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Jaffe, Peter R.,Park,Seok S. 이화여자대학교 환경문제연구소 1997 이화환경연구 Vol.1 No.-
A numerical model was developed to simulate the vertical profile of the redox potential in the benthic sediments. The benthic sediments were subdivided vertically into six zones, each with different microbial and chemical reactions: aerobic respiration, denhtrification, managanese reducation, iron reducation, sulfate reduction, and methanogenesis. Microbial degradation of organic matter and subsequent chemical reactions of interest were formulated using stoichiometric relationships and considering the vertical advective/dispersive transport in the sediments. The kinetics of utilization of the different electron acceptors during the biodegradation of the organic matter were described by Monod-type formulation. Eleven coupled differential equations were derived and solved interactively utilizing an iterative multistep numerical method. The model input parameters include the rate of solid deposition, concentrations of electron acceptors in the water overlaying the sediments, activities of the benthic fauna, and molecular diffusion. The model simulates the redox potential as well as eleven chemical constituents in the sediments, three solids(particulate organic matter, manganese oxide, and iron oxide), and eight dissolved species(oxygen, nitrate, sulfate, ammonia, dissolved manganese, dissolved iron, sulfide and methane). The model demonstrated that accurate estimates of the flux of primary electron acceptors and donors from the overlying water to the benthic sediments is important to determine the redox conditions in sediments. Bioturbation and the rate of pore-water infiltration are processes that have a major influence on this flux.
Zhang, Zheyun,Moon, Hee Sun,Myneni, Satish C.B.,Jaffé,, Peter R. Elsevier 2017 Journal of hazardous materials Vol.321 No.-
<P><B>Abstract</B></P> <P>Microbial redox transformations of arsenic (As) are coupled to dissimilatory iron and sulfate reduction in the wetlands, however, the processes involved are complex and poorly defined. In this study, we investigated the effect of dissimilatory iron and sulfate reduction on As dynamics in the wetland rhizosphere and its bioaccumulation in plants using greenhouse mesocosms. Results show that high Fe (50μM ferrihydrite/g solid medium) and SO<SUB>4</SUB> <SUP>2−</SUP> (5mM) treatments are most favorable for As sequestration in the presence of wetland plants (<I>Scirpus actus</I>), probably because root exudates facilitate the microbial reduction of Fe(III), SO<SUB>4</SUB> <SUP>2−</SUP>, and As(V) to sequester As(III) by incorporation into iron sulfides and/or plant uptake. As retention in the solid medium and accumulation in plants were mainly controlled by SO<SUB>4</SUB> <SUP>2−</SUP> rather than Fe levels. Compared to the low SO<SUB>4</SUB> <SUP>2−</SUP> (0.1mM) treatment, high SO<SUB>4</SUB> <SUP>2−</SUP> resulted in 2 times more As sequestered in the solid medium, 30 times more As in roots, and 49% less As in leaves. An As speciation analysis in pore water indicated that 19% more dissolved As was reduced under high SO<SUB>4</SUB> <SUP>2−</SUP> than low SO<SUB>4</SUB> <SUP>2−</SUP> levels, which is consistent with the fact that more dissimilatory arsenate-respiring bacteria were found under high SO<SUB>4</SUB> <SUP>2−</SUP> levels.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High Fe and SO<SUB>4</SUB> <SUP>2−</SUP> treatment is most favorable for As sequestration in soils in the presence of wetland plants. </LI> <LI> As retention in soil and accumulation in plants was mainly controlled by SO<SUB>4</SUB> <SUP>2−</SUP> rather than Fe levels. </LI> <LI> High SO<SUB>4</SUB> <SUP>2−</SUP> can stimulate the growth of As dissimilatory reduction bacteria, leading to more As(V) reduction to As(III). </LI> </UL> </P>
Phosphate enhanced abiotic and biotic arsenic mobilization in the wetland rhizosphere
Zhang, Zheyun,Moon, Hee Sun,Myneni, Satish C.B.,Jaffé,, Peter R. Elsevier 2017 CHEMOSPHERE - Vol.187 No.-
<P><B>Abstract</B></P> <P>Although abiotic process of competitive sorption between phosphate (P) and arsenate (As(V)), especially onto iron oxides, are well understood, P-mediated biotic processes of Fe and As redox transformation contributing to As mobilization and speciation in wetlands remain poorly defined. To gain new insights into the effects of P on As mobility, speciation, and bioavailability in wetlands, well-controlled greenhouse experiments were conducted. As expected, increased P levels contributed to more As desorption, but more interestingly the interactions between P and wetland plants played a synergistic role in the microbially-mediated As mobilization and enhanced As uptake by plants. High levels of P promoted plant growth and the exudation of labile organic carbon from roots, enhancing the growth of heterotrophic bacteria, including As and Fe reducers. This in turn resulted in both, more As desorption into solution due to reductive iron dissolution, and a higher fraction of the dissolved As in the form of As(III) due to the higher number of As(V) reducers. Consistent with the dissolved As results, arsenic-XANES spectra from solid medium samples demonstrated that more As was sequestered in the rhizosphere as As(III) in the presence of high P levels than for low P levels. Hence, increased P loading to wetlands stimulates both abiotic and biotic processes in the wetland rhizosphere, resulting in more As mobilization, more As reduction, as well as more As uptake by plants. These interactions are important to be taken into account in As fate and transport models in wetlands and management of wetlands containing As.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Increased PO<SUB>4</SUB> <SUP>3−</SUP> loading to wetlands stimulates abiotic and biotic As mobilization. </LI> <LI> Increased PO<SUB>4</SUB> <SUP>3−</SUP> loading results in more As-reducing bacteria in wetland sediments. </LI> <LI> Increased PO<SUB>4</SUB> <SUP>3−</SUP> loading results in more As reduction in wetland sediments. </LI> <LI> Increased PO<SUB>4</SUB> <SUP>3−</SUP> loading results in more As uptake by wetland plants. </LI> <LI> Increased PO<SUB>4</SUB> <SUP>3−</SUP> loading to wetlands results in lower ORP and less Fe reduction. </LI> </UL> </P>