Land-use changes and urbanization impacts on livelihood and groundwater sustainability of coastal areas of Lagos, SW-Nigeria: integrated GIS-based, livelihood and hydrochemical assessments

Abstract

Water and food security are essential to human survival, livelihood and well-being vis-a-vis sustainable resources management and attainment of the SDGs. This study employed GIS-based, livelihood and hydrochemical assessments of impacts of land use and urbanization on community livelihood and groundwater sustainability with emphasis on the resilience and security of coastal water supply in Lagos metropolis, SW-Nigeria. For the assessment of land-use changes and associated impacts on community livelihood, Spot 5 satellite imagery of 1984, 2002 and 2017 of Lagos area alongside with Landsat ETM+ and OLI were used to generate the land use / land cover (LULC) changes using ArcGIS 10.3 Software. In addition, purposive and random sampling was used to select 500 respondents for the socio-economic assessment of perceived effects of land use changes on livelihood activities of coastal communities in the study area, while the data were analyzed using both quantitative and qualitative approaches. Furthermore, hydrochemical quality assessment of seventy (70) water samples collected from different household water points (wells and boreholes) within study coastal environs were subjected to in-situ physicochemical parameters (pH, Temperature, TDS and EC) followed by laboratory analyses of major cations and anions. GIS-based 2 2 assessment revealed a significant increase in the built-up areas from 447.3km in 1984 to 951km in 2017 representing 85% increase with corresponding loss of about 5% of the forested coastal wetlands. This is a clear indication of rapid urbanization in the last three decades with attendant impacts on coastal livelihood and water quality. For the livelihood assessment, the average age of respondents was 52±7.7 years while most (66.2%) were males, married, (90.0%), literate (57.7%) with an average 34±5.2 years of residency. Fishing and farming were the major activities while the evaluated data revealed a decline in livestock production by 92.0%, cash crops by 90.0% and food crops by 79.0%. This is also a clear indication of impacts land-use changes as two-third of the respondents diversified into nonfarming activities. Hydrochemical assessment revealed elevated electrical conductivity (EC) of >1,000μS/cm alongside with elevated Na (51-230mg/l), Cl (300-980mg/l) and SO (36-88mg/l) concentrations in shallow wells and boreholes tapping the upper unconfined aquifer. This is a clear fingerprint of groundwater vulnerability to saline intrusion and contamination. Therefore, in the face of reality of impacts of anthropogenic land-use and climateinduced changes, there is the need for a clear governance structure to regulate the rate of groundwater abstraction and indiscriminate groundwater development to ensure sustainable groundwater resources management and attainment of SDG-6 and avoidance of water supply crisis. Such crisis can be avoided, if appropriate knowledge-based choices, planning / management options are employed; failure of which will likely be very costly.