Provision of water to wildlife is crucial during dry season along the Great Ruaha River (GRR) in Ruaha National Park due to mismanagement of water resources upstream. This paper shows that wildlife in the dry areas of the park utilizes effectively the water from natural and artificial waterholes dug in the sandy riverbed of the GRR. Artificial water holes help alleviate the effects of artificial water shortage in the river, and because the location of the artificial water holes varies annually, the impact on the vegetation of aggregating herbivores around water holes was minimized. Water quality was comparable in natural and artificial water holes, and was the highest in holes dug by elephants in the sandy river bed.
Twenty-two years of rainfall data from six sites, 5 years of animal migration data and 2 years of water quality at 13 sites were explored to quantify the role of water in the Tarangire ecosystem. Inter-annual fluctuations in rainfall were large and not predictable solely from the Southern Oscillation Index. Seasonal fluctuations of rainfall were pronounced, with marked wet and dry seasons. In the dry season, the only drinking water available for wildlife was the Tarangire River and a number of small, scattered wetland-fringed water holes. Their salinity was often high (>8 ppt) and was higher in dry years than in wet years, as well as at the start of the wet season. Water quantity and quality may control the annual migration of wildebeest, zebra, elephants and buffaloes. These animals aggregate in the dry season in areas with the least salty water. The timing of seasonal variations in rainfall is largely predictable and controls annual migration. All wildebeest and most zebras migrated out of Tarangire National Park and into the wider Tarangire ecosystem at the start of the wet season, and they returned into the park in the dry season. Some elephants and buffaloes also migrated in out of the park and a larger resident population remained, whose size may vary inter-annually depending on surface water quantity and quality. The extent of the migration zone may also vary inter-annually.
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