Headwater streams are the smallest parts of rivers but make up the majority of river miles. The chemistry and macroinvertebrate composition of such streams are among the most important indicators of their environmental health. Macroinvertebrates are affected namely by runoff genesis and, in many regions of the world, also by acid atmospheric deposition and its consequences. The aim of this paper is to evaluate the impacts of an extreme summer flash flood on the physical environment, chemistry and macroinvertebrates in a small headwater stream located in the Beech-woods National Nature Reserve of the Jizera Mts. (Northern Bohemia, Czech Republic). The studied stream is characterized by a pluvial hydrologic regime with perennial streamflow uniformly distributed within the year, with peak-flows originating mainly from summer rainstorms, and moderate current anthropogenic acidification. During the observed summer flash flood of the return period near 1,000 years, high currents (1-2.5 m s^-1) flushed out 2.7 m³ of sand and gravel from the streambed, resulting in a devastating effect on macroinvertebrates. Both number of species/taxa and diversity were reduced by about 50% while the abundance of surviving taxa was reduced to about 10% compared with before the flood. The following spring after the event, both number of species/taxa, diversity and abundance increased, partially due to the temporary unsuccessful colonization of the site by several alien species creating a peak of biological diversity, but complete recovery of the original macroinvertebrate assemblages was not observed even during the subsequent two years. On the other hand, a significant drop in sulphate contents and rising alkalinity observed in stream waters during base flow conditions after the flood indicate positive effects on recovery of the aquatic environment by depleting the catchment sulphur pool. Thus, the flood did not significantly alter the long-term recovery of the studied headwater stream from acidification.

源头溪流是河流的最小部分，但占河流英里的大部分。这些流的化学和无脊椎动物组成是其环境健康的最重要指标。大型无脊椎动物受到径流成因的影响，在世界许多地区也受到酸性大气沉积及其后果的影响。本文的目的是评估极端的夏季山洪对位于伊泽拉山（Jizera Mts）山毛榉森林国家自然保护区中的小上游水源中的物理环境，化学物质和大型无脊椎动物的影响。（捷克共和国北部波西米亚）。所研究的河流的特征是多雨的水文状况，常年流量在一年内均匀分布，峰值流量主要来自夏季暴雨，和中等电流的人为酸化。在观测到的近1000年的夏季闪回洪水期间，大电流（1-2.5 ms^-1）冲洗2.7 m ³流中的沙子和砾石，对大型无脊椎动物产生毁灭性影响。与洪灾之前相比，物种/分类单元的数量和多样性都减少了约50％，而存活的分类单元的丰度却降低了约10％。事件发生后的第二年春季，物种/分类群的数量，多样性和丰度都增加了，部分原因是由于几种外来物种暂时在该地点定居而未能成功，从而造成了生物多样性的高峰，但原始巨无脊椎动物组合并未完全恢复。甚至在随后的两年中也观察到。另一方面，在洪灾发生后的基本流量条件下，溪流水中的硫酸盐含量显着下降，碱度升高，这表明通过耗尽集水区的硫磺池对水环境的恢复具有积极作用。因此，洪水并没有显着改变所研究的源于酸化的源头水流的长期恢复能力。