Pollution blockades marine organisms [Archives:2005/903/Health]
By: Dr. Akram Al-Kershi
Good quality water and clean bottom are essential for healthy growth and survival of marine organisms. However, some places in our marine environment, especially coastal areas, are now under direct threat from the increasing level of various types of pollution. In the main coastal cities, only about 30 to 40 percent of inhabitants are served by sewage networks. In Aden, most of the sewage is discharged directly into the sea. The discharge point is located near the port and a bad smell is widespread in the area. Some official reports have recorded bacterial contamination in the area. In Al-Hodeidah, wastewater is discharged to a series of oxidizing ponds and eventually into the sea. In Mukalla and the other smaller towns, sewage is discharged directly into the sea without treatment. Sewage effluent with high concentrations of nitrogen, phosphorous and organic matter, has the potential to cause eutrophication when discharged into coastal waters. High nutrient concentrations cause phytoplankton and macro algal blooms. Death and decay of algae will cause oxygen depletion and death of marine organisms. Corals and sea grass may be degraded by macro algae and epiphytic overgrowth. The use of fertilizers and pesticides is widespread in Yemen. These harmful substances eventually end up in the sea. Tin cans, broken glass, plastic bags, nets and many other items can be seen in waters near fishing harbors, coastal villages and offshore islands. These substances can affect marine organisms by entanglement or ingestion. Entanglement is a problem for many marine organisms, such as turtles, birds and marine mammals. Ingestion of plastic bags may cause a problem for the leatherback turtle, which normally eats jellyfish. Litter may also deform the aesthetic value of coastal areas, posing a threat to tourism. The discharge of increased amounts of sediment from wadis (seasonal small rivers) and dust storms increases water turbidity reducing light penetration, limiting growth and causing death of coral reefs and sea grass beds.
Potential sources of oil pollution in the Yemeni marine environment include ships passing through the Red Sea and the Gulf of Aden, oil export terminals, unloading and shipping operations and oil derived from land runoff or groundwater discharge. There is the potential for significant environmental damage in the event of an oil spill by export pipelines and storage tankers. The October 2002 MV Limburg accident off our southern coast is an example of unexpected environmental damage due to oil pollution. Approximately 16,000 ships pass through the strait of Bab-al-Mandab annually, many of which dump their waste in Yemeni waters. Dirty ballast waters lead to formation of tar balls that have been found in many parts of our marine habitats. Solid waste from passing ships can be seen on our beaches. There are three oil export terminals, one at Ras Isa on the Red Sea and two at Bir Ali and Shihr on the Gulf of Aden. There is the possibility of small operational spills during loading. Daily bunkering supply in the port of Aden is approximately 40,000 metric tons. A bunker barge sank in 1995 causing considerable oil pollution in the Tawahi area. Aden refinery loads and unloads millions of tons annually. Oily water resulting from the refining process is separated and the effluent water discharged into the sea (Khor Gadir). Oil and its derivatives are very toxic to marine plankton, harming all other marine organisms depending on them. It contaminates gills and respiratory organs of fishes and other marine creatures causing suffocation and death. Contaminated feathers of seabirds make them unable to fly, so they may sink or slowly die on beaches. It may also directly harm marine mammals by contaminating their fur, skin and respiratory tracts, or indirectly by killing their food. In the event of a large spill, winds and currents drive the oil into very sensitive areas of extensive coral reefs, sea grass, mangroves and sabkhah communities and valuable finfish and shrimp fishing grounds. In Yemen, there is limited contingency planning and sensitive areas have not been mapped.
Hot cooling water discharged into the marine environment by electric power stations may have long-term harmful effects on organisms of limited temperature range. Electric power stations at Ras Katheeb, Mokha and Al-Hiswa discharge salinated hot water directly into the sea, raising the temperature of surrounding waters. The effects of this have not yet been estimated.
Widespread coral mortality has already occurred on Yemen's coral reefs. In many areas, this appears to be associated with recent coral bleaching. Increased coral bleaching and mortality are related to global warming and climate change due to atmospheric pollution by carbon dioxide and other greenhouse gases. When pollutants enter the marine food chain, pollution can become a serious problem and be lethal to plants, animals and man.
Dr.Akram Al-Kershi is an assistant professor in the Department of Environmental & Earth Sciences at the Faculty of Sciences, University of Sana'a.
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