Distribution and Accumulation of Arsenic among Solid, Aqueous, and Plant Phases in the Guandu Wetland of Taiwan
Date Issued
2012
Date
2012
Author(s)
Chen, Yen-Yu
Abstract
The purpose of this study was to determine the distribution and accumulation of arsenic (As) among aqueous, solid, and plant phases in the Guandu Wetland of Taiwan. Chemical compounds and isotopic compositions in porewater samples of dry season and mineral compositions in the sediment samples of wet season were analyzed to characterize the As distribution with depth. Arsenic concentrations in plant samples were analyzed to assess the translocation factor (TF) and bioconcentration factor (BCF), and to understand the distribution and accumulation of As in the plant, solid, and liquid phases. Chemical compounds concentration were applied the factor and cluster analyses in porewater samples to delineate the vertical profile of oxidation zone (shallow layer), buffer zone (mid layer), and reduction zone (deep layer); and to elucidate the mechanism of As possible mobile in each zone. As-bearing minerals were not found in all sediment samples by using X-ray diffraction (XRD). However, the result of As species transformation indicated mild As(V) (arsenate) shifting to As(III) (arsenite) in the deep layer by X-ray absorption near-edge structure (XANES) of X-ray absorption spectra (XAS). The results implicate that reduction gradient was tended to increase with depth in this wetland systems. The cluster analysis was applied to determine the boundary of shallow zone and deep zone using isotopic compositions data of the sediment samples. The high values of sulfur isotope fractionation factor (ε) occurred in deep zone which was caused by the bacterial sulfate reduction. The results of sulfur isotope indicate that the source of water in shallow zone and deep zone are mainly from mixing of the seawater/surface water and Batou groundwater, respectively. Kandelia obovata is one of the most dominant plant species in mangrove ecosystems of the study area. In this study, As concentrations in plants (23.69 mg/kg) were higher than in the surrounding water (0.0018 mg/L) and soils (17.24 mg/kg). The order of arsenic concentration in various plant tissues at maturity was as follows: roots (19.74 mg/kg) > stems (1.76 mg/kg) > leaves (1.71 mg/kg) > seedlings (0.48 mg/kg), suggesting a high accumulation in the roots. The low translocation factors (TFstems/roots= 0.088, TFleaves/roots= 0.088 and TFseedlings/roots= 0.024) indicate that the translocation of As in various plant tissues is extremely low depending on salt tolerance mechanism of K. obovata. The significant tidal effects result in high BCFplant/water that the As concentrations in wetland water is diluted by seawater. A high BCFplant/soil (BCFplant/soil> 1) between plants and soil indicates that the uptake and bioaccumulation of As in K. obovata are significant; therefore, K. obovata is an As accumulator. The uptake mechanism of plants might depend on the formation of As-contained iron oxides in the root zone, causing the uptake of As in plants to be from soil.
Subjects
Arsenic
Guandu Wetland
X-ray Absorption Near-edge Structure
Surfur Isotope
Translocation Factor
Bioconcentration Factor
SDGs
Type
thesis
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