Evaluation of Water Quality and Plankton Communities in Tiga Dam, Kano State

Freshwater reservoirs in semi-arid regions of Nigeria are vital for irrigation, drinking water supply, and inland fisheries, making their ecological health a matter of critical importance. This study evaluated the water quality and plankton community structure of Tiga Dam in Kano State, North West Nigeria. Water samples were collected from four stations during both wet and dry seasons using standard limnological equipment. Physicochemical parameters including temperature, pH, dissolved oxygen, transparency, conductivity, nitrate, phosphate, and total dissolved solids were measured in the field and laboratory. Phytoplankton and zooplankton samples were collected using plankton nets and identified under microscopy. A total of 29 phytoplankton and 21 zooplankton taxa were recorded. Cyanophyta dominated the phytoplankton assemblage, particularly during the dry season when water levels fell and nutrient concentrations increased. Dominant zooplankton groups included rotifers and copepods. Conductivity and total dissolved solids were elevated beyond acceptable limits at the station receiving agricultural return flows. Dissolved oxygen values fell below 5 milligrams per litre at the central station during the dry season, indicating oxygen stress. Seasonal comparison using Mann-Whitney U test revealed statistically significant differences in most physicochemical variables. Pearson correlation confirmed strong positive relationships between phosphate and cyanophyte abundance, suggesting eutrophication risk. The study recommends reduced agricultural chemical inputs into the dam catchment and the installation of nutrient monitoring stations around the irrigation inflows. Keywords: Tiga Dam, water quality, plankton communities, eutrophication, Kano State.