Phytoplankton functional dynamics in relation to some physicochemical parameters in Lake Kuriftu (Oromia, Ethiopia)

Abstract

The water quality of Lake Kuriftu is deteriorating, and monitoring programs are almost nonexistent in Ethiopia. Phytoplanktons are good indicators of environmental changes due to their fast response to a wide range of stressors. The phytoplankton functional groups (FGs) can be used as water quality indicators. This study aimed to assess the dynamics of phytoplankton functional groups (FGs) in relation to some physicochemical water quality parameters measured at three sites in Lake Kuriftu. Samples for the analysis of biological and physicochemical parameters were collected monthly, from December 2020 to April 2021. The results of the physicochemical parameters revealed that Lake Kuriftu is turbid (21.37 to 59.86 NTU), has a thin euphotic depth (ZSD0.304 to 0.548 m), and is eutrophic. Ninety-seven (97) phytoplankton taxa were identified and classified into 16 Reynolds Functional Groups (RFGs), of which six (J, MP, X1, Lo, S1, and F) were represented by more than six species. FGs S1, SN, Lo, and Lm, which often form Harmful Algal Blooms, contributed together about 33.54 mg L−1, or 87.84 %, of the total biomass recorded for Lake Kuriftu, demonstrating the water quality of the lake is deteriorating. Among the FGs, the most dominant (in terms of biomass) was S1, followed by J at all sites and in all sampling months. The results of redundancy analysis (RDA) revealed that the main driving factors of phytoplankton FG biomass and composition were TP, ZSD, TN, Salinity, and ammonia. Among these, TP and salinity impacted the FGs negatively, while TN and ammonia influenced them positively. Thus, the physicochemical parameters have a significant impact on the distribution of phytoplankton FGs, suggesting that the use of FGs for water quality monitoring programs is useful. To promote wise use and conservation of the lake ecosystem, more intensive study should be carried out on the biological and physicochemical aspects of the lake, as it is part of a tourist attraction area and a source of income for local inhabitants.