Water quality characterization of Lake Abaya, a water body under increasing anthropogenic pressure in Southern Ethiopia

This study on Lake Abaya aimed to update information on its water quality in the wet and dry seasons. Water samples were collected from five lake sites on three dates in the dry and wet seasons. Two sites on the main inflowing river were sampled on two dates in each season. Analysis was carried out for selected nutrients total ammonia nitrogen (TAN), nitrate (NO3-N), total phosphate (TP), soluble reactive phosphorus (SRP) as well as chlorophyll-a and silicate. Dissolved Oxygen (DO), % saturation, temperature, pH, electrical conductivity (EC), total suspended solids (TSS), turbidity, and secchi readings were measured in situ. Lamparelli’s (2004) tropic state index (TSI) formula was used to assess trophic conditions. The key water quality issues identified are related to elevated concentrations of TSS, turbidity, and nutrients. TSS value (200 mg L^− 1) and turbidity were high in wet. TAN levels were elevated in the lake (0.243 mg L^− 1N) and the calculated unionized ammonia exceeded the no-effect limit. The SRP (0.927 mg L^− 1P) and total phosphorus concentration were also elevated and significantly higher in the dry season. The lake is a hypertrophic system with the aforementioned sediment and nutrient levels exceeding thresholds for the protection of aquatic life. The lake is impacted by multiple co-occurring stressors. Land-use changes in the catchments and the use of various types of chemical fertilizers and pesticides to protect crops are exerting accelerated pressures on water quality in the lake and inflowing river. A suite of interventions both in terms of policy and practice, is urgently needed to halt its further degradation.