Ammonium-derived nitrous oxide is a global source in streams.

Area of Science:

• Environmental Science
• Microbial Ecology
• Biogeochemistry

Background:

• Global riverine nitrous oxide (N2O) emissions have surged over the past century.
• Hyporheic zones in small streams are estimated to contribute ~85% of these emissions.
• Mechanisms controlling hyporheic N2O production remain poorly understood.

Purpose of the Study:

• To identify dominant pathways of hyporheic nitrous oxide (N2O) production in agricultural streams.
• To investigate the role of ammonia and nitrate in N2O generation within stream ecosystems.
• To provide insights for mitigating N2O emissions from riverine systems.

Main Methods:

• Analysis of N2O fluxes in agricultural streams globally.
• Correlation analysis between N2O fluxes and ammonia/nitrate concentrations.
• Metagenomic analysis of microbial communities and N2O metabolic pathways.

Main Results:

• Ammonia-derived pathways are the dominant source of hyporheic N2O (69.6 ± 2.1%).
• N2O fluxes positively correlate with ammonia concentrations.
• Nitrifying bacteria possess more N2O-related genes than denitrifying bacteria.

Conclusions:

• Ammonia, not nitrate, is the primary driver of hyporheic N2O production in agricultural streams.
• Mitigating agriculturally derived ammonium is crucial for controlling riverine N2O emissions.
• Global riverine models require improved representation of ammonia-driven N2O pathways.