Abstract/Summary

Floodplains downstream of urban catchments are sinks for potentially toxic Trace Elements (TEs). An intensification of the hydrological cycle and changing land use will result in floodplains becoming inundated for longer durations in the future. We collected intact soil cores from a floodplain meadow downstream of an urban catchment and subjected them to an inundation/drainage cycle in the laboratory to investigate the effect of flood duration on TE concentrations in the soil porewater. The porewater concentrations of Ni, Cr and Zn increased, while Cu and Pb decreased, with flood duration. All the Cr present in porewaters was identified as Cr(III). Cu concentrations increased after drainage, but Pb mobility remained suppressed. Both pH and dissolved organic carbon (DOC) increased with flood duration but were lower in treatments that were drained for the longest (which were also the treatments flooded for the shortest duration). The porewater concentrations of Cr and Ni decreased after drainage to levels below that observed prior to inundation, mirroring the DOC concentrations. We conclude that the duration of floodplain inundation does have an influence on the environmental fate of TEs but that flooding does not influence all TEs in the same way. The implications of an intensification of the hydrological cycle over the coming decades are that floodplains may become a source of some TEs to aquatic and terrestrial ecosystems.