The in-stream processing of nutrients plays an important role in the fluvial nutrient transport from lands to the ocean, but few empirical studies have addressed the temporal dynamics of net nutrient removal rates in large river systems. The present study applied the recently developed Lagrangian approach to the sixth-order Fuji River to identify the seasonal dynamics of in-stream uptake rates for inorganic nitrogen and phosphorus by tracking a specific water parcel along the river course. The Lagrangian measurements revealed temporal variability of nutrient uptake metrics, but the overall pattern showed a net positive uptake of ammonium (NH₄) and a net release of nitrite (NO₂) and nitrate (NO₃) from the riverbed from May through December. The net uptake rates of phosphate (PO₄) showed both positive and negative values depending on the sampling periods. Environmental correlates of the net areal uptake rates (U_net) suggested that biological transformation processes such as assimilation for organic matter synthesis and utilization for energy in oxidation–reduction reactions, as well as abiotic sorption processes, influenced the nutrient removal in the Fuji River. The present study highlights that physical factors (temperature and light), reaction substrates and epilithic organisms may responsible for nutrient dynamics in large river ecosystems.

中文翻译：

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拉格朗日跟踪测量揭示了一条日本大河中氮和磷螺旋运动的时间动态

养分的流式处理在河流养分从陆地到海洋的运输中起着重要作用，但是很少有实证研究涉及大型河流系统中净养分去除率的时间动态。本研究将最近开发的拉格朗日方法应用于六阶富士河，通过跟踪沿河道的特定水域来确定无机氮和磷的流内吸收速率的季节动态。拉格朗日测量显示营养素吸收指标随时间变化，但总体模式显示铵态氮（NH ₄）净正吸收，亚硝酸盐（NO ₂）和硝酸盐（NO ₃）净释放）从五月到十二月。磷酸盐（PO ₄）的净吸收率根据采样周期显示正值和负值。净面积吸收率（U _net）的环境相关性表明，生物转化过程（例如有机物合成的同化和氧化还原反应中的能量利用以及非生物吸附过程）影响了富士河中的养分去除。本研究强调，物理因素（温度和光），反应底物和上石器生物可能是大型河流生态系统中养分动态的原因。