Effects of macronutrients and rainfall pattern on microalgal spectrum of tidal creeks adjoining Lagos Lagoon, southwest, Nigeria

Abstract

Variations in macronutrient contaminants and microalgal spectrum of three tidal creeks adjoining Lagos Lagoon, southwest Nigeria were investigated for six months (September, 2013 – February, 2014). Microalgae samples were collected using a 55 µ mplankton net hauled at low speed for 5mins. Physico-chemical parameters of surface waters analysed showed monthly variations linked to seawater intrusion and rainfall distribution pattern. Air and water temperatures were high (≥ 25°C) all through the sampling period. Transparency and total dissolved solids increased in the dry months (≤ 75.5 cm, ≤14100 mg/L) while the total suspended solids were low throughout the study period (≤1.5 mg/L). The waterbodies were slightly alkaline (≤ 8.2) all through the sampled months. Salinity and conductivity values increased steadily during the dry months Dissolved oxygen ranged between 1.1 and 8.0 mg/L while Chemical Oxygen Demand and Biochemical Oxygen Demand values at the creeks were low (£ 50.0 mg/L; £ 4.2 mg/L). Macronutrients concentration were higher in the dry months than in the wet months, whereas, heavy metals occurred as traces (£ 4 mg/L) throughout the period. Microalgal biomass in terms of numbers was relatively higher in the wet months than in the dry months. A total of 25 species from 20 genera were recorded. The observed classes in terms of abundance were Bacillariophyceae (83 %), Cyanophyceae (13 %) and Chlorophyceae (4 %). There was no significant difference (p > 0.05) in species diversity between the three creeks investigated.