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Methane dynamics and carbon dioxide exchange in a California rice paddy.

机译：加利福尼亚稻田中的甲烷动力学和二氧化碳交换。

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摘要

Rice paddies are responsible for a significant fraction of the atmospheric CH4 burden but may also sequester atmospheric CO2. Previous studies based on putative relationships between net CO2 exchange and CH4 emissions have asserted that globally significant amounts of carbon can be stored in rice paddy soils. However, the annual ratio of CH4 emissions to net CO2 exchange has not previously been measured. We measured the net exchange of CO2 by eddy covariance over a period of 2.4 years in a California rice paddy. In the final year of the study, methane emission rates were also measured using a flux gradient technique and weekly chamber sampling. Net CO2 uptake over a ∼150 day growing season exceeded that of the ∼215 day fallow period by −414 to −466 g CO2-C m−2. However, when the carbon lost by harvesting the rice and nocturnal stability artifacts were accounted for, this paddy was either close to a carbon balance or a source of atmospheric CO2. Estimates of annual net CO 2 exchange (including carbon lost via harvest) ranged from gains of ∼90 ± 10 kg C ha−1 to losses of 550 ± 18.7 kg C ha−1 depending on the integration period. Using an assemblage of all possible integration periods over the course of the study, we estimate the mean annual exchange of carbon to be 190 ± 380 t C ha−1 y−1 (loss to the atmosphere). During rice growth, CH4 emission rates were negatively correlated to net CO2 exchange and, on a molar basis, were 2% of the net CO 2 uptake rate. Over an entire year, CH4 emissions represented a higher proportion (7%) of the net CO2 uptake.; In a separate study, we investigated the influence of rice straw management practices on CH4 dynamics. Measurements of flux rates and δ 13C of emitted CH4 were related to the size and δ 13C of soil CH4 and CO2 pools in fields where, following harvest, rice straw was either incorporated in to the soil or burned. We estimated the relative importance of methanogenesis pathways and methanotrophy on the quantity and δ13C of emitted CH4. Methane emissions in straw amended plots were 2.8 times greater than in burned plots. High emission rates were associated with an increasing proportion of CH 4 formed from acetate fermentation rather than H2/CO 2 reduction. The fraction of CH4 oxidized did not exert an over-riding control on the amount of CH4 released to the atmosphere.
机译：稻田负责大气中CH 4 的大部分负担，但也可能隔离大气中的CO 2 。先前基于净CO 2 交换量与CH 4 排放量之间推定关系的研究断言，全球稻田土壤中可以储存大量的碳。但是，以前尚未测量CH 4 排放量与CO 2 净交换量的年比率。我们在加州稻田中通过涡度协方差测量了2.4年内CO 2 的净交换。在研究的最后一年，还使用通量梯度技术和每周的腔室采样来测量甲烷排放率。在大约150天的生长季节中，CO 2 的净吸收量比215天的休耕期高-414至-466 g CO 2 -C m - 2 。但是，考虑到收割水稻造成的碳损失和夜间的稳定性伪像，则该稻要么接近碳平衡，要么成为大气中CO 2 的来源。每年的CO 2 净净交换量（包括因收获而损失的碳）的变化范围从〜90±10 kg C ha -1 的增加到550±18.7 kg C ha的损失 -1 取决于积分周期。使用研究过程中所有可能的整合时期的组合，我们估计碳的年平均交换量为190±380 t C ha -1 y -1 （对大气的损失）。在水稻生长过程中，CH 4 排放速率与净CO 2 交换呈负相关，以摩尔为基准，为净CO 2的2％。 sub>吸收率。在整个一年中，CH 4 排放量占CO 2 净吸收量的比例更高（7％）。在另一项研究中，我们调查了稻草管理措施对CH 4 动态的影响。 CH 4 释放的通量率和δ 13 的测量值与土壤CH 4 <的大小和δ 13 的大小有关/ sub>和CO 2 库在田地中，收获后将稻草混入土壤或燃烧。我们估计了甲烷生成途径和甲烷氧化对甲烷排放CH 4 的数量和δ 13 C的相对重要性。秸秆改良区的甲烷排放量是燃烧区的2.8倍。高排放率与乙酸盐发酵形成的CH 4 比例的增加有关，而不是与H 2 / CO 2 的减少有关。氧化后的CH 4 部分并没有控制释放到大气中的CH 4 量。

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  • 作者

    McMillan, Andrew Michael Stuart.;

  • 作者单位

    University of California, Irvine.;

  • 授予单位 University of California, Irvine.;
  • 学科 Biogeochemistry.; Environmental Sciences.; Agriculture Agronomy.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 p.121
  • 总页数 260
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 生物地球化学、气体地球化学;
  • 关键词

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