Abstract
The wetland Argialbolls pedon was chosen to investigate the effects of pedogenic processes and anthropogenic activities on the vertical distribution of lead and mercury concentration and to assess the potential use of soil as an archive of atmospheric Pb and Hg pollution. The soil was sampled from 5 cm from the surface to a depth of 90 cm at two locations in the Sanjiang Plain in northeastern China. The soil was analyzed for pH, soil organic matter (SOM), Fe, Mn, and Al. The results indicate that the SOM concentration gradually decreased with depth, while Fe and Mn were reductively leached from the upper horizons and accumulated significantly in the lower argillic horizons. Atmospheric Pb and Hg deposition and their redistribution during the pedogenic process led to a unique vertical distribution in the wetland Argialbolls. Overall, Pb was leached from the upper horizons and then accumulated in the lower argillic horizons. However, the Hg concentration decreased with depth, following the SOM distribution. The Pb concentration was significantly correlated to the Fe and Mn concentrations in the Argialbolls profiles, while the Hg concentration was significantly correlated with SOM. Post-depositional mobility along the wetland Argialbolls profile is higher for Pb and low for Hg. Therefore, the Argialbolls profile does not provide an accurate reconstruction of atmospheric Pb deposition, but might provide an accurate reconstruction of net atmospheric Hg deposition.
Highlights
Wetlands are areas that are sporadically or permanently flooded; and develop anoxic conditions and subsequent soil bioreduction [1]
In the upper horizons of the wetland soil (0 to 55 cm depth for core 1 and 0 to 35 cm depth for core 2, where soil organic matter (SOM) generally accumulated), which were low in Fe and Mn oxides, Fe and Mn concentrations were only approximately 2.2 to 2.8% and 145 to 281 mg kg-1, respectively, lower than the median concentrations of Fe and Mn for worldwide soils [23]
We found that SOM has significantly accumulated in the upper horizons of the wetland Argialbolls, while Fe and Mn have been significantly leached from the upper horizons and accumulated in the low horizons
Summary
Wetlands are areas that are sporadically or permanently flooded; and develop anoxic conditions and subsequent soil bioreduction [1]. Trace metal/metalloid mobility depends on variables such as redox potential (Eh) and pH, organic matter, and Fe/Mn oxides content [2]. Oxidative sediment conditions generally stabilize trace metals in Fe/Mn oxides, while reduction and the concomitant desorption of organic matter release trace metals/metalloids into the soil solution with subsequent downward leaching [2,3,4]. Vertical distributions of trace metals in soils depend on both pedogenic processes and the influences of anthropogenic activity.
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