Indirect Nitrous Oxide Emission Factors for Agricultural Field Drains and Headwater Streams

摘要

Agriculture is a major source of nitrous oxide (N_2O) emissions, a potent greenhouse gas. While direct N_2O emissions from soils have been widely invest¾ated, indirect N_2O emissions from nitrogen (N) enriched surface water and groundwater bodies are poorly understood In this contribution, indirect N_2O emissions from subsurface agricultural field drains and headwater streams were monitored over a two-year period (2013-2015) in an intensive arable catchment in eastern England. Indirect N_2O emission factors for groundwater (EF_(sg)) and surface ranoff (EF_(Sr)) were calculated for both field drain and streamwater samples, respectively, using two approaches： the N_2O-N/NO_3-N ratio and the IPCC (2006)mediodology. Mean EF_(Sg) values derived from the N_2O-N/NO_3-N ratio were 0.0012 for field drains and 0.0003 for streamwater. Using the IPCC (2006) methodology, the mean EF_(Sg) values were 0.0011 for field drains and 0.0001 for streamwater. Thus, EF values derived from both methods were below the current IPCC (2006) default value of 0.0025 and a downward revision to 0.0012 for EF_(Sg) and 0.0002 for EF_(Sr) is recommended. Such revision would halve current estimates of N_2O emissions associated with nitrogen leaching and ranoff from agriculture for both the UK and globally.