Limnological Study of Lake Alau, Borno State: Water Quality and Productivity

Lake Alau, a reservoir impoundment in Borno State, North East Nigeria, serves as a critical freshwater resource for irrigation, domestic supply, and inland fisheries for communities in the semi-arid Sahel-Sudan transition zone. The lake faces mounting threats from evaporation intensification under climate change, sediment infilling, and abstraction pressure. This study conducts a comprehensive limnological assessment of Lake Alau, characterising water quality, primary productivity, and fish community structure across four seasons during 2023 to 2024. Water quality parameters including turbidity, pH, electrical conductivity, dissolved oxygen, temperature, total dissolved solids, nitrate, and phosphate are measured at eight sampling stations. Primary productivity is estimated through phytoplankton chlorophyll-a concentration and carbon uptake rates determined using the light-dark bottle incubation method. Zooplankton and phytoplankton are sampled using plankton nets and counted using Sedgwick-Rafter cells. Fish diversity and catch-per-unit-effort data are collected in collaboration with artisanal fishers using standardised gill nets. Findings are expected to indicate a productive mesotrophic system with evidence of increasing turbidity related to catchment erosion from surrounding agricultural land. The study provides data to support the Borno State Integrated Water Resources Management programme and recommends catchment reforestation as a long-term lake health strategy. Keywords: limnology, Lake Alau, Borno State, water quality, primary productivity