Seasonal variability in faecal bacteria of semiarid rivers in the Serengeti National Park, Tanzania

Humans and livestock are known contributors of faecal waste to surface water. However, little is known about natural fluctuations of faecal bacteria, especially where wildlife may contribute substantial amounts of waste. I tested the hypotheses that ecological factors, including seasonal animal impacts, rainfall and physiochemical water quality, influence the abundance of total coliform (TC) and Escherichia coli faecal bacteria in five rivers of the Serengeti National Park, Tanzania. TC and E. coli are indicators commonly used to assess water quality and their abundance can be determined quantitatively by using defined-substrate technology. Results demonstrated substantial variation in faecal bacteria across rivers and seasons. In the southern two rivers, faecal bacteria increased significantly during the wet season, compared with dry-season levels, whereas there were few seasonal differences in the northern rivers, suggesting that large populations of resident wildlife in the north dampen the seasonal influence of migratory wildlife. Faecal bacteria were positively related to rainfall and total ammonia/ammonium, and had a negative quadratic relationship with salinity. The present results demonstrated that wildlife in protected regions can be major contributors of faecal bacteria to surface waters, and as demand for water resources increases, pose a significant threat to human health. Additional keywords: E. coli, hippo pool, migration, precipitation, total coliform. Received 31 March 2011, accepted 31 May 2011, published online 12 August 2011