Water Quality Parameters Effect on Zooplankton Distribution, Diversity, and Abundance in Water Pans in Semi-Arid Narok Socio-Ecological Landscape, Kenya

Abstract

Water pans in the semi-arid Narok County are essential resources supporting domestic use, livestock production, small-scale irrigation, and aquatic biodiversity. However, these systems face increasing threats from climate variability, population growth, and land-use pressures that alter water quality and ecosystem functioning. Limited empirical data linking specific water-quality stressors such as elevated nitrogen and phosphorus, turbidity, and conductivity to zooplankton populations and ecosystem services hinders effective management in this landscape. This study examined the distribution, diversity, and abundance of zooplankton in relation to water-quality variations and contrasting land-use practices across 20 water pans in the Narok socio-ecological system. Monthly sampling was conducted in February, June, and July 2023, representing the late dry season, early wet season, and postrainy period. Physico-chemical parameters were measured in situ, while nutrients and chlorophyll-a were analyzed using APHA 2017 standard protocols. Chlorophyll-a ranged from 19.08 ± 1.05 µg/L (M118) to 176.61 ± 140.19 µg/L (M396). TN varied from 393.00 ± 30.25 µg/L (M100) to 2,609.43 ± 52.47 µg/L (M392), and TP ranged from 295.43 to 1331.14 µg/L. Zooplankton communities were dominated by Rotifera (48.9%), followed by Copepoda (25.8%), Cladocera (19.9%), and Ostracoda (5%). Taxa richness increased from the dry season (14.21 ± 0.79) to the wet season (16.43 ± 0.67; 4(1), 2026 Original Article p = 0.043), while Shannon-Wiener Index rose from 1.76 to 1.96 and Simpson’s Index reached 10.72. Diversity and richness showed a negative correlation with TN, indicating nutrient enrichment as a major stressor. The dominance of stress-tolerant Rotifers in nutrient-rich pans reflected catchment land-use influences. Conserving these semi-arid water pans through riparian buffer restoration, controlled livestock access, and improved water abstraction is important for sustaining zooplankton biodiversity and ecological integrity.