Background

Benthic invertebrate communities are an integral and longstanding component of stream biomonitoring. However, multiple stressors driven by global change threaten benthic invertebrate communities. In particular, climate warming is expected to disrupt freshwater ecosystems. While an increasing number of studies have shown changes in benthic invertebrate community composition in response to climate warming, the effect on stream assessments has rarely been investigated. As several community composition metrics are also used in stream assessments, we predicted that climate warming would worsen stream assessment results. Therefore, we used a comprehensive data set of 2865 benthic invertebrate samples taken between 2000 and 2014 from small central European low mountain streams. We examined the effects of changes in temperature on common community and stream assessment metrics. We used 31 metrics covering composition, richness, tolerance and function of communities, of which many are used in various stream assessment schemes.

Results

Against our expectations, we identified a decreasing air temperature trend of − 0.18 °C over 15 years. This trend was accompanied by significant changes in community composition, for example, increases in species richness and decreases in the community temperature index (CTI). Further, we identified slight concomitant improvements of various globally used stream quality assessment metrics, such as a decreasing saprobic index and an increasing BMWP.

Conclusions

While temperature increased by + 0.9 °C during the past 30 years (1985–2014), our 15-year study period (2000–2014) showed a decrease by − 0.18 °C. Therefore, we regard the concomitant improvement in several assessment metrics as a recovery from prior increasing temperatures. In turn, we assume that increases in water temperature will lead to opposite effects and therefore cause declining assessment results. Water managers should be aware of this linkage that in turn could provide a chance to mitigate the effects of global warming by, for example, planting trees along the rivers and the removal of artificial barriers to increase current velocity to minimize a warming effect.

中文翻译：

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温度变化是否会影响中欧河流的符合《欧盟水框架指令》的评估结果？

背景

底栖无脊椎动物群落是河流生物监测不可或缺的长期组成部分。然而，全球变化驱动的多种压力源威胁着底栖无脊椎动物社区。特别是，气候变暖有望破坏淡水生态系统。尽管越来越多的研究表明底栖无脊椎动物群落组成随气候变暖而变化，但很少研究对河流评估的影响。由于在河流评估中也使用了一些社区组成指标，因此我们预测气候变暖会恶化河流评估的结果。因此，我们使用了2000年至2014年间从欧洲中部小山区河流采集的2865个底栖无脊椎动物样本的综合数据集。我们研究了温度变化对普通社区和河流评估指标的影响。我们使用了31个指标，涵盖了社区的组成，丰富性，容忍度和功能，其中许多指标用于各种流评估方案中。

结果

与我们的预期相反，我们发现15年内气温下降趋势为-0.18°C。这种趋势伴随着群落组成的重大变化，例如物种丰富度的增加和群落温度指数（CTI）的降低。此外，我们发现各种全球使用的溪流质量评估指标略有改善，例如，腐生指数下降和BMWP上升。

结论

在过去30年（1985-2014年）中，温度升高了+ 0.9°C，而我们15年的研究期（2000-2014年）却降低了− 0.18°C。因此，我们认为伴随着几个评估指标的提高是从先前温度上升中的恢复。反过来，我们假定水温升高会导致相反的影响，因此会导致评估结果下降。水务管理者应意识到这种联系，而这反过来又可以提供一个减轻全球变暖影响的机会，例如，通过在河流上种树和去除人为障碍物来增加水流速度，从而最大程度地降低变暖的影响。