Physico-chemical Characterization of the Waters of Lake Dogodogo Located in Bujumbura Province, Burundi

Abstract

Water pollution is an environmental problem caused by various discharges from human activities like agriculture. Therefore, a study on Lake Dogodogo was conducted in 2022. The objective was to assess the physico-chemical quality of its waters to protect this fishery resource for the surrounding population from the lake. To achieve this, six sites were identified, four in littoral zone and two in pelagic zone based on different characteristics. Sampling was carried out during six monthes between 10 A.M. and 12 P.M. Parameters such as temperature, pH, electrical conductivity, and total dissolved solids were measured in situ using a multimeter device Consort C6010 with several specific probes. Dissolved oxygen, ammonium, nitrates, nitrites, phosphates, chemical oxygen demand, and biochemical oxygen demand over 5 days were analyzed in the laboratory following APHA and AFNOR methods. The results showed that the studied parameters varied spatially and temporally. Electrical conductivity values were high and varied in the same way as total dissolved solids. These two were positively correlated. Also BOD₅ and COD were positively correlated and the ratio COD/BOD₅ reveals the biodegradability of organic matter. In this study, the ratio ranged from 0.66 to 1.82, all below 2, indicating the lake’s pollutants are biodegradable. Nutrient concentrations were very low during the study period due to their absorption by aquatic plants. Principal component analysis linked the parameters and sites to identify those with similar environmental conditions. Understanding these abiotic conditions helped assess the ecological balance of this vital aquatic ecosystem. The Organic Pollution Index indicated that the waters fall into the "high organic pollution" category. Overall, the lake’s degradation is not alarming, but it is subject to pollution from agricultural sources such as phosphorus and nitrogen. Hence, there is a need to protect this lake and its organisms for the benefit of the surrounding population.