Perrot, D., Molotch, N.P., Williams, M.W., Jepsen, S.M., Sickman, J.O.
Water Resources Research
NWT Accession Number: NWT1824
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.
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
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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