A first assessment of megaherbivore subsidies in artificial waterholes in Hwange National Park, Zimbabwe

Abstract

The transfer of terrestrial organic matter by terrestrial wild and domestic animals when they urinate and defecate directly in Savanna Rivers has already been studied. However, the eulittoral zone around waterholes receives organic matter during the dry season, which is diluted in the ecosystem when the waterholes returns to its wet season level. In our study, we evaluated this pathway of subsidies in Hwange National Park, Zimbabwe, by estimating dung density in the eulittoral zone at the peak of the dry season. We also collected dung from different herbivore species during the dry and wet seasons to measure nutrient content and estimate nitrogen and phosphorus leaching rates. Our results show a decrease in carbon:phosphorus and nitrogen:phosphorus ratios in the dry season compared to the wet season. During the dry season, the deposition of total carbon, nitrogen, and phosphorus, mostly due to elephants, is estimated to be 8.65, 0.25, and 0.06 g/m2/day, respectively, while the leaching rates of dissolved inorganic nitrogen and phosphorus are 1.52 mg and 6.59 mg m2/day, respectively. No specific coloured dissolved organic matter signature for dung was identified. We discuss the temporal dynamics of the subsidies as a distinctive feature of the system.