Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH4 emissions reduced in favor of greater CO2 losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on N2O or global warming potential. We report greenhouse gas fluxes (CH4, CO2, N2O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that is, pasture). This ecosystem was a net source of CH4 (25.8 ± 1.4 mg CH4-C m−2 d−1) and N2O (6.4 ± 0.4 mg N2O-N m−2 d−1). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N2O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale CH4 fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables, especially soil moisture. Elevated CH4 and N2O fluxes contributed to a high overall ecosystem global warming potential (531 g CO2-C equivalents m−2 y−1), with non-CO2 trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating the relative importance of each gas for ecosystem global warming potential.
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机译：人们认为，农业排水会改变温带泥炭地的温室气体排放，减少CH 4 排放量，从而增加CO 2 损失。人们关注的焦点主要集中在碳微量气体上，而对农业转化对N 2 O或全球变暖潜力的影响知之甚少。我们报告了萨克拉曼多-圣华金河三角洲一个排干的泥炭地的温室气体通量（CH 4 ，CO 2 ，N 2 O），美国加利福尼亚州目前作为牧场（牧场）进行管理。该生态系统是CH 4 （25.8±1.4 mg CH 4 -C m -2 d -1 ）和N 2 O（6.4±0.4 mg N 2 ON m −2 d -1 ） 。甲烷通量与其他管理温带泥炭地的通量相当，而N 2 O通量非常高。相当于来自大量施肥的农业生态系统和热带森林的通量。生态系统规模的CH 4 通量是由“热点”（排水沟）驱动的，“热点”占陆地面积的不到5％，但排放量却超过84％。甲烷通量对气候的季节性波动无响应，并且显示出最小的时间变化。一氧化二氮通量更均匀地分布在整个景观中，并响应环境变量（尤其是土壤湿度）的波动。 CH 4 和N 2 O通量升高导致生态系统总体变暖潜力较高（531 g CO 2 -C当量m −2 y -1 ），非CO 2 微量气体通量抵消了光吸收作用的大气“冷却”效应。这些数据表明，受控三角洲泥炭地可能是区域性温室气体的主要来源，土壤水分的空间异质性调节了每种气体对生态系统全球变暖潜力的相对重要性。
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