causing erosion along rivers.
- Water storage projects, such as reservoirs and hydroelectric dams, change the pattern of seasonal water levels and reduce the amount of freshwater flowing downstream. This diminished flow can change the delicate balance of salt and freshwater in estuaries, affecting the kinds of wildlife that can flourish there.
- Causeways (raised roads over water bodies) ruin habitat for bottom dwellers, increase siltation, and restrict the ebb and flow of water.
- Construction causes erosion and sedimentation, smothering plants and fish-spawning areas. Coral reefs are especially sensitive, as coral needs clear water to reproduce.
- Draining and filling for agricultural purposes have resulted in the destruction of 85 percent of Canadian salt marshes and freshwater wetlands over the last 200 years.
- Forest logging causes the erosion of earth, which washes into the ocean and forms sediment.
- Fishing nets from trawlers destroy habitat for bottom dwellers like seaweeds, sponges, molluscs, starfish, and anemones.
- All-terrain vehicles crush beach plants and animals, boat waves drown aquatic bird nests, and hikers trample over well-camouflaged ground nests.
- Increased tourism means more sewage, traffic, and noise, destroying natural areas and scaring away the very wildlife tourists come to see.
Scientists estimate that, at the current rate of extinction, as many as 25 percent of all species on Earth — from microscopic organisms to plants, mammals, and birds — could disappear forever by the early decades of the 21st century. Of the approximately 1,100 fish species in Canada alone, four have become extinct, two extirpated, and 54 listed as endangered, threatened, or vulnerable.
- Biodiversity disappears through habitat disruption, overfishing, poaching, and the accidental or intentional introduction of exotic (non-native) species into aquatic ecosystems. These exotic invaders sometimes prey on native wildlife or compete with them for food and nesting spots. Thus, the balance of an ecosystem is upset, at times so badly that native species vanish. For example, the wildflower purple loosestrife was brought to Canada from Europe. Many people planted it in their gardens. Now, this exotic species is rapidly invading Canadian wetlands, choking out native cattails and bulrushes. As these important plants disappear, so do the species that rely on them for food.
- Loss of biodiversity is a serious concern. When a species disappears, everything else in its ecosystem suffers too. For instance, sea otters along B.C.'s and Alaska's coasts were nearly hunted into extinction for their pelts early in this century. Then populations of purple sea urchins — the otters' principal prey — went out of control. They munched away the kelp forests inhabited by many marine species, debilitating the entire ecosystem. Birds like bald eagles, which had depended on kelp forest fish, began to disappear. Now sea otters are protected, and the other inhabitants of this ecosystem are reaping the benefits.
- While the genes of many life forms have allowed scientists to develop life-saving medicines, there's no telling how many scientific discoveries will be lost if we let wild species vanish.
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