MAPPING AND MONITORING SPATIAL DISTRIBUTION OF WETLANDS USING INDEX BASED ALGORITHM IN ILAJE LOCAL GOVERNMENT AREA, ONDO STATE

Abstract

Ilaje is located along the coastal area of Ondo State, which harbors wetland, but a large portion of its wetland area is diminishing due to human activities, such as; urbanization,and industrialization, which can trigger adverse effect on the environment such as; flood, water pollution, shoreline erosion loss of ecosystem biodiversity. The study assessed the spatial distribution of wetlands in Ilaje Local Government Area, Ondo State with a view to initialize wetland resource managment. In this study, wetland and its components (Hydric soil, Hydrophytic vegetation and Water/Hydrology) were delineated using different index-based algorithms such as: Normalized Difference Moisture Index (NDMI), Normalized Difference Vegetation Index (NDVI), and Normalized Difference Water Index (NDWI). Normalized Difference Built-up Index (NDBI), which is an index specially built for mapping of built environment, was then used for the mapping of built environment in the study area in order to determine and monitor the encroachment of built environment into the wetland. The results showed that: (i) the spatial extent of Water/Hydrology component of wetland slightly declined between 1986 and 2018, but inclined between 2015 and 2019. Hydric Soil and Hydrophytic vegetation components increased between 1986 and 2015 but declined between 2015 and 2019. In general, the spatial extent of the entire wetland an inclination between 1986 and 2015 but experienced a declination between 2015 and 2019; (ii) the influence of urban development was also determined and it was realized that there were some parts of the wetland were converted into built-up environments, but despite the increase in encroachment into the wetland, the spatial extent of wetland increased between 1986 and 2015 by 101.7 Sq.km but decreased by 39.6 Sq.km between 2015 and 2019, showing that urban development is not the only determinant factor for the increase or decrease in the spatial extent of wetland; (iii) a forecast for the year 2030 is estimated to be 318.14 Sq. Km, which shows there will be an increase in the spatial extent of the entire wetland between the year 2019 and 2030.this method is recommended for use in other wetland areas, It was also recommended that this research should be further developed in the area of component specific wetland delineation and futuristic prediction to improve the accuracy of mapping and assessing wetland and hence for comprehensive wetland resource management.