Slight flow volume rises increase nitrogen loading to nitrogen-rich river, while dramatic flow volume rises promote...

Area of Science:

• Environmental Science
• Water Quality Management
• Biogeochemistry

Background:

• Concentrated rainfall and water transfer projects can lead to nitrogen recontamination in rivers.
• Understanding nitrogen dynamics at the water-sediment interface is crucial for managing riverine ecosystems.

Purpose of the Study:

• To quantify nitrogen transport and transformation fluxes at the water-sediment interface under varying flow conditions.
• To analyze changes in microbial functional genes related to nitrogen cycling.
• To investigate the impact of slight and dramatic flow increases on nitrogen processes in the Fu River.

Main Methods:

• Coupling of hydrodynamic and biochemical reaction models.
• Quantification of diffusive transport and transformation fluxes of nitrogen.
• High-throughput sequencing of microbial functional genes.
• Investigation of ammonium (NH4+-N) and nitrate (NO3--N) exchange, mineralization, nitrification, and denitrification.

Main Results:

• A slight flow increase enhanced ammonium release, inhibited nitrate sedimentation, decreased mineralization, and increased nitrification, raising river nitrogen load.
• A dramatic flow increase elevated nitrogen exchange fluxes, inhibited mineralization, promoted nitrification-denitrification, and increased inorganic nitrogen consumption.
• Changes in microbial functional gene abundance were observed in response to flow variations.

Conclusions:

• Flow volume significantly influences nitrogen cycling at the water-sediment interface, with different effects for slight versus dramatic increases.
• The study provides insights into mitigating nitrogen recontamination during water management projects.
• Results suggest a potential overlooked global nitrogen sink in river systems.