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Use of geostatistical models to evaluate landscape and stream network controls on post-fire stream nitrate concentrations
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  • Allison E. Rhea,
  • Tim Covino,
  • Charles C. Rhoades,
  • Alexander C. Brooks
Allison E. Rhea
Colorado State University

Corresponding Author:[email protected]

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Tim Covino
Colorado State University
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Charles C. Rhoades
USDA Forest Service Rocky Mountain Research Station
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Alexander C. Brooks
Colorado State University
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Forested watersheds provide many ecosystem services that have become increasingly threatened by wildfire. Stream nitrate (NO 3 -) concentrations often increase following wildfire and can remain elevated for decades. We investigated the drivers of persistent elevated stream NO 3 - in nine watersheds that were burned to varying degrees 16 years prior by the Hayman fire, Colorado, USA. We evaluated the ability of multiple linear regression and spatial stream network modeling approaches to predict observed concentrations of the biologically active solute NO 3 - and the conservative solute sodium (Na +). Specifically, we quantified the degree to which landscape and stream network characteristics predict stream solute concentrations. No landscape variables were strong predictors of stream Na +. Rather, stream Na + variability was largely attributed to flow-connected spatial autocorrelation, indicating that downstream hydrologic transport was the primary driver of spatially distributed Na + concentrations. In contrast, vegetation cover, measured as mean normalized differenced moisture index (NDMI), was the strongest predictor of spatially distributed stream NO 3 - concentrations. Furthermore, stream NO 3 - concentrations had weak flow-connected spatial autocorrelation and high spatial variability. This pattern is likely the result of spatially heterogeneous wildfire behavior that leaves intact forest patches interspersed with high burn severity patches that are dominated by shrubs and grasses. Post-fire vegetation also interacts with watershed structure to influence stream NO 3 - patterns. For example, severely burned convergent hillslopes in headwaters positions were associated with the highest stream NO 3 concentrations due to the high proportional influence of hillslope water in these locations. Our findings suggest that reforestation is critical for the recovery of stream NO 3 - concentrations to pre-fire levels and targeted planting in severely burned convergent hillslopes in headwater positions will likely have a large impact on stream NO 3 - concentrations.
28 May 2022Submitted to Hydrological Processes
11 Jun 2022Submission Checks Completed
11 Jun 2022Assigned to Editor
11 Jun 2022Reviewer(s) Assigned
08 Jul 2022Review(s) Completed, Editorial Evaluation Pending
11 Jul 2022Editorial Decision: Revise Minor
16 Aug 20221st Revision Received
17 Aug 2022Submission Checks Completed
17 Aug 2022Assigned to Editor
17 Aug 2022Reviewer(s) Assigned
17 Aug 2022Review(s) Completed, Editorial Evaluation Pending
22 Aug 2022Editorial Decision: Accept
Sep 2022Published in Hydrological Processes volume 36 issue 9. 10.1002/hyp.14689