Assessment of the effects of water quality parameters on zooplankton distribution, diversity, and abundance in water pans of semi-arid Narok, Kenya

Abstract

Freshwater pans in Kenya’s semi-arid regions play an important role in supporting domestic use, irrigation, livestock, and aquatic biodiversity. However, they are increasingly threatened by climate variations, eutrophication, sedimentation, and overexploitation, all of which affect water quality and biological productivity. Understanding the interactions between water quality and zooplankton population is essential for maintaining the ecological integrity of these systems. This study therefore aimed to (i) assess variations in physico-chemical parameters, (ii) determine variations in zooplankton distribution, diversity, and abundance, and (iii) evaluate the influence of water quality parameters on zooplankton diversity and abundance in selected water pans of Narok County, Kenya. Sampling was conducted twice monthly between February and July 2023 across 20 water pans. In situ measurements were taken for temperature, dissolved oxygen (DO), pH, and electrical conductivity (EC), while nutrients (total nitrogen and total phosphorus) and chlorophyll-a were analyzed using standard laboratory methods. Zooplankton were identified and enumerated microscopically, and diversity indices were computed. Results showed that temperature ranged from 16.65–26.20 °C, DO from 0.40–9.55 mg/L, pH from 6.70–9.30, and EC from 79.83–761.85 µS/cm. Chlorophyll-a concentrations varied from 19.08–176.61 µg/L, total nitrogen from 393.00–2609.43 µg/L, and total phosphorus from 295.43–1331.14 µg/L. Zooplankton communities were dominated by Rotifera (48.9%), followed by Copepoda (25.8%), Cladocera (19.9%), and Ostracoda (5%). Diversity increased from February to June/July, with Shannon-Wiener Index rising from 1.76 to 1.96 and taxa richness from 14.21 ± 0.79 to 16.43 ± 0.67 (p = 0.043). Weak correlations between zooplankton abundance and most water quality parameters indicated that multiple interacting factors influence community composition. The study concluded that Narok water pans support diverse zooplankton under varying environmental conditions. Strengthening riparian vegetation, managing nutrient inflows, and regulating water abstraction are recommended to sustain ecosystem health and productivity.