Measurements of nitrogen isotope ratios (δ¹⁵N) along vertical porewater profiles are instrumental in localizing sources and sinks of nitrous oxide (N₂O) in wetland ecosystems. We present the first N₂O concentration and isotope data for porewaters of ombrotrophic, mountain-top bogs. Our two study sites, situated in the Czech Republic at elevations higher than 1000 m, have been affected by atmospheric N pollution for more than 100 years. In recent decades, the northeastern site KB received over 30 kg N ha⁻¹ yr⁻¹ via atmospheric deposition, the southwestern site BS was 3 times less polluted. Both peat bogs were surrounded by defoliated, dead spruce stands. We hypothesized that elevated nitrate (NO₃⁻) inputs in rain-fed bogs may cause sizeable N₂O _{emissions. Porewater N2O concentrations in the studied ombrotrophic bogs were 400–800 times higher, compared to fens in nearby Bavaria (Germany). The highest N2O concentrations and the lowest δ¹⁵N–N2O values were found at the bottom of the sampled porewater profiles, 40–60 cm below surface. Low δ¹⁵N–N2O values resulted from a N isotope fractionation associated with denitrification. The site with the lower historical N pollution, BS, exhibited up to 7 times higher porewater N2O concentrations than KB, possibly due to a higher denitrification potential determined as abundance of nirK and nirS genes. Upcore, N2O abundance decreased and δ¹⁵N–N2O increased, indicating N2O reduction. Processes of N2O formation and consumption at different depths were integrated by measuring N2O fluxes across the peat – atmosphere interface. These fluxes were minute (<0.02 μmol N2O m⁻² h⁻¹). We even observed scavenging of air-borne N2O by the bog substrate. Nitrogen pollution of ombrotrophic bogs led to vigorous N cycling, manifested by extremely high peat porewater N2O concentrations. However, effective in-situ consumption of the produced N2O greatly reduced its warming potential.}