THREATS AND POTENTIALS OF INVASIVE MACROPHYTE SPECIES TO INLAND FRESHWATERS IN RELATION TO CHANGING CLIMATE IN NORTHERN NIGERIA

Abstract

There are over 12 million hectares of inland freshwater bodies in Nigeria. This includes mainly river systems and streams, natural and man-made lakes, naturally occurring and excavated seasonal ponds etc. Field studies over a period of two decades in northern Nigeria identified species of invasive aquatic macrophytes that pose major concerns to the ecosystem. In addition to other species considered of minor significance, the major species of concern were the water hyacinth (Eichhornia crassipes), Water lettuce, (Pistia stratiotes), Niger grass (Echinochloa stagnina), and the Cattail (Typha sp). These and other species considered of less nuisance were found to occur in natural and man-made lakes and other water bodies that are mainly used as sources of domestic drinking water, for fishing, recreation and significantly, for irrigation. Farm run-off such as fertilizers, increase nutrient loading of the water and this results in the explosive growth of aquatic vegetation. Changing climatic patterns have been predicted to among other impacts, alter precipitation patterns world- wide. In the arid and semi-arid regions, this will result in the decrease in duration and intensity of rainfall. Increasing intensity of soil tillage for irrigated agriculture will therefore lead to declines in available water volume in such water bodies, due to both an increase in water demand and a decreased volume. This threatens the maintenance of the aquatic ecosystems. Presently, in order to safeguard ecosystem health emphasis on management of aquatic vegetation is placed on their removal and destruction. However, there are potentials for beneficial utilization of aquatic plant resources, at subsistence and perhaps industrial levels. These potentials have largely neither been evaluated nor explored. This paper reports data collected from field observations and surveys involving indigenous human populations on the potentials of identified species of aquatic vegetation, as well as possibilities for the beneficial exploitation and management of these aquatic resources in northern Nigeria.