Water quality and ecology of Lake Kanyaboli, Kenya: Current status and historical changes

Abstract

Small waterbodies are the most threatened freshwater habitats because of the large ratio between their size and the catchment they drain. The present study assessed the current and historical changes in the physical, chemical and biological variables of Lake Kanyaboli, a satellite lake on the northern shores of Lake Victoria in western Kenya. Primary and secondary data on pH, electrical conductivity (EC), dissolved oxygen (DO) concentration, temperature, Secchi depth (SD), and nitrate (${\text{NO}}_3^{-}$), nitrite (${\text{NO}}_2^{-}$), ammonium (${\text{NH}}_4^{+}$), soluble reactive phosphorus (SRP), total nitrogen (TN), and total phosphorus (TP) and chlorophyll-a (Chl-a) concentrations were utilized in the present study. The results indicated Secchi depth and chlorophyll-a were the most erratic of all the analyzed environmental variables studied, exhibiting a range of 0.69 ± 0.29–0.87 ± 0.34 m and 9.03 ± 0.81–34.97 ± 3.36 µg/L respectively. Two-way ANOVA yielded no significant interactions between sampling sites and seasons for all the variables. Except chlorophyll-a, there also were no significant differences among the sampling sites for the studied variables. Seasonality yielded significant differences for Secchi depth, dissolved oxygen and chlorophyll-a. The Carlson Trophic Index for Chl-a and SD indicated Lake Kanyaboli is currently eutrophic, while the TP concentration indicated hypereutrophic conditions. The lake, however, has fluctuated between eutrophic and hypereutrophic conditions over the past years. Although historical water quality data for the lake is scanty and infrequent, most physical and chemical variables reflected anthropogenic effects on a temporal scale. Interestingly, despite its eutrophic status, the general lake condition is still relatively good, attributable to the buffering effect from the extensive macrophytes fringing it. The present study identified nutrient loading, wetland reclamation and connectivity with the Yala River through a feeder canal as the management issues of critical concern. Accordingly continuous monitoring of the lake's water quality to detect anthropogenic effects is recommended for management intervention purposes.