Environmental factors affecting greenhouse gas fluxes of green roofs in temperate zone

Abstract

This paper investigates the full seasonal greenhouse gas (GHG) dynamics of fluxes from three green roof systems (lightweight clay aggregate-based green roof – LR; grass roof – GR; sod roof – SR) and natural control site on shallow Leptosol (NC), using closed static chambers in the period April 2014 to December 2015. CO2, CH4 and N2O fluxes are measured and their relationships to meteorological parameters and substrate physicochemical characteristics are quantified. Median CO2 flux values were 21 (LR), 38 (GR), 62 (SR), and 82 (NC) mg CO2-C m−2 h−1. The results show ecosystem respiration (Reco) clearly increased until July and then decreased until November. Net ecosystem CO2 exchange (NEE) was more variable than Reco, depending on plant growth phase and weather conditions. Median NEE values for study period (from April to November 2015) were −7 (LR), −17 (GR), −136 (SR), and −82 (NC) mg CO2-C m−2 h−1. The percentage of autotrophic respiration (Ra) in Reco showed clear rise from LR (35%) to NC (62%). CH4 consumption dominated resulting in median fluxes as follows: −2 (LR), −1 (GR), −15 (SR), and −23 (NC) μg CH4-C m−2 h−1. N2O flux was low and highly variable in time, with median values varying from −0.07 (GR) to 2.18 (NC) μg N2O-N m−2 h−1. During the maximum vegetation growth, NEE exceeded Reco value. Green roofs are effective CH4 sinks, but they do not significantly affect N2O flux. The main environmental factors determining GHG fluxes in linear models were parameters describing moisture regime, meteorological parameters and soil physical characteristics. These models can be used to predict GHG fluxes from similar green roof systems in analogous climatic conditions. We conclude that green roof technology may be used to mitigate excessive ambient GHG levels in urban areas.