Rivers draining contrasting landscapes exhibit distinct potentials to emit diffusive methane (CH₄)

Area of Science:

• Environmental Science
• Geochemistry
• Climate Science

Background:

• Methane (CH4) is a potent greenhouse gas, second only to carbon dioxide.
• River networks are increasingly recognized as significant sources of CH4 emissions, exacerbated by human activities.
• Limited data exists on CH4 emission potentials across rivers with diverse watershed landscapes.

Purpose of the Study:

• To investigate the spatial variability of diffusive CH4 emissions in rivers.
• To identify key environmental factors driving CH4 production in different river reaches.
• To compare CH4 emission potentials across agricultural, urban, forested, and mixed-landscape rivers.

Main Methods:

• Field sampling and analysis of CH4 concentrations in river water.
• Measurement of environmental parameters including carbon sources, total phosphorus, dissolved oxygen, and oxidation-reduction potential.
• Application of Monte Carlo simulations for CH4 flux estimation.

Main Results:

• Urban rivers showed the highest CH4 concentrations (5.46 μmol L⁻¹), significantly exceeding those in agricultural, forested, and mixed-landscape rivers.
• Carbon availability and total phosphorus were primary drivers of CH4 production in agricultural and urban rivers.
• Dissolved oxygen and oxidation-reduction potential were key factors in forested and mixed-landscape rivers, respectively.
• Urban rivers exhibited the highest CH4 emissions (9.44 mmol m⁻² d⁻¹), 5.1-10.4 times greater than other river types.

Conclusions:

• Riverine CH4 emissions vary significantly based on watershed landscape characteristics.
• Urban rivers represent critical hotspots for CH4 emissions.
• Management strategies must be tailored to specific river reaches and consider landscape-driven environmental influences to mitigate CH4 release.