Click on image to view larger version.
Fig. 4. Detailed portion from Fig. 2, showing the two denitrification lines calculated from the two estimated initial 
15N and 18O values (gray hexagons). Open symbols represent river samples, closed symbols represent tile drain samples. Letters indicate river sample locations (D = Davenport, Q = Quincy, C = Chester). Tick marks on the vectors indicate an estimation of the extent of denitrification (percentage of original NO3– lost, using 
values of –15.9 for 15N and –8 for 18O in Eq. [3] for NO3– having initial values of 4.4
for 15N and 6.4 for 18O [solid lines] and for NO3– having initial values of 6.1 for 15N and 7.2 for 18O [dashed lines]).
