Methane flux determination in an urban wetland via Eddy Covariance

Abstract

Methane (CH4) is the second most potent greenhouse gas in the atmosphere after carbon dioxide. Demand for more urban green spaces, such as wetlands, as a way to combat climate change and improve biodiversity is increasing. However, there is limited literature on the impacts of climate change on these artificial systems as well as the potential contribution that these wetlands might make to climate change. Wetlands as a greenhouse gas source or sink are poorly defined due to the wide variety of wetland ecosystems and the challenges involved in long term monitoring of these gases. New robust technology for measuring methane concentration over long durations is now available in the form of eddy covariance flux towers. This study aims to apply this technique to an urban wetland in Adelaide, South Australia, thereby adding to knowledge of the urban carbon budget. Methane fluxes in the artificially constructed Urrbrae Wetlands were measured continually over three months using an eddy covariance flux tower. Mean methane flux (FCH4) of the wetland was found to be 0.2603 ± 0.1865 μmol m-2 s-1 which is a factor of 10 higher than typical values found in previous studies for natural wetlands. There is no statistically significant difference between mean night and daytime FCH4. Linear correlations between FCH4 and air temperature, air pressure and wind speed were observed. A peak in the early afternoon occurred diurnally, which coincided with the mean maximum daily temperature. No longer-term patterns were observed for the duration of the study. It is concluded that artificial urban wetlands are potentially a significant source of atmospheric methane which requires further investigation.