Ecological Characterization and Indices of Degradation in Two Watersheds of Southeastern Nigeria

Abstract

Watershed degradation, driven by anthropogenic activities, threatens ecosystem services and biodiversity in southeastern Nigeria. This study quantified the ecological status of two watersheds in Awka, Anambra State, by evaluating vegetation structure, biodiversity indices, and soil nutrient dynamics. Using systematic quadrat sampling, we surveyed plant species across head, tail, left, and right aspects of the watersheds. Soil samples were analyzed for nitrogen (N), phosphorus (P), and potassium (K) at different depths. The study revealed 55 plant species from 26 families, with a successional shift from tree-dominated to herbaceous ecosystems, dominated by Andropogon tectorum and Tridax procumbens. The overall Shannon-Wiener diversity index was low (H' = 1.13), indicating significant ecological disturbance. Soil nutrients analysis indicated vertical enrichment of nitrogen and phosphorus with depth, suggesting leaching and surface loss; phosphorus and nitrogen generally increased with soil depth, suggesting leaching and surface nutrient loss. The tail segments and left aspects exhibited higher species diversity and soil nutrient levels compared to the more disturbed head segments and right aspects. The study concludes that intense anthropogenic pressure, primarily from construction and urbanization, has led to significant biodiversity loss, soil alteration, and watershed degradation. The documented regime shift and low diversity provide a critical baseline for urgent restoration planning and sustainable watershed management in the region.