*3.3. Depletion of Atrazine and Its Metabolites with Time in Eastern Nebraska Counties*

In Figure 4a, a time-dependent groundwater atrazine decline was observed despite continuous atrazine usage during the same period. This corresponded to a decrease in groundwater D.E.A. and D.I.A. (Figure 4b,c).

**Figure 4.** *Cont*.

**Figure 4.** Linear relationship of atrazine and its metabolites over time (1995–2014). (**a**) Time series plot of atrazine (ppb). (**b**). Time series plot of D.E.A. (ppb). (**c**) Time series plot of D.I.A. (ppb).

#### *3.4. Precipitation and Temperature trend in Eastern Nebraska Counties*

Precipitation and temperature trends between 1995 and 2014 were characterized in Figure 5a,b, respectively. The observed counties seem to record lower precipitation in 1995, 2000, and 2012, Figure 5a.

**Figure 5.** Climatic changes with time, PRISM (1995–2014). (**a**) Precipitation. (**b**) Temperature.

*3.5. Seasonal Variation of Atrazine and Its Metabolites in Eastern Nebraska Counites*

Figure 6a–c shows that the average groundwater atrazine, D.E.A., and D.I.A. concentration by month was consistently higher during Nebraska's winter and early springs (December-March). Moreover, the highest precipitation was recorded in May-June (Figure 6d), and the highest mean daily temperature was reported in July-August (Figure 6e).

**Figure 6.** Seasonal variation in groundwater atrazine and its metabolites (**a**) Average atrazine concentration by month. (**b**) Average D.E.A. concentration by month. (**c**) Average D.I.A. concentration by month (**d**). Average annual precipitation by month. (**e**) Mean daily temperature by month.
