Fig. 5
Evolution of the nitrogenous species, pH and pressures after injection of Intervals 1 and 2 with nitrate during tests INT1_2014 and INT2_2013 (Table 2). a, b Evolution of nitrate (blue), nitrite (red) and ammonium (green) concentrations after injection of a Interval 1 with 15 mM \({\text{NO}}_{3}^{ - }\) only and pulse injection with H2 after 54 days or b Interval 2 with 25 mM \({\text{NO}}_{3}^{ - }\) only and pulse injection with acetate after 70 days. c Evolution of the pH (purple) and gas pressure in the HEU (orange) after injection of Interval 1. d Evolution of the pH (purple) and water pressure (green) in Interval 2. Stages I and III: nitrate reactivity without additional electron donor; Stage II: nitrate reactivity during pulse injection with either H2 (Interval 1) or acetate (Interval 2). The errors on the values are 1% (pH), 10% ([\({\text{NH}}_{4}^{ + }\)], [CH3COO−]), 7–15% ([\({\text{NO}}_{3}^{ - }\)]) and 15–20% ([\({\text{NO}}_{2}^{ - }\)]) for a 95% confidence interval. The uncertainties (95% confidence) on the pressures are 2 kPa (gas pressure) and 30 kPa (water pressure)