Data_Sheet_8_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、冰川融化以及永冻土层融化，导致淡水径流量向沿海水域的不断增加。在融化季节，陆地径流将富含碳和营养物质的淡水输送到北极沿海水域，对在陆地-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了未知的后果。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年融化季节早期（六月）和晚期（八月）在斯瓦尔巴德群岛的伊塞霍登系统（Isfjorden）中微生物群落结构的变化。通过对从伊塞霍登的浅河河口和冰川前沿到外海的峡湾横断面采集的水柱、河流和沉积物样本，生成了16S rRNA基因的扩增子序列。我们根据环境梯度研究了群落的变化，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在时间和空间上发生了强烈的重组。微生物多样性模式突显出从六月的丰富群落向八月更加均匀且贫瘠的群落重组。六月，富含溶解有机碳（DOC）的水域为包括Sulfitobacter和Octadecabacter在内的富营养型类群提供了生态位。在八月，较低的DOC浓度和大西洋水流流入与向通常与夏季分层期相关的更普遍的类群（例如，SAR11 Ia支系）和普遍的寡营养型海洋支系（OM60、SAR92）的转变相一致。较高的河流溶解无机营养物和悬浮颗粒物质的输入也在八月对群落的空间重组做出了贡献。这个晚夏峡湾环境的哨兵类群包括来自Verrucomicrobiae类群（如Roseibacillus、Luteolibacter）的类群，这可能表明颗粒附着细菌的比例更高。本研究突出了陆地径流对北极沿海微生物群落的生态相关性，以及其对学生物地球化学条件的影响可能使这些群落更容易受到气候变化的影响。