Greenhouse gas emissions from urban ponds in Denmark

Abstract

Ponds are increasingly recognized as significant sources of greenhouse gases (GHG) emitted to the atmosphere. Concomitant with increasing urbanization, more urban ponds are created, many with the aim of buffering peak runoff flow 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) four 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 concentrations of 1938±2208 µg C-CO2 L -1 , 44±198 µg C-CH4 L -1 , and 0.8±1.8 µg N-N2O 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 Danish national level showed that urban ponds emit about 38x10 9 g CO2-equivalent per year, which suggests that urban ponds are significant sources of GHG in urban landscapes.

Small artificial waterbodies are widespread and persistent emitters of methane and carbon dioxide

“…There were significantly higher CH 4 fluxes in waterbodies with the largest TP concentrations, in keeping with a wide body of literature showing higher emissions in nutrient-rich waterbodies including ditches and artificial ponds (Audet et al, 2020;Beaulieu et al, 2019;Herrero Ortega et al, 2019;Ollivier et al, 2019a;Peacock et al, 2017Peacock et al, , 2019Webb, Hayes, et al, 2019). However, high TP concentrations did not guarantee high fluxes, and this is in agreement with a recent synthesis of ditch CH 4 emissions (Peacock et al, 2021 Note: Soil type had a significant effect on CO 2 concentrations (p < 0.001, d = 0.71, effect size = medium) and CH 4 concentrations (p = 0.041, d = 0.19, effect size = very small).…”

“…the same magnitude as fluxes from subtropical ponds (1070-2950 mg CO 2 m −2 day −1 , Gorsky et al, 2019;Ollivier et al, 2019a;Panneer Selvam et al, 2014), grassed temperate urban ditches (8600 mg CO 2 m −2 day −1 , McPhillips et al, 2016) and temperate urban ponds (2300-3480 mg CO 2 m −2 day −1 , Audet et al, 2020;van Bergen et al, 2019).…”

Drainage Ditches Contribute Considerably to the CH4 Budget of a Drained and a Rewetted Temperate Fen

“…Diffusion as well as ebullition uxes were explained best by temperature, as was also found in other small water bodies recently (Audet et al 2020). Increased CH 4 production is often associated with an increase in temperatures of aquatic environments (Kelly and Chynoweth 1981;Duc et al 2010).…”

“…Our analyses of nutrient concentrations in the ditches allowed for analyzing potential impacts of nutrient loads on CH 4 production and emission. For instance, nitrate is known to have an inhibitory effect on CH 4 production because it acts as a more favourable electron acceptor when organic substrate is limited (Watson and Nedwell 1998;Audet et al 2020). The low CH 4 emissions in PD-p and PD-o may be explainable by the comparably high nitrate concentrations in these ditches.…”

“…Across both sites, the ditches with higher phosphate concentrations showed higher diffusive and ebullitive CH 4 emissions. Generally, it is important to note that the nutrient status can also indirectly in uence CH 4 emissions through its effects on dominant vegetation (Davidson et al 2015;Audet et al 2020).…”