Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
Institute of Biology, Freie Universität Berlin (FU), Berlin, Germany.
Glob Chang Biol. 2019 May;25(5):1591-1611. doi: 10.1111/gcb.14537. Epub 2019 Feb 25.
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.
气候变化和人为压力正在改变全球间歇性河流和短暂性溪流（IRES）的分布和范围，这些河流和溪流占全球河流网络面积的一半。IRES 的特点是水流停止期间，河道基质积累并发生物理化学变化（预处理），以及水流恢复期间，这些基质重新湿润并释放溶解养分和有机物质（OM）的脉冲。然而，目前还没有关于浸出物质的数量和质量的估计，也没有关于在全球范围内起作用的潜在环境限制的信息。我们在标准实验室条件下实验模拟了从五个主要气候区的 205 条 IRES 中在干燥阶段收集的叶子、河床沉积物和附生生物膜的再湿润过程。我们确定了浸出养分和 OM 的数量和定性特征，并估计了从河床流出的面积通量。此外，我们评估了浸出特性与选定环境变量和基质特性之间的方差。我们发现，由于河床中沉积物的数量较大，因此在再湿润事件期间对溶解物质的总通量贡献最大（56%-98%），并且通量率在气候区之间明显不同。溶解有机碳、酚类和硝酸盐对面积通量的贡献最大。在大陆性气候区发现的浸出物质最多，与浸出 OM 的最低潜在生物利用度相吻合。在干旱区则发现了相反的模式。预计在气候变化下会发生变化的环境变量（即潜在蒸散量、干旱度、干燥期持续时间、土地利用）与浸出物质的数量相关，与沉积物的相关性最强。这些结果表明，应该在全球生物地球化学循环中考虑 IRES 的作用，特别是因为由于干燥事件的严重程度增加，IRES 的普遍性将会增加。
