『Abstract
　Temporal variations in the iron isotopic composition, δ⁵⁶Fe between -0.13‰ and 0.31‰, have been measured in the suspended fraction in a Boreal river. The major mechanism behind these variations is temporal mixing between two types of particles - colloids, Fe-oxyhydroxides and Fe-C colloids. Data in this study indicate that these two types of colloids have different Fe-isotope composition. The Fe-C colloid has a negative δ⁵⁶Fe value whereas the Fe-oxyhydroxide colloid is enriched in ⁵⁶Fe.
　These two types of colloidal matter have different hydrogeochemical origin. The Fe-C colloid reaches the river during storm events when the upper sections of the soil profile (O and E horizons) are flooded by a rising water table. Colloidal Fe-oxyhydroxides reach the river via inflow and subsequent oxidation of groundwater enriched in dissolved Fe(II).

Keywords: Fe isotopes; Kalix River; suspended matter; Fe-colloids; temporal variation』

1. Introduction
2. Sampling
3. Analytical methods
4. Results and discussion
　4.1. The origin and influence of Fe-oxyhydroxide particulate-colloidal matter
　4.2. The influence of detrital particles on the δ⁵⁶Fe value in the suspended fraction
　4.3. The origin and influence of Fe-C colloids
　4.4. The influence of precipitation of dissolved Mn and the formation of Mn-rich particles in the river
　4.5. Concluding remarks
Acknowledgements
References