Figure S5.Validation of estimated deep
groundwater nitrate concentration (Cdw) against field
measurements from the National Ground-Water Monitoring Network. Within
each red circle, estimated and measured Cdw are first
averaged and then compared (results see Figure 4b). Red circles are
determined by the proximity of location and data availability (i.e., at
least one estimated Cgw point for comparison with
measurements). Iowa and Florida have more direct comparison because
there are more estimated Cgw points (triangle markers)
located in these regions and more measured Cgw points
(circle markers) in proximity.