Estimating internal dissolved methane loading in rivers using a mass balance approach

Area of Science:

• Environmental Science
• Geochemistry
• River Ecology

Background:

• Riverine methane emissions contribute to global warming.
• Quantifying internal methane loading is vital for effective mitigation strategies.
• Current methods for measuring methane flux are complex and site-specific.

Purpose of the Study:

• To develop and validate a simplified mass balance approach for estimating internal methane loading in rivers.
• To assess the feasibility of this method for large-scale river system evaluations.
• To provide accurate data for reducing riverine methane emissions.

Main Methods:

• A mass balance approach was employed in selected river reaches of the Kokai River, Japan.
• Dissolved methane concentrations were measured at upstream and downstream sampling points.
• Methane oxidation rates, atmospheric emission fluxes, and net riverbed flux were calculated.

Main Results:

• Dissolved methane concentrations varied significantly across river reaches.
• Methane oxidation rates ranged from -1.2 ± 0.8 to 66 ± 19 µmol m⁻² h⁻¹.
• Net flux of dissolved methane from the riverbed ranged from -33 to 160 µmol m⁻² h⁻¹.

Conclusions:

• The proposed mass balance method is a simple and effective tool for quantifying internal methane loading.
• This approach facilitates methane flux measurements across various sites and environmental conditions.
• The method is suitable for large-scale assessments of riverine methane dynamics and mitigation efforts.