Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/175

Environmental Impact of the Oil Industry rivers and the cutting of canals (known as Slots). This causes some of the greatest damage that the oil industry inflicts to the Fresh and Brackish water ecozones, and especially to the dynamic and spatially extensive ecotone where the two ecozones meet. The World Bank, in its 1995 report, identifies nine specific problems associated with canalisation. These are:
 * destruction of fishing grounds;
 * changes in soil salinity with negative effects on forest vegetation;
 * changes in water flow patterns, disturbing patterns of erosion and sediment deposition;
 * dredging temporarily increases muddiness and reduces the water's oxygen content–this harms fish stocks;
 * during the rainy season dredging spoils can erode, making water muddy and sometimes poisonous;
 * a short-term increase in the biochemical oxygen demand because of dredging material and waste from houseboats;
 * reduced farm yields because of toxic substances in the dredging spoil;
 * reduced farm yields because of flooding; and
 * destruction of mangrove and fresh water swamp forests.

Also, it should be remembered, regular dredging and deposition of dredging spoil, often onto farmland, is a necessary part of maintaining access.

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