Assessing Environmental Impact on Aquatic Macrophyte Species Structure in a Near Coastal Tropical River, Southeastern Nigeria

Abstract

Impact of environmental variables on distribution and composition of aquatic macrophyte community in a tropical river was assessed for one year (March 2009 to February 2010). Hypothesis tested was that the spatial variation in environmental variables on the river’s longitudinal gradient affects macrophyte species assemblages. Modified method of floral collection was used with a random sampling technique. Eighteen physico-chemical parameters were sampled and analyzed using standard and analytical methods of water analysis. Generated databases obtained were subjected to statistical analyses at P>0.05 and Canonical Correspondence Analysis. Thirty-three families, 64 genera and 98 species of macrophyte were identified. 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 oxygen demand were at their lowest levels. Phosphatephosphorus showed positive relationship with five macrophytes species: in Stations 27, 29, 32 and 34, whereas current velocity correlated with nine macrophyte species at stations 16, 18, 19, 20, 21 and 23. These species can be used as indicators since macrophyte species distributions are not considered to randomly occur but influenced by prevailing environmental conditions. 

Key Words: Canonical correspondence analysis, macrophyte species, environmental factors, Ikpa River