Biogeochemistry

, Volume 105, Issue 1–3, pp 53–74

Amazon deforestation alters small stream structure, nitrogen biogeochemistry and connectivity to larger rivers

  • Linda A. Deegan
  • Christopher Neill
  • Christie L. Haupert
  • M. Victoria R. Ballester
  • Alex V. Krusche
  • Reynaldo L. Victoria
  • Suzanne M. Thomas
  • Emily de Moor
Article

DOI: 10.1007/s10533-010-9540-4

Cite this article as:
Deegan, L.A., Neill, C., Haupert, C.L. et al. Biogeochemistry (2011) 105: 53. doi:10.1007/s10533-010-9540-4

Abstract

Human activities that modify land cover can alter the structure and biogeochemistry of small streams but these effects are poorly known over large regions of the humid tropics where rates of forest clearing are high. We examined how conversion of Amazon lowland tropical forest to cattle pasture influenced the physical and chemical structure, organic matter stocks and N cycling of small streams. We combined a regional ground survey of small streams with an intensive study of nutrient cycling using 15N additions in three representative streams: a second-order forest stream, a second-order pasture stream and a third-order pasture stream. These three streams were within several km of each other and on similar soils. Replacement of forest with pasture decreased stream habitat complexity by changing streams from run and pool channels with forest leaf detritus (50% cover) to grass-filled (63% cover) channel with runs of slow-moving water. In the survey, pasture streams consistently had lower concentrations of dissolved oxygen and nitrate (NO3) compared with similar-sized forest streams. Stable isotope additions revealed that second-order pasture stream had a shorter NH4+ uptake length, higher uptake rates into organic matter components and a shorter 15NH4+ residence time than the second-order forest stream or the third-order pasture stream. Nitrification was significant in the forest stream (19% of the added 15NH4+) but not in the second-order pasture (0%) or third-order (6%) pasture stream. The forest stream retained 7% of added 15N in organic matter compartments and exported 53% (15NH4+ = 34%; 15NO3 = 19%). In contrast, the second-order pasture stream retained 75% of added 15N, predominantly in grasses (69%) and exported only 4% as 15NH4+. The fate of tracer 15N in the third-order pasture stream more closely resembled that in the forest stream, with 5% of added N retained and 26% exported (15NH4+ = 9%; 15NO3 = 6%). These findings indicate that the widespread infilling by grass in small streams in areas deforested for pasture greatly increases the retention of inorganic N in the first- and second-order streams, which make up roughly three-fourths of total stream channel length in Amazon basin watersheds. The importance of this phenomenon and its effect on N transport to larger rivers across the larger areas of the Amazon Basin will depend on better evaluation of both the extent and the scale at which stream infilling by grass occurs, but our analysis suggests the phenomenon is widespread.

Keywords

15Ammonium uptake length Brazil Nitrification Nitrogen cycling Pasture Stable isotopes Stream ecosystem Tropical forest 

Supplementary material

10533_2010_9540_MOESM1_ESM.doc (68 kb)
Supplementary material 1 (DOC 69 kb)

Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Linda A. Deegan
    • 1
  • Christopher Neill
    • 1
  • Christie L. Haupert
    • 1
    • 4
  • M. Victoria R. Ballester
    • 2
  • Alex V. Krusche
    • 2
  • Reynaldo L. Victoria
    • 2
  • Suzanne M. Thomas
    • 1
  • Emily de Moor
    • 3
    • 5
  1. 1.The Ecosystems Center, Marine Biological LaboratoryWoods HoleUSA
  2. 2.Laboratório de Análise Ambiental e Geoprocessamento, Centro de Energia Nuclear na AgriculturaUniversidade de São PauloPiracicabaBrazil
  3. 3.Department of Ecology and Evolutionary BiologyBrown UniversityProvidenceUSA
  4. 4.CH2M Hill Polar ServicesFairbanksUSA
  5. 5.Department of GeographyUniversity of California Santa BarbaraSanta BarbaraUSA

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