Spatial variations in nutrients and other physicochemical variables in the topographically closed Lake Baringo freshwater basin (Kenya)

Abstract

Spatial physicochemical parameters were determined from 39 sampling sites distributed throughout Lake Baringo during December 2010. Mean values of temperature, dissolved oxygen concentration and electrical conductivity decreased successively with depth, while the pH remained constant. Only the turbidity values increased marginally with depth. Of the surface water parameters, mean (range) values of dissolved oxygen (DO), pH, electrical conductivity, water transparency and turbidity were 6.9 (4.5–8.4) mg L−1, 8.3 (7.8–8.5), 573 (556–601)μS cm−1, 33 (28–37) cm and 43.3 (32.7–54.6) NTU, respectively. Mean and range values of total nitrogen (TN), nitrate‐nitrogen(NO3‐N), ammonia nitrogen (NH4‐N), total phosphorus (TP) and soluble reactive phosphorus (SRP) were 788.4 (278–4486) μg L−1, 4.5 (2.4–10.0) μg L−1, 42.6 (33.8–56.3) μg L−1, 102.9 (20.3–585.3) μg L−1 and 23.5 (15.2–30.5) μg L−1, respectively. Dissolved silica concentrations ranged from 19.7 to 32.7 mg L−1, with a mean value of 24.7 mg L−1. The chlorophyll‐a concentrations were quite low, ranging from 1.4 to 4.9 μg L−1, with a mean value of 4.2 μg L−1. In contrast to previous reported values, a key finding in the present study is a relatively high water transparency, indicating a relatively clear water column, due possibly to the fact that the sampling was conducted during the dry period. The nutrient levels remained low, and the chlorophyll‐a concentration also was an almost all time low value. A TP value of 20 μg L−1 and higher confirms strongly eutrophic conditions prevailing in the lake, with an extremely low potential for fish production and low species diversity, consistent with other studies. The results of the present study, therefore, reinforce the database for future management and monitoring plans for the Lake Baringo ecosystem, which lies adjacent to known geothermally active zones and a saline Lake Bogoria.