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Shallow lakes in agricultural landscapes will emit significantly greater amounts of methane in warmer world

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January 22, 2018 Aarhus University read full ScienceDaily article here
Shallow lakes in agricultural landscapes will emit significantly greater amounts of methane, mostly in the form of bubbles (ebullition) in a warmer world, which is a potential positive feedback mechanism to climate warming. Submerged plants are key predictors of methane ebullition. The combination of warming with the loss of plants appears to transform shallow lakes into methane bubbling machines.
Methane is a potent greenhouse gas with 25 times greater warming potential than carbon dioxide.

Shallow lakes are increasingly recognised as playing an important role in global greenhouse gas cycling. Given the number of shallow lakes globally they potentially have a large influence on atmospheric methane concentrations, which continue to rise.

Methane is released from lakes in a number of ways, both by diffusion of dissolved gas and by bubbles released from the sediments, also called ebullition.

….In the absence of nutrient enrichment, warming alone increased annual methane ebullition by around 50% and its relative contribution to total methane emission rose from about 50% to 75%.

In stark contrast to this, when nutrient levels were high, warming increased total methane emission by at least six fold and in some cases 17 fold, and the proportion of ebullition increased to 95% of total annual methane flux.

….The current study identified the abundance of submerged plants as a key predictor of methane ebullition. However, where plants were abundant, methane ebullition was reduced compared to when plants were absent, even at higher temperatures.

This suggests that through careful management of agricultural landscapes and fresh waters ensuring the proliferation of submerged plants, ebullition of methane can be minimised and in addition ecological condition and fresh water biodiversity will benefit.

Thomas A. Davidson, Joachim Audet, Erik Jeppesen, Frank Landkildehus, Torben L. Lauridsen, Martin Søndergaard, Jari Syväranta. Synergy between nutrients and warming enhances methane ebullition from experimental lakes. Nature Climate Change, 2018; DOI: 10.1038/s41558-017-0063-z

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