Institute of Aquatic Ecology, Faculty of Sciences, University of Girona, Campus Montilivi, 17003, Girona, Spain; Catalan Institute for Water Research (ICRA), Carrer Emili Grahit 101, 17003, Girona, Spain.
Catalan Institute for Water Research (ICRA), Carrer Emili Grahit 101, 17003, Girona, Spain; University of Girona, Plaça de Sant Domènec 3, 17004, Girona, Spain.
Sci Total Environ. 2021 May 20;770:144675. doi: 10.1016/j.scitotenv.2020.144675. Epub 2021 Jan 21.
Flow cessation affects river ecosystems submitted to low precipitation and increased water demand, and creates unfavourable conditions to aquatic biological communities. Diatoms are amongst the most sensitive biological groups to hydric stress, making them good indicators of preceding hydrological conditions. We here analyse the response of diatom assemblages to the duration and frequency of non-flow periods in 23 Mediterranean temporary streams. All of them experienced a strong decrease in water flow during summer, leading to a period of flow cessation. In addition, other ten permanent streams (zero dry days during the study period) were included in the study for comparative purposes. Temporary and permanent streams showed similar diatom species richness, evenness, and alpha diversity. However, beta diversity was higher in temporary than permanent streams, regardless rare taxa (<1% occurrence) had similar numbers in the two types of streams. Alpha diversity, richness, and evenness of diatom assemblages in the temporary streams changed with the duration of the non-flow period. Durations of 50-100 days were associated to higher alpha diversity, richness, and evenness, but longer non-flow periods caused their decrease. Diatoms thriving under the most extreme conditions were mostly aerophilic, pioneer, and motile taxa. The proportion of aerophilic diatom taxa increased beyond 100 dry days, particularly in those sites receiving more intense solar radiation. Overall, the taxonomical and functional composition of diatom assemblages mostly responded to the duration of the non-flow period, irrespectively of these being consecutive or not. This study shows that diatom assemblages from temporary streams contain taxa adapted to non-flow conditions, but remain vulnerable to further reductions of water flow associated to climate or global change. 'Unimpacted' watercourses in the Mediterranean region, independently of their flow regime, should be urgently protected and used as taxonomical and functional early indicators of climate change.
流量停止会影响到低降水量和用水量增加的河流生态系统，并为水生生物群落创造不利条件。硅藻是对水胁迫最敏感的生物群体之一，是水文条件的良好指示物。本研究分析了 23 条地中海间歇性溪流中硅藻组合对非流动期持续时间和频率的响应。在夏季，所有溪流的水流都经历了强烈的下降，导致了一段时间的停流。此外，还为比较目的纳入了另外 10 条永久性溪流（研究期间没有干燥天数）。永久性和间歇性溪流的硅藻物种丰富度、均匀度和α多样性相似。然而，β多样性在间歇性溪流中高于永久性溪流，尽管稀有类群（<1%的出现率）在这两种类型的溪流中数量相似。间歇性溪流中硅藻组合的α多样性、丰富度和均匀度随非流动期的持续时间而变化。非流动期持续时间为 50-100 天与较高的α多样性、丰富度和均匀度相关，但较长的非流动期会导致其减少。在最极端条件下茁壮成长的硅藻主要是好气性、先锋性和运动性的类群。好气性硅藻类群的比例在 100 个干燥日后增加，特别是在那些接受更强太阳辐射的地点。总的来说，硅藻组合的分类和功能组成主要响应非流动期的持续时间，而与非流动期是否连续无关。这项研究表明，间歇性溪流中的硅藻组合包含适应非流动条件的类群，但仍然容易受到与气候或全球变化相关的水流进一步减少的影响。无论其水流模式如何，地中海地区未受影响的水道都应紧急保护，并作为气候变化的分类和功能早期指标。
