Impact of Urbanization on Wetland Degradation: A Case Study of Eleyele Wetland, Ibadan, South West, Nigeria

Abstract

Nigeria is richly endowed with both coastal and inland wetlands, many of which are being threatened by anthropogenic drivers such as land use activities, urbanization, agricultural activities in addition to the emerging threats of climate change. Therefore, this study highlights the environmental assessment of urbanization land-use impacts on degradation of Eleyele Wetland in Ibadan SW-Nigeria. For the study, a GIS-based remote sensing assessment was employed to characterize the temporal changes in land-use dynamics within the catchment areas of the Eleyele Wetland. In addition, about 40 water samples (from both the main Lake and feeding streams) and 25 bottom sediments samples were collected and subjected to chemical analyses of the major cations and trace metals using inductively coupled plasma mass spectrometer and atomic Emission spectrometer (ICP-MS /-AES) methods respectively. The GIS-based assessment revealed a reduction in the riparian wetland forest of 1.25 km² as at 1984 to 0.70km² by 2004 with a projected decline of 0.42 km² by 2014. These clearly signify considerable impact of human activities with loss of 45-70% of the wetland riparian and light forests due to about 70% increase in build-up areas between 1998 and 2004. The measured physico-chemical parameters of the water revealed relatively higher values in the feeder streams compare to that of the main wetland Lake with pH values of 6.5 to 8.8 and 6.7 to 10.1 and EC of 141 to 1252µS/cm and 142 to 424µS/cm respectively. The average Ca, Mg Na and K concentrations in the lake revealed values of 29.1, 9.3, 29.6 and 13.0 mg/l respectively while those of the feeder streams are 43.9, 9.9, 39.7 and 13.49mg/l respectively. The results of the trace metals such as Cr, Cd, Co, Cu,  Pb, Ni,  Fe,  Al, Mn and Zn also show the similar trend of higher values in the feeder streams over those of the lake samples, a situation which could be attributed to impacts of urban waste water and effluent discharges to the feeder streams. However, the lower concentration in the main lake can be attributed to the dilution effect. The overall results highlight the negative impacts of the human-induced influence on the Wetland ecosystem through land-use and waste effluent discharges with attendant degradation / loss; hence, the need for Integrated Water Resources and Environmental Management in order to safeguard the overall quality of the wetland ecosystem.