Interactions between soil, rainfall, and wildlife drive surface water quality across a savanna ecosystem

Abstract

Surface water resources play an important role in the transportation of nutrients within and between regions. Water quality varies spatially across landscapes, but the extent of this variability and the interaction between water quality and wildlife are not well‐known. In some savannas, heterogeneous climatic and geologic patterns result in gradients of precipitation and soil nutrients, leading to temporal and regional differences in soil and vegetation quality. Wildlife utilise these seasonal patterns, influencing soil nutrient dynamics and vegetation. However, the impact of seasonally abundant wildlife, climate, and soils on surface water quality is unknown in savannas. Fluctuations in surface water quality were measured across the Serengeti ecosystem at 6‐month intervals, and the influence of rainfall, watershed, and seasonal wildlife migration were then modelled. The results suggest that although soil composition in watersheds influences the concentration of soil‐derived nutrients in rivers, rainfall and wildlife have a significant effect on the seasonal concentrations of most nutrients. The role of migratory wildlife in surface water quality in some watersheds is likely dampened by the large influence of resident species across seasons and habitats. The alteration of rainfall patterns by climate change is expected to influence nutrient transport into savanna rivers. Copyright © 2012 John Wiley & Sons, Ltd.

The role of water quality in large mammal migratory behaviour in the Serengeti

“…These results indicate that there are significant regional differences in water quality across the Serengeti at the end of the wet season, likely related to precipitation, geology and biological differences (Anderson and Talbot, 1965). The primary driver of Ca and PO 4 in water is soil composition, whereas precipitation and seasonality drive NH 3 -N, TSS, DO and NO 3 (Strauch, 2012). This is the result of the calcium carbonate hardpan that exists in the south owing to extensive volcanic ash input, resulting in highly alkaline and saline soils with a high Ca and phosphorus content (Pearsall, 1957;Anderson and Talbot, 1965).…”

“…Contrastingly, the northern, heavily weathered granite-derived and quartzite-derived soils are nutrient deficient (Ruess and Seagle, 1994). Despite greater precipitation in the northern watersheds, fewer nutrients are leached into rivers (Strauch, 2012). Four steps are proposed to explain how it is possible that soil-derived nutrients are responsible for both the movement southward to the short-grass plains (driven by nutritional forage quality) and the movement northward away from these plains (driven by water quality).…”

“…The migration then spends the dry season months in the northern portion of the ecosystem, where rainfall is greater and forage is more plentiful. Strauch (2012) determined how seasonal and spatial differences in precipitation and soil composition affect surface water quality, and Gereta et al (2009) discussed the importance of shifting water availability and quality to maintaining seasonal patterns of wildebeest behaviour. Numerous studies have focused on the large-scale causes and long-term consequences of this migratory behaviour, but there is little consensus regarding the mechanisms involving the initiation of the northward migration (Boone et al, 2006;Fryxell, 1995;Holdo et al, 2009).…”

“…Kreulen (1975) postulated that lactating female wildebeest prefer the southern plains because of increased calcium content in forage, and wildebeest have been shown to move along nutritional gradients to reduce nutrient limitations (McNaughton and Banyikwa, 1995;McNaughton, 1990). Water quality varies greatly across spatial and temporal scales in the Serengeti (Strauch, 2011(Strauch, , 2012. In other systems, the importance of water quality for wildlife health was discussed by Kubly (1990) and Broyles (1995), but neither author identified the potential behavioural implications in any detail.…”

Is ecohydrology missing much of the zoo?

“…There are clear examples of how synergies between animal ecologists and hydrologists can lead to a greater understanding of how fauna affect (or can be used to infer) ecosystem hydrological processes. For example, Palandačić et al () describe a new method by which water flow can be traced in very complex groundwater systems using molecular signatures of fish; Strauch () reports on using surface water quality to improve the understanding of the migratory behaviour of large animals in the Serengeti; Uetake et al () shed light on how biological activity on glaciers reduces reflectance of solar energy, which leads to an enhanced rate of retreat. Further, the literature is rich with reports of how ecosystem engineers, animals that directly regulate resource availability (Jones et al , ), influence hydrological processes.…”