Studies on the primary productivity of a polluted mangrove pond in Lagos, Nigeria

Abstract

The primary productivity of a polluted mangrove pond in Lagos was investigated for six months (October 2010-March 2011) using the chlorophyll-a method. Air and water temperatures were high (≥21°C) while transparency was lower than 11.5 cm at the mangrove pond. Total suspended solids were ≥2.0 mg/L while total dissolved solids values remained high (≥284 mg/L) only between October 2010 and December 2010. Salinity and conductivity values were ≤4.2 ‰ and ≤6600 μS/cm respectively throughout the sampling period. Dissolved oxygen values were relatively low (≤5.1mg/L) while biochemical oxygen demand and chemical oxygen demand values were high (≥8.0 mg/L). Reactive phosphorus, reactive nitrogen, sulphate, reactive silicate values ranged between 0.03 mg/L and 3.70 mg/L, 0.20 mg/L and 5.30 mg/L, 0.01 mg/L and 2.63 mg/L, 0.01 mg/L and 0.23 mg/L respectively during the sampling period. Chlorophyll-a values ranged from 0.001 μg/L - 0.005 μg/L at the mangrove pond. Heavy metals occurred all through the sampling period as traces. Trophic state index (TSI) values using reactive nitrogen showed oligotrophic to eutrophic conditions. The microalgal taxa were dominated by pennate forms notably Bacillaria paradoxa Gmelin, Cymbella minuta Hilse, Navicula cuspidata Kutzing and a few centric formsCoscinodiscus centralis Ehrenberg and Coscinodiscus radiatus Ehrenberg.

Keywords: Algae, mangrove pond, primary productivity, pollution, trophic state index