Assessment of Illegal Sand Mining and Its Impacts on Riparian Vegetation Along the Ogun River, Ogun State

Illegal sand mining has emerged as a significant threat to riparian vegetation and aquatic habitat along the Ogun River in southwestern Nigeria, with consequences extending well beyond the immediate extraction sites to affect downstream water quality, bank stability, and biodiversity. This study assesses the spatial distribution of illegal sand mining activity and its impacts on riparian vegetation structure along a 55-kilometre stretch of the Ogun River in Ogun State. Remote sensing change detection using high-resolution Google Earth imagery from 2018 and 2023 identified and mapped active, abandoned, and recovering mining sites. Field surveys at thirty paired sites, comparing mined and unmined riparian sections, measured vegetation parameters including plant species richness, canopy cover, tree density, and seedling regeneration. Soil physical properties including bulk density, texture, and organic matter were determined for mined and control plots. Mining intensity was classified based on surface disturbance extent and substrate removal depth. Results show 218 discrete illegal mining sites within the study stretch, with clustering near bridge access points and peri-urban reaches. Plant species richness was 64% lower in actively mined sections compared to intact riparian controls. Bank erosion rates were significantly elevated at mined sites, contributing to channel widening and increased turbidity. Abandoned sites showed minimal vegetation regeneration after three years, attributed to severe topsoil loss. Recommendations include state-level inter-agency enforcement, mandatory site rehabilitation bonds, and community riparian patrol committees. Keywords: sand mining, riparian vegetation, Ogun River, bank erosion, illegal extraction