SOURCES OF WATER POLLUTION (Cont)
As people pump and use water from these underground aquifers, the water must be replaced. Aquifers are replenished or recharged by water seeping down through the soil from surface water supplies. In some parts of the country, groundwater supplies are very deep, and pollutants may be filtered out by layers of soil, sand, and gravel.
In parts of Nigeria, there are more direct links to the groundwater. In some parts of north-central and south of Nigeria, the groundwater supply may come within a few meters of the soil surface. That’s why this area of south is covered with wetlands and prairie potholes. In these areas, there is much less filtration by the soil and a greater risk of contamination by animal wastes, pesticides, and other pollutants. In other parts of the country, like the east and some part of the south west corner, limestone sits just below the soil surface. This limestone layer, or karst, can crack, erode, and form caverns that allow water and any pollutants to travel with little filtering from the soil.