Wang Zhe, Jimenez-Fernandez Oscar, Osenbrück Karsten, Schwientek Marc, Schloter Michael, Fleckenstein Jan H, Lueders Tillmann
Chair of Ecological Microbiology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany; Institute of Groundwater Ecology, Helmholtz Zentrum München - German Research Centre for Environmental Health, Neuherberg, Germany; School of Life Sciences, Technical University of Munich, Freising, Germany.
Center for Applied Geoscience, University of Tübingen, Tübingen, Germany; Department of Hydrogeology, Helmholtz-Zentrum für Umweltforschung GmbH - UFZ, Leipzig, Germany.
Water Res. 2022 Jun 15;217:118334. doi: 10.1016/j.watres.2022.118334. Epub 2022 Mar 21.
The input of nitrate and other agricultural pollutants in higher-order streams largely derives from first-order streams. The streambed as the transition zone between groundwater and stream water has a decisive impact on the attenuation of such pollutants. This reactivity is not yet well understood for lower-order agricultural streams, which are often anthropogenically altered and lack the streambed complexity allowing for extensive hyporheic exchange. Reactive hot spots in such streambeds have been hypothesized as a function of hydrology, which controls the local gaining (groundwater exfiltration) or losing (infiltration) of stream water. However, streambed microbial communities and activities associated with such reactive zones remain mostly uncharted. In this study, sediments of a first-order agriculturally impacted stream in southern Germany were investigated. Along with a hydraulic dissection of distinct gaining and losing reaches of the stream, community composition and the abundance of bacterial communities in the streambed were investigated using PacBio long-read sequencing of bacterial 16S rRNA gene amplicons, and qPCR of bacterial 16S rRNA and denitrification genes (nirK and nirS). We show that bidirectional water exchange between groundwater and the stream represents an important control for sediment microbiota, especially for nitrate-reducing populations. Typical heterotrophic denitrifiers were most abundant in a midstream net losing section, while up- and downstream net gaining sections were associated with an enrichment of sulfur-oxidizing potential nitrate reducers affiliated with Sulfuricurvum and Thiobacillus spp. Dispersal-based community assembly was found to dominate such spots of groundwater exfiltration. Our results indicate a coupling of N- and S-cycling processes in the streambed of an agricultural first-order stream, and a prominent control of microbiology by hydrology and hydrochemistry in situ. Such detailed local heterogeneities in exchange fluxes and streambed microbiomes have not been reported to date, but seem relevant for understanding the reactivity of lower-order streams.
高阶溪流中硝酸盐和其他农业污染物的输入很大程度上源自一阶溪流。河床作为地下水与溪水之间的过渡带，对这类污染物的衰减具有决定性影响。对于常受人为改变且缺乏能实现广泛潜流交换的河床复杂性的低阶农业溪流而言，这种反应性尚未得到充分理解。这类河床中的反应热点被假定为水文状况的函数，水文状况控制着溪水的局部补给（地下水渗出）或流失（渗入）。然而，与这类反应区相关的河床微生物群落和活动大多仍未被探明。在本研究中，对德国南部一条受农业影响的一阶溪流的沉积物进行了调查。除了对溪流不同补给和流失河段进行水力剖析外，还利用细菌16S rRNA基因扩增子的PacBio长读长测序以及细菌16S rRNA和反硝化基因（nirK和nirS）的定量聚合酶链反应，研究了河床中群落组成和细菌群落丰度。我们发现，地下水与溪流之间的双向水交换是沉积物微生物群，尤其是硝酸盐还原菌群的重要控制因素。典型的异养反硝化菌在中游净流失段最为丰富，而上下游净补给段则与隶属于硫弯菌属和硫杆菌属的具有硫氧化潜力的硝酸盐还原菌的富集有关。基于扩散的群落组装被发现主导着这类地下水渗出点。我们的结果表明，在一条农业一阶溪流的河床中，氮循环和硫循环过程相互耦合，并且水文状况和原位水化学对微生物学具有显著控制作用。这种交换通量和河床微生物群落中如此详细的局部异质性迄今尚未见报道，但似乎对于理解低阶溪流的反应性至关重要。
