Abstract:
Urban soil quality is influenced by anthropogenic activities, which can adversely affect sustainable land use. Soil Quality (SQ) assessment can assist in early detection of adverse effects of urban land use. However, limited information is available on influence of land use and effective methods of assessing SQ for urban areas. Therefore, this study was carried out to determine land use changes over a 32-year (1984-2016) period in Akure and Okitipupa and to assess the SQ of the Urban Land Use Types (ULUTs).
Satellite imageries of Akure and Okitipupa from Landsat Thematic Mapper and Enhanced Thematic Mapper were analysed to investigate land use changes using maximum likelihood classifier. Soil quality associated with ULUTs - commercial, urban agriculture, wetland, residential and institutional were assessed in 2016 using Weighted Additive Quality Index (SQIwa), Statistically Modeled Index (SQIsm) based on principal component analysis and Soil Environmental Quality Index (SEQI). Data were analysed using descriptive statistics and ANOVA at α0.05.
In 1984, the area covered by built-up areas, forest, water bodies and farmlands at Akure were 18, 239, 35 and 19 km2, whereas, in 2016 the corresponding areas changed to 72, 112, 63 and 64 km2, respectively. At Okitipupa, the respective area covered changed from 60, 298, 10 and 29 km2 in 1984 to 206, 107, 34 and 50 km2respectively, in 2016 indicating that larger area of forest land was converted to built-up areas at both locations. The SQ indices (SQIwa, SQIsm and SEQI),were significantly different among the ULUTs, and wetlands had the highest ratings at both Akure and Okitipupa. At Akure, the SQIwa ranged from 0.35±0.02 (residential) to 0.59±0.02 (wetland), and from 0.31±0.01 (institution) to 0.63±0.02 (wetland) at Okitipupa. The SQIsm ratings were in the order of residential (0.49±0.02) ˂ commercial (0.56±0.02) ˂ institution (0.64±0.02) ˂ urban agriculture (0.81±0.02) ˂ wetland (0.90±0.03) at Akure. However, at Okitipupa, SQIsmwas in the order of institution (0.46±0.01) ˂ commercial (0.48±0.01) ˂ residential (0.54±0.01) ˂ urban agriculture (0.59±0.02) ˂ wetland (0.73±0.02). Compared to wetlands, SQIsm was significantly lower by 45.5, 10.0, 37.8 and 28.9% in residential, urban agriculture, commercial and institution, respectively, at Akure. At Okitipupa, the respective decrease in SQIsm were 26.0, 19.2, 34.2 and 40.0% when compared with wetlands. The SEQI ratings at Akure differed significantly among the ULUT and ranged from 0.50±0.01 (commercial) to 0.66±0.02 (wetland). The SEQI were in the order of commercial (0.50±0.01) ˂ residential (0.54±0.01) ˂ institution (0.55±0.01) ˂ urban agriculture (0.64±0.02) ˂ wetland (0.66±0.02). On the other hand, SEQI ranged from 0.47±0.01 (commercial) to 0.63±0.02 (wetland) and was in the order of commercial (0.47±0.01) ˂ institution (0.49±0.01) ˂ residential (0.54±0.01) ˂ urban agriculture (0.56±0.01) ˂ wetland (0.63±0.02) at Okitipupa.
Akure and Okitipupaexperienced steady changes in land use and cover during the 32-year periodresulting to reduction in soil quality.
