FIG. 4.

N₂O production in systems containing aqueous Fe²⁺ (2 mmol liter⁻¹) and NO₂⁻ (3 mmol liter⁻¹) (Δ), aqueous Fe²⁺, NO₂⁻, and 50 mmol liter⁻¹ goethite (▴), and NO₂⁻ and 50 mmol liter⁻¹ goethite (•). Error bars indicate the standard deviations of the means (n = 3).