Nonlinear Dynamics of Peatlands and Potential Feedbacks on the Climate System
Nonlinear Dynamics of Peatlands and Potential Feedbacks on the Climate System
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DOI：
10.1029/2008gm000829
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发表时间：
2009-01-01
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影响因子：
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通讯作者：
Belyea, Lisa R.
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作者：
Belyea, Lisa R.
泥炭地具有对全球气候系统产生强烈反馈的潜力，但它们对未来气候变化的反应具有高度不确定性。在本章中，1 回顾了一系列证明泥炭地动力学是非线性的证据。泥炭地不是收敛于单一主导路径并与外部强迫频率相匹配的渐进变化，而是表现出（1）对初始条件的敏感性和对多种发展路径的分歧，（2）长时间的小变化，即使在弱或稳定的环境强迫下也会出现状态的突然转变，以及（3）对意外频率的外部强迫的响应。当稳定力（即负反馈机制）占主导地位时，非线性系统表现出持久性；当不稳定力（即正反馈机制）占主导地位时，非线性系统会经历快速转变。在泥炭地，稳定力和不稳定力是由水文过程、有机质动力学和能量交换之间的相互作用产生的。泥炭导水率的深度依赖性往往会稳定水文条件，而当维管植物蒸腾作用较高时，局部水流网络可能会放大水损失。泥炭的形成速度通常受到水储存变化的限制，但有时会引发非饱和带厚度的快速增加或减少。从区域来看，蒸散量的增加可能会被泥炭地蒸发水的循环和沉淀所抵消，而泥炭地和周围森林的反照率和能量分配的对比可能会促进春季快速解冻。为了预测对气候系统的反馈，必须通过识别控制非线性行为的关键变量和相互作用来降低泥炭地的复杂性。
Peatlands have potential for strong feedback on the global climate system, but their response to future climate change is highly uncertain. In this chapter, 1 review a range of evidence demonstrating that peatland dynamics are nonlinear. Rather than gradual change that converges on a single dominant pathway and matches the frequency of external forcing, peatlands show (1) sensitivity to initial conditions and divergence onto multiple pathways of development, (2) long periods of little change, punctuated by abrupt transitions of state even under weak or steady environmental forcing, and (3) responses to external forcing at unexpected frequencies. Nonlinear systems exhibit persistence when stabilizing forces (i.e., negative feedback mechanisms) dominate and undergo rapid transformation when destabilizing forces (i.e., positive feedback mechanisms) dominate. In peatlands, stabilizing and destabilizing forces result from interactions among hydrological processes, organic matter dynamics, and energy exchanges. The depth dependence of peat hydraulic conductivity tends to stabilize hydrological conditions, whereas local flow networks may amplify water losses when vascular plant transpiration is high. Peat formation rate is generally constrained by water storage change but occasionally can trigger a rapid increase or decrease in thickness of the unsaturated zone. Regionally, increases in evapotranspiration may be counteracted by recycling and precipitation of evaporated water over peatlands, whereas contrasts in albedo and energy partitioning across peatlands and surrounding forests may promote rapid spring thaw. In order to predict feedbacks on the climate system, it will be essential to reduce the complexity of peatlands by identifying the key variables and interactions that control nonlinear behavior.