Streambank legacy sediments may be important sources of sediment and nutrients from Mid-Atlantic watersheds. However, little is known about the nutrient processing roles of microorganisms that inhabit legacy sediments, let alone their composition, diversity, and distributions. In this study, we sampled 15 streambanks at multiple depths throughout four watersheds in the Mid-Atlantic Region of the USA. High throughput sequencing of 16S ribosomal RNA genes indicated that streambank microbial community composition varied within site depth and across contemporary land uses. Collectively, the most abundant microbial taxa in legacy sediments included Acidobacteria (25–45%), Proteobacteria (15–40%), Nitrospirae (2–10%), Chloroflexi (1–5%), and Actinobacteria (1–10%). Bacterial community composition was distinct between agriculture and urban sites as well as suburban and urban sites. There was significant variation in community composition between the top (1–25%), upper-middle (26–50%), and bottom layers (76–100%) of sediments, while the relative abundances differed between layers for only Acidobacteria and Proteobacteria. Several streambank chemistry variables (metals, %TC, and %TN) had weak positive correlations with community composition. Compared to ammonia-oxidizing bacteria, nitrifying archaea were more predominant. This study provides the first insights into detailed microbial composition of legacy sediments and identifies environmental drivers for community structure and nitrogen processing. Future studies should consider exploring the role of this unique microbial environment for nutrient processing and leaching from legacy sediments and its implications for watershed water quality.

中文翻译：

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河岸遗留沉积物中的细菌群落和氮转化基因及其对生物地球化学处理的影响

河岸遗留沉积物可能是大西洋中部流域沉积物和养分的重要来源。然而，人们对居住在遗留沉积物中的微生物的营养处理作用知之甚少，更不用说它们的组成、多样性和分布了。在这项研究中，我们在美国中大西洋地区的四个流域中对 15 个不同深度的河岸进行了采样。16S 核糖体 RNA 基因的高通量测序表明，河岸微生物群落组成在场地深度和当代土地利用中各不相同。总的来说，遗留沉积物中最丰富的微生物类群包括酸杆菌 (25-45%)、变形菌 (15-40%)、硝化螺菌 (2-10%)、绿屈菌 (1-5%) 和放线菌 (1-10%) ）。农业和城市场地以及郊区和城市场地的细菌群落组成不同。沉积物的顶层（1-25%）、中上层（26-50%）和底层（76-100%）的群落组成存在显着差异，而层间的相对丰度差异仅针对酸杆菌和变形菌。几个河岸化学变量（金属、%TC 和 %TN）与群落组成呈弱正相关。与氨氧化细菌相比，硝化古细菌更占优势。这项研究首次提供了对遗留沉积物详细微生物组成的见解，并确定了群落结构和氮处理的环境驱动因素。