![]() CO2 fluxes, a proxy for sediment community respiration, were rapidly and strongly affected by drying in all treatments. Fungal amplicon sequence variants (ASVs) from Dothideomycetes (Ascomycota) had by far the highest relative abundance in all our treatments at the end of the drying experiment, making up 65.1% to 94.0% of the fungal reads. After 90 days of drying, Bacilli (Firmicutes) became the dominant bacterial class in most treatments, except in sediments with low OM content under the most severe drying treatment. Milder drying surprisingly triggered a more rapid and drastic change in the microbial community composition and diversity. Our results demonstrate that drying attributes (duration and intensity) and sediment organic matter (OM) content play a crucial role in sediment microbial community assembly and functioning throughout drying. Riverbed sediment collected in a flowing reach of the Spree river in northeastern Germany was dried under different rates in outdoor mesocosms during the summer months of 2018. In this study, we evaluated how sediment bacterial and fungal community structure and composition (based on 16S rRNA gene and ITS metabarcoding) and microbial functions (community respiration and extracellular enzymatic activities) respond to different riverbed drying intensities over 90 days. Riverbed drying can significantly affect sediment microorganisms, crucial drivers of biogeochemical processes in lotic systems. Non-perennial rivers and streams are mapped globally, showing that more than half of rivers worldwide experience no flow for at least one day per year.Ĭombined effects of climate change and increasing anthropogenic water demand have increased and extended dry period occurrences in rivers worldwide. By mapping the distribution of non-perennial rivers and streams, we provide a stepping-stone towards addressing this grand challenge in freshwater science. To understand and adequately manage the world’s flowing waters, their biodiversity and functional integrity, a paradigm shift is needed towards a new conceptual model of rivers that includes flow intermittence. Our findings challenge the assumptions underpinning foundational river concepts across scientific disciplines9. ![]() Leveraging global information on the hydrology, climate, geology and surrounding land cover of the Earth’s river network, we show that non-perennial rivers occur within all climates and biomes, and on every continent. Here we predict that water ceases to flow for at least one day per year along 51–60 per cent of the world’s rivers by length, demonstrating that non-perennial rivers and streams are the rule rather than the exception on Earth. ![]() This oversight contributes to the degradation of the main source of water and livelihood for millions of people5. ![]() Although the importance of permanent watercourses is well recognized, the prevalence, value and fate of non-perennial rivers and streams that periodically cease to flow tend to be overlooked, if not ignored6–8. Flowing waters have a unique role in supporting global biodiversity, biogeochemical cycles and human societies1–5. ![]()
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