Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter
Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter
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DOI：
10.1111/gcb.14537
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发表时间：
2019-05-01
影响因子：
11.6
通讯作者：
Zarfl, Christiane
中科院分区：
文献类型：
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作者：
Shumilova, Oleksandra;Zak, Dominik;Zarfl, Christiane
气候变化和人类压力正在改变间歇河流和短暂溪流（IRES）的全球分布和范围，这些河流和短暂溪流占全球河网面积的一半。IRES的特征是水流停止期，在此期间通道底物积累并经历物理化学变化（预处理），以及水流恢复期，当这些底物被重新湿润并释放溶解的营养物质和有机物（OM）脉冲。但是，没有对浸出物质的数量和质量的估计，也没有关于在全球范围内运作的潜在环境制约因素的资料。在标准的实验室条件下，我们模拟了5个主要气候带205个IRES在干燥期收集的叶片、河床沉积物和附着生物膜的再湿润过程。我们确定了浸出的营养物和有机质的数量和质量特征，并估计了它们从河床的面积通量。此外，我们还评估了与选定的环境变量和基质特征相关的渗滤液特征的差异。我们发现沉积物，由于其在河床内的大量，在再湿润事件中对溶解物质的总通量贡献最大（56%-98%），并且通量率在气气带之间存在明显差异。溶解的有机碳、酚类和硝酸盐对面积通量贡献最大。在大陆性气候带发现的浸出物质最多，与浸出OM的潜在生物利用度最低相一致。在干旱区发现了相反的模式。预计在气候变化下被改变的环境变量（即潜在蒸散、干旱、干旱期持续时间、土地利用）与浸出物质的数量相关，与沉积物的关系最强。这些结果表明，在全球生物地球化学循环中应该考虑到IRES的作用，特别是因为由于干燥事件的严重性增加，IRES的发生率将增加。
Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%-98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.