Riverbanks play the key role in ammonium removal from runoff entering river. Currently, microplastics (MPs) are frequently detected in riverbanks receiving urban and agricultural runoff. Nevertheless, the effect of MPs accumulation on ammonium removal in riverbanks is still unknown. We utilized sediment flow-through reactors to investigate the impact and mechanism of MPs accumulation on ammonium removal in riverbanks. These results revealed that MPs accumulation decreased ammonium removal in sediment by 8.2 %−12.8 % resulting from the reduction in nitrifier abundance (Nitrososphaera and Nitrososphaeraceae) and genes encoding ammonium and hydroxylamine oxidation (amoA, amoB, amoC, and hao) by MPs accumulation. Furthermore, MPs accumulation decreased the substrate and gene abundance of hydroxylamine oxidation process to reduce N₂O emission (16.3 %−34.3 %). Notably, mathematic model verified that sediment physical properties changed by MPs accumulation were direct factors affecting ammonium removal in riverbank. It was suggested that both the biotoxicity of MPs and sediment physical properties should be considered in the ammonium removal process. To summarize, this study for the first time comprehensively clarifies the impact of MPs on the ammonium removal capacity of riverbanks, and provides information for taking measures to protect the ecological function of the riverbank and river ecosystem from MPs and ammonium pollution.

河岸在从进入河流的径流中去除铵中起关键作用。目前，在接收城市和农业径流的河岸中经常检测到微塑料 (MPs)。然而，MPs 积累对河岸铵去除的影响仍然未知。我们利用沉积物流通反应器来研究 MPs 积累对河岸除铵的影响和机制。这些结果表明，由于硝化菌丰度（Nitrososphaera和Nitrososphaeraceae）以及编码铵和羟胺氧化的基因（amo A、amo B、amo C 和hao) 通过国会议员的积累。此外，MPs 的积累降低了羟胺氧化过程的底物和基因丰度，从而减少了 N ₂ O 排放（16.3 %-34.3 %）。值得注意的是，数学模型验证了MPs积累改变的沉积物物理性质是影响河岸铵去除的直接因素。有人建议在除铵过程中应同时考虑 MPs 的生物毒性和沉积物物理性质。综上所述，本研究首次全面阐明了 MPs 对河岸除铵能力的影响，为采取措施保护河岸生态功能和河流生态系统免受 MPs 和铵污染提供了信息。