Assessing the unique effect of land use on fish biodiversity after accounting for water quality

Land use affects aquatic ecosystems through water quality pathways, yet its independent influence on fish biodiversity beyond water quality effects remains poorly understood. This study quantified the unique effects of land use activities on fish abundance and species richness after controlling for simultaneous water quality effects across the Chicago and Des Plaines River watersheds during 2001, 2010, and 2020. Using a two-stage likelihood-based modeling framework with zero-inflated and standard negative binomial regressions, the study assessed land use effects within 300 m and 1 km buffer scales while accounting for effects of principal component-derived water quality gradients. The results revealed that land use significantly explain residual variation (4.7 to 18.6%) in fish abundance and species richness beyond water quality effects. Increasing temporal decline in fish abundance and species richness was noted as zero inflation increased from 55 to 78% of sampling stations. Species richness demonstrated greater land use sensitivity than abundance, and wider-scale (1 km) effects generally exceeded local riparian (300 m) influences. By 2020, land use activities within 1 km of sampling stations significantly explained huge variations in both fish abundance (10.2%) and species richness (18.3%). The study has established that land use activities significantly impact fish abundance and species richness. These findings demonstrate that land use exerts independent ecological pressures beyond water quality. The study recommends that effective conservation in the area should integrate watershed-scale management, combining development controls with strategic riparian restoration, alongside establishing impervious surface thresholds before the urban riverine ecosystem cross degradation limits.