| dc.description.abstract | Fish farming is now a major source of global and local fish requirements for food, supplementing the dwindling output from the wild waters. Several systems are now in place, including using earthen, concrete, linear ponds, and raceways. Earthen ponds are of major concern as they mainly depend on natural stream water sources and release their effluents containing elevated levels of nutrients as a result of fertilizers and feeds used during pond management activities to the streams.
This study was done at the Aquaculture Research and Development Centre (ARDC), Kajjansi farm located 13km from Kampala city along Entebbe Road in Wakiso district. The objective was to assess the effect of discharge from earthen fishponds on the water quality of the stream using phytoplankton and the physico-chemical state as indicators.
In the present study, water quality and the community structure of phytoplankton were investigated for two weeks at 6 sampling sites i.e., 3 ponds, a water source, and 2 sites along the stream. Results from the study indicated nutrient pollution with the highest value of phosphorus concentration in ponds (0.69± 0.09mg/l) and the lowest value in water source (0.08 ± 0.04mg/l), total nitrogen concentration as highest in ponds (5.98± 0.85mg/l) and lowest in water source site (4.34± 0.29mg/l), Turbidity as highest is ponds (103.83± 5.8NTU ) and lowest at water source (66.0± 9.13NTU), Electrical Conductivity as highest at downstream 20m after discharge (194.0± 7.07µS/cm) and lowest at water source (93.25± 4.99µS/cm), pH as highest in ponds (7.78± 0.17) and lowest at downstream 20m after discharge (7.07± 0.46), Dissolved Oxygen as highest in water source (8.35± 0.57mg/l) and lowest at downstream discharge point (5.24± 0.97mg/l) while temperature had the highest value in ponds (26.22± 1.320C) and the lowest value at downstream 20m after discharge (22.02 ± 0.570C). There was a significant difference for each of the water parameters in the 6 sampling sites. Microscopic analysis showed that phytoplankton comprised 32 species belonging to six families in which Cyanophyceae, Chlorophyceae, and Bacillariophyceae accounted for the most important constituents of the river’s phytoplankton assemblage. The highest value of Shannon-Wiener's index (H ') was recorded at water source (2.674), followed by downstream 20m after discharge (2.552), and then pond 1 (2.490), pond 3(2.382), downstream at discharge point (2.305), and finally pond 2 (2.085). It means that-diversity index of water source and downstream 20m after discharge are categorized as moderately stable communities.
Keywords: Phytoplankton diversity, Water quality parameters and Earthen Pond. | en_US |
