February 2016 Vol. 4 No.2

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Shaheen SM
Elbasiouny H

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Original Research Article

Spatial distribution and mobilization of heavy metals in different wetland soils and sediments in north of the Nile Delta as affected by wetting and drying conditions

Sabry M. Shaheen¹, Mohamed S. Shams¹, Shaban M. Ibrahim¹, Fathy A. Elbehiry^1* and Heba Elbasiouny²

¹Department of Soil and Water Sciences, Faculty of Agriculture, University of Kafrelsheikh, 33516- Kafr El-Sheikh, Egypt.
²Biological and Environmental Sciences Department, Faculty of Home Economic, Al-Azhar University, 31511 Tanta, Egypt

*Corresponding Author’s E-mail Fathyelbehiry@gmail.com

Accepted February 14, 2016

Abstract

Heavy metal contamination of soils has been a long-standing environmental problem in many parts of the world, and poses enormous threats to ecosystem and human health. Spatial distribution and mobilization of heavy metals in wetlands is crucial to assessing environmental risks from contaminated soils and sediments. In this study, the spatial variability of total and mobile concentrations of copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn) in soils and sediments of three different wetland soils and sediments in north of the Nile Delta, Egypt were assessed. Furthermore, the impact of wetting and drying conditions on the total and mobilization of the metals in the different wetlands were investigated. Soil and sediment samples were collected under dry and wet conditions from three different wetland ecosystems i.e., rice paddy soils (RS), fish farms sediments (FFS), and Burullus Lake sediments (BLS). Total (Aqua regia) and mobile (ammonium bicarbonate–diethylene triamine penta acetic acid) concentrations of the metals were extracted. Geo-statistical analytical technique (ArcGIS 10) was used to interpolate data for mapping spatial variability of the metals in the studied area. The soils were alkaline and poor in organic carbon content. The texture of the RS and FFS was dominated by silt and clay, while the BLS was characterized by a relatively high content of sand followed by silt, and clay respectively. The total metal concentrations (mg kg^-1) ranged from 4.0 to 76.5 for Cu, 3100.0 to 80350.0 for Fe, 86.8 to 1107.0 for Mn, 0.2 to 3.8 for Pb, and from 14.3 to 140.0 for Zn. The concentrations (mg kg^-1) of mobile Cu, Fe, Mn, Pb, and Zn varied from 0.2 to 16.0, 8.0 to 123.1, 0.3 to 4.8, 0.2 to 3.8, and from 0.04 to 4.5, respectively. Mobilization of Cu decreased significantly under wetting/reducing conditions in in the three wetlands probably caused by sulfide precipitation and as a result of the reduction of Cu²⁺ to Cu¹⁺. Mobilization of Fe and Mn significantly increased under wetting conditions in the three wetlands, which might be explained by reduction of Fe-Mn (hydr)oxides to soluble Fe²⁺ and Mn²⁺. Mobilization of Pb and Zn showed an inconsistent trend under drying and wetting conditions in the wetlands. Our findings suggest that the wetland types and flood-dry conditions affect metal mobilization in the soils and sediments. These results are an aid to provide information’s aiming to develop a reliable risk assessment and the sustainable management of those wetland ecosystems.

Key words: Metal solubility, Redox potential, Risk assessment, Trace elements, Wetlands