Dynamic carbon dioxide exchange through snowpack by wind‐driven mass transfer in a conifer‐broadleaf mixed forest in northernmost Japan
Dynamic carbon dioxide exchange through snowpack by wind‐driven mass transfer in a conifer‐broadleaf mixed forest in northernmost Japan
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DOI：
10.1029/2004gb002272
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发表时间：
2005-06
影响因子：
5.2
通讯作者：
K. Takagi;M. Nomura;Daitaro Ashiya;Hiroyuki Takahashi;K. Sasa;Y. Fujinuma;H. Shibata;Yukio Akibayashi-Yukio
中科院分区：
文献类型：
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作者：
K. Takagi;M. Nomura;Daitaro Ashiya;Hiroyuki Takahashi;K. Sasa;Y. Fujinuma;H. Shibata;Yukio Akibayashi-Yukio
积雪覆盖期间的二氧化碳排放可能是积雪生态系统年度碳收支中的一个重要碳源。然而，积雪中二氧化碳的行为以及雪面排放的机制仍不清楚。我们对一个针叶阔叶混交林积雪层中的二氧化碳浓度进行了连续（每半小时一次）的隆冬测量，发现积雪层中的二氧化碳浓度随着风速变化而显著波动。考虑到气流引起的混合作用，雪面排放被评估为积雪层中二氧化碳储存量的变化以及从土壤到积雪层的二氧化碳输入量之和。52天的中位数值（49毫摩尔每平方米每天）与通过涡度协方差技术和空气柱中储存变化通量估算的这片森林的每日净生态系统交换率（50毫摩尔每平方米每天）几乎相同。这些数值明显大于我们使用菲克扩散定律估算的值。这些结果表明，气流可能是隆冬时节积雪层内混合的主要原因。此外，在积雪层下的土壤孔隙中，二氧化碳浓度主要与气温相关，这意味着即使在1米厚的积雪层下，土壤呼吸也直接对气温而非土壤温度作出反应。我们推断气温通过树干影响树木的根系活动，并且根系呼吸的变化强烈影响积雪层下土壤中二氧化碳浓度的波动。
CO2 efflux in the period of snow cover can be a large carbon source in the yearly carbon budget of snowy ecosystems. However, the behavior of CO2 in snowpacks and the mechanisms of the snow surface efflux are still unclear. We performed continuous (half‐hourly) midwinter measurements of CO2 concentrations in a conifer‐broadleaf mixed forest snowpack, and found that concentrations in the snowpack fluctuated significantly as wind speeds varied. The snow surface efflux was evaluated as the sum of the CO2 storage change in the snowpack and the CO2 input from the soil to the snowpack, taking into account the mixing due to airflow. The median value over 52 days (49 mmol m−2 d−1) was almost the same as the daily net ecosystem exchange rate in this forest (50 mmol m−2 d−1) estimated by the eddy covariance technique and the storage‐change flux in the air column. These values are clearly larger than the value we estimated using Fick's law of diffusion. These results show that airflow can be a dominant cause of mixing within snowpacks in midwinter. In addition, in the soil pores under the snowpack, the CO2 concentration was primarily related to air temperature, implying that soil respiration responds directly to air temperature, not to soil temperature, even beneath a 1‐m‐thick snowpack. We infer that the air temperature affected the root activity of trees through their trunks and that the variation in root respiration strongly affected the CO2 concentration fluctuation in soil under the snowpack.