pesticides, and continue to industrialise (the River Niger is a prime site for industrial projects). A major source of local industrial pollution is the wastes of motor-boats.
Solid wastes mainly take the form of non-degradable manufactured items of which plastic is the prime offender, and farmers now complain about the amount of plastic bags which occur in the alluvium deposited on the seasonal flood plains.
Oil pollution is an epidemic throughout the Niger Delta, primarily as a result of careless management and the use of materials and standards that would not be acceptable in Europe and North America.
Canal Construction
Canals, known as Slots, built to give access to oil extraction facilities can damage local water resources and affect the salinity levels of water in the Fresh-water/Brackish-water ecotone. Detailed discussion of this problem is covered in Chapter 15.4.3.
Conclusion
It has to be said that the outlook for the purity of the Niger Delta's water is bleak, although international pressure in recent times has caused oil companies, at least, to reassess their responsibilities in the area.
11.4 FISH
11.4.1 AN INDICATOR ANIMAL FOR AQUATIC ECOSYSTEMS
The biomass, bioproductivity and biodiversity of fish in the Fresh-water ecozone depend upon three factors.
- The nutrients and solutes in the water, which are the beginnings of food chains, and which (in terms of individual chemicals) influence a wide range of physiological activities from nervous reactions, to breathing and breeding.
- Oxygen, which enters the water as a product of photosynthesis (by the phytoplankton and the higher plants), and directly from the atmosphere in fast and turbulent rivers. Not all the oxygen is available for the fish, which have to compete for it with other life forms, especially the decomposers. Also, turbidity reduces the ability of fish to take up oxygen through their Gills.
Gills: a series of organs on each side of a fish's mouth cavity which are bit like the pages of a book. They act as its lungs. A fish takes in water through its mouth, forcing it out of the mouth cavity again through its Gills. As the water passes through the Gills over a series of Gill Plates - the leaves of the book - the fish is able to take up oxygen from the water.
- Light, which decreases with depth and turbidity, and which influences oxygen levels from photosynthesis and the ability of fish to search for food.
Fish are so sensitive to their environment in terms of these factors that any decline in overall fish populations, in the weight of individual fish and/or in fish biodiversity, for a given ecosystem, suggests that something is going wrong. In this respect the health and the trends in the health of fish populations provide an indication of the health of aquatic ecosystems, just as birds make good indicators for terrestrial ecosystems. In this respect fish are often termed Indicator Species.
