Small headwater streams interlink catchment soils with the river network. As water makes its way from the hillslopes to the stream, it may transport dissolved organic carbon (DOC) and potentially soil microbes into stream water. In this study, we aimed at quantifying the dynamic transfer of DOC and microbial life, namely bacteria from catchment soils into streams. We hypothesized that increased soil saturation enhances the lateral inflow of bacteria and DOC into streams. To address this hypothesis, we sampled six first order streams and three soil transects at two different depths located within the pre-alpine Oberer Seebach (OSB) catchment in Austria over a duration of 2 years. We found a strong variation in DOC concentrations (range 0.4–5.6 mg L −1 ) and bacterial abundances (range < 500,000–3,863,000 cells mL −1 ) measured by flow-cytometry. The highest values of DOC and bacterial cells occurred during high flow events. DOC concentration and bacterial abundance were correlated across all streams and seasons. In soils, DOC ranges were higher and were also correlated with bacterial abundance, while DOC concentrations were ∼ 10 times higher per bacterial cell than in streams. Overall we show that soils provide a dynamic inflow of bacteria and DOC to first order streams. Most probably, this results in a dynamic and reoccurring inoculation of small streams from catchment soils during runoff events. We propose that this dynamic microbial inoculation of small streams is potentially relevant for microbial community dynamics of downstream receiving waters.

中文翻译：

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水文事件中土壤细菌和溶解有机碳向小溪流的动态转移

小型源头溪流将集水土壤与河网连接起来。当水从山坡流向溪流时，它可能会将溶解有机碳 (DOC) 和潜在的土壤微生物输送到溪水中。在这项研究中，我们旨在量化 DOC 和微生物生命（即细菌从集水土壤到溪流）的动态转移。我们假设增加的土壤饱和度会增加细菌和 DOC 向溪流的横向流入。为了解决这个假设，我们在 2 年的时间里对位于奥地利前高山 Oberer Seebach (OSB) 流域内两个不同深度的六个一级河流和三个土壤断面进行了采样。我们发现通过流式细胞术测量的 DOC 浓度（范围 0.4-5.6 mg L -1 ）和细菌丰度（范围 < 500,000-3,863,000 个细胞 mL -1 ）存在很大差异。DOC 和细菌细胞的最高值出现在高流量事件期间。DOC 浓度和细菌丰度在所有河流和季节中都有关联。在土壤中，DOC 范围更高，并且还与细菌丰度相关，而每个细菌细胞的 DOC 浓度比溪流中高约 10 倍。总的来说，我们表明土壤为一级流提供了细菌和 DOC 的动态流入。最有可能的是，这会导致在径流事件期间从集水区土壤中动态和反复接种小溪流。我们提出，小溪流的这种动态微生物接种可能与下游受纳水体的微生物群落动态相关。DOC 浓度和细菌丰度在所有河流和季节中都有关联。在土壤中，DOC 范围更高，并且还与细菌丰度相关，而每个细菌细胞的 DOC 浓度比溪流中高约 10 倍。总的来说，我们表明土壤为一级流提供了细菌和 DOC 的动态流入。最有可能的是，这会导致在径流事件期间从集水区土壤中动态和反复接种小溪流。我们提出，小溪流的这种动态微生物接种可能与下游受纳水体的微生物群落动态相关。DOC 浓度和细菌丰度在所有河流和季节中都有关联。在土壤中，DOC 范围更高，并且还与细菌丰度相关，而每个细菌细胞的 DOC 浓度比溪流中高约 10 倍。总的来说，我们表明土壤为一级流提供了细菌和 DOC 的动态流入。最有可能的是，这会导致在径流事件期间从集水区土壤中动态和反复接种小溪流。我们提出，小溪流的这种动态微生物接种可能与下游受纳水体的微生物群落动态相关。总的来说，我们表明土壤为一级流提供了细菌和 DOC 的动态流入。最有可能的是，这会导致在径流事件期间从集水区土壤中动态和反复接种小溪流。我们提出，小溪流的这种动态微生物接种可能与下游受纳水体的微生物群落动态相关。总的来说，我们表明土壤为一级流提供了细菌和 DOC 的动态流入。最有可能的是，这会导致在径流事件期间从集水区土壤中动态和反复接种小溪流。我们提出，小溪流的这种动态微生物接种可能与下游受纳水体的微生物群落动态相关。