Preprints
https://doi.org/10.5194/hess-2021-228
https://doi.org/10.5194/hess-2021-228

  10 May 2021

10 May 2021

Review status: this preprint is currently under review for the journal HESS.

Watershed zonation approach for tractably quantifying above-and-belowground watershed heterogeneity and functions

Haruko M. Wainwright1,2, Sebastian Uhlemann1, Maya Franklin1, Nicola Falco1, Nicholas J. Bouskill1, Michelle Newcomer1, Baptiste Dafflon1, Erica Woodburn1, Burke J. Minsley3, Kenneth H. Williams1,4, and Susan S. Hubbard1 Haruko M. Wainwright et al.
  • 1Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
  • 2University of California, Berkeley, CA 94720, USA
  • 3U.S. Geological Survey, Denver, CO 80225, USA
  • 4Rocky Mountain Biological Laboratory, Crested Butte, CO, 81224, USA

Abstract. In this study, we develop a watershed zonation approach for characterizing watershed organization and function in a tractable manner by integrating multiple spatial data layers. Recognizing the coupled ecohydrogeological-biogeochemical interactions that occur across bedrock through canopy compartments of a watershed, we hypothesize that (1) suites of above/belowground properties co-varying with each other, (2) hillslopes are representative units for capturing watershed-scale heterogeneity, (3) remote sensing data layers and clustering methods can be used to identify watershed hillslope zones having unique distributions of bedrock-through-canopy properties relative to neighboring parcels, and (4) property suites associated with the identified zones can be used to understand zone-based functions, such as response to early snowmelt or drought, and associated solute exports to the river. We demonstrate this concept using unsupervised clustering methods that synthesizes airborne remote sensing data (LiDAR, hyperspectral, and electromagnetic surveys) along with satellite and streamflow data collected in the East River Watershed, Crested Butte, Colorado, USA. Results show that, (1) hillslope-average elevation and slope are significantly correlated with near-surface bedrock electrical resistivity (top 20 m), (2) elevation and aspect are independent controls on plant and snow signatures, (3) the correlation between hillslope-averaged above- and below- ground properties are significantly higher than pixel-by-pixel correlation and (4) K-means, hierarchical clustering, and Gaussian mixture clustering methods generate similar zonation patterns across the watershed. Using independently collected data, it is shown that the identified zones provide information about zone-based watershed functions, including foresummer drought sensitivity and river nitrogen exports. The approach is expected to be extensible to other sites and generally useful for guiding the selection of hillslope experiment locations and informing model parameterization.

Haruko M. Wainwright et al.

Status: open (until 08 Jul 2021)

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Haruko M. Wainwright et al.

Haruko M. Wainwright et al.

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Short summary
This paper has developed an approach for characterizing watershed heterogeneity and its relationship to key functions such as ecosystem sensitivity to droughts and nitrogen export. We have applied several clustering methods to classify hillslopes into “watershed zones” that have distinct distributions of bedrock-to-canopy properties as well as key functions. This is a powerful approach for guiding watershed experiments and sampling, as well as informing hydrological and biogeochemical models.