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.
