Water pollution is caused by the sudden or ongoing, accidental or deliberate, dis- charge of a polluting material. In Chapter 6, we saw how increasing human pop- ulations put pressure on the oceans and marine environment. More and more people on the planet lead to more of the following:
•
Sewage produced;•
Fertilizers, herbicides, and pesticides used for crops, lawns, golf courses, and parks;•
Fossil fuels extracted and burned;•
Oil leaked and spilled;•
Land deforested and developed; and•
Various byproducts of manufacturing and shipping generated.Cultural, political, and economic forces affect the types, amounts, and man- agement of waste produced. Increasing population is just one contributor to increasing pollution. As with everything in the environment, the causes and effects are complex.
Groundwater has been contaminated by leaking underground storage tanks, fertilizers and pesticides, unregulated hazardous waste sites, septic tanks, drainage wells, and other sources. This contamination threatens the drinking water of 50% of the United States’ population.
The three major sources of water pollution are municipal, industrial, and
agricultural.Municipal water pollution comes from residential and commercial waste water. In the past, the main way to treat municipal wastewater was to reduce suspended solids, oxygen-demanding materials, dissolved inorganic compounds,
and harmful bacteria. Today, the focus is on the improvement of solid residue disposal from municipal treatment processes.
The agricultural midwest of the United States has developed water pollution problems. For example, in Iowa where chemical fertilizers are used over 60% of the state, some private and public drinking water wells have gone over safety standards for nitrates. A substantial number of towns in Nebraska have also shown high nitrate levels and require monthly well testing.
Pollution of marine ecosystems includes runoff from land, rivers, and streams, direct sewage discharge, air pollution, and discharge from manufacturing, oil operations, shipping, and mining.
Although coastal cities have the greatest impact on ocean ecosystems, pollu- tion from runoff is not limited to coastal regions. Runoff from over 90% of the Earth’s land surface (inland and coastal) eventually drains into the sea, carrying sewage, fertilizers, and toxic chemicals. Similarly, air pollution from inland as well as coastal cities, including byproducts of fossil fuel consumption, poly- chlorinated byphenyls (PCBs), metals, pesticides, and dioxins, eventually finds its way into the oceans after rain or snow.
Increased oil demand has increased offshore oil drilling operations and oil transport. These activities have resulted in many oil spills. The number of oil spills worldwide of between 7 and 700 tons and greater than 700 tons has var- ied in the past 30 years, with some years being better than others. Table 8-1 lists the top fifteen oil spills (excluding acts of war) recorded by the International Oil Tanker Owners’ Pollution Federation (IOTPF). The IOTPF measures all oil lost to the environment, including that burned and released into the atmosphere or still held in sunken ships.
For comparison, the well-known Valdezspill of 1989, thought by many to be a particularly bad spill, was not the worst ever seen. That spill (rated 35th in largest spills), off the coast of Alaska, was not as extensive as many others, but had a huge impact on the delicate and pristine polar environment.
Spills account for only 10% of marine oil pollution. About 50% of oil pollu- tion in marine waters comes from ongoing low-level sources such as marine terminal leaks, offshore dumping, oil drilling mud, land runoff, and atmospheric pollution from incompletely burned fuels. We will learn more about the various polluting effects of fossil fuels in Chapter 13.
Cumulative pollution effects on ocean ecosystems are very serious. For example, in the Gulf of Mexico, scientists have identified “dead zones” in once highly productive waters. These zones have been traced to excessive nutrients from farms, lawns, and inadequately treated sewage. This stimulates rapid plankton growth that in turn leads to oxygen depletion in water.
Blooms of toxic phytoplanktons and red tides have increased in frequency over the last two decades, and may be linked to coastal pollution. For example, storm water runoff carries with it suspended particulates, nutrients, heavy metals, and toxins. The effects of the storm water runoff often cause dinoflagellate (red tide) blooms following storms. These events cause mass mortality among some fish species, resulting in marine mammal deaths, and can be a serious threat to human health.
Volume Rank Ship Year Location (tons)
1 Atlantic Empress 1979 Off Tobago, West Indies 287,000 2 ABT Summer 1991 700 nautical miles off Angola 260,000 3 Castillo de Bellver 1983 Off Saldanha Bay, South Africa 252,000 4 Amoco Cadiz 1978 Off Brittany, France 223,000 5 Haven 1991 Genoa, Italy 144,000 6 Odyssey 1988 700 nautical miles off 132,000
Nova Scotia, Canada
7 Torrey Canyon 1967 Scilly Isles, UK 119,000 8 Sea Star 1972 Gulf of Oman 115,000 9 Irenes Serenade 1980 Navarino Bay, Greece 100,000 10 Urquiola 1976 La Coruna, Spain 100,000 11 Hawaiian Patriot 1977 300 nautical miles off Honolulu 95,000 12 Independenta 1979 Bosphorus, Turkey 95,000 13 Jakob Maersk 1975 Oporto, Portugal 88,000 14 Braer 1993 Shetland Islands, UK 85,000 15 Khark 5 1989 120 nautical miles off 80,000
Atlantic coast of Morocco
35 Exxon Valdez 1989 Prince William Sound, 37,000 Alaska, USA