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.
