Abstract
The effect of hydroclimatic conditions on phytoplankton was investigated in Ejirin, part of Epe lagoon, south-western Nigeria from December, 2012 to May, 2013. The data obtained for hydroclimatic features responded to rainfall pattern during the study period. The water remained acidic throughout the sampling period as pH value was ≤ 6.6 and salinity value ≤ 0.01%. The micronutrients varied throughout the sampling period and showed a correlation with rainfall. Chlorophyll a (Chl. a) concentration showed a correlation with conductivity, rainfall and surface water temperature, with a mean value of 0.021 mg L-1. Transparency, salinity, silicate and reactive phosphate showed a dominant effect on the phytoplankton community. The total number of phytoplankton species recorded during dry months differed significantly with that of the wet months (t* = 2.723, P > 0.05). A total of 105 species belonging to 5 divisions were recorded throughout the study period: Bacillariophyta (81.3%); Cyanobacteria (10.71%); Chlorophyta (6.5%), Eugleanophyta (1.35%) and Chrysophyta (0.13%). Diatoms were the dominant species in both the dry and wet months with 12 centric and 35 pennate forms. Phytoplankton density correlated significantly with silicate and TDS, indicating the possible effect of silicate on the diatoms and TDS on the whole community. Key words: Cyanobacteria, phosphate, salinity, transparency.
Highlights
Good water quality depends largely on a number of hydroclimatic conditions (such as total dissolved solids (TDS), total suspended solids (TSS), pH, dissolved oxygen (DO), conductivity, transparency, micronutrients, etc.) and the magnitude and sources of any pollution load
Four replicate samples were made on each trip for the following analysis, micronutrients, biological oxygen demand (BOD), chemical oxygen demand (COD) and chlorophyll a content
The surface water temperature reported from the study is notable for tropical waters (Inyang et al, 2015; Nwankwo, 1984)
Summary
Good water quality depends largely on a number of hydroclimatic conditions (such as total dissolved solids (TDS), total suspended solids (TSS), pH, DO, conductivity, transparency, micronutrients, etc.) and the magnitude and sources of any pollution load. Lagoons dominate the southwest region of Nigeria and as such are important aquatic ecosystems that have attracted so many scientific researches. Lagoons in this region are interconnected and run parallel to the coastline of the Gulf of Guinea over a distance of 237 km (Hill and Webb, 1958). Onyema (2007) reported that phytoplankton satisfy conditions to be qualified as suitable indicators in that they are simple, capable of quantifying changes in water quality, applicable over large geographical areas and can furnish data on background conditions and natural variability of aquatic ecosystems. This study was conducted within the Ejirin tributary of Epe lagoon at the southwest region of Nigeria and aimed to assess the response of phytoplankton to hydroclimatic changes and to evaluate the dominant hydroclimatic factors
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