Data_Sheet_7_Terrestrial Inputs Shape Coastal Bacterial and Archaeal Communities in a High Arctic Fjord (Isfjorden, Svalbard).PDF

The Arctic is experiencing dramatic changes including increases in precipitation, glacial melt, and permafrost thaw, resulting in increasing freshwater runoff to coastal waters. During the melt season, terrestrial runoff delivers carbon- and nutrient-rich freshwater to Arctic coastal waters, with unknown consequences for the microbial communities that play a key role in determining the cycling and fate of terrestrial matter at the land-ocean interface. To determine the impacts of runoff on coastal microbial (bacteria and archaea) communities, we investigated changes in pelagic microbial community structure between the early (June) and late (August) melt season in 2018 in the Isfjorden system (Svalbard). Amplicon sequences of the 16S rRNA gene were generated from water column, river and sediment samples collected in Isfjorden along fjord transects from shallow river estuaries and glacier fronts to the outer fjord. Community shifts were investigated in relation to environmental gradients, and compared to river and marine sediment microbial communities. We identified strong temporal and spatial reorganizations in the structure and composition of microbial communities during the summer months in relation to environmental conditions. Microbial diversity patterns highlighted a reorganization from rich communities in June toward more even and less rich communities in August. In June, waters enriched in dissolved organic carbon (DOC) provided a niche for copiotrophic taxa including Sulfitobacter and Octadecabacter. In August, lower DOC concentrations and Atlantic water inflow coincided with a shift toward more cosmopolitan taxa usually associated with summer stratified periods (e.g., SAR11 Clade Ia), and prevalent oligotrophic marine clades (OM60, SAR92). Higher riverine inputs of dissolved inorganic nutrients and suspended particulate matter also contributed to spatial reorganizations of communities in August. Sentinel taxa of this late summer fjord environment included taxa from the class Verrucomicrobiae (Roseibacillus, Luteolibacter), potentially indicative of a higher fraction of particle-attached bacteria. This study highlights the ecological relevance of terrestrial runoff for Arctic coastal microbial communities and how its impacts on biogeochemical conditions may make these communities susceptible to climate change.

北极正经历着剧烈的变化，包括降水增加、冰川融化以及永久冻土层解冻，导致淡水径流量向沿海水域不断增加。在融雪季节，陆源径流将富含碳和营养物质的淡水带入北极沿海水域，对在陆地与海洋界面决定陆地物质循环和命运的关键微生物群落产生未知的影响。为了确定径流对沿海微生物（细菌和古菌）群落的影响，我们调查了2018年融雪季节早期（六月）和晚期（八月）在斯瓦尔巴德群岛的伊世弗德恩系统（Isfjorden）中微生物群落结构的变化。从水柱、河流和沉积物样本中提取的16S rRNA基因扩增子序列在伊世弗德恩沿岸的峡湾横断面中生成，这些样本从浅河流河口和冰川前沿延伸至外峡湾。在环境梯度相关性的研究中，我们探讨了群落变化，并将其与河流和海洋沉积物微生物群落进行了比较。我们发现，在夏季月份，微生物群落的结构和组成随着环境条件发生了显著的时间和空间重组。微生物多样性模式突显了从六月丰富的群落向八月更为均匀且贫瘠的群落重组。六月，溶解有机碳（DOC）含量丰富的水域为包括Sulfitobacter和Octadecabacter在内的丰营养类群提供了生态位。八月，DOC浓度降低和大西洋水流入与向通常与夏季分层期相关的更普遍类群（例如，SAR11 Clade Ia）和普遍的寡营养海洋类群（OM60、SAR92）的转变相一致。更高的河流输入溶解无机营养物和悬浮颗粒物也促进了八月份群落的空间重组。这个晚期夏季峡湾环境的哨兵类群包括来自类群Verrucomicrobiae（Roseibacillus、Luteolibacter）的类群，这可能表明颗粒附着细菌的比例较高。本研究突显了陆地径流对北极沿海微生物群落生态学的重要性，以及其对生物地球化学条件的影响可能使这些群落对气候变化更加敏感。