The Impacts of Organic Pollution on the Hydrochemistry and Community Structure of Benthic Macrofauna of Lagos Lagoon, Southwest Nigeria

Abstract

The Lagos lagoon is a coastal lagoon and hence, is highly impacted by pollutants from anthropogenic sources. The greater percentage of these pollutants is organic in origin. Hydrochemistry and benthic fauna assemblage of five anthropogenically impacted sites of the Lagos lagoon, Nigeria were studied from May to October, 2016 to investigate the effects of organic pollution on them. Water and composite benthic samples were collected monthly at each study station and analysed in the laboratory following standard procedures. The analysis of variance (ANOVA) indicated no significant difference (p > 0.05) in values of the water parameters measured among the study stations. Higher pH values were recorded at Carter Bridge sampling station and this could be attributed the introduction of carbonates into the water through the washing of cement bags. Salinity of the water was generally low due to the season of the sampling. Introduction of large volumes of biodegradable wastes both reduced the dissolved oxygen level and increased the total suspended solids in the waters of critical sites. A total of 243 benthic macrofauna individuals comprising three Phyla, four Classes, four Orders, eight Families, eight Genera and eight Species were sampled. The gastropods, Pachymelania aurita and Tympanotonus fuscatus dominated the benthic macrofauna assemblage of the study area accounting for 40.3% and 19.3% respectively. The relatively low abundance of the filterfeeding bivalves and the highly sensitive arthropod species in the study area may be indicative of organic pollution of the area.

Keywords: Organic; Pollution; Hydrochemistry; Benthic; Macrofauna; Coastal