Invertebrate-mediated leaf litter decomposition is frequently used to assess stress-related implications in stream ecosystem integrity. In situ measures such as the mass loss from leaf bags or the feeding of caged invertebrates deployed for days or weeks may, however, fail to detect transient effects due to recovery or compensatory mechanisms. We assessed the relevance of transient effects using the peak exposure towards an insecticide (i.e., etofenprox) as a model scenario at three levels of complexity. These were 1) the assessment of the decomposition realised by invertebrate communities in stream mesocosms over 21 days via leaf bags, 2) 7-days lasting in situ bioassays quantifying the leaf consumption of Gammarus fossarum, and 3) a laboratory experiment determining the daily feeding rate of the same species over 7 days. Etofenprox did not trigger a significantly altered decomposition by invertebrate communities during the leaf bag assay, while in situ bioassays detected a significant reduction in gammarids’ feeding rate at the highest tested concentration. The laboratory bioassay suggests that observed mismatches might be explained by recovery and post-exposure compensation. As leaf-shredding invertebrates are likely in a vulnerable state following transient effects, biomonitoring for implications of peak exposures and other pulsed stress events must happen at an adequate temporal resolution.

无脊椎动物介导的凋落物分解经常用于评估河流生态系统完整性中与压力相关的影响。然而，由于恢复或补偿机制，原位测量（例如叶包的质量损失或部署数天或数周的笼中无脊椎动物的进食）可能无法检测到短暂的影响。我们使用三个级别的复杂性模型环境中的杀虫剂（即etofenprox）的最高暴露量来评估瞬态效应的相关性。这些是1）通过叶袋评估21天内无脊椎动物群落在中流中的分解，2）持续7天的原位生物测定法，定量了镰刀菌的叶片消耗，以及3）一项实验室实验，确定7天之内相同物种的每日摄食率。在叶袋试验期间，Etofenprox不会引起无脊椎动物群落的分解变化，而原位生物测定法则在最高测试浓度下检测到了γ射线的摄食率显着降低。实验室生物测定法表明，观察到的不匹配现象可以用恢复和曝光后补偿来解释。由于切叶无脊椎动物可能会在瞬态效应后处于脆弱状态，因此必须以足够的时间分辨率对峰值暴露和其他脉冲胁迫事件的影响进行生物监测。