Dynamics of nutrient and phytoplankton in Epe Lagoon, Nigeria: possible causes and consequences of reoccurring cyanobacterial blooms

Abstract

The impact of environmental variables and processes of nutrient enrichment on phytoplankton community at Epe lagoon was studied for 18 months (November 2012-April 2014. Two cyanobacterial bloom incidences were observed in the two dry seasons during this period. Rainfall pattern regulated nitrogen limitation which triggered cyanobacterial bloom development and influenced the bloom duration. Nutrient-laden influx from agricultural practices accounted for the increase in nitrate, phosphate and the relatively low silicate. Hypoxic conditions during the two bloom episodes reflected the vulnerability of this lagoon ecosystem. The cyanobacterial blooms were dominated by potentially toxic species; Anabaena circinalis, A. flos-aquae, A. limnetica and A. spiroides. A comparison of ambient nutrient ratios with the Redfield ratio (N/P/Si = 16:1:16) showed clear temporal variations that coincided with phytoplankton dynamics and the bloom regime. Low N/P ratios were recorded during the first 8 months, and there was a shift to higher ratios during the subsequent 8 months, followed by low N/P ratios in the last 2 months. Higher silicate values coincided with decreased cyanobacterial biomass, cyanobacteria bloom collapse and proliferation of diatoms during the first annual cycle. Cyanobacterial abundance exceeded the alert level 1 and almost reached alert level 2 which call for continuous environmental monitoring and management of coastal waters.

Study on Transmission of Visible Light in Selected Water Bodies of Southwest Nigeria for Underwater Wireless Optical Communication

“…Epe Lagoon has a somewhat low salinity, conductivity and TDS compared to those of some rivers in the hinterland despite having human activities such as fishing, farming and wastes from domestic use; and lying between Lagos Lagoon and Lekki Lagoon which are both close to the Atlantic Ocean. The values obtained in this study are close to the range of values obtained by [15]. This might be due to Osun River that empties into it which has low salinity, thereby diluting the Epe River and lowering its salinity and conductivity.…”

“…Some physicochemical parameters including pH, and total dissolved solids were measured and analysed. Authors of [15] studied the impact of environmental variables and processes of nutrient enrichment on the phytoplankton community at Epe Lagoon. Some physicochemical parameters including pH, total dissolved solids, and salinity were measured and analysed.…”

Modelling Freshwater Eutrophication with Limited Limnological Data Using Artificial Neural Networks

“…The second scenario, which is related with DIN perturbations, also showed a reduction to Chl-a levels when the DIN parameter decreased. The DIN parameter has similar behavior with the TP parameter; therefore, any increase of nitrogen levels is associated with increased algal productivity [62]. The linkage between nutrient loading and eutrophication is often non-linear, because of the complex mechanisms by which hydrological and meteorological conditions interfere with the nutrients [63].…”

Comparative study on seasonal variations in physico-chemical characteristics of four soda lakes of Ethiopia (Arenguade, Beseka, Chitu and Shala)

“…The ambient temperature in the Lakes Beseka & Shala region is higher during the dry season (Jan–May). Higher DO concentrations during the rainy season in lakes Arenguade, Beseka and Chittu might be due to higher solubility of oxygen at lower temperature, low biological activity and mixing of surface water with atmospheric oxygen [ 46 , [66] , [67] , [68] ]. However, in Lake Shala the highest amount of DO was recorded during the dry season.…”