Water quality parameters affect dynamics of phytoplankton functional groups in Lake Hawassa, Ethiopia

The water quality of Lake Hawassa has been deteriorating due to high influent loads from various sources, including influents of a hospital, industries, hotels, and agricultural runoff, which can induce changes in Reynolds functional groups of phytoplankton (RFGs). The functional associations of algae can also be affected by the dominant zooplankton and macrophytes coverage. RFGs (species with similar ecological requirements) are indicative of water quality but have not been studied in Lake Hawassa. The functional approach detects stressorinduced changes in phytoplankton assemblages more effectively than taxonomy-based methods due to its higher discriminatory power. The main objective of this study was, therefore, to investigate the factors affecting the dynamics of RFGs in Lake Hawassa through monthly sampling (April-August in 2019) from four sites. A total of 130 species of phytoplankton were identified and classified into 17 RFGs. The dominant ten RFGs (D, J, K, LO, M, N, P, SN, TD, and W2) contributed 96.1% of the total fresh weight biomass. Redundancy analysis indicated that the RFGs were correlated significantly with electrical conductivity, dissolved oxygen, pH, turbidity, Secchi depth, and total phosphorus revealing the overriding importance of these parameters in influencing the dynamics of the algal functional assemblage in Lake Hawassa. The results supported our hypothesis that the biotic and the human-induced abiotic factors have significant impact on RFGs. Our findings could serve as baseline information for efforts directed toward water quality improvements.

Automated summary

The water quality of Lake Hawassa is deteriorating due to high influent loads from various sources. The dynamics of phytoplankton functional groups in the lake are affected by dominant zooplankton and macrophyte coverage. Electrical conductivity, dissolved oxygen, pH, turbidity, Secchi depth, and total phosphorus were found to play an important role in influencing the dynamics of algal functional assemblage in Lake Hawassa.