Source-Specific Nitrogen Inputs Are Associated with Pathway Partitioning Between Denitrification and DNRA in River...

Area of Science:

• Environmental microbiology
• Riverine biogeochemistry
• Nitrogen cycling

Background:

• Understanding nitrogen sources is crucial for managing river water quality and mitigating greenhouse gas emissions.
• External inputs profoundly influence nitrogen transformation pathways in aquatic ecosystems.

Purpose of the Study:

• To investigate how different external nitrogen sources affect nitrogen fate and cycling pathways in river water.
• To identify critical timeframes for observing source-dependent nitrogen cycle responses.

Main Methods:

• Short-term microcosm incubations with diverse nitrogen sources.
• Integration of hydrochemical analysis, bacterial community profiling, metagenomics, RT-qPCR, and process-rate measurements.
• Analysis of functional gene expression (nrfA, nirS, nosZ) and nitrogen transformation rates.

Main Results:

• Manure inputs led to high nitrogen loading, suppressed nitrification, and promoted DNRA (dissimilatory nitrate reduction to ammonium), favoring nitrogen retention.
• Sewage inputs maintained high nitrate, enhanced denitrification, but increased nitrous oxide (N2O) production.
• A 12-hour window was identified as critical for rapid, source-dependent shifts in nitrogen cycling pathways.

Conclusions:

• Nitrogen management strategies must be source-specific, considering both nitrogen loading and hydrochemical influences on nitrate fate.
• Short-term monitoring is essential for capturing rapid nitrogen cycle dynamics in response to pollution.
• Distinct nitrogen cycling pathways are activated depending on the type of external nitrogen input, impacting river water quality and greenhouse gas emissions.