Colloids (1-1,000 nm) are important phosphorus (P) carriers in agricultural soils. However, most studies are based on colloids from soil waters extracted in the laboratory, thus limiting the understanding of the natural transfer of colloidal P along the soil-to-stream continuum. Here, we conducted a field study on the colloidal P in both natural soil waters and their adjacent stream waters in an agricultural catchment (Kervidy-Naizin, western France). Soil waters (10-15 cm, Albeluvisol) of two riparian wetlands and the adjacent stream waters were sampled monthly during wet seasons of the 2015-2016 hydrological year (seven dates in total). Ultrafiltration at three pore sizes (5 kDa, 30 kDa, and 0.45 µm) was combined with inductively coupled plasma mass spectrometry (ICP-MS) to investigate variability in colloidal P concentration and its concomitant elemental composition. Results showed that colloidal P represented, on average, 45 and 30% of the total P (<0.45 µm) in the soil waters and stream waters, respectively. We found that colloidal P was preferentially associated with (a) organic carbon in the fine nanoparticle fraction (5-30 kDa) and (b) iron-oxyhydroxides and organic carbon in the coarse colloidal fraction (30 kDa-0.45 µm). The results confirmed that colloidal P is an important component of total P in both soil waters and stream waters under field conditions, suggesting that riparian wetlands are hotspot zones for the production of colloidal P at the catchment scale, which has the potential to be transported to adjacent streams.

中文翻译：

---

胶体作为农业集水区天然土壤/溪流水中重要磷载体的证据

胶体 (1-1,000 nm) 是农业土壤中重要的磷 (P) 载体。然而，大多数研究都是基于从实验室提取的土壤水中的胶体，因此限制了对胶体 P 沿土壤到河流连续体的自然转移的理解。在这里，我们对农业集水区（法国西部 Kervidy-Naizin）中天然土壤水及其邻近河流水中的胶体磷进行了实地研究。在 2015-2016 水文年（共 7 个日期）的雨季期间，每月对两个河岸湿地和相邻河流水域的土壤水（10-15 cm，Albeluvisol）进行采样。三种孔径（5 kDa、30 kDa 和 0. 45 µm) 与电感耦合等离子体质谱 (ICP-MS) 相结合，以研究胶体 P 浓度及其伴随元素组成的变化。结果表明，胶体磷平均分别占土壤水和溪水中总磷（<0.45 µm）的 45% 和 30%。我们发现胶体 P 优先与 (a) 细纳米颗粒部分 (5-30 kDa) 中的有机碳和 (b) 粗胶体部分 (30 kDa-0.45 µm) 中的铁羟基氧化物和有机碳相关。结果证实，在田间条件下，胶体磷是土壤水和溪水中总磷的重要组成部分，表明河岸湿地是流域规模胶体磷生产的热点区域，有可能被输送到相邻的溪流。