Droughts are expected to become more common with climate change resulting in more frequent occurrences of flow intermittency in temperate streams. As intermittency has deleterious effects on fluvial microbial biofilms, there is a need to better understand how droughts affect the microbial functioning and thereby nutrient and organic matter processing in temperate stream ecosystems. Here, the hyporheic zone is of particular importance as it has been shown to be a hot spot for biogeochemical activity under flow intermittence. This study evaluates how drought duration affects microbial biofilm dynamics in the hyporheic zone of intermittent temperate streams. To do so, we used outdoor hyporheic flumes that were subject to periods of drought ranging from 4 to 105 days. Sediment was sampled before and during the drought, and at several occasions after rewetting. Samples were analyzed for extracellular enzymatic activity, bacterial respiration, and bacterial abundances including live to dead cell ratios. The high moisture content remaining in the hyporheic zone of the flumes allowed for the sustained microbial functioning during drought, regardless of drought duration. This can be attributed to cooler temperatures in these climate zones and shading by riparian forests. The high moisture content inhibited the local habitat and community changes that the biofilm might have undergone during more severe desiccation. However, the change in the hyporheic flow regime (flow cessation and resumption) may stimulate microbial processing in these moderate drought conditions. We suggest that the hyporheic zone may act as a buffer against drought and the factors determining this buffer capacity, such as sediment characteristics and climatic regions, need to be analyzed in more detail in future.

预计干旱将随着气候变化而变得更加普遍，从而导致在温带河流中流动间歇性的发生更加频繁。由于间歇性对河流微生物生物膜具有有害作用，因此有必要更好地了解干旱如何影响微生物的功能，从而在温带水流生态系统中处理营养物质和有机物质。在这里，流变区特别重要，因为它已被证明是流动间歇条件下生物地球化学活性的一个热点。这项研究评估了干旱持续时间如何影响间歇性温带水流下流带的微生物生物膜动力学。为此，我们使用了户外排泄水渠，这些水渠遭受了4至105天的干旱期。在干旱之前和干旱期间对沉积物进行了采样，并在重新润湿后多次使用。分析样品的细胞外酶活性，细菌呼吸和细菌丰度，包括活细胞与死细胞的比率。不论干旱持续时间如何，残留在排水沟中的水分含量高，都能在干旱期间保持微生物的持续功能。这可以归因于这些气候区的温度较低以及河岸森林的遮荫。高水分含量抑制了在更严重的干燥过程中生物膜可能经历的局部生境和群落变化。但是，在这些中度干旱条件下，流变流动方式的变化（停止流动和恢复流动）可能会刺激微生物的加工。