Aquatic Ecosystems Source of Half of Global Methane Emissions

“One issue that stood out is how humans have impacted methane emissions from aquatic sources.

“Anything human-driven or human-impacted had much higher fluxes than more natural sites,’’ says Rosentreter, a Yale Institute for Biospheric Studies Hutchinson Fellow.

Globally, rice cultivation releases more methane per year than all coastal wetlands, the continental shelf and open ocean combined. Fertilizer runoff causes nutrient-rich lakes and reservoirs to release methane. Coastal aquaculture farms have methane fluxes per area that are 7-430 times higher than from non-converted coastal habitats, such as mangrove forests, salt marshes or seagrasses.

But the study notes that there are opportunities to reduce human-impacted emissions with the right management techniques.

“The intense methane emissions from aquatic ecosystems offers opportunities for intervention providing potential quick wins in reducing greenhouse emissions, provided the much large role per molecule emitted of methane compared to carbon dioxide,’’ says study co-author Carlos M. Duarte, professor at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.

Fluctuating between flooded and non-flooded conditions in aquaculture farms and rice paddies; restoring tidal flow in degraded coastal wetlands; and reducing nutrient and organic matter in freshwater lakes, reservoirs, and rivers can all help reduce emissions, the study notes.

“Reducing methane emissions from aquatic systems will be an important part of stabilizing the Earth’s temperature,’’ says co-author Bradley Eyre Director, Centre for Coastal Biogeochemistry at Southern Cross University in Australia.”