Fig. 7. Dissolved gas data for piezometer nest HC9 beneath the cultivated field, indicating effects of denitrification: (A) concentrations of Ar and N₂, with solid curves indicating aqueous gas concentrations in equilibrium with humid air for a range of temperatures (10–20°C) and addition of either 0 or 2 cm³ (STP) L^–1 unfractionated air, and with shading indicating approximate concentrations assumed for recharge in the denitrified samples; (B) isotopic composition of dissolved N₂ gas, showing the interpreted value for the denitrification component.