Nitrous oxide emissions from a large, impounded river: the Ohio River.

Area of Science:

• Environmental Science
• Microbiology
• Atmospheric Chemistry

Background:

• Microbial activity in rivers is a major source of anthropogenic nitrous oxide (N2O), a potent greenhouse gas.
• Current estimates of N2O emissions are uncertain due to limited direct measurements, especially in large river systems.
• Nitrous oxide contributes to climate change and stratospheric ozone depletion.

Purpose of the Study:

• To quantify the nitrous oxide (N2O) budget for a large, nitrogen-enriched river.
• To measure direct N2O emissions from the water surface and N2O production in sediments and the water column.
• To investigate the influence of urban centers and seasonality on riverine N2O dynamics.

Main Methods:

• Direct measurement of N2O emissions from the river's water surface.
• Quantification of N2O production rates within river sediments and the water column.
• Analysis of seasonal variations and spatial distribution of N2O emissions and production.

Main Results:

• The study presents the first comprehensive N2O budget for a large temperate river.
• Maximum N2O emissions were observed downstream of an urban center, linked to wastewater treatment plant effluent and increased in situ production.
• Microbial N2O production occurred in both water column and sediments, with water column rates nearly double those in sediments.
• N2O emissions showed significant seasonal patterns, peaking in summer and reaching lowest levels in winter.

Conclusions:

• Large rivers, particularly those enriched with nitrogen and influenced by urban areas, are significant sources of nitrous oxide (N2O).
• Riverine N2O dynamics are strongly influenced by seasonal cycles, with higher emissions during warmer months.
• The pelagic zone (water column) plays a crucial role in N2O production within large temperate rivers.