Ecosystems

, Volume 10, Issue 8, pp 1231–1249

Nutrient Vectors and Riparian Processing: A Review with Special Reference to African Semiarid Savanna Ecosystems

  • S. M. Jacobs
  • J. S. Bechtold
  • H. C. Biggs
  • N. B. Grimm
  • S. Lorentz
  • M. E. McClain
  • R. J. Naiman
  • S. S. Perakis
  • G. Pinay
  • M. C. Scholes
Article

Abstract

This review article describes vectors for nitrogen and phosphorus delivery to riparian zones in semiarid African savannas, the processing of nutrients in the riparian zone and the effect of disturbance on these processes. Semiarid savannas exhibit sharp seasonality, complex hillslope hydrology and high spatial heterogeneity, all of which ultimately impact nutrient fluxes between riparian, upland and aquatic environments. Our review shows that strong environmental drivers such as fire and herbivory enhance nitrogen, phosphorus and sediment transport to lower slope positions by shaping vegetative patterns. These vectors differ significantly from other arid and semiarid ecosystems, and from mesic ecosystems where the impact of fire and herbivory are less pronounced and less predictable. Also unique is the presence of sodic soils in certain hillslopes, which substantially alters hydrological flowpaths and may act as a trap where nitrogen is immobilized while sediment and phosphorus transport is enhanced. Nutrients and sediments are also deposited in the riparian zone during seasonal, intermittent floods while, during the dry season, subsurface movement of water from the stream into riparian soils and vegetation further enrich riparian zones with nutrients. As is found in mesic ecosystems, nutrients are immobilized in semiarid riparian corridors through microbial and plant uptake, whereas dissimilatory processes such as denitrification may be important where labile nitrogen and carbon are in adequate supply and physical conditions are suitable—such as in seeps, wallows created by animals, ephemeral wetlands and stream edges. Interaction between temporal hydrologic connectivity and spatial heterogeneity are disrupted by disturbances such as large floods and extended droughts, which may convert certain riparian patches from sinks to sources for nitrogen and phosphorus. In the face of increasing anthropogenic pressure, the scientific challenges are to provide a basic understanding of riparian biogeochemistry in semiarid African savannas to adequately address the temporal and spatial impact of disturbances, and to apply this knowledge to better regional land and water management. An integrated, multidisciplinary approach applied in protected as well as human-disturbed ecosystems in southern Africa is essential for underpinning a strong environmental basis for sustainable human-related expansion.

Key words

riparian biogeochemistry nitrogen phosphorus semiarid landscapes fluvial disturbance South Africa 

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • S. M. Jacobs
    • 1
    • 9
  • J. S. Bechtold
    • 1
  • H. C. Biggs
    • 2
  • N. B. Grimm
    • 3
  • S. Lorentz
    • 4
  • M. E. McClain
    • 5
  • R. J. Naiman
    • 1
  • S. S. Perakis
    • 6
  • G. Pinay
    • 7
    • 10
  • M. C. Scholes
    • 8
  1. 1.School of Aquatic and Fishery SciencesUniversity of WashingtonSeattleUSA
  2. 2.Scientific ServicesKruger National ParkSkukuzaSouth Africa
  3. 3.School of Life SciencesArizona State UniversityTempeUSA
  4. 4.School of Bioresources Engineering and Environmental HydrologyUniversity of KwaZulu-NatalScottsvilleSouth Africa
  5. 5.Department of Environmental StudiesFlorida International UniversityMiamiUSA
  6. 6.USGS Forest and Rangeland Ecosystem Science CenterCorvallisUSA
  7. 7.Centre d’Ecologie Fonctionnelle & EvolutiveCNRSMontpellier Cedex 5France
  8. 8.School of Animal, Plant and Environmental SciencesUniversity of the WitwatersrandWITSSouth Africa
  9. 9.Department of Conservation Ecology and EntomologyUniversity of StellenboschMatielandSouth Africa
  10. 10.University of BirminghamBirminghamUK

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