Resolving systematic errors in estimates of net ecosystem exchange of CO2 and ecosystem respiration in a tropical forest biome
Resolving systematic errors in estimates of net ecosystem exchange of CO2 and ecosystem respiration in a tropical forest biome
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DOI：
10.1016/j.agrformet.2008.03.007
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发表时间：
2008-07-04
影响因子：
6.2
通讯作者：
Wofsy, Steven C.
中科院分区：
文献类型：
--
作者：
Hutyra, Lucy R.;Munger, J. William;Wofsy, Steven C.
热带雨林对二氧化碳吸收和释放的控制以及对气候变化的响应是全球气候变化模式的主要不确定性。涡旋协方差测量有可能提供这些森林中二氧化碳交换和对环境响应的详细数据，但对二氧化碳净生态系统交换（NEE）和生态系统呼吸（R-eco）的准确估计需要仔细分析数据的代表性，处理数据空白，并纠正系统误差。本研究使用了我们在巴西圣塔伦附近的一个古老热带雨林的研究地点的综合数据，来检查NEE和R-eco的偏差可能与涡旋协方差数据中两个最重要的系统误差来源有关：丢失的夜间通量和丢失的冠层储存测量。我们提出了我们站点的净碳平衡和Reco的多种估计，包括传统的“u*过滤器”，详细的自下而上的呼吸预算，与Rn-122的相似性估计，以及通过外推白天涡旋通量数据到零光的独立呼吸估计。2002 - 2006年的涡旋协方差测量结果表明，该地区生态系统净碳损失量为0.25 +/- 0.04 μ mol m(-2) s(-1)，平均呼吸速率为8.60 +/- 10.11 μ mol m(-2) s（-1）。我们发现夜间流量的减少可能会对这些结果产生明显的偏差。我们开发了强有力的方法来纠正这些偏差，表明在适当的情况下，可以使用特定地点的u*阈值来避免碳交换估计中的系统性偏差。由于数据中存在空白，以及储存和湍流之间的昼夜不对称，因此包括冠层储存对于准确评估NEE至关重要。我们发现，在没有常规测量储量的地点，短期的储量测量可能足以准确地模拟用于获得生态系统碳平衡的储量。本研究中使用的分析框架可以应用于其他eddy -协方差站点，以帮助校正和验证碳循环及其组成部分的测量。(C) 2008 Elsevier B.V.版权所有
The controls on uptake and release Of CO2 by tropical rainforests, and the responses to a changing climate, are major uncertainties in global climate change models. Eddy-covariance measurements potentially provide detailed data on CO2 exchange and responses to the environment in these forests, but accurate estimates of the net ecosystem exchange of CO2 (NEE) and ecosystem respiration (R-eco) require careful analysis of data representativity, treatment of data gaps, and correction for systematic errors. This study uses the comprehensive data from our study site in an old-growth tropical rainforest near Santarem, Brazil, to examine the biases in NEE and R-eco potentially associated with the two most important sources of systematic error in Eddy-covariance data: lost nighttime flux and missing canopy storage measurements. We present multiple estimates for the net carbon balance and Reco at our site, including the conventional "u* filter", a detailed bottom-up budget for respiration, estimates by similarity with Rn-122, and an independent estimate of respiration by extrapolation of daytime Eddy flux data to zero light. Eddy-covariance measurements between 2002 and 2006 showed a mean net ecosystem carbon loss of 0.25 +/- 0.04 mu mol m(-2) s(-1), with a mean respiration rate of 8.60 +/- 10.11 mu mol m(-2) s(-1) at our site. We found that lost nocturnal flux can potentially introduce significant bias into these results. We develop robust approaches to correct for these biases, showing that, where appropriate, a site-specific u* threshold can be used to avoid systematic bias in estimates of carbon exchange. Because of the presence of gaps in the data and the day-night asymmetry between storage and turbulence, inclusion of canopy storage is essential to accurate assessments of NEE. We found that short-terrn measurements of storage may be adequate to accurately model storage for use in obtaining ecosystem carbon balance, at sites where storage is not routinely measured. The analytical framework utilized in this study can be applied to other Eddy-covariance sites to help correct and validate measurements of the carbon cycle and its components. (C) 2008 Elsevier B.V. All rights reserved.