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A tale of two catchments: Causality analysis and isotope systematics reveal mountainous watershed traits that regulate the retention and release of nitrogen
  • +15
  • Nick Bouskill,
  • Michelle E. Newcomer,
  • Rosemary W.H. Carroll,
  • Curtis A Beutler,
  • Markus Bill,
  • Wendy S Brown,
  • Mark E Conrad,
  • Wenming Dong,
  • Nicola Falco,
  • Taylor Maavara,
  • Alexander Newman,
  • Patrick O Sorensen,
  • Tetsu K Tokunaga,
  • Jiamin Wan,
  • Haruko Murakami Wainwright,
  • Qing Zhu,
  • Eoin Brodie,
  • Kenneth Hurst Williams
Nick Bouskill
Lawrence Berkeley National Laboratory

Corresponding Author:[email protected]

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Michelle E. Newcomer
Lawrence Berkeley National Laboratory (DOE)
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Rosemary W.H. Carroll
Desert Research Institute
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Curtis A Beutler
Rocky Mountain Biological Laboratory
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Markus Bill
Lawrence Berkeley National Laboratory
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Wendy S Brown
Rocky Mountain Biological Laboratory
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Mark E Conrad
Lawrence Berkeley Laboratory
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Wenming Dong
Lawrence Berkeley Natiional Laboratory
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Nicola Falco
Lawrence Berkeley National Laboratory (DOE)
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Taylor Maavara
University of Leeds
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Alexander Newman
Rocky Mountain Biological Laboratory
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Patrick O Sorensen
Lawrence Berkeley National Laboratory
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Tetsu K Tokunaga
Lawrence Berkeley National Laboratory
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Jiamin Wan
Lawrence Berkeley National Lab
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Haruko Murakami Wainwright
Lawrence Berkeley National Laboratory (DOE)
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Qing Zhu
Lawrence Berkeley National Laboratory (DOE)
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Eoin Brodie
Lawrence Berkeley National Laboratory (DOE)
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Kenneth Hurst Williams
Lawrence Berkeley National Laboratory (DOE)
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Abstract

Mountainous watersheds are characterized by variability in functional traits, including vegetation, topography, geology, and geomorphology, which together determine nitrogen (N) retention, and release. Coal Creek and East River are two contrasting catchments within the Upper Colorado River Basin that differ markedly in total nitrate (NO3-) export. The East River has a diverse vegetation cover, sinuous floodplains, and is underlain by N-rich marine shale, resulting in a three to twelve times greater total NO3- export relative to the conifer-dominated Coal Creek. While this can partly be explained by the larger size of the East River, the distinct watershed traits of these two catchments imply different mechanisms controlling the aggregate N-export signal. A causality analysis shows biogenic and geogenic processes were critical in determining NO3- export from the East River catchment. Stable isotope ratios of NO3- (δ15NNO3 and δ18ONO3) show the East River catchment is a strong hotspot for biogeochemical processing of NO3- at the soil-saprolite interface and within the floodplain prior to export. By contrast, the conifer-dominated Coal Creek retained nearly all (~97 %) atmospherically-deposited NO3-, and its export was controlled by catchment hydrological traits (i.e., snowmelt periods and water table depth). The conservative N-cycle within Coal Creek is likely due to the abundance of conifer trees, and a smaller riparian region, retaining more NO3- overall and reduced processing prior to export. This study highlights the value of integrating isotope systematics to link watershed functional traits to mechanisms of watershed element retention and release.
29 Apr 2023Submitted to ESS Open Archive
02 May 2023Published in ESS Open Archive