Ecology, Environment and Conservation Paper

Vol.13, Issue 1, 2007; Page No.(13-18)

ANNUAL CHANGES IN THE PHYSICO-CHEMICAL AND MACRO- BENTHIC INVERTEBRATE CHARACTERISTICS OF THE LAGOS LAGOON SEWAGE DUMP SITE AT IDDO, SOUTHERN NIGERIA

C.A. Edokpayi and J.A. Nkwoji

Abstract

An ecological study of the physico-chemical and macrobenthic invertebrate characteristics of a sewage dumpsite along the bank of Lagos lagoon was carried out for six months. Samples were collected monthly between 08001-i and 1200h from three stations, A (upstream of point source), B (point source) and C (downstream of point source). There was significant difference among the study sites in six (DO, BOD, COD, conductivity, iron and zinc) of the 16 physical and chemical parameters studied. The lowest DO value (mean= 3.0mg/L) was recorded at station B. Higher BOD and COD were recorded also for station B than Stations A and C. The high oxygen demand required in biodegrading the raw sewage may have been responsible for this trend. The 15 taxa and 383 individuals belonging to 13 families recorded were dominated by two families, Nereidae and Aloididae both accounting for over 80% of the total individuals observed. Although the overall abundance of benthos was lowest (3.3%) at station B, Kruskal-Wallis index showed no significant difference in the fauna abundance between the study sites. The low diversity indices recorded at the three sites indicates the stressed nature of the study area. The absence of Abides trigona (Aloididae) in station B despite its dominant status in the study area suggests its sensitivity to high sewage pollution.

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