Data for: Large aquatic nitrous oxide emissions downstream of intensive horticulture driven by rain events

Nutrient leaching from agricultural systems is a global threat to waterways. However, indirect aquatic emissions of the potent greenhouse gas nitrous oxide (N2O) from agricultural runoff remain poorly understood. Here, we assess how episodic rain events flushing an agricultural catchment drive nutrients, radon (a natural groundwater tracer) and N2O emissions. We reveal significant nitrate + nitrite (NOX) loads and N2O emissions consistent with N leaching and runoff in Hearnes Lake, Australia. Aquatic nitrogen loads were equivalent to ~15% of applied fertiliser and dominated by NOX (78%). Aquatic N2O (up to 5655% sat.) and atmospheric emissions (up to 2859 µmol m2 day-1) were amongst the highest reported from global waterways. N2O fluxes experienced large variations (~800 fold) between dry and rain periods. Observed N2O emissions and IPCC EF5 N2O emissions were 6.27 N2O-N yr-1 and 26.5 kg N2O-N yr-1, respectively. Estimated N2O emissions ~2 km downstream of farms were 0.79% of DIN loads and 0.004% of applied fertiliser. Aquatic N2O emissions represented ~10% of the total (CO2 + CH4 + N2O) CO2 equivalent emissions which is ~60% higher than the IPCC global N2O average. Episodic rain events rather than groundwater seepage traced by radon were the major drivers of both NOX and N2O, highlighting the importance of detailed sampling approaches to capture extreme variability in heavily fertilised catchments.农业系统中的养分淋失是全球水道生态系统面临的共性威胁。然而，农业径流产生的强效温室气体一氧化二氮（nitrous oxide, N₂O）的间接水生排放，目前仍未得到充分研究。本研究评估了间歇性降雨事件冲刷农业集水区（catchment）时，如何驱动养分、氡（radon，天然地下水示踪剂）以及一氧化二氮的排放过程。研究团队在澳大利亚赫恩斯湖（Hearnes Lake）中观测到显著的硝酸盐+亚硝酸盐（nitrate + nitrite, NOₓ）负荷与一氧化二氮排放特征，其规律与氮淋失及径流过程相符。水生氮负荷约占同期施用肥料氮总量的15%，且以硝酸盐+亚硝酸盐为主要组分（占比78%）。水体中一氧化二氮浓度最高可达饱和状态的5655%，大气排放通量最高达2859 μmol·m⁻²·d⁻¹，该数值位列全球已报道的水道一氧化二氮排放数据前列。一氧化二氮排放通量在旱季与降雨期之间存在高达约800倍的剧烈波动。观测得到的一氧化二氮排放量与基于政府间气候变化专门委员会（Intergovernmental Panel on Climate Change, IPCC）EF5排放因子估算的排放量分别为6.27 kg N₂O-N·yr⁻¹与26.5 kg N₂O-N·yr⁻¹。据估算，农场下游约2公里处的一氧化二氮排放量占溶解无机氮（Dissolved Inorganic Nitrogen, DIN）负荷的0.79%，占同期施用肥料氮总量的0.004%。水生一氧化二氮排放量约占总（二氧化碳（carbon dioxide, CO₂） + 甲烷（methane, CH₄） + 一氧化二氮（nitrous oxide, N₂O））二氧化碳当量排放量的10%，该数值较IPCC全球一氧化二氮平均排放水平高出约60%。研究表明，间歇性降雨事件而非氡所示踪的地下水渗流，是硝酸盐+亚硝酸盐与一氧化二氮排放的主要驱动因素，这凸显了精细化采样方法对于捕捉高施肥强度集水区极端排放波动的重要性。