Characteristics of annual CO2 and N2O emissions and soil NO3– 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 (Q 10 ) 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. Non-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.