Water Quality, Phytoplankton Composition, and Microcystins Concentrations in Water Pans in Narok Semi-Arid Landscape, Kenya

Abstract

Water pans in the semi-arid Narok socio-ecological landscape provide essential ecosystem services to local communities, livestock, and wildlife, but are increasingly threatened by land use changes, demographic expansion, and climate variability. There is thus an urgent need to safeguard the ecological integrity of these water bodies. This study was conducted to establish factors that determine phytoplankton and algal structure in relation to their toxins, impact on water quality, and ecosystem health from January to July 2023. Triplicate samples for phytoplankton enumeration and algal toxins were collected from twenty purposively selected water pans identified in Google Earth. Dissolved oxygen, temperature, conductivity, and pH were measured in-situ using hand-held meters while chemical concentrations were analyzed using standard procedures as guided by APHA, (2017). Enumeration and identification of phytoplankton were done at 400x magnification. Chlorophyll a concentration was determined by filtration followed by cold extraction in ethanol. Microcystin algal toxins were analyzed using the Elisa Kit Model No. 357 C. The main algal taxa identified were: Cyanophyceae, Bacillariophyceae, Chlorophyceae, Euglenophyceae, Zygnematophyceae and Dinophyceae. The most dominant algal species were Microcystis aeruginosa (25.44 %), Merismopedia spp (23.49 %), and Anabaena flos-aquae (16.06 %). Five Microcystin toxins were identified namely MC-LR, MC-YR, MC-LA, MC-RR, and MC-dmLR. Concentrations of MC-LR and MCYR exceeded WHO acceptable standards and were significantly correlated. There was a significant difference in chlorophyll a, temperature, dissolved oxygen, conductivity, and pH among different water pans (ANOVA; p<0.05). The total phosphate concentration to total nitrogen concentration ratios (TP:TN) for all the water pans differed from the expected TP:TN ratio of 1:16. The presence of micro toxins in the water pans presents a concern over the suitability of the water for domestic, livestock, and wildlife use. This situation is likely to worsen with increasing episodes of drought, resulting in the concentration of the toxins in water.