Coupled nitrification and N₂ gas production as a cryptic process in oxic riverbeds

Area of Science:

• Environmental Science
• Microbiology
• Biogeochemistry

Background:

• The nitrogen cycle is crucial for ammonia recycling to the atmosphere.
• Research assumes nitrification products (nitrite/nitrate) freely mix before N2 gas production.
• Distinguishing N2 gas sources in nitrogen cycling remains a challenge.

Purpose of the Study:

• To investigate the spatial patterns of N2 gas production from ammonia in oxic riverbeds.
• To challenge the assumption of free mixing of nitrification intermediates.
• To identify alternative mechanisms controlling nitrogen cycling.

Main Methods:

• Field studies in oxic riverbeds.
• Analysis of N2 gas production patterns.
• Comparison of observed patterns with predicted models for denitrification and anammox.

Main Results:

• N2 gas production patterns deviated significantly (3- to 16-fold) from predictions based on free porewater intermediates.
• Observed patterns align with a model involving a cryptic pool, isolated from porewater.
• This cryptic pool challenges conventional understanding of nitrogen cycling.

Conclusions:

• A cryptic pool, not free porewater mixing, likely governs ammonia to N2 gas coupling in oxic riverbeds.
• This finding necessitates a re-evaluation of current models for nitrogen cycling.
• It suggests a potentially novel pathway or coupling mechanism within the nitrogen cycle.