Colloidal and nanoparticle transport in a temperate river system: Hydrological controls and geochemical signatures in the Seine Basin

Colloids, including nanoparticles, play a significant role as contaminant carriers in surface waters due to their high sorption capacity for both metals and organic pollutants. However, the impact of hydrological regimes and land use patterns on colloid distribution and flux is not well understood, particularly at a large scale where major rivers receive cumulative inputs from numerous tributaries and a variety of land uses. The dynamics of colloids were explored in the Seine River and its tributaries, the Marne and the Oise Rivers, by single particle time of flight inductively coupled plasma mass spectrometry (spICP-ToF-MS). In addition to direct water analysis, Dreissena polymorpha was investigated for its potential as a colloid bioindicator, with promising results. Colloid concentration in river water appeared to be controlled mainly by the water discharge. Similar colloid populations and water chemistry have allowed conservative particle mixing between the Seine and its tributaries without undergoing significant aggregation, dissolution, or transformation. The impact of sporadic events such as flooding was also discussed. The comparable composition of suspended matter and colloids in the Seine River basin has suggested that colloids could be a finer subset of sediments, formed through similar processes. The export of colloids was significantly influenced by land use and erosion patterns, as well as agricultural activities. The rates of colloid export were estimated and aligned with the findings of previous studies despite differences between the studied areas.