Water pollution at Lake Natron Ramsar site in Tanzania: A threat to aquatic life

Abstract

Lake Natron Ramsar site is a recognized Ramsar site and Important Bird and Biodiversity Area (IBA) in Tanzania. It is a breeding site for 75% of the global population of lesser flamingo (Phoeniconaias minor). Water quality changes can affect the plankton composition and diversity, causing alteration of LNRS ecosystem abundance. Water quality assessment at LNRS was conducted after reported alkaline tilapines (Alcolapia species) and pelican (Pelecanus onocrotalus) mortalities. Water samples were collected from five sampling sites in Engaresero and Pinyinyi rivers during wet and dry seasons. Physico-chemical parameters including pH, turbidity, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), nitrates, chloride, sodium, ammonium, electrical conductivity and total alkalinity were assessed. Additionally, plankton composition and abundance were analyzed to investigate the cause of reported mortalities. Observation method was used to assess the anthropogenic activities taking place along inlet rivers. BOD, COD, ammonium and pH values were higher compared to the Tanzania Environmental Management Act of 2004 and World Health Organization recommended values for freshwater, resulting into low DO levels. There were no zooplankton or phytoplankton colonies observed from sampled water. The study observed anthropogenic activities (unsustainable crop cultivation, deforestation and overgrazing) at the LNRS catchment. The reported physico-chemical changes could be due to such anthropogenic activities at the LNRS catchment which could have resulted into the reported fish mortalities. Watershed management using nature-based solutions such as restoration of riparian vegetation and environment management awareness are recommended for LNRS ecosystem sustainability.