Effect of Water Table Level on Metal Mobility at Different Depths in Wetland Soils of the Scheldt Estuary (Belgium)

Abstract

An experiment was set up to assess the factors affecting metal mobility in five wetland soils of the Scheldt estuary at different sampling depths when subjecting the soils to various water table levels. Pore water metal concentrations were monitored for 10 months at four sampling depths (10, 30, 60 and 90 cm) upon adjusting the water table level to 0, 40 and 80 cm below the surface of the soils. Nickel (Ni) release is facilitated by reductive conditions. These reductive conditions mainly occur below the water table. The fate of chromium (Cr) under reductive conditions seems to be promoted by the presence of dissolved organic matter. However, Cr fate seems to be inconsistent between the soils, as it is affected by a series of counteracting mechanisms. Copper (Cu), zinc (Zn) and especially cadmium (Cd) are all primarily released above the water table under high salinity conditions. These elements are also released below or just above the water table when organic matter is being decomposed, resulting in calcium (Ca), manganese (Mn), Ni and/or iron (Fe) release upon CO 2 accumulation and Fe/Mn oxide reduction, without being accompanied by sulphide production. Their mobility is low under reducing conditions, i.e. in the presence of sulphides, whereas the complexation by soluble organic matter especially seems to promote Cu mobility.

Controlled variation of redox conditions in a floodplain soil: Impact on metal mobilization and biomethylation of arsenic and antimony

“…3) could be caused by sulphide precipitation, as also found by other authors (Carbonell et al, 1999;Koretsky et al, 2007;Schröder et al, 2008;Van der Geest and Paumen, 2008;Du Laing et al, 2007, 2009a. The dark colour and the typical odour suggest that sulphides were formed in the MCs at reducing conditions in our experiment.…”

“…On the other hand, elements such as As can also be immobilized due to co-precipitation with or adsorption to Fe and Mn (hydr)oxides under oxic conditions. Moreover, divalent metal immobilization can be induced under anoxic conditions due to the presence of hardly soluble sulphides (Van Griethuysen et al, 2005;Du Laing et al, 2007, 2009a. Brümmer (1974) mentioned that sulphides are generated from sulphates below E H −50 mV at pH 7 (corresponds to E H 68 mV at pH 5).…”

“…In addition to the reduction of Fe and Mn (hydr)oxides and concurrent release of associated As, reduction of arsenate to arsenite can lead to an increased As mobility under reducing conditions (Masscheleyn et al, 1991;Mitsunobu et al, 2006;Du Laing et al, 2009a). Antimony (Sb), another metalloid in the same periodic group like arsenic, was found to be more stable, and therefore less available, than As in soils, even under reducing conditions (Thayer, 2002;Mitsunobu et al, 2006).…”

Role of rhizosphere and soil properties for the phytomanagement of a salt marsh polluted by mining wastes

“…For Mn and Zn this ratio ranged between 25 and 45 %, while for Cu and Pb it was of around 20 %. Previous works have shown that Cd and to a lesser extent Cu and Zn are more available under high-salinity conditions (Du Laing et al 2009a). …”

Delayed immobilization of heavy metals in soils and sediments under reducing and anaerobic conditions; consequences for flooding and storage

“…Only few studies report on the effects of reduction with respect to metal mobility and emissions to surrounding groundwater systems. There are some useful studies that include field or laboratory measurements (e.g., Han et al 2001;Burton et al 2008;Du Laing et al 2009), and also modelling studies that use a thermodynamic approach have been reported (e.g., De Rooij and Gerrits 1995; Griffioen et al 2006). However, the outcomes of the measurements in the field and modelling studies are not always in agreement, indicating that the uncertainty around soil inundation or sediment storage is still large.…”