High carbon burial rates by small ponds in the landscape

Temperate ponds may be important sinks and sources of greenhouse gases but just how quickly ponds bury carbon (C) is poorly understood. We derived – to the best of our knowledge – the first organic carbon (OC) burial rates for small ponds of known age by digging out the whole sediment from ponds, and determined that the average C burial rate was 142 g m？2 yr？1, with a range of 79–247 g m？2 yr？1, depending on the ponds' vegetation. Burial rates in the ponds were 20–30 times higher than rates estimated for many other habitat types, such as woodlands or grasslands, and higher than those of other natural wetlands. Although small ponds occupy a very small proportion of the landscape as compared to these other habitats, their high OC burial rates result in comparable annual OC burial overall. Ponds are easy to create, can fit in with other land uses, and are a globally ubiquitous habitat. Our results indicate that ponds have the potential to be a very useful additional tool for mitigating C emissions. The 2015 United Nations Climate Change Conference (in Paris, France) recognized the potential for vegetated habitats to buffer the effects of anthropogenic emissions of greenhouse gases (GHGs), including through afforestation and habitat restoration in areas subject to agricultural intensification (Lamb et al. 2016; Fischer et al. 2017). We argue that ponds and small wetlands can also make substantial contributions as carbon (C) sinks. Although ponds are ubiquitous throughout the world's terrestrial biomes and are relatively easy to create, evidence of their capacity to bury C has been scarce until now (Downing 2010). Emerging research has described the importance of inland waters for processing organic carbon (OC), and highlights the need to include them in strategies for mitigating climate change (Battin et al. 2009). However, efforts to quantify rates of OC burial in freshwater systems have generally focused on larger habitats (eg lakes), and understanding of the efficiency of the C burial process is confounded by the wide variability among habitat types (Cole et al. 2007; Kayranli et al. 2010). Current knowledge about the time required for habitats to become effective C sinks or how vegetation influences rates of OC burial (Kayranli et al. 2010) is limited. A comprehensive study on OC burial in freshwater ecosystems identified disproportionately high rates of OC burial in smaller water bodies (Downing 2010), but these results were obtained largely from work in artificial habitats, such as agricultural impoundments. Dean and Gorham (1998) estimated OC burial