Waterholes in Tsavo National Park, Kenya.
The evolution of natural waterholes is attributed to the erosion of surrounding termitaria by wildlife. The physico-chemical characteristics of soil from the reservoirs (which are formed by deepening and widening the natural waterholes) and termitaria are similar, and the centres of natural waterholes are clayed and contain more potassium and sulphate ions than artificial waterholes do. The mineral composition of the water fluctuates seasonally, the highest values being recorded from reservoirs topped up with water from boreholes during the dry season and the lowest values from natural clay pans during the rains. No single mineral attracts wildlife to the waterholes but herbivores possibly augment the low mineral status of their diets by drinking at sodium-rich waterholes during the dry season. The development of artificial waterholes should be discontinued in water-logged, black-cotton soil because the montmorillonitic clay shrinks and cracks when dehydrated and allows water to soak away. Moreover the development of artificial waterholes in Tsavo may permit an increase in the number of animals, especially elephants, and this would aggravate the already alarming rate of removal of woody vegetation in the Park.