Figure 4. Validation of
estimated Csw and Cdw (this study). (a)
A linear relationship (red line with slope = 0.95 and
R2 = 0.94) derived from estimations in this work
(colored markers), compared to the linear relationship (black line,
slope = 0.83, R2 = 0.70) from measurements (gray
markers) compiled in Sudduth et al. (2013). The dotted gray circle at
the top left corner is an outliner and was excluded from data fitting.
The similar slope and correlation indicate that Cswestimated from stream chemistry approximates measured
Csw. The Cstream from this study are
flow-weighted concentrations calculated by dividing annual nitrate load
by annual discharge. (b) Estimated Cdw from this work
vs. measured groundwater concentration (as a proxy for
Cdw) from the National Ground Water Monitoring Network.
The measured groundwater concentrations were averaged for close by
regions (Figure S5). Most symbols fall close to the 1:1 line, indicating
estimated Cdw can be used to approximate groundwater
concentration. Error bars are for one standard deviation in nearby
regions.