Riverine colloids are important carriers of macronutrients, trace metals, and pollutants into marine waters. The aim of the current study was to extend the understanding of iron (Fe) and organic carbon (OC) colloids in boreal rivers and their fate at higher salinities. X‐ray absorbance spectroscopy (XAS) and dynamic light scattering (DLS) were combined to explore Fe speciation and colloidal characteristics such as size and surface charge and how these are affected at increasing salinity. XAS confirmed the presence of two Fe phases in the river waters—Fe‐organic matter (OM) complexes and Fe(oxy)hydroxides. From DLS measurements on filtered and unfiltered samples, three particle size distributions were identified. The smallest particles (10–40 nm) were positively charged and suggested to consist of essentially bare Fe(oxy)hydroxide nanoparticles. The largest particles (300–900 nm) were dominated by Fe(oxy)hydroxides associated with chromophoric molecular matter. An intermediate size distribution (100–200 nm) with a negative surface charge was presumably dominated by OM and containing Fe‐OM complexes. Increasing the salinity resulted in a removal of the smallest distribution. Unexpectedly, both the intermediate and largest size distributions were still detected at high salinity. The collective results suggest that Fe(oxy)hydroxides and Fe‐OM complexes are both found across the wide size range studied and that colloidal size does not necessarily reflect either Fe speciation or stability toward salinity‐induced aggregation. The findings further demonstrate that also particles beyond the typically studied <0.45‐μm size range should be considered to fully understand the riverine transport and fate of macronutrients, trace metals, and pollutants.

中文翻译：

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高盐度下北方河流中铁和有机碳胶体的特征及其命运

河流胶体是大量营养素，微量金属和污染物进入海水的重要载体。当前研究的目的是扩大对北方河流中铁（Fe）和有机碳（OC）胶体及其在较高盐度下的命运的了解。结合X射线吸收光谱（XAS）和动态光散射（DLS）来研究铁的形态和胶体特性，例如大小和表面电荷，以及它们在盐度增加时如何受到影响。XAS证实了河水中存在两个铁相-铁有机物（OM）络合物和氢氧化铁（氧）。从过滤和未过滤样品的DLS测量中，可以确定三种粒径分布。最小的粒子（10–40 nm）带正电，建议由基本上裸露的氢氧化氢氧化铁组成。最大的颗粒（300-900 nm）主要是与发色分子物质相关的氢氧化氢氧化铁。带有负表面电荷的中等尺寸分布（100-200 nm）大概是由OM所控制，并且含有Fe-OM络合物。增加盐度导致去除最小的分布。出乎意料的是，在高盐度下仍能检测到中等和最大粒度分布。总体结果表明，在所研究的大尺寸范围内均发现了氢氧化氢氧化Fe和OM-OM络合物，胶体尺寸不一定反映出Fe的形态或对盐分诱导的聚集的稳定性。这些发现进一步表明，超出通常研究的<0的颗粒也是如此。