Title : Climate–water quality pathways shaping fish biodiversity in the upper Niger basin
Abstract:
Freshwater ecosystems in tropical basins are biodiversity hotspots, yet they face increasing pressure from climate change. Understanding the causal pathways linking climate variability to biodiversity is critical for effective conservation. This study aimed to disentangle the direct and indirect (water quality-mediated) effects of hydroclimatic factors on multiple facets of fish biodiversity (taxonomic, functional, and beta diversity) in the dam-regulated Upper Niger Basin, Nigeria. We developed and refined a Structural Equation Model (SEM) using a comprehensive dataset (N=48 site-months) of hydroclimatic, water quality, and fish assemblage data. The final, well-fitting model (CFI = 0.916, SRMR = 0.076) revealed a complex network of interactions. Air temperature was the dominant driver of ecosystem degradation, strongly negatively affecting the overall Water Quality Index (WQI; β = -0.42). Rainfall exhibited a dual role, indirectly increasing turbidity via runoff (β = 0.20) while acting as a direct stressor negatively impacting taxonomic diversity (β = -0.27). The response of the fish community was differentiated: taxonomic diversity was primarily limited by dissolved oxygen (β = 0.32), whereas community structure (beta diversity) was shaped by turbidity, with higher turbidity leading to community homogenisation (β = -0.21). We conclude that fish biodiversity in the Upper Niger Basin is under a dual threat from both direct climatic disturbances and the indirect degradation of water quality. Our findings underscore the urgent need for integrated management strategies that address watershed-scale land use and the systemic impacts of regional climate change to avert irreversible biodiversity loss and safeguard the ecosystem services underpinning regional livelihoods.
Keywords: Structural Equation Modelling (SEM); Climate Change; Fish Biodiversity; Community Homogenization; Tropical Rivers; Water Quality.
