Colloid-associated export of arsenic in stream water during stormflow events

Significant correlations between arsenic concentrations and those of iron and natural organic matter (NOM) have been found in run-off from wetlands. This has been suggested to be a result of mobilization of arsenic-NOM colloids. The aim of this study was therefore to elucidate the possible association of iron and arsenic with colloids in surface water from a small, forested catchment area. The impacts that groundwater levels prior to stormflow events and the chemistry of the hydraulically active soil layers have on the release and formation of colloids, such as NOM and iron (oxy)hydroxide colloids, were also investigated.At baseflow, the NOM, iron, and arsenic concentrations in the stream water were relatively low (