Effect of Fluctuating Hydrological Conditions on the Mobility of Heavy Metals in Soils of a Freshwater Estuary in the Netherlands

The objective of this study was to measure the mobility of heavy metals in freshwater estuary soils that are seasonally inundated and to characterize the distribution of sulfide precipitates in these soils. Precipitation and dissolution of labile sulfides may account for changing pore water concentrations of heavy metals in freshwater wetland soils that are subject to temporary flooding or fluctuating groundwater levels. The presence of authigenic zinc- and iron-(mono)sulfide in this type of soils during periods with a high groundwater level was demonstrated by electron microprobe analyses. Because sulfide precipitates are strongly associated with root remnants, fresh soil organic material may be an important intermediary in the sulfur cycling and, consequently, in the behavior of heavy metals in these freshwater soils. Oxidation of labile sulfides may be partly responsible for the increased zinc and sulfate concentrations in the pore water during periods with low groundwater levels. Heavy metals may also be mobilized by degradation of their host phase organic matter during periods with high biodegradation.