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

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 (r²= 0.9334). This could be related to other processes that produced extra N₂ in denitrification and anammox system.

GRAPHICAL ABSTRACT

KEYWORDS:

• Denitrification rate
• anammox rate
• slurry-based ¹⁵N tracer incubation
• quantitative relationship
• nitrogen mass balance

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author or the first author upon reasonable request.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number 41973017]; the Natural Science Foundation of Tianjin [grant number 19JCZDJC40700].