Characteristics of annual CO$_2$ and N$_2$O emissions and soil NO$_3^–$ leaching from different urban greenspace landscapes in Denmark

Urban greenspace landscapes are becoming increasingly common as a result of rapid global urbanization. However, the extent to which soil carbon (C) and nitrogen (N) dynamics differ between these urban greenspaces remains poorly understood. This study reports on a field campaign conducted at the city level in Denmark. During the campaign, we conducted year-round measurements of soil carbon dioxide (CO$_2$) and nitrous oxide
(N$_2$O) fluxes, as well as soil nitrate (NO$_3^–$) leaching in five types of urban greenspace: sports fields, roadside patches, residential lawns, urban parks and urban forests. Our results show that the temporal variability in soil N$_2$O emissions was controlled by the synergistic changes in soil water content and temperature, though neither factor had a strong individual effect. However, soil temperature overrode the effects of soil water content, emerging as the primary factor triggering temporal variations in soil CO$_2$ fluxes, with temperature sensitivity (Q10) values varying from 2.88 to 3.65. We estimated cumulative annual N$_2$O and CO$_2$ emissions for all urban greenspaces to be 0.67–4.08 kg N ha$^{-1}$ yr$^{-1}$ and 12.0–21.2 Mg C ha$^{-1}$ yr$^{-1}$, respectively. ... mehrNon-growing season emissions contributed 8.4–48.1% for N$_2$O and 12.8–21.0% for CO$_2$ to these annual budgets. Annual soil NO$_3^–$ leaching rates for the studied greenspace ecosystems ranged from 1.2 to 11.8 kg N ha$^{-1}$ yr$^{-1}$. Of the five greenspace landscapes, sports fields exhibited the highest annual losses of soil N$_2$ O and NO$_3^–$ leaching, while significantly lower values were observed in urban parks and forests. These differences in soil N losses between greenspace types are driven by variations in soil water content and soil NO$_3^–$availability. Cumulative annual CO$_2$
emissions across all greenspace landscapes were positively correlated with annual N$_2$O emissions. At the city scale, the average annual N$_2$O and CO$_2$ emissions and soil NO$_3^–$ leaching, weighted by the areal extent of the different urban greenspace types, were estimated at 1.35 kg N ha$^{-1}$ yr$^{-1}$ (N$_2$O), 17.2 Mg C ha$^{-1}$ yr$^{-1}$ (CO$_2$) and 2.44 kg N ha$^{-1}$ yr$^{-1}$ (NO$_3^–$ leaching), respectively. Overall, our findings offer valuable insights for better predicting the potential role of urban greenspace ecosystems in regional greenhouse gas and N loss budgets.