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Journal of Environmental Quality Abstract - Landscape and Watershed Processes

Colloid Mobilization and Seasonal Variability in a Semiarid Headwater Stream

 

This article in JEQ

  1. Vol. 46 No. 1, p. 88-95
     
    Received: July 20, 2016
    Accepted: Nov 01, 2016
    Published: January 12, 2017


    * Corresponding author(s): millstj@colorado.edu
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doi:10.2134/jeq2016.07.0268
  1. Taylor J. Mills *ab,
  2. Suzanne P. Andersonb,
  3. Carleton Berna,
  4. Arnulfo Aguirrec and
  5. Louis A. Derryc
  1. a USGS Colorado Water Science Center (Main Office), Denver Federal Center, MS-415 Building 53, Denver, CO 80225
    b Institute of Arctic and Alpine Research, Univ. of Colorado, 4001 Discovery Drive, Boulder, CO 80303
    c Dep. of Earth and Atmospheric Sciences, Cornell Univ., 112 Hollister Drive, Ithaca, NY 14853-1504
Core Ideas:
  • Riverine colloids were quantified across a wide range of flow and antecedent moisture conditions.
  • Colloids were dominated by kaolinite and illite clays with lesser amounts of amorphous iron.
  • Colloid composition was constant across wide ranges in flow.
  • Mobilization occurred after dry periods and increased with decreasing stream ionic strength.

Abstract

Colloids can be important vectors for the transport of contaminants in the environment, but little is known about colloid mobilization at the watershed scale. We present colloid concentration, composition, and flux data over a large range of hydrologic conditions from a small watershed (Gordon Gulch) in the foothills of the Colorado Front Range. Colloids, consisting predominantly of Si, Fe, and Al, were present in most stream samples but were not detected in groundwater samples. Mineralogical and morphological analysis indicated that the colloids were composed of kaolinite and illite clays with lesser amounts of amorphous Fe-hydroxides. Although colloid composition remained relatively constant over the sampled flow conditions, colloid concentrations varied considerably and increased as ionic strength of stream water decreased. The highest concentrations occurred during precipitation events after extended dry periods. These observations are consistent with laboratory studies that have shown colloids can be mobilized by decreases in pore-water ionic strength, which likely occurs during precipitation events. Colloidal particles constituted 30 to 35% of the Si mass flux and 93 to 97% of the Fe and Al mass fluxes in the <0.45-µm fraction in the stream. Colloids are therefore a significant and often overlooked component of mass fluxes whose temporal variations may yield insight into hydrologic flowpaths in this semiarid catchment.

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