1. Climate change is altering hydrologic regimes globally. In the Mediterranean climate region of south-western Australia (SWA), climate drying has caused many perennial streams to switch to intermittent flow regimes. Shifts in flow regime are expected to alter physical and biological processes in streams, including litter decomposition, which is the basis of detrital food webs.
2. Decomposition of jarrah (Eucalyptus marginata) leaves and associated macroinvertebrates, were measured over 320 days in 2018–19 using leaf bags in four headwater streams in SWA. Two streams retained perennial reaches and two were formerly perennial streams that are now intermittent. Pre-planned comparisons that formed a partial multiple before–after, control–impact design were used to compare the results to an experiment conducted in 1982–83 in some of the same streams when all were perennially flowing. Both experiments used coarse and fine-mesh bags containing 10 g of dry leaves.
3. In one perennial stream, coarse bags lost more weight than fine bags at the last sampling time only, when shredding caddisflies arrived on the leaf bags. In the other perennial stream, leaf-mining chironomids entered fine-mesh bags and accelerated decomposition so that they lost more weight than the coarse-mesh bags. There was no difference in weight loss between fine and coarse-mesh leaf bags in the two intermittent streams.
4. In 2018–19, decomposition was slower in dry reaches of intermittent streams than in perennial reaches. Leaf weight loss increased with the resumption of flow in intermittent streams, so that by the end of the experiment, similar amounts of leaf weight had been lost in intermittent and perennial reaches. Thus, although the temporal pattern of decomposition differed between intermittent and perennial reaches, after 320 days, they had reached a similar endpoint.
5. Over similar experimental duration, mean leaf weight remaining in perennial reaches at the end of the experiment did not differ between the 1982–83 study and 2018–19, showing that leaf decomposition had not changed in reaches that retained perennial flow. As mean leaf weight remaining also did not differ between intermittent and perennial streams in 2018–19, leaf decomposition was robust to flow regime change. However, since 1982–83, these streams have lost populations of shredding caddisflies and stoneflies, which were replaced by other shredders (e.g. leaf mining chironomids Stenochironomus sp.), showing that there was some redundancy amongst shredder species.
6. As climate change progresses, drying flow regimes will become commonplace in Mediterranean (and other) climate regions globally. This study indicates that litter decomposition may be maintained as streams transition to intermittency although shredder species may change. However, the impact of shredding species on leaf decomposition varies amongst studies, so effects of the loss of shredder species sensitive to drying may also vary, and in some cases their loss may substantially alter ecosystem processes.

中文翻译：

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流态变化会改变破碎机的特性，但不会改变受严重永久性干燥影响的上游河流中的落叶分解物

1. 气候变化正在改变全球的水文状况。在澳大利亚西南部 (SWA) 的地中海气候区，气候干燥导致许多常年河流转向间歇性流动状态。流态的变化预计会改变河流中的物理和生物过程，包括垃圾分解，这是碎屑食物网的基础。
2. 在 2018-19 年间，使用叶袋在 SWA 的四个源头溪流中测量了jarrah ( Eucalyptus marginata ) 叶子和相关大型无脊椎动物的分解情况超过 320 天。两条河流保留多年生河段，两条以前是多年生河流，现在断断续续。预先计划的比较形成了部分倍数，控制影响设计用于将结果与 1982-83 年在一些相同的河流中进行的实验进行比较，当时所有河流都常年流动。两个实验都使用粗网和细网袋，分别装有 10 克干叶。
3. 在一条多年生溪流中，仅在最后一次采样时，粗袋比细袋损失更多的重量，当时碎石蝇到达叶袋。在另一条多年生溪流中，采叶摇蚊进入细网袋并加速分解，因此它们比粗网袋失去更多的重量。在两个间歇流中，细网和粗网叶袋的重量损失没有差异。
4. 2018-19 年间，断断续续干流河段的分解速度比常年河段慢。随着间歇溪流中水流的恢复，叶片重量损失增加，因此到实验结束时，间歇性和多年生河段的叶片重量损失量相似。因此，尽管间歇性和常年性河段的分解时间模式不同，但在 320 天后，它们达到了类似的终点。
5. 在相似的实验持续时间内，实验结束时多年生河段剩余的平均叶重在 1982-83 年的研究和 2018-19 年之间没有差异，表明保留多年生流量的河段的叶子分解没有变化。由于 2018-19 年间断流和多年生流之间的平均剩余叶重也没有差异，因此叶分解对流态变化很稳健。然而，自 1982-83 年以来，这些溪流已经失去了碎石蝇和石蝇种群，取而代之的是其他碎纸机（例如采叶摇蚊Stenochironomus sp.），表明碎纸机物种之间存在一些冗余。
6. 随着气候变化的进展，干旱流态将在全球地中海（和其他）气候区变得司空见惯。这项研究表明，尽管碎纸机种类可能会发生变化，但随着溪流过渡到间歇性，垃圾分解可能会保持不变。然而，粉碎物种对叶片分解的影响因研究而异，因此对干燥敏感的粉碎物种损失的影响也可能不同，在某些情况下，它们的损失可能会大大改变生态系统过程。