Effects of Microplastic Pollution on Microalgal Diversity and Community Structure in River Ginzo, Katsina State, Northwestern Nigeria

Abstract

Microplastic pollution is an emerging threat to freshwater systems, yet its effects on microalgal communities in northern Nigeria remain poorly understood. This study investigated microplastic occurrence, seasonal distribution, characteristics, polymer composition, and association with microalgal diversity and community structure in River Ginzo, Katsina State, Nigeria. Water samples were collected from nine stations at Kofar Marusa, Kofar Sauri, and Kofar Durbi during dry (March–May) and wet (June–August) seasons in 2025. Microplastics were extracted using sieving, peroxide digestion, density separation, filtration, and microscopy, with polymers confirmed by Fourier-transform infrared spectroscopy. Physicochemical parameters, microalgal abundance, diversity, and chlorophyll-a were determined using standard methods. Microplastic abundance ranged from 12.6 to 31.8 particles L⁻¹ and was higher during the wet season, with Kofar Marusa as the contamination hotspot. Fibres predominated, followed by fragments and films, while polyethylene, polypropylene, and polyethylene terephthalate were dominant polymers. Wet-season increases in electrical conductivity, dissolved solids, turbidity, biochemical oxygen demand, oxygen demand, nitrate, and phosphate indicated enhanced runoff, organic loading, and contaminant transport. Twenty-five microalgal taxa from six divisions were identified, dominated by Bacillariophyta, Chlorophyta, and Cyanobacteria. Kofar Durbi recorded the highest microalgal abundance, chlorophyll-a, richness, diversity, and evenness, whereas Kofar Marusa showed reduced diversity and greater cyanobacterial and euglenophyte dominance. Principal Component Analysis showed seasonal environmental structuring, with the first two components explaining 92.0% of the variance. The concurrence of elevated microplastic abundance and reduced microalgal diversity at Kofar Marusa suggests ecological stress, although nutrient enrichment, organic pollution, turbidity, and anthropogenic pressures may also influence responses.