Rising sea levels linked to unexpected methane emissions: study

Scientists have discovered that rising sea levels are causing higher methane emissions from certain wetlands than previously estimated. This new finding contradicts the earlier belief that an increase in seawater in tidal wetlands would reduce methane production.

A team from the Berkeley Lab and UC Berkeley led the research, involving a detailed study of 11 different wetland areas. Against all odds, they found a low-salinity estuary ecosystem in the Bay Area to release significantly high levels of methane. This finding was particularly surprising as they found freshwater sites to emit much less methane.

Using advanced sequencing techniques, the researchers examined the DNA of organisms in soil samples and identified genes involved in various metabolic processes. The study indicates that predicting the factors determining the amount of greenhouse gas stored or released in natural landscapes is more intricate and harder than previously thought.

Susannah Tringe, the senior author of the study, explained, “We studied the presence of methanogens, the organisms that produce methane, in the soils at these sites. However, their presence didn’t correlate well with the observed methane levels. Even considering methanotrophs, organisms that consume methane, along with methanogens, didn’t fully explain the situation.”

A specific site, which was restored to its original wetland state from pastureland in 2010, showed high methane emissions despite having moderate seawater levels. This challenges the assumption that more sulfate from seawater would lead to less methane production, as bacteria using sulfate were thought to outcompete methanogens.

Tringe further explained, “We found significant influences from other bacterial groups, like those that break down carbon and even organisms known for nitrogen cycling. We couldn’t readily explain the methane emissions by something as simple as the availability of sulfate or the number of methanogens.”

Restored wetlands

People increasingly recognize wetlands as critical ecosystems that boost carbon storage, improve water quality, and support wildlife. In recent years, there has been widespread effort to restore wetlands.

The study co-author, Dennis D. Baldocchi, models work that suggests that, while the restored wetland site currently contributes greenhouse gasses to the atmosphere, it may transform into a net carbon sink within 100 to 150 years. Stakeholders who aim for immediate carbon sequestration through ecosystem restoration find this timeline significant.

“We want to know if these systems will act as long-term carbon sinks,” said Baldocchi. “And these microbiological investigations can help refine our models and predictions.”

"Tringe noted that both Duke University and North Carolina State University also conducted studies that observed similar findings of increased methane production with increased salinity. This research collectively suggests that the effects of seawater intrusion and ecosystem restoration are more complicated than previously understood."

Tringe said, 'We had this expectation that sulfate would be the most important thing. Our studies showed that not only did salt water stimulate methane production, which is somewhat counter to the prevailing belief that sulfate is important, it happened regardless of whether you had sulfate there or not. Sulfate didn't significantly affect the methane emissions.'"

“So I think these experimental manipulations are reconfirming the story that there’s more nuanced effects of seawater intrusion than just a sulfate addition, and also more nuanced factors behind ecosystem restoration.”

Keep Reading

• Budget 2024: How viability gap funding for offshore wind energy projects is crucial?
• Deforestation’s impact on flood risk often overlooked, study warns
• New species of skinks found in Tiger Reserve of Tamil Nadu

Follow Ground Report for Climate Change and Under-Reported issues in India. Connect with us on Facebook, Twitter, Koo App, Instagram, Whatsapp and YouTube. Write us on [email protected].