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Relationships between stream nitrate concentration and spatially distributed snowmelt in high-elevation catchments of the western U.S., 2014


Perrot, D., Molotch, N.P., Williams, M.W., Jepsen, S.M., Sickman, J.O.


Water Resources Research 50
DOI: 10.1002/2013WR015243
NWT Accession Number: NWT1824

Abstract

This study compares stream nitrate (NO-3) concentrations to spatially distributed snowmelt in two alpine catchments, the Green Lakes Valley, Colorado (GLV4) and Tokopah Basin, California (TOK). A snow water equivalent reconstruction model and Landsat 5 and 7 snow cover data were used to estimate daily snowmelt at 30 m spatial resolution in order to derive indices of new snowmelt areas (NSAs). Estimates of NSA were then used to explain the NO-3 flushing behavior for each basin over a 12 year period (1996–2007). To identify the optimal method for defining NSAs and elucidate mechanisms underlying catchment NO-3 flushing, we conducted a series of regression analyses using multiple thresholds of snowmelt based on temporal and volumetric metrics. NSA indices defined by volume of snowmelt (e.g., snowmelt <= 30 cm) rather than snowmelt duration (e.g., snowmelt <= 9 days) were the best predictors of stream NO-3 concentrations. The NSA indices were better correlated with stream NO-3 concentration in TOK (average R2 = 0.68) versus GLV4 (average R2 = 0.44). Positive relationships between NSA and stream NO-3 concentration were observed in TOK with peak stream NO-3 concentration occurring on the rising limb of snowmelt. Positive and negative relationships between NSA and stream NO-3 concentration were found in GLV4 with peak stream NO-3 concentration occurring as NSA expands. Consistent with previous works, the contrasting NO-3 flushing behavior suggests that streamflow in TOK was primarily influenced by overland flow and shallow subsurface flow, whereas GLV4 appeared to be more strongly influenced by deeper subsurface flow paths.

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Citation

Perrot, D., Molotch, N.P., Williams, M.W., Jepsen, S.M., Sickman, J.O., (2014) Relationships between stream nitrate concentration and spatially distributed snowmelt in high-elevation catchments of the western U.S.. Water Resources Research 50 , DOI: 10.1002/2013WR015243

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This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-1637686. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necesarily reflect the views of the National Science Foundation.

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