Impacts of land-based pollutants on water chemistry and benthic macroinvertebrates community in a coastal lagoon, Lagos, Nigeria

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Tropical coastal waters are prone to increased influx of pollutants from land during the rains. The effects of pollution influx on the water and macrobenthic fauna of a coastal lagoon, Lagos, Nigeria were investigated. Six sampling stations were established at point sources of different pollutants inflow into the lagoon. Surface water temperature at each station was measured in situ. Water samples were collected using Hydrobios Water Sampler while benthic samples were collected using the Van-veen grab, and analysed in the laboratory following standard procedures. Result of water analysis shows high Turbidity (50.1 ± 9.0), Total Suspended Solids (79.5 ± 10.1), Total Organic Carbon (4.2 ± 1.9) and Nitrates (8.5 ± 0.6), and low Dissolved Oxygen (4.4 ± 0.7) indicating a deteriorating water quality. Tympanotonus fuscatus, Nereis diversicolor and Capitella capitata which are more tolerant to organic pollution were relatively higher in abundance than Clibanarius africana and Pachymelania aurita which are less tolerant. The low diversity and abundance of the benthic macroinvertebrates could be attributed to a high influx of pollutants from land which was exacerbated by the rainfall. The use of the benthic macroinvertebrates as bioindicators in the monitoring of the Lagos lagoon should be enhanced in order to forestall the increasing pollution menace and improve its ecosystem functions.