Greenhouse gas emissions from urban ponds in Denmark

ABSTRACT

Ponds are increasingly recognized as significant sources of greenhouse gases (GHGs) emitted to the atmosphere. Concomitant with increasing urbanization, more urban ponds are created, many with the aim of buffering peak runoff and improving water quality in downstream waterbodies. However, the impact of urban ponds on GHG emissions is poorly elucidated. In this study, we measured the dissolved concentrations of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) 4 times over a year in 37 ponds located in the city of Silkeborg, Denmark. The results show that the ponds generally acted as a source of GHG with CO₂-C concentrations (standard deviation) of 1938 (2208) µg L⁻¹, CH₄-C of 44 (198) µg L⁻¹, and N₂O-N of 0.8 (1.8) µg L⁻¹. Boosted regression tree models show that vegetation cover, water temperature, and nitrate concentration were the main drivers of CO₂, CH₄, and N₂O concentrations, respectively. Upscaling of the results to the Danish national level showed that urban ponds emit about 38 × 10⁹ g CO₂-equivalents per year, suggesting that urban ponds are significant sources of GHG in urban landscapes.

KEYWORDS:

• carbon dioxide
• greenhouse gas
• methane
• nitrous oxide
• ponds
• stormwater

Acknowledgements

The authors thank Marlene Venø Skjærbæk and Dorte Nedergaard for their technical assistance and Anne Mette Poulsen for improving the English language. Silkeborg municipality and Silkeborg Forsyning are acknowledged for granting access to the ponds. JA thanks Mike Peacock for fruitful discussions on the topic of GHG emissions from ponds.

Disclosure statement

No potential conflict of interest was reported by the author(s).