CURRENT DIVERSITY OF AQUATIC MACROPHYTES IN NIGERIAN FRESHWATER ECOSYSTEM

Uka, U.N.; Mohammed, H.A. & Ovie, S.I. 2009. Current diversity of aquatic macrophytes in Nigerian freshwater ecsustem. Braz. J. Aquat. Sci. Technol. 13(2):9-15. ISSN 1808-7035. In Nigerian inland waters, eight aquatic plants have been incriminated as weeds. From the current study, the most prevalent of these weeds are water hyacinth and cattail plants. These aquatic weeds, once it invades a water body, not only disrupts the ecology of the systems but adversely affects the sociological, cultural and economic realities of the local communities within the area, especially the artisanal fisher folks. This paper showcases aquatic weeds distribution country wide based on its hydrological areas as well as their controlling methods. These methods, when employed in aquatic weed infested water bodies, will manifestly contribute to the success of approaches geared to solving aquatic weed problems.


INTRODUCTION
It is a known fact that about 70% of the earth surface is covered with water.About 98% is unconducive for agriculture and drinking.Only extremely small amount are readily available as rivers, streams and lakes.Unfortunately, the available freshwater is not evenly distributed throughout the world.It now rests on man to properly manage this ecosystem.The importance of freshwater bodies as an environmental resource that can be used for the benefit of mankind cannot be overemphasized.These water bodies are important for fisheries, domestic and industrial water supplies among others.Therefore the management of water from its source to utilization is necessary in order to maintain the life functions.
The infestation of freshwater bodies by aquatic weeds influences water management in waterways, rivers, reservoirs and canals.Aquatic weeds are aquatic plants which interfere with the use of water, or in some way constitute a nuisance to man or hazard to human welfare, or growing on a water body where it is not desired (Mitchell,1985).There is an ecosystem imbalance between aquatic plants and other aquatic organisms when the plants invade the system and grows excessively to a nuisance level.The excessive growth of aquatic weed restricts fishing, swimming and recreational activities, causes foul taste and odour of drinking water supplies.It also leads to stunting of fish populations and fish kill due to decomposition (AERF, 2005).Some alien aquatic plants, for example water hyacinth, have invaded Nigerian freshwater ecosystem causing considerable socio-economic problems.These invasive aquatic weeds affect biodiversity as well as water quality (Uka, 2006).Vegetative reproduction of aquatic plants is well developed that once introduced, they can propagate vigorously in suitable habitat.The uniformity and mildness of aquatic environments as compared to terrestrial ones are also factors that enable the spread of many alien aquatic plants over a wide range.This paper therefore attempts to review the status of aquatic weed infestation in Nigeria and as well discuss components of aquatic plant management plan.

AQUATIC WEED DISTRIBUTION IN NIGERIA
The distribution of aquatic weeds in Nigeria has basically been influenced by human factors such as environmental manipulation, pollution, expanded use and development of water bodies for irrigation, transportation, recreation and other public purposes (NIFFR, 2002).Other factors include flooding, environmental factor and photosynthetic efficiency.The comprehensive checklist of the aquatic plants in Nigeria is presented in Table 1.The dominant aquatic weeds of the aquatic environment of Nigeria are shown in Table 2.The spatial distribution of aquatic weeds in major inland water bodies found in the hydrological areas is as shown in table 3.
National Institute for Freshwater Fisheries Research estimated the abundance of water hyacinth and other aquatic weeds in Nigeria using Line intercept method (Madsen, 1999).The qualitative rating of aquatic weeds infestation in Nigeria inland waters as shown in table 3 revealed that Eichhornia crassipes (Water hyacinth) and Typha latifolia (Cattail) are the most noxious aquatic macrophytes in our waters and more so, they are widely distributed.In order to manage these invasive aquatic there is the need to fashion out management strategies.These will prevent introduction of nuisance plants, provide an early detection and rapid response programme on the waterbody so that new introductions can be managed quickly at minimal cost, and aid in identifying problems at an early stage.Planning will show case known information as well as knowledge gap.

STRATEGIES FOR WATER HYACINTH MANAGEMENT AND CONTROL
One of the ways of adopting an effective control and planning is premised on the establishment of the abundance and distribution of the weed infestation.Surveillance trips are usually undertaken first to establish the extent and types of infestation and to decide on the method of control to be used.
In 1994, the Nigerian government initiated water control measure in Kainji Lake Basin, enlightenment campaign was carried out to determine knowledge level of the fisher-folks concerning the water hyacinth infestation on the lake and the associated problems, deciding on plan of action towards controlling and eliminating the weed on lake Kainji and enlightening fisherfolks on additional scientific information on the characteristics of the weed (Alamu et al., 2000).The enlightenment campaign attracted many stakeholders who were greatly involved in the physical removal of the weed from the beaches.The campaign contributed in no small measure in increasing the knowledge level of the local people.Organized training sessions were conducted for members of the local communities and Technical Staff who were actually involved in the control program.
It is necessary to include the monitoring of other biological communities in reservoir, to evaluate if adopted management options have positive or negative effects on the water body.It is also desirable to include baseline data collection in monitoring Programs.In Kainji lake, monitoring team was set up by the National Institute for Freshwater Fisheries Research and the Nigerian German Kainji Fisheries Promotion Project were responsible for monitoring the extent of the clearing activities in the communities and liaising with fishing communities on progress made concerning other methods by the Nigerian government.A remarkable achievement was made with co-operation of the fishing communities.

METHODS OF AQUATIC WEED CONTROL
The aquatic weed control is carried out using these methods; Physical or mechanical control; Biological control and Chemical control.These methods have been summarized in Table 4 below.

RECOMMENDATIONS
According to Madsen 2005 Components of a plan includes: Prevention, Problem Assessment, Project Management, Education, Monitoring, Site-or problemspecific management goals, and Evaluation.Prevention seeks to reduce the influx of new invaders into the resources, and respond rapidly once they are found.Problem assessment is to quantify the distribution and abundance of the target plant and its impacts on the resource.
Project Management includes tracking available resources to fight the problem, including funds and labor.Education involves informing both the resource agency and the public in the problem and potential solutions.
A monitoring component tracks the general condition of the resource in both biotic and abiotic attributes, to detect other changes associated with the resource.a Site-or problem-specific goal addresses the  management of target species based on a specific site basis, rather than attempting to find a single solution to the target plant problem through time for all locations.
Aquatic weeds infestation in Nigeria waters is increasing geometrically.This can be attested to considering its infestation in almost all the streams, lakes, rivers and reservoirs.Government intervention is basically during critical situations.Therefore adequate budgetary provisions should be made and institutions involved in management and control of aquatic weeds strengthened.
Our freshwater is a public amenity and as such should be in harmony with the environment.None of the control methods will guarantee the success of aquatic weed management.An integrated approach, including utilization of weeds as a resource is a way of protecting the quality of the environment.Therefore to develop more effective ways of managing aquatic weeds, better knowledge of biological, ecological and economical aspects of aquatic macrophytes are needed.

Table 1 -
Checklist of Nigerian aquatic plants.

Table 2 -
Aquatic vegetation incriminated as weeds in Nigeria.

Table 3 -
Distribution of aquatic weeds in major inland water bodies found in the hydrological areas.

Table 4 -
Qualitative rating of level of aquatic weeds infestation in Nigeria inland waters.