 SENSITIVITY OF COASTAL ENVIRONMENTS TO OIL  The U.S. Coastguard have listed shoreline types, from the least (low figures) to the most sensitive ones to oil pollution:Exposed rocky cliffs and seawalls Wave cut rocky platforms Fine to medium-grained sand beaches Coarse-grained sand beaches Mixed sand and gravel beaches Gravel beaches/Riprap Exposed tidal flats Sheltered rocky shores/man-made structures Sheltered tidal flats Marshes It should be noted that other shore types and shallow underwater habitats are also very sensitive to oil pollution, including:Mangroves (And according to ITOPF: "Leaving residual oil to weather and degrade naturally is usually recommended for sensitive shoreline types such as salt marshes and mangroves, because they have been shown to be more easily damaged by the physical disturbance caused by clean-up teams and vehicles than by the oil itself. If any cleaning is attempted, it should be carried out with specialist guidance and advice.") Coral reefs See also NOAA. EFFECTS Spilled oil and certain cleanup operations can threaten different types of marine habitats in different ways. Coral reefs are important nurseries for shrimp, fish, and other animals as well as recreational attractions for divers. Coral reefs and the marine organisms that live within and around the reefs are at risk from exposure to the toxic substances within oil as well as smothering. Exposed sandy, gravel or cobbled beaches are usually cleaned by manual techniques. Although oil can soak into sand and gravel, few organisms live full-time in this habitat, so the risk to animal life or the food chain is less than in other habitats, such as tidal flats. Sheltered beaches have very little wave action to encourage natural dispersion. If timely cleanup efforts are not begun, oil may remain stranded on these beaches for years. Tidal flats are broad, low-tide zones, usually containing rich plant, animal, and bird communities. Deposited oil may seep into the muddy bottoms of these flats, creating potentially harmful effects on the ecology of the area. Salt marshes are found in sheltered waters in cold and temperate areas. They host a variety of plant, bird,and mammal life. marsh vegetation, especially root systems, is easily damaged by fresh light oils. Mangrove forests are located in tropical regions and are home to a diversity of plant and animal life. Mangrove trees have long roots, called prop roots, that stick out well above the water level and help to hold the mangrove tree in place. A coating of oil on these prop roots can be fatal to the mangrove tree, and because they grow so slowly, replacing a mangrove tree can take decades. Sea-bottoms. Oil contamination of the seabed may cause serious long- and short term effects on bottom-dwelling organisms (animals, algae and microorganisms). Filtering organisms such as oysters and mussels and clams which filters large volumes of water to get their food are especially likely to accumulate oil or oil components. In addition, if tar-like clumps of oil sink to the bottom, they may destroy living conditions for bottom-living organisms, as well as nursing grounds for fish and shellfish. At low temperatures, oil tends to persist for long periods because of the low rates of evaporation. The frozen ground prevents it from seeping in, and this has the effect of making it travel for long distances. Disturbance of the thin layer of vegetation covering a frozen soil can precipitate catastrophic meeting of the underlying ice and result in extensive thermokarst erosion. Tundra environments are particularly susceptible to disturbance, and effects remain visible for many years. Many of the Arctic plants are very susceptible to pollutants, especially lichens which are the main food of reindeer.RECOVERY The negative effects of on oil spill may eventually fade away, but in many cases it will be matter of several years, even decades, before an area or ecosystem has fully recovered from a spill that caused extensive damages. Every situation is unique and depending on the particular conditions and circumstances in that area, and on the characteristics of the spill. Some areas might recover in a matter of weeks, others will need up to 20 years. The recovery of the affected habitats and species following an oil spill will to a large extent depend on the type of ecosystem , the vulnerability of the species and not least the climate of the region where the oil spill occurs. Generally, recovery will proceed faster in warmer climates and on rocky shores compared to cold climates and, for example, marshes. The long-term effects on deeper bottoms (i.e., if oil sinks and is absorbed in bottom sediments) is also a matter of concern. The best documented evidence concerning the recovery of ecosystems affected by massive oil pollution are from the Persian Gulf and resulting from the discharges associated with the Gulf War in 1991. Studies (GESAMP) suggest that the chronic and acute releases that took place were rather rapidly accommodated by the system. Already at the end of 1992, researchers reported that many of the worst hit beaches in Saudi Arabia were almost clean of oil. It is believed that this may have been the result of the warm water of the Gulf and the fact that its bacterial populations were able to degrade and weather the oil much more quickly than previously believed to be possible. The experience gained from the Exxon Valdez spill has been documented, and could serve as one example of what happens in the aftermath of a major spill in a sensitive area. See, for example, the web site of the Exxon Valdez Oil Spill Trustee Council, and NOAA Office of Response and Restoration ("NOAA biologists have been monitoring the long-term effects of the spill and cleanup efforts. Here are some of their reports, along with links to more information elsewhere"). The economic recovery of an area will depend on the possibilities to regain the confidence of the consumers for marine products from the region and convince the tourists that the area is once more clean and as attractive as ever before. Intense marketing campaigns (possibly financed by some of the money paid as compensation) might be important in such endeavours.The information above has been compiled from several sources, including the following:
|
Páginas
▼
Sem comentários:
Enviar um comentário
1) Identifique-se com o seu verdadeiro nome e sem abreviaturas.
2) Seja respeitoso e cordial, ainda que crítico.
3) São bem-vindas objecções, correcções factuais, contra-exemplos e discordâncias.