Arsenic speciation and turnover in intact organic soil mesocosms during experimental drought and rewetting

Blodau, Christian; Fulda, Beate; Bauer, Markus; Knorr, Klaus‐Holger

doi:10.1016/j.gca.2008.04.040

Cited by 58 publications

(52 citation statements)

References 56 publications

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“…On the other hand there was a strong positive correlation of DOC and iron in pore water, groundwater, and surface water. The detailed pore water investigations of this and former studies (Knorr et al, 2009;Blodau et al, 2008) support the hypothesis, that DOC was predominantly released during phases of iron reducing activity (e.g., Fig. 5).…”

Section: Pore Water Biogeochemistry and Associated Doc Dynamicssupporting

confidence: 83%

“…An enrichment of iron at the transition from anoxic to oxic conditions was also observed for the capillary fringe of wetlands (Küsel et al, 2008;Knorr et al, 2009;Biester et al, 2012). Moreover, an expected stoichiometric ratio of such a flocculation product, with iron to carbon ranging from 0.05 to 0.07 would coincide well with iron to carbon ratios in the peat at capillary fringe at this particular site (based on data from Blodau et al, 2008;Goldberg et al, 2008). Iron was also found to be the most prominent metal cation present in the peat besides iron (Knorr, 2010, unpublished).…”

Section: Processes At the Wetland-stream Interfacesupporting

confidence: 54%

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DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

2013

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Dissolved organic carbon (DOC) exports from many catchments in Europe and North-America are steadily increasing. Several studies have sought to explain this observation. As possible causes, a decrease in acid rain or sulfate deposition, concomitant reductions in ionic strength and increasing temperatures were identified. DOC often originates from riparian wetlands; but here, despite higher DOC concentrations, ionic strength in pore waters usually exceeds that in surface waters. In the catchment under study, DOC concentrations were synchronous with dissolved iron concentrations in pore and stream water. This study aims at testing the hypothesis that DOC exports are mediated by iron reduction/oxidation cycles. Following the observed hydrographs, δ<sup>18</sup>O of water and DOC fluorescence, the wetlands were identified as the main source of DOC. Antecedent biogeochemical conditions, i.e., water table levels in the wetlands, influenced the discharge patterns of nitrate, iron and DOC during an event. The correlation of DOC with pH was positive in pore waters, but negative in surface waters; it was negative for DOC with sulfate in pore waters, but only weak in surface waters. Though, the positive correlation of DOC with iron was universal for pore and surface water. The decline of DOC and iron concentrations in transition from anoxic wetland pore water to oxic stream water suggests a flocculation of DOC with oxidising iron, leading to a drop in pH in the stream during high DOC fluxes. The pore water did not per se differ in pH. There is, thus, a need to consider processes more thoroughly of DOC mobilisation in wetlands when interpreting DOC exports from catchments. The coupling of DOC with iron fluxes suggested that increased DOC exports could at least, in part, be caused by increasing activities in iron reduction, possibly due to increases in temperature, increasing wetness of riparian wetlands, or by a shift from sulfate dominated to iron reduction dominated biogeochemical regimes

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Section: Pore Water Biogeochemistry and Associated Doc Dynamicssupporting

confidence: 83%

Section: Processes At the Wetland-stream Interfacesupporting

confidence: 54%

DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

2013

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“…One more factor should also be mentioned as possible explanation to the fact that As concentrations in pore water of BL-treated, waterlogged, ZS soils remained high for a long time. Apart from the reductive dissolution of adsorbing soil phases, i.e., oxides (Bauer and Blodau 2006;Blodau et al 2008;Wenzel 2013;Shaheen et al 2014), that takes place under anoxic conditions, also As (V) gets reduced to As (III), a species that has much lower affinity to soil sorption sites. Moreover, the sorption of As (III) is believed to decrease with increasing pH in the pH range 8-10 (Casiot et al 2007).…”

Section: Discussionmentioning

confidence: 99%

Transformation of beech forest litter as a factor that triggers arsenic solubility in soils developed on historical mine dumps

et al. 2018

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Purpose Soils that develop on the dumps in historical arsenic mining sites contain high concentrations of As thus constituting a serious environmental risk. This study was aimed to examine the changes in arsenic solubility in mine soils as induced by organic matter introduced with forest litter. Materials and methods Four large samples of initially developed soils were collected from the dumps remaining in former mining sites and were incubated for 90 days at various moistures: 80% of maximum water holding capacity and 100% (flooded conditions), with and without addition of beech forest litter (BL), 50 g/kg. Soils contained up to 5.0% As. Soil pore water was collected periodically with MacroRhizon suction samplers and examined on As, Mn, and Fe concentrations, pH, Eh, and dissolved organic carbon (DOC). The properties of dissolved organic matter were characterized by UV-VIS spectroscopic parameters A4/A6 and SUVA 254 . Results and discussion Application of BL resulted in an intensive release of As from soils, particularly at 100% moisture. As concentrations in soil pore water increased strongly during the first 2 or 4 weeks of incubation and then started to decrease in all cases, except for one flooded soil. As was released particularly intensively from carbonate-containing soils. The mechanisms of As mobilization, including reductive dissolution of Mn and Fe oxides and the competition with DOC for sorption sites on the oxides, were discussed as related to soil properties. Pore water concentrations of DOC were increasing at the beginning of incubation and started to decrease after two or four weeks. Spectroscopic parameters of dissolved organic matter in ZS soils indicated increasing aromaticity and progress of humification. Conclusions Forest litter introduced to mine dump soils causes a mobilization of As into soil pore water. This effect, particularly strong in carbonate-rich soils, is apparently related to high concentrations of DOC and usually declines with time, which may be explained by the progress in humification. The relationships between DOC properties and As speciation in soil pore water should be dissected for better interpretation of experimental results.

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“…The degree of nutrient release will be strongly dependent on the elemental composition of the soil (peat) column profile. The majority of relevant studies of peatlands have been devoted to cycles of CO 2 , CH 4 and nutrients (Freeman et al, 2001;Macrae et al, 2012;Blodau, 2002;Blodau et al, 2004;Knorr et al, 2008), but there are only a few studies on trace elements and metal biogeochemistry related to the change in the hydrological conditions of the peat (cf., Tipping et al, 2003;Blodau et al, 2008;Szkokan-Emilson et al, 2013). The application of the available results to a prediction of the effect of peat thaw on the change in the water surface chemistry and element delivery to the ocean from the western Siberian wetlands is hindered by the lack of knowledge on the trace element concentration in the peat cores, related to specific microenvironments of the wetlands.…”

Section: Introductionmentioning

confidence: 99%

Elemental composition of peat profiles in western Siberia: Effect of the micro-landscape, latitude position and permafrost coverage

Степанова

Pokrovsky

Viers

et al. 2015

Applied Geochemistry

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Arsenic speciation and turnover in intact organic soil mesocosms during experimental drought and rewetting

Cited by 58 publications

References 56 publications

DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

Transformation of beech forest litter as a factor that triggers arsenic solubility in soils developed on historical mine dumps

Elemental composition of peat profiles in western Siberia: Effect of the micro-landscape, latitude position and permafrost coverage

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