Geological regulation of nitrous oxide emission risks in rivers globally

Fertilizer application has been recognized as the major driver of nitrous oxide (N2O) emissions in rivers. However, the intrinsic risk of N2O emissions in responding to nitrogen discharge (i.e., ratios between N2O emissions and dissolved inorganic nitrogen or fertilizer) may vary across rivers but remains unclear. Here we uncover the hidden yet substantial control of riverine N2O emissions by bedrock geology through field observations and global data analyses. We discover lower denitrification but higher N2O production rates in rivers with silicate-dominated bedrocks compared to those with carbonate-dominated bedrocks. On one hand, the larger sediment grain size found in the silicate-dominated rivers shortens porewater residence time for reaction, which diminishes the likelihood of complete denitrification (NO3−$$\to$$N2) but simultaneously increases the potential for N2O production through incomplete denitrification (NO3−$$\to$$N2O). Concurrently, lower sediment total organic carbon and water pH abate N2O reductase and enhance N2O production in silicate-dominated rivers. More importantly, the dissimilarities in N2O production due to bedrock geology are reflected in N₂O emissions risks. By developing a geological factor, we interpret the heterogeneous N2O emission risks in rivers globally. Hence, we highlight the geologically uneven urgency of improving fertilizer management to mitigate N2O emissions. Silicate-dominated rivers exhibit lower denitrification but higher N2O production than carbonate-dominated rivers due to coarser sediments, lower organic carbon, and reduced pH, according to global statistical analyses and field sampling in the Pearl River Basin.