Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/55

What is the Niger Delta? Soils are important to humankind because we depend upon the plants which grow in them for our survival. We depend on the ability of plants to trap sunlight energy in the synthesis of carbohydrates, the start of our foodchain; and on the oxygen they produce in this process that we need to make use of this stored energy.

But plants need some of this oxygen, too. While it is the green leaves of plants above the surface of the ground that receive and process energy from the sun, a great deal of a plant's activity occurs below the surface. With a few notable exceptions, such as the water hyacinth, plants depend upon the soil for their anchorage, nutrition, water supply and for their oxygen.

An understanding of soil conditions, particularly in wet areas like the Niger Delta, must include the realisation that plants can drown just as we do, if the soil surrounding them is so waterlogged that they cannot take up oxygen through their roots. Particularly where water is not moving through the soil, the oxygen supply is limited and even the best-adapted plants may suffer.

4.5.4 GEOGRAPHICAL FACTORS AFFECTING SOILS

Human use of the soil resources of the Delta has further increased the variety of soil types. However, Delta soils have all developed in relation to the following geographical factors:

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Material brought down from the ancient landscapes of the West African interior by the River Niger are not rich in nutrients. These sediments are largely made up of quartz and kaolinite, plus some iron oxides. Quartz, or silicon dioxide, is one of the most common minerals in the earth's crust and is more or less inert in chemical terms. Kaolinite, a silicate clay, is also relatively unreactive; its molecular structure makes it less prone to swelling and shrinking than other clays.

Material brought down from the volcanic rock of the Adamawa massif by the river Benue (see Map 3) is richer in nutrients, but forms a far smaller proportion of the parent material.

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This is generally low and flat; the gully erosion so common further north is not a problem here. However topography still has an effect, and even the small undulations of the Delta bring about substantial variations in soil conditions within a small area, known as soil 53