A study of the sediments and communities in Lagos Lagoon, Nigeria

Abstract

Recent increased human pressures on the environment have led to biological consequences in Lagos' coastal waters, notably in the Lagos lagoon and its drainage channel to sea. Two broad surveys were conducted in February and June 1985 and repeated in 1986 to obtain information on the distribution, habitats and communities in the Lagos lagoon in relation to environmental factors. The samples were used for biological, sediment particle size, organic matter, heavy metal and hydrocarbon analyses. A wide variety of sediments occurred throughout the study area. These ranged from fine, medium and coarse sands to admixtures of silt and clay which provided a wide selection of habitats. The western industrialized areas contained high levels of selected heavy metals. Petroleum hydrocarbon contamination was present in most samples. The percentage of total organic matter was closely associated with the sediment types and the influence of waste inputs. The distribution of several species was influenced by the salinity regime and nature of bottom deposits. Benthic macro-infauna was dominated by molluscs, which were most common in the shallow shoal sands of the northeastern portions of the study area. Species characteristic of stressed environments, notably Capitella capitata, Nereis sp. and Polydora sp., were more abundant in the polluted western industrialized portions. Several species showed seasonal population fluctuations. Diversity indices indicated that the communities exhibited high dominance with a small number of species.