PROBLEMS - Hydrogeology: Objectives, Methods, Applications - page 333

Figure 8 Hydrologic cycles and nitrate concentrations in boreholes in the Durance aquifer
(Mudry, 1988).
Figure 8 (after Mudry, 1988) shows the nitrate concentrations of 2
boreholes in the Saignonne catchment fi eld in Avignon, in the Lower
Durance aquifer (F1 located 800 m from the Durance and F11 located 560
m from the river).
Question 1: How does the piezometry react to the aquifer being under
irrigation?
Question 2: What mechanisms reveal the monitoring of the nitrate
concentrations?
Answer 1:
The Eyragues piezometer, which experiences only local recharge (natural
regime), shows piezometric maxima centered on periods of rainfall. The
piezometry at Plan d'Orgon is more regular and is high from May to
September, due to the recharge of the aquifer by part of the water used for
irrigation.
Answer 2:
The F11 borehole, closer to the Durance, shows a seasonal sinusoidal signal
with a principal peak in the summer (8 mg·L -1 ), and a secondary peak in the
winter (6 mg·L -1 ). The minimum, of 4 mg·L -1 is observed in the fall. The F1
borehole, further from the river, shows a seasonal sinusoidal signal with a
more marked principal peak in the summer (16 mg·L -1 ), but no secondary
peak. The minimum of mg·L -1 is observed in the fall.