Relationship between denitrification and anammox rates and N2 production with substrate consumption and pH in a riparian zone

Abstract

ABSTRACT Denitrification and anaerobic ammonium oxidation (anammox) are the key processes to quantitatively remove nitrate (NO3 −) and balance the nitrogen (N) budget of the ecosystem. In this paper, a slurry-based 15N tracer approach was used to study the correlation and quantitative relation of substrate consumption and pH with rates of denitrification and anammox in a riparian zone. The results showed that the fastest rates of 0.93 µg N h−1 and 0.32 µg N h−1 for denitrification (Denitrif-N2) and anammox (Denitrif-N2), respectively. N2 produced by denitrification occupied 74.04% and produced by anammox occupied 25.96% of the total N2, proving denitrification is the dominant process to remove NO3 −. The substrate content (NO3 −, NH4 + and TOC) and pH varied during incubation and were significantly correlated with Dentrif-N2 and Anammox-N2. Nitrate and TOC as the substrates of denitrification demonstrated a significant correlation with Anammox-N2, which was associated with the products of denitrification involved in the anammox process. This proved a coupling of denitrification and anammox. A quantitative relationship was observed between Dentrif-N2 and Anammox-N2 in the range of 2.75–2.90 when TOC, NH4 + and NO3 − consumption per unit mass or pH changed per unit. Nitrogen mass balance analysis showed that 1 mg N substrate (NO3 −+NH4 +) consumption in the denitrification and anammox can produce 1.05 mg N2 with a good linear relationship (r 2 = 0.9334). This could be related to other processes that produced extra N2 in denitrification and anammox system.