New research supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Hydro-Quebec has improved the accuracy in measuring the relationship between lake size and eutrophication and the volume of greenhouse gases emissions from lakes globally. The paper, Greenhouse gas emissions from lakes and impoundments: Upscaling in the face of global change, was published this week in the journal Limnology and Oceanography Letters.

Although carbon dioxide is the most well-known greenhouse gas, methane and nitrous oxide, which are also emitted from lakes, could be far more disruptive to the global climate, due to their greater warming potential.

“Our work shows conclusively that methane, which is emitted from lakes in bubbles, is the dominant greenhouse gas coming from lakes and surface waters globally,” said lead author Tonya DelSontro, now a researcher at the University of Geneva. “The greener or more eutrophic these water bodies become, the more methane is emitted, which exacerbates climate warming.”

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The researchers found that past estimates of the effects of lake size and productivity on GHG emissions and their relationship to total global output had been inaccurately measured. Their revised measurements found that aquatic GHG emissions are equivalent to approximately 20 per cent that of carbon dioxide emitted by fossil fuel use. And they wrote that the volume will increase as global waters become more productive.

Methane bubbles to the surface Lake Kariba, Africa, of the world’s largest man-made lake and reservoir by volume. Credit: Christian Dinkel.

“Our research pioneers a new way of determining the global atmospheric effect of lakes using satellite information on lake greenness and size distribution,” said co-author John A. Downing, University of Minnesota Sea Grant director and professor of biology at the University of Minnesota Duluth. “This is important because the world’s lakes and surface waters will emit more greenhouse gases as they become greener and more nutrient-rich.”

The researchers stated that this is the largest global data set on lake emission rates of carbon dioxide, methane, and nitrous oxide to have ever been collected. The data showed that lake size matters a lot in determining the volume of carbon dioxide and nitrous oxide discharged to the atmosphere. The research also found that methane emissions might be of disproportionate importance due to their link with lake productivity and the potency of methane as a greenhouse gas.

“We need to know how much of these greenhouse gases are being emitted to be able to predict how much and how fast the climate will change,” said DelSontro. “This paper is significant because we developed a more effective approach to estimate current and future global lake emissions.”

If the world’s lakes and other surface waters become more eutrophic, it could negate the reductions that society makes by reducing fossil fuel emissions.

“Even moderate increases in lake and surface water eutrophication over the next 50 years could be equivalent to adding 13 percent of the effect of the current global fossil fuel emissions,” said Downing. “By keeping our community waters clean, we make better water available to future generations and we decrease worldwide emissions of methane that speed climate change.”

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