Understanding the ecological impacts of water-abstraction and changes in surface water availability in the Kilimanjaro landscape, Tanzania.

Abstract

For decades, surface water has been extracted for human use in the wildlife-rich Kilimanjaro landscape, northern Tanzania that includes the Kilimanjaro and Arusha National Parks. This study evaluates the natural and human-induced changes in the availability and quality of surface water, and the ecological impact on the surrounding vegetation and large herbivorous mammals. Excessive and unsustainable water abstraction takes place within and outside the parks, as between 70% and 90% of the available water is removed within 20 km of the park boundaries. Annual rainfall did not decrease in recent decades, suggesting that the water shortage is not currently exacerbated by climate change. Abstraction resulted in reduced water quality due to increased evaporation and reduced dilution, including of the organic and inorganic material emanating from crop irrigation. Salinity, fluoride and nitrate, increased downstream in the Ngarenanyuki River and water holes in the dry season to concentrations that may be harmful to wildlife. Levels of iron and aluminium were above acceptable limits for wildlife use in the downstream reaches of the Simba River and, again, in some water holes. Because of upstream water abstraction in the National Parks by the local communities, the large herbivores concentrated around the remaining surface water sources in the lowland semi-arid areas. Animal abundance increased towards the water sources, including those with high salinity and mineral content, suggesting that water availability overrides water quality during periods of water scarcity. Plains zebra and wildebeest, which are among the water-dependent species, were more associated with the available surface water sources than browsers such as giraffe and impala. An increase in riparian wetland vegetation was observed in Arusha National Park, and this was likely due to an increase in surface water following increased rainfall. In contrast, the downstream semi-arid lowland areas showed a substantial loss in riparian and adjacent floodplain vegetation due to excessive upstream water abstraction and associated increased siltation. Vegetation cover loss was caused by overgrazing and trampling by wild animals and livestock seeking drinking water from the scarce water resources. Therefore, an increase in rainfall leads to an increase in water in the upstream and hence increased riparian vegetation. However, excessive water abstraction leads to water shortage in the downstream areas, increased mineralisation, decreased riparian vegetation and increased number of mammals. This thesis has demonstrated that the existing water abstraction in the National Parks and the upland villages around the parks is unsustainable, leading to a developing water crisis that is adversely affecting the ecology of the Kilimanjaro landscape. A number of solutions are proposed to improve water resource management and to mitigate the ecological impacts of water abstraction.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Keith White (Supervisor) & Susanne Shultz (Supervisor)