Positive Feedback Loop Implicated in Methane Emissions from Aquatic Environments

By Meenu Johnkutty ‘21

Figure 1. Researchers have found that higher global temperatures directly contributed to the increase in methane, setting in place a vicious positive feedback cycle.

Figure 1. Researchers have found that higher global temperatures directly contributed to the increase in methane, setting in place a vicious positive feedback cycle.

Scientists have long forewarned of the detrimental effects of climate change on the planet. Rising global temperatures coupled with the lack of due diligence in handling the environmental crisis have scores of ecologists worried about the many fragile ecosystems on the brink of a biodiversity crisis.

A recent study conducted by researchers from Radboud University Nijmegen in the Netherlands provides new insight into current methane (CH4) levels in the atmosphere and the effects that rising global temperatures will have on concentrations of this greenhouse gas. Since natural CH4 emissions originate from wet environments, the researchers focused their work on shallow lakes, ponds, and rivers, honing in on the source of CH4 emission called “ebullition.” According to the researchers, “ebullition”, or bubbling, is caused by sediment within aquatic environments. By using a controlled year-round experiment, the scientists investigated the link between this mechanism in freshwater systems and the concentration of CH4 in the atmosphere.

First, the researchers used 1,000 liters of water, natural lake sediment, and plankton communities to replicate a freshwater environment; they then created a second freshwater environment to act as the control. Over the course of a year, the team simulated temperature changes in the experimental system using climate change projections. A GHG (greenhouse gas) analyzer collected data on the concentration of gases present within the experimental freshwater environment; additionally, an “inverted funnel-type bubble trap” collected the methane bubbles resulting from ebullition and measured their CH4 concentrations.

The scientists found the growth of microbe colonies as well as a 51 percent increase in ebullition in the experimental group; they implicated the bacteria as the primary contributors to the observed increase in ebullition. This increase in methane replicates a positive feedback loop: as temperatures increase, methane concentrations also increase. Since methane is a greenhouse gas, increasing methane concentrations will also increase temperatures, thereby setting the stage for a vicious cycle of global warming.

Though the study forecasts a grim future for freshwater systems, the researchers state that by reducing greenhouse emissions, temperatures will drop, and the amount of methane released into the environment will decrease. By promoting climate change awareness and implementing effective legislation that fights climate change, the difficult process of reversing the effects of global warming can begin.

References:

  1. C. Aben, et al., Cross continental increase in methane ebullition under climate change. Nature Communications 8, (2017). doi: 10.1038/s41467-017-01535-y.
  2. Image retrieved from: https://static.pexels.com/photos/86172/pexels-photo-86172.jpeg
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