The combined influence of glacial retreat and penguin guano on soil greenhouse gas fluxes in South Georgia

The transfer of nutrients from sea to land at marine bird colonies such as penguins has a major influence on regional soil processes. In many polar areas retreating glaciers open up new coastal ground for marine animals to colonise, yet, little is known about on the combined effect of glacial retreat and penguin-induced fertilisation on soil processes, succession and gas fluxes with the atmosphere.

​A new paper revealed the combined effects of glacial retreat and fertilisation by King Penguins on soil greenhouse gas fluxes on the soil succession at St. Andrews Bay, South Georgia; the largest King Penguin colony in the world (~150,000 breeding pairs). The production and consumption of three greenhouse gasses (CO2, CH4 and N2O) were assessed based on laboratory incubations of soil cores, as well as incubation experiments with added nutrients and water. 

​We found that soils located at a greater distance from the retreating glacier front showed a successive development, with expanding vegetation cover and increasing soil nutrient content, coinciding with increased CO2 production and CH4 consumption rates. Towards sites with an increase in penguin activity and guano deposition, the CO2 production increased by 4–16-fold while the  CH4 consumption decreased by about half. N2O production rates were not affected by exposure time since glacial retreat, but increased markedly (approximately 120-fold) at the site with the highest penguin activity. Along the transect, labile C and moisture were considered the key limiting factors for CO2 production, while moisture likely explain the limitation of  CH4 consumption. 

CO2, CH4 and N2O production/consumption rates based on incubated intact soil cores (n = 10). The transect (A-E) runs from the glacier front (A) to the penguin colony (E), with increasingly older soil and more penguin-affected soil at E. Different lower-case letters indicate significance between sites at p=0.05 using non-parametric Kruskal-Wallis multiple comparison tests. For more detail see paper.

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Overall, we can conclude that recently deglaciated coastal areas with expanding penguin colonies are high greenhouse gas emission hotspots, with a particularly strong influence on N2O emissions. A future expansion of penguins into newly available ice-free polar coastal areas may therefore markedly increase the local greenhouse gas budget.

​For more information see:
Wang P., D'Imperio L., Biersma E.M., Ranniku R., Xu W., Tian Q., Ambus P., Elberling B. (2019). Combined effects of glacial retreat and penguin activity on soil greenhouse gas fluxes on South Georgia, sub-Antarctica. Science of the Total Environment, 135255.
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