The phytoplankton, photosynthetic pigments, nutrients and heavy metals in the dry season of an estuarine Lagoon, Lagos, Nigeria

Abstract

The Agboyi creek is one of the two tributaries of the Ogun River as it enters Lagos state and the Atlantic Ocean through the Lagos lagoon. It serves as a major drainage channel receiving domestic and industrial wastes from nearby industries at Maryland, Isheri, Bariga, Magodo and Ogudu areas of the Lagos metropolis. Sand mining, mangrove cuttings for fuel wood and brush parks (Acadja) as well as unregulated waste discharges are also rampant in the area. Water chemistry, photosynthetic pigment and microscopic analyses on water and plankton samples from these parts of the Lagos lagoon were carried out in the dry season (Nov. 2015 to Apr. 2016). The water climate showed marked effects of reduction in floodwater incursions and the increased influx of tidal sea water into the Lagos lagoon. The Phytoplankton population was represented by four divisions namely; Bacillariophyta (60.16%), Chlorophyta (4.15%), Cyanophyta (34.03%) and Euglenophyta (1.66%). The bacillariophyta (diatoms) was the most frequently occurring and numerically more important group of species. Additionally, higher photosynthetic pigments values were directly connected to the high microalgal biomass. Elevated saline conditions encouraged the development of marine phytoplankton taxa such as Odontella, Pleurosigma, Nitzschia and Oscillatoria spp. Comparative to previous studies, the reduction in algal species diversity is possibly linked to the increasingly limiting effect of heavy metals on the expression and utilization of nutrients by phytoplankton species.