Effects of cage fish farming on water and sediment quality in Lake Kivu, Rwanda

Abstract

Human activities in the lakes and around the lake water such as settlements, ports, agriculture, households, industry, and cage fish farming are increased due to population growth and good climate around the lakes. This caused an increase of water and sediment pollution and effect aquatic organisms. The aim of this research conducted on lake Kivu from October to December 2022 was to investigate the effect of cage fish farming on the environment. Water and sediment samples were collected in three sites, namely one site with cage farming at Kigufi and two control sites hot spring and, Nyamwenda. Variables measured in water are depth, nitrate-nitrogen, ammonium-nitrogen, phosphate-phosphorus, total suspended solids (TSS), secchi disk, and chlorophyll a as indicators of water quality. Variable measured in sediment was organic matter content as an indicator to show the quality of sediment. One way ANOVA was used to test statistical significance between caged area and control site. P > 0.05 indicates statistical insignificance, whereas P < 0.05 indicates significance. The results from analysis showed that there were variations in Nitrate-nitrogen, phosphate-phosphorus, chlorophyll a analysis at all profile level but were not significantly different between the inside the cage and control site in October, November, and December (ANOVA, P>0.05) and were under the permissible limit according to World Health Organization (WHO) guideline. Secchi disk results showed statistical significantly all months (ANOVA, P<0.05 and range between 4 – 2 m but does not exceed permissible limit for all parameter tested. Total organic matter in October ranges from 5.89-7.72% and 5.1-7.57% in November, suggesting that Lake Kivu may not have been contaminated by organic matter. Total Organic Matter (TOM) levels did not differ significantly from those at the reference location (p> 0.05) in November and October. Sediment in the lake Kivu was sand has low organic matter due to greater pores that allow water for good oxidation. All of the analyzed parameters were within the recommended ranges and did not show any significant changes. In this research, we found that there is no environmental pollution caused by cage fish farming activities, therefore it can be allowed in Lake Kivu, Rwanda, with close monitoring of its impacts.