Survey of Aquatic Macrophytes and Their Role in Nutrient Cycling in Tiga Dam, Kano State

Aquatic macrophytes are foundational components of freshwater ecosystems, playing key roles in nutrient cycling, habitat provision, and water quality regulation. This study surveyed aquatic macrophyte diversity and estimated their contribution to nutrient cycling processes in Tiga Dam, one of the largest irrigation reservoirs in Kano State. Sampling was conducted at twelve stations representing open water, shallow nearshore, and emergent vegetation zones. Macrophyte species were identified, their percentage cover estimated, and fresh and dry biomass measured. Tissue nutrient content including nitrogen and phosphorus was analysed to estimate nutrient storage capacity. Water column nutrient concentrations were simultaneously determined. Results identified twenty-one macrophyte species, with Nymphaea lotus, Potamogeton pectinatus, and Vossia cuspidata as the most abundant. Above-ground biomass nitrogen accumulation was highest in emergent species, which stored an estimated 34 kilograms of nitrogen per hectare. Inverse relationships were observed between macrophyte biomass and water column phosphorus, suggesting active nutrient uptake. Invasive water hyacinth was recorded at three stations, with dense mats restricting water circulation and dissolved oxygen penetration in affected areas. The study recommends integrating macrophyte management into Tiga Dam operations, including strategic harvesting to remove stored nutrients and control invasive species expansion. Keywords: aquatic macrophytes, nutrient cycling, Tiga Dam, Kano State, water quality.