Spatial and temporal patterns of methane uptake in the urban environment

Abstract

The environmental changes associated with urbanization have a considerable impact on soil-atmosphere gas exchange, which directly affects the level of greenhouse gases in the atmosphere. At the same time, the CH4 storage in urban ecosystems can be underestimated as a result of human disturbances through land management practices, as well as climatic conditions. The primary aim of this study, therefore, was to investigate anthropogenically induced and environmental factors controlling seasonal and spatial heterogeneity of CH4 uptake under different land uses (grasslands, city park, arable lands) across the city. An attempt has also been made in estimating methane oxidation on the urban scale (Wroclaw, Poland) and quantifying its role in urban C balance in a one-year period. The soil CH4 fluxes were collected biweekly from July 2017 to August 2018, using the static chamber method and analyzed by the CRDS laser spectroscopy Picarro G2201-i system.The observations of CH4 magnitude proved that urban soil ecosystems act as the sinks for atmospheric CH4, despite large part of the city grounds are excluded from the active oxidation surface. The efficiency variability of this sink is pronounced both spatially and temporally. The significantly higher (p > 0.05) net CH4 uptake occurred in the urban park soils and grasslands (locally exceed 0.66 ± 0.17 nmol·m−2·s−1), while the consumption of methane in arable lands was about one and half times lower than on all of the sites explored. The estimated seasonal differences in CH4 uptake between study sites indicate that atmospheric exchange of CH4 in urban soils mainly depends on temperature dynamics, which reduce methane consumption by 50–80% for the summer and winter periods. Using land-cover data, the current estimates of CH4 sink in the land uses across the city of Wroclaw accounted for −45 ± 18 tones CH4 on an annual basis.