Respiration of dissolved organic matter (DOM) in streams contributes to the global CO₂ efflux, yet this efflux has not been linked to specific DOM sources and their respective uptake rates. Further, removal of DOM inferred from longitudinal concentration gradients in river networks has been insufficient to account for observed CO₂ outgassing. We hypothesize that understanding in‐stream dynamics of DOM, which is a heterogeneous mixture spanning a wide range of biological labilities, requires considering that DOM lability decreases during downstream transport. To test this hypothesis, we paired seasonal bioreactor measurements of DOM biological lability with whole‐stream tracer data from White Clay Creek, Pennsylvania, USA, and used a particle‐tracking model to predict in‐stream DOM dynamics. The model simulates continuous inputs of DOM and uses storage time in the stream bioactive regions plus kinetic parameters from bioreactors to assess differential uptake of DOM fractions (i.e., fractionation) in the stream. We compared predictions for in‐stream dynamics of bulk DOM concentration (quantified as dissolved organic carbon) and fluorescent DOM components. Our model‐data synthesis approach demonstrates that more labile fractions of DOM in stream water preferentially originate and are consumed within short travel distances, causing spiraling metrics to change with downstream distance. Our model can account for local sources of rapidly cycled labile DOM, providing a basis for improved interpretation of DOM dynamics in streams that can reconcile apparent discrepancies between respiratory outgassing of CO₂ and longitudinal DOM concentration gradients within river networks.

中文翻译：

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降低生物不稳定性对河流中溶解有机物动力学的影响

溪流中溶解性有机物（DOM）的呼吸作用促进了全球CO _2的排放，但是这种排放尚未与特定的DOM来源及其各自的吸收率相关。此外，从河流网络中的纵向浓度梯度推断出的DOM的去除不足以解决观测到的CO _{2的问题。}放气。我们假设，了解DOM的流内动力学是一种横跨多种生物不稳定性的异质混合物，因此需要考虑DOM的不稳定性在下游运输过程中降低。为了验证这一假设，我们将季节性生物反应器对DOM生物学不稳定性的测量结果与来自美国宾夕法尼亚州White Clay Creek的全流示踪数据进行了配对，并使用了颗粒追踪模型来预测流中DOM的动态。该模型模拟DOM的连续输入，并使用物流生物活性区域中的存储时间以及生物反应器的动力学参数来评估物流中DOM组分（即分馏）的差异吸收。我们比较了对DOM浓度（量化为溶解的有机碳）和荧光DOM成分的流内动力学的预测。我们的模型数据综合方法表明，溪流水中的DOM不稳定部分优先在较短的行驶距离内产生并被消耗，从而导致螺旋度量随下游距离而变化。我们的模型可以说明快速循环的不稳定DOM的本地来源，从而为改进对流中DOM动力学的解释提供基础，从而可以解决CO呼吸放气之间的明显差异。₂和河网中的纵向DOM浓度梯度。