Shelf sea areas are the primary oceanic source for methane release, the most abundant hydrocarbon in the atmosphere. As such, the southern North Sea’s methane concentration is mainly determined by river runoff and tidal marshes. Within such a highly variable temperate estuary, this study is the first to reveal detailed information on the in situ activity, abundance and community structure of methane oxidizing bacteria along a transect from the marine environment near Helgoland island to the riverine harbor of Hamburg, Germany. The in situ methane oxidation rate was determined with a radio tracer, and methane concentration with the head-space method. Abundance and diversity of the methanotrophic bacterial community in the water column was assessed with quantitative polymerase chain reaction for the particulate methane monooxygenase and monooxygenase intergenic spacer analysis. Median abundances ranged from 2.8 × 104 cells l−1 in the marine environment to 7.5 × 105 cells l−1 in the riverine environment. Except for salinity, no conclusive linear correlation between any environmental parameter and the abundance of methanotrophs could be determined. Relating activity with abundance of methanotrophs showed that about 70% of the population is inactive, especially in the coastal and marine environment. This study found distinct operational taxonomic unit (OTU) community compositions among the 3 environmental categories (river, coast, marine). Several identified OTUs have been reported previously and imply a wide geographic occurrence. Overall, we propose that salinity is the most important driver of differing communities in the riverine, coastal and marine environment.

中文翻译：

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易北河口和北海南部甲烷营养菌的丰度、活性和多样性

大陆架海域是甲烷释放的主要海洋来源，甲烷是大气中最丰富的碳氢化合物。因此，北海南部的甲烷浓度主要由河流径流和潮汐沼泽决定。在如此多变的温带河口内，这项研究首次揭示了从黑尔戈兰岛附近的海洋环境到德国汉堡的河流港口的横断面上甲烷氧化细菌的原位活动、丰度和群落结构的详细信息。原位甲烷氧化率用无线电示踪剂测定，甲烷浓度用顶空法测定。通过定量聚合酶链反应对颗粒甲烷单加氧酶和单加氧酶基因间间隔区分析，评估了水体中甲烷氧化菌群落的丰度和多样性。中值丰度范围从海洋环境中的 2.8 × 104 个细胞 l−1 到河流环境中的 7.5 × 105 个细胞 l−1。除盐度外，无法确定任何环境参数与甲烷氧化菌丰度之间的决定性线性相关性。与甲烷氧化菌丰度相关的活动表明，大约 70% 的种群处于非活动状态，尤其是在沿海和海洋环境中。本研究在 3 个环境类别（河流、海岸、海洋）中发现了不同的操作分类单元 (OTU) 群落组成。之前已经报道了几个确定的 OTU，这意味着广泛的地理发生。总的来说，我们认为盐度是河流、沿海和海洋环境中不同社区的最重要驱动因素。