COS 1-4
Assessing environmental impact on aquatic macrophyte species structure in a near coastal tropical river in Nigeria
Impact of environmental variables on distribution and composition of aquatic macrophyte community in a tropical river (southern Nigeria) was assessed from three sampling stations for 12 calendar months (March 2009 - February 2010). Hypothesis tested was that the spatial in environmental variables on the river’s longitudinal gradient affect macrophyte species assemblages. Modified method of floral collection was used with a random sampling technique, where 1m2 floatable quadrat thrown from a boat was adopted. Thirty heterogeneous units at the rate of 5 units per trip were sampled. The macrophyte species contained in each sampled quadrat were hand-pulled into polyethylene bags with their flowers, seeds and roots. The specimens were rinsed and carried to the laboratory for identification. Fifteen physico-chemical parameters (current velocity, water level, air temperature, water temperature, transparency, total dissolved solids, total suspended solids, total hardness, total alkalinity, conductivity, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, free carbondioxide and hydrogen ion concentration) and three nutrients (nitrate-nitrogen, phosphate-phosphorus and sulphate) were sampled and analyzed using field kit with sensitive probes and standard and analytical methods of water analysis. Generated databases obtained were subjected to statistical analyses including ANOVA (P > 0.05) and Canonical Correspondence Analysis (CCA).
Results/Conclusions
Results of spatio-temporal interactions between macrophyte species and physico-chemical variables indicated that species such as Typha australis, Polygonium salicifolium, Ipomoea aquatica, Ludwigia stolonifera, L. abyssinia and Salvinia nymphellula clustered in sampling stations 1, 3, 4, 5, 11, 12, 13 and 14 where transparency was highest and water level, water temperature, sulphate and biochemical were at their lowest levels. Phosphate-phosphorus showed positive relationship with these macrophytes species: Chromolaena odorata, Aspilia africana, Alternanthera sessile, Hypoestes verticillaris and Luffa aegyptiaca in stations 27, 29, 32 and 34, whereas current velocity correlated with Lactuca tacaxacifolia, Kyllinga squamulata, K. Bulbosa, K. pumila, Typha augustifolia, Phragmites karka, Leptochlea sannulescens, Sacciolepis arundinaceum and Achyranthes aspera at stations 16, 18, 19, 20, 21 and 23. Phosphate-phosphorus, transparency, water level and current velocity explained 48.0% of the variation in the macrophyte species-environmental matrix. These species can be used as indicators since macrophyte species distributions are not considered to randomly occur but by prevailing environmental conditions. Our findings show that aquatic macrophyte assemblages can be utilized for wetland conservation planning because they are important water reservoirs and for animal husbandry. This research is a contribution to the scarce data bank on this river and will be used for sustainable management.