Stinson Beach, CA subterranean estuary microbiome analysis

Subterranean estuaries (STEs) are critically important ecosystems at the interface of meteoric groundwater and subsurface seawater that are threatened by sea level rise. To characterize the influences of tides and waves on the STE microbial community, we collected porewater samples from a high-energy beach STE (Stinson Beach, CA, USA) over the two-week neap-spring tidal transition during a wet and a dry season. The microbial community, analyzed by 16S rRNA gene (V4) amplicon sequencing, clustered according to consistent features found in STEs: shallow, nitrate-enriched fresher groundwater and deep, ammonia-enriched saltier groundwater with a distinct transition zone between the layers, as well as an intertidal saltwater cell near the surf zone. The porewater community harbored relatively abundant Proteobacteria, Verrucomicrobiota, and Bacteroidota, as well as members of the archaeal DPANN and bacterial Candidate Phyla Radiation groups. The taxa present were inferred to have a broad variety of aerobic and anaerobic metabolic capabilities. Salinity, dissolved inorganic nitrogen, and dissolved organics were important environmental correlates with microbial community structure. While tidal conditions were not associated with microbial community composition, a wave overtopping event did significantly impact the beach microbiome. Our results elucidate the unique dynamics of an STE microbiome as a baseline for environmental change.

地下河口（Subterranean estuaries，STEs）是位于大气降水地下水与地下海水交汇带的关键生态系统，正面临海平面上升的威胁。为阐明潮汐与波浪对地下河口微生物群落的影响，我们于雨季与旱季期间，在为期两周的大小潮过渡期内，从一处高能海滩型地下河口——美国加利福尼亚州斯廷森海滩（Stinson Beach, CA, USA）——采集了孔隙水样本。通过16S rRNA基因（V4区）扩增子测序分析的微生物群落，按照地下河口的典型特征进行聚类：浅层富硝酸盐低盐地下水、深层富氨高盐地下水，两层间存在清晰的过渡带，同时激浪带附近还存在一处潮间带咸水体。孔隙水群落中相对富集变形菌门、疣微菌门与拟杆菌门，同时还包含古菌DPANN超门以及细菌候选门辐射群（Candidate Phyla Radiation，CPR）的类群。所检出的类群被推断具备丰富多样的有氧与无氧代谢能力。盐度、溶解态无机氮与溶解态有机物是与微生物群落结构显著相关的关键环境因子。尽管潮汐条件与微生物群落组成并无关联，但一次波浪越顶事件却对海滩微生物组产生了显著影响。本研究结果阐明了地下河口微生物组的独特动态变化，可为环境变化研究提供基准参照。