A review of indirect N2O emission factors from agricultural nitrogen leaching and runoff to update of the default IPCC values.

Abstract Indirect N 2 O emissions from agricultural nitrogen (N) leaching and runoff in water bodies contribute significantly to the global atmospheric N 2 O budget. However, considerable uncertainty regarding this source remains in the bottom-up N 2 O inventory. Indirect N 2 O emission factor associated with N leaching and runoff (EF 5 ; kg N 2 O N per kg of NO 3 ⁻−N) incorporate three components for groundwater and surface drainage (EF 5g), rivers (EF 5r), and estuaries (EF 5e). The 2006 IPCC default EF 5 value was based on a small number of studies available at the time. Here we present the synthesis of 254 measurements of EF 5 , dissolved N 2 O, and nitrate from 106 studies. Our results do not support the further downward revision of EF 5g by the IPCC and suggest an upward revision of EF 5g of 0.0060. The emission factors for groundwater and springs (0.0079) was higher than that for surface drainage (0.0040). The emission factor for lakes, ponds, and reservoirs was 0.0012, whereas that for rivers was 0.0030, and a combined EF 5r was 0.0026. Estimated EF 5r and EF 5e (0.0026) values from the study were close to the current IPCC default values (0.0025 each). We estimated an updated default EF 5 value of 0.01 for the refinement of IPCC guidelines. Graphical abstract Image 1 Highlights • We summarized 254 field data on indirect emission factor from N leaching and runoff. • Mean emission factor (EF) for ground water and surface drainage (EF 5g) was 0.0060. • Mean EF for lakes, ponds & reservoirs, and rivers (EF 5r) was 0.0026. • Mean EF for estuaries (EF 5e) was 0.0026. • Combined EF (EF5) was 0.01, higher than IPCC 2006 default EF (0.0075). We summarized 254 field datasets and estimated indirect N 2 O emission factor from leaching and runoff of agricultural N (EF 5) of 0.01, higher than IPCC 2006 default EF (0.0075). [ABSTRACT FROM AUTHOR]