Water Quality, Biodiversity and Abundance of Blue-Green Algae in Nyong and Kienké River Mouths (South-Cameroon)

Abstract

A survey was undertaken from March to June 2014 on the water quality and the occurrence of Cyanobacteria bio-indicator species in Nyong and Kienké warm river mouths. Physico-chemical parameters were measured <i>in-situ. </i>Species were identified and counted in laboratory. The pH varied from slightly acidic to slightly basic. Temperature, pH and transparency were within the tolerable limits for drinking water or fish farming. NO₃^-, Chlorophyll a and biomass were lower than standards. DO and FC were higher than upper limits, except DO in Kienké. NO₂^- was higher in Nyong than the upper limit. It was within the recommended range in Kienké. TSS was within acceptable standards for fish farming but above the upper limit for drinking water. NO₂^-, NH₄⁺ and PO₄^3- proved good conditions for bio-fertilizers or toxin-producers. Chlorophyll a and biomass contains were low but FC and TSS exceeded standards for drinking water, and were within standards for fish farming. Thirty-seven species belonging to 28 genera, 15 families and four orders, were divided into 25 freshwater species and 12 tolerant species. Sixteen toxigenic species, 15 useful species and six species of unknown status were identified. The species diversity was low and Microcystaceae (Chroococales) was the most species-rich family (eight species i.e. 21.6%) and was the most abundant (34.7%), followed by Rivulariaceae (Nostocales) (five species i.e. 13.5% and 12.4% of abundance), Aphanizomenonaceae (Nostocales) (four species i.e 10.8% and 20.8% of abundance), Hapalosiphonaceae (Nostocales) (two species i.e.5.4% and 0.8% of abundance), Microcoleaceae (Oscillatoriales) (two species i.e. 5.4% and 2.1% of abundance), Nodulariaceae (Nostocales) (three species i.e. 8.1% and 7.9% of abundance), Nostocaceae (Nostocales) (two species i.e. 5.4% and 1.9% of abundance), and Oscillatoriaceae (Oscillatoriales) (three species i.e. 8.1% and 0.8% of abundance). Eight families [Chroococcaceae (Chroococales), Coelosphaeriaceae (Synechococcales), Cyanothecaceae (Gomontiellales), Cymatolegaceae (Nodosilineales), Cyanothrichaceae (Chroococales), Gomphosphaeriaceae (Chroococales), Pseudanabaenaceae (Pseudanabaenales), and Tolypothrichaceae (Nostocales)] presented each one rare species (2.7%). According to abundances, species classification in descending order is <i>Raphidiopsis mediterranea</i> (14.3%), <i>Synechocystis aquatilis</i> (11.9%), <i>Aphanothece elabens</i> (7.3%), <i>Microcystis aeruginosa</i> (5.1%). Other species were rare. Twenty-three co-dominants (62.2%) were identified. Globally, a positive association was noted between species in each river. The pooled assemblage at low tide fitted the log-linear niche partitioning model with a high environmental constant while other assemblages fitted the lognormal model with in each case a low environmental constant. Although these two river mouths were suitable for fish farming, direct consumption of raw water is detrimental to human health.