The St. Lawrence Estuary (SLE), in eastern Canada, is a dynamic coastal environment where no recent description of the particles’ composition and size distribution has been completed. In this study, we characterize the particle size distribution (PSD) of suspended particulate matter in the SLE, both vertically and horizontally, and evaluate its variability during ice-free (May 2010) and ice-covered (February 2019) conditions. The results showed the importance of sedimentation in the Lower Estuary as coarse particles, larger than $63\mathrm{\mu }\mathrm{m}$, in May 2010 and particles between $4\mathrm{\mu }\mathrm{m}$ and $63\mathrm{\mu }\mathrm{m}$ in February 2019 were less present than in the Upper Estuary. In the Lower Estuary, coarse particles had a higher number density in ice-covered than in ice-free conditions, possibly due to ice transport and the higher suspended matter load of regulated rivers. Alternatively, larger particles could also be flocs composed of finer matter. In the Upper Estuary, no substantial vertical variability is present during the ice-free season and in the zone of maximum turbidity during the ice-covered season due to vertical mixing. The mineralogical and elemental geochemical composition of the suspended detrital particles during ice-covered conditions was similar throughout the estuary and indicated a primary origin from the Canadian Shield with the Appalachian province as a secondary source. While the PSD variability between the two contrasting environmental periods was greater than the spatial variability, this was not the case for the mineralogical and elemental geochemical composition which was similar both spatially and temporally. These results provide new information on the dynamics of suspended matter for a large estuarine and subarctic environment.

加拿大东部的圣劳伦斯河口（SLE）是一个充满活力的沿海环境，最近没有完成有关颗粒成分和尺寸分布的描述。在这项研究中，我们表征了 SLE 中悬浮颗粒物的垂直和水平粒度分布 (PSD)，并评估了其在无冰（2010 年 5 月）和有冰（2019 年 2 月）条件下的可变性。结果表明，在下河口沉积的重要性是粗颗粒，大于$63\mathrm{\mu }\mathrm{米}$, 2010 年 5 月与粒子之间 $4\mathrm{\mu }\mathrm{米}$ 和 $63\mathrm{\mu }\mathrm{米}$2019 年 2 月的出现少于上河口。在下河口，冰覆盖条件下的粗颗粒数密度高于无冰条件，这可能是由于冰运输和受管制河流较高的悬浮物负荷。或者，较大的颗粒也可以是由较细的物质组成的絮凝物。在上河口，由于垂直混合，在无冰季节和在冰覆盖季节的最大浊度区不存在显着的垂直变化。在冰覆盖条件下悬浮碎屑颗粒的矿物学和元素地球化学组成在整个河口是相似的，表明主要来自加拿大地盾，而阿巴拉契亚省是次要来源。虽然两个对比环境时期之间的 PSD 变异性大于空间变异性，但对于在空间和时间上都相似的矿物和元素地球化学组成而言，情况并非如此。这些结果提供了关于大型河口和亚北极环境中悬浮物质动力学的新信息。