Variations in the Composition and Biomass of Phytoplankton Species as a Function of Physicochemical Factors in Lake Kuriftu, Central Ethiopia

Chlorophyll-a; Nutrients; Phytoplankton; Water Quality Index


January 1, 2024


Background: Analyzing the spatio-temporal dynamics of physicochemical and phytoplankton communities provide valuable insights into water quality, ecosystem health, pollution sources, and supports effective water resource management and conservation efforts.
Objective: The objective of this study was, therefore, to evaluate water quality status of Lake Kuriftu using a combination of both biotic and abiotic factors.
Materials and Methods: Water samples were collected from the Lake in triplicates both in the dry and wet seasons from five different sampling sites based on Lake zonation, and human interference during the wet and dry season in 2018. Physico-chemical parameters such as temperature, pH, dissolved oxygen and electrical conductivity of the water were measured in situ with a portable multimeter probe (HACH, HQ 40d, USA) designed for water samples, while turbidity was measured by a portal digital Turbidimeter (T-100 Singapore). Secchi depth (ZSD) was estimated using a 20 cm diameter Secchi disk. Concentrations of nutrients and heavy metals were determined following standard methods. Abundance of phytoplankton and their seasonal dynamics were estimated in terms of biovolume and calculated using the appropriate geometric shape of the major species. The data were then analyzed with a multivariate analytic technique Redundancy Analysis (RDA) to illustrate the correlations between abundance of dominant phytoplankton species and physicochemical characteristics. Correlation between dominant phytoplankton specie and environmental variables were analyzed by the Bi-plot of the constrained Redundancy Analyses (RDA). 
Results: The pH, TDS, DO and Turbidity were in the ranges of 8.55 ± 0.13–9.06 ± 0.02, 134 ± 1–137 ±2 mg L–1 , 7.26–9.42 mg L–1 and 8.39–78.6 NTU, respectively. Cadmium and chromium concentrations were below the detectable level both in the dry and wet seasons while the concentration of lead was above the WHO permissible limits in the dry season. The concentration of iron was high in the dry season and low in most of the sites in the wet season. A total of six major phytoplankton groups were identified. These
were Chlorophyceae, Cyanophyceae, Bacillariophyceae, Dinophyceae, Cryptophyceae and Euglenophyceae in order of their abundance and frequency of occurrence. The species richness varied among the sampling sites in the lake and a total of 30 species belonging to six families and 24 genera were recorded from the lake.
Conclusion: The water quality parameters such as, pH, TDS, DO, and Turbidity exhibited consistent ranges within acceptable limits. Cadmium and chromium concentrations remained undetectable throughout both the dry and wet seasons while the concentration of lead was above the WHO permissible limits in the dry season. Phytoplankton distribution showed a remarkable difference and Blue-green algae was the most dominant species. Thus, further research should be conducted to explore long-term phytoplankton trends and factors influencing Blue-green algae dominance.