Abstract
The physicochemical variables and cyanobacteria of Mid-Cross River, Nigeria, were studied in six stations between March 2005 and August 2006 to determine the relationship between water quality and cyanobacteria abundance. Canonical Correspondence Analysis (CCA) showed that biological oxygen demand (BOD), dissolved oxygen, pH, water velocity, width and depth were important environmental factors that influenced cyanobacteria abundance. Trace metals, phosphate and nitrate increased significantly from values of previous studies indicating increased eutrophication of the river but were weakly correlated with cyanobacteria abundance and could be scarcely regarded as regulating factors. A higher cyanobacteria abundance was recorded during the wet season in most of the sampled stations. The dominant cyanobacteria included Microcystis aeruginosa, Aphanizomenon flos-aquae, Oscillatoria limnetica and Anabaena spiroides. The toxins produced by these species could degrade water quality. The factors favouring cyanobacteria abundance were identified as increased pH, width and depth. Increase in cyanobacteria abundance was associated with reduction in dissolved oxygen and increase in BOD values.
Highlights
Cyanobacteria in water pose a serious concern, as they can be harmful in several ways
This paper focuses on the cyanobacteria abundance of Mid-Cross River floodplain ecosystem, a source of municipal water and region of high fisheries and recreational activities
The highest cyanobacteria abundance was recorded in Station V were total abundance reached values of 1.7x 105 cells/L while the lowest values were recorded in Station II (Fig. 1)
Summary
Cyanobacteria in water pose a serious concern, as they can be harmful in several ways Their blooms reduce the aesthetic value of recreational water, decaying algal blooms may result in anoxia, due to high biological activity, and may lead to mortality of fish and other aquatic organisms. The dominance of cyanobacteria may be due to their low need for uptake of nutrients during the benthic life phase buoyancy control, tolerance to high temperature and pH, release of allelopathic compounds, grazing resistance and phosphorous and nitrogen storing (Keating 1977, Smith 1986, Reynolds et al 1987, Robarts and Zohary 1987, Sterner 1989, Shapiro 1990, Blomqvist et al 1994, Hyenstrand et al 1998, Mur et al 1999, Mitrovic et al 2001, Hanson et al 2007) Cyanobacteria can produce both hepatotoxic peptides which cause liver damage and are tumor-inducing e.g. microcystin (produced by M. aeruginosa) as well as neurotoxic alkaloids e.g. aphanotoxin from Aphanizomenon flosaquae and anatoxin-a produced by Anabaena and Oscillatoria This paper focuses on the cyanobacteria abundance of Mid-Cross River floodplain ecosystem, a source of municipal water and region of high fisheries and recreational activities
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