Mountain lakes provide clear drinking water to humankind but are strongly impacted by global change. Benthic biofilms are crucial for maintaining water quality in these oligotrophic lakes, yet little is known about the effects of global change on mountain biofilm communities. By combining analyses of metabarcoding data on 16S and 18S rRNA genes with climatic and environmental data, we investigated global change effects on the composition of biofilm prokaryotic and micro-eukaryotic assemblages in a five-year monitoring program of 26 Pyrenean lakes (2016–2020). Using time-decay relationships and within-lake dissimilarity modelling, we show that the composition of both prokaryotic and micro-eukaryotic biofilm communities significantly shifted and their biodiversity declined from 2016 to 2020. In particular, analyses of temporal trends with linear mixed models indicated an increase in the richness and relative abundance of cyanobacteria, including potentially toxigenic cyanobacteria, and a concomitant decrease in diatom richness and relative abundance. While these compositional shifts may be due to several drivers of global change acting simultaneously on mountain lake biota, water pH and hardness were, from our data, the main environmental variables associated with changes for both prokaryotic and micro-eukaryotic assemblages. Water pH and hardness increased in our lakes over the study period, and are known to increase in Pyrenean lakes due to the intensification of rock weathering as a result of climate change. Given predicted climate trends and if water pH and hardness do cause some changes in benthic biofilms, those changes might be further exacerbated in the future. Such biofilm compositional shifts may induce cascading effects in mountain food webs, threatening the resilience of the entire lake ecosystem. The rise in potentially toxigenic cyanobacteria also increases intoxication risks for humans, pets, wild animals, and livestock that use mountain lakes. Therefore, our study has implications for water quality, ecosystem health, public health, as well as local economies (pastoralism, tourism), and highlights the possible impacts of global change on mountain lakes.

高山湖泊为人类提供清澈的饮用水，但受到全球变化的强烈影响。底栖生物膜对于维持这些寡营养湖泊的水质至关重要，但人们对全球变化对山区生物膜群落的影响知之甚少。通过将 16S 和 18S rRNA 基因的元条形码数据分析与气候和环境数据相结合，我们研究了全球变化对 26 个比利牛斯湖泊的五年监测计划（2016-2020）中生物膜原核生物和微型真核生物组合组成的影响。 。利用时间衰减关系和湖内差异模型，我们表明，从 2016 年到 2020 年，原核生物和微真核生物膜群落的组成发生了显着变化，其生物多样性下降。特别是，使用线性混合模型对时间趋势进行的分析表明，蓝藻丰富度和相对丰度增加，包括潜在产毒蓝藻，硅藻丰富度和相对丰度随之下降。虽然这些成分变化可能是由于全球变化的几个驱动因素同时作用于山湖生物群，但根据我们的数据，水的 pH 值和硬度是与原核生物和微型真核生物组合变化相关的主要环境变量。在研究期间，我们湖泊的水 pH 值和硬度有所增加，并且由于气候变化导致岩石风化加剧，比利牛斯山脉湖泊的水 pH 值和硬度也会增加。鉴于预测的气候趋势，如果水的 pH 值和硬度确实导致底栖生物膜发生一些变化，这些变化在未来可能会进一步加剧。这种生物膜成分的变化可能会在山区食物网中引起级联效应，威胁整个湖泊生态系统的恢复力。潜在产毒蓝藻的增加也增加了使用高山湖泊的人类、宠物、野生动物和牲畜的中毒风险。因此，我们的研究对水质、生态系统健康、公共卫生以及当地经济（畜牧业、旅游业）具有影响，并强调了全球变化对高山湖泊可能产生的影响。