Measuring diurnal cycles of evapotranspiration in the Arctic with an automated chamber system
Measuring diurnal cycles of evapotranspiration in the Arctic with an automated chamber system
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使用自动化室系统测量北极蒸散量的昼夜循环
DOI：
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发表时间：
2015
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通讯作者：
B. Newman
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作者：
L. Cohen;N. Raz‐Yaseef;J. Curtis;Jessica M. Young;T. Rahn;C. Wilson;S. Wullschleger;B. Newman
适当量化蒸散发（ET）是确定水和能量平衡的关键步骤，特别是在土壤含水量和淹没的时空异质性明显的北极景观中。虽然涡旋相关方差技术作为一种估算总尺度ET的方法已经得到了广泛的应用，但在更精细的空间尺度上估算ET仍然存在问题。因此，对高度变化的冻土带景观的ET估计很差，尽管这一过程对模型的参数化和验证很重要。为了克服这种方法上的限制，我们开发了一种通过修改LI‐8100A （LI‐COR, Lincoln， NE， USA）来测量日ET的方法，LI‐8100A是一种通常用于测量土壤二氧化碳通量的室内仪器。为了使LI - 8100A能够用于ET测定，我们设计了一种校准方法，并通过在北极和半干旱地区的实验室和独立野外测量来实施。校准后，该仪器于2013年6月至9月在美国阿拉斯加州巴罗附近的北极沿海平原上进行了ET的日常测量。我们通过对比LI‐6400‐09土壤CO2通量系统测量的四个相邻地块来验证该系统，该系统也经过校准以计算水蒸气通量。总之，我们确定，通过校准，LI - 8100A可以进行长期、高频的ET测量，即使在低通量、连续的永久冻土景观中也是如此。这项技术提供了一个机会来评估小尺度ET及其在低中心和高中心多边形上的地形控制，并将这些测量结果与通过涡动相关方差获得的总通量进行严格比较。版权所有©2014 John Wiley & Sons， Ltd。
Properly quantifying evapotranspiration (ET) is a critical step in determining water and energy balances, especially in Arctic landscapes where spatial and temporal heterogeneity in soil water content and inundation is pronounced. Although the eddy covariance technique has gained popularity as an approach for estimating ET at aggregate scales, obtaining ET estimates at finer spatial scales remains problematic. Thus, ET is poorly estimated for highly variable tundra landscapes, despite the importance of this process for parameterization and validation of models. To overcome this methodological limitation, we developed an approach to measure diurnal ET by modifying a LI‐8100A (LI‐COR, Lincoln, NE, USA), a chamber‐based instrument typically used for measuring soil CO2 fluxes. To enable the use of the LI‐8100A for ET determinations, a calibration method was designed and implemented through laboratory and independent field measurements in Arctic and semi‐arid locations. Once calibrated, the instrument was deployed June–September 2013 for diel measurements of ET on the Arctic coastal plain near Barrow, Alaska, USA. We validated the system by comparison to four adjacent plots measured by a LI‐6400‐09 soil CO2 flux system that was also calibrated to calculate water vapour flux. In conclusion, we determined that with calibration, the LI‐8100A can make long‐term, high‐frequency measurements of ET, even in low flux, continuous‐permafrost landscapes. This technique provides an opportunity to assess fine‐scale ET and its topographic controls across low‐centre and high‐centre polygons and to rigorously compare such measurements with aggregate fluxes obtained with eddy covariance. Copyright © 2014 John Wiley & Sons, Ltd.