Properties of Fe-Organic Matter Associations via Coprecipitation versus Adsorption

Chen, Chunmei; Dynes, James J.; Wang, Jian; Sparks, Donald L.

doi:10.1021/es503669u

Cited by 465 publications

(528 citation statements)

References 51 publications

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“…The association between OC and Fe R occurs through simple sorption onto discrete iron oxide particles or the iron oxide surfaces of aluminosilicate minerals, or OC can bind to Fe R through the coprecipitation of OC and Fe R in the sediments [ Eusterhues et al ., ; Lalonde et al ., ; Chen et al ., ]. Coprecipitation occurs when reduced iron migrating through anoxic pore waters is oxidized in the presence of dissolved OC at the oxic/anoxic interface [ Riedel et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Enhanced terrestrial carbon preservation promoted by reactive iron in deltaic sediments

Shields

Bianchi

Gélinas

et al. 2016

Geophysical Research Letters

106

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We examined the role of reactive iron (FeR) in preserving organic carbon (OC) across a subaerial chronosequence of the Wax Lake Delta, a prograding delta within the Mississippi River Delta complex. We found that ~15.0% of the OC was bound to FeR, and the dominant binding mechanisms varied from adsorption in the youngest subaerial region to coprecipitation at the older, vegetated sites. The δ13C of the iron‐associated OC was more negative than the total OC (mean = −2.6‰), indicating greater preference for terrestrial material and/or compounds with more negative δ13C values. However, only the adsorbed OC displayed preferential binding of lignin phenols. We estimate that ~8% of the OC initially deposited in deltaic systems is bound to FeR (equivalent to 6 × 1012 gC yr−1), and this percentage increases postdepositionally, as coprecipitation of FeR and OC allows for an even greater amount of OC to be bound to FeR.

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Section: Resultsmentioning

confidence: 99%

Enhanced terrestrial carbon preservation promoted by reactive iron in deltaic sediments

Shields

Bianchi

Gélinas

et al. 2016

Geophysical Research Letters

106

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“…2), it is reasonable to postulate that there is a lower lignin phenol content in the Sphagnum -dominated peat per unit of SOC relative to vascular plant-dominated soils. Varied lignin phenol contents may influence the speciation and concentration of Fe through sorption and complexation processes2758 and thereby regulate the balance between O 2 and Fe(II) effects on phenol oxidative activities. Alternatively, the majority (five out of seven) of the studies reporting a negative enzyme response to increasing O 2 were based on mineral soils or organic horizons overlaying mineral soils (as is this study).…”

Section: Discussionmentioning

confidence: 99%

“…4c). Alternatively, Chen et al 58. showed that a pH decline may increase the amount of OM adsorbed to ferrihydrite.…”

Section: Discussionmentioning

confidence: 99%

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Iron-mediated soil carbon response to water-table decline in an alpine wetland

et al. 2017

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The tremendous reservoir of soil organic carbon (SOC) in wetlands is being threatened by water-table decline (WTD) globally. However, the SOC response to WTD remains highly uncertain. Here we examine the under-investigated role of iron (Fe) in mediating soil enzyme activity and lignin stabilization in a mesocosm WTD experiment in an alpine wetland. In contrast to the classic ‘enzyme latch’ theory, phenol oxidative activity is mainly controlled by ferrous iron [Fe(II)] and declines with WTD, leading to an accumulation of dissolvable aromatics and a reduced activity of hydrolytic enzyme. Furthermore, using dithionite to remove Fe oxides, we observe a significant increase of Fe-protected lignin phenols in the air-exposed soils. Fe oxidation hence acts as an ‘iron gate’ against the ‘enzyme latch’ in regulating wetland SOC dynamics under oxygen exposure. This newly recognized mechanism may be key to predicting wetland soil carbon storage with intensified WTD in a changing climate.

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“…In-teractions of DOM with dissolved polyvalent cations (e.g., Fe 3+ and Al 3+ ) may also result in its coagulation and coprecipitation with nucleating metal (oxy)hydroxides (Chen et al, 2014a;Eusterhues et al, 2011). Drying of OM-mineral complexes can affect the mode of interaction.…”

Section: Introductionmentioning

confidence: 99%

Wet–dry cycles impact DOM retention in subsurface soils

2018

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Abstract. Transport and reactivity of carbon in the critical zone are highly controlled by reactions of dissolved organic matter (DOM) with subsurface soils, including adsorption, transformation and exchange. These reactions are dependent on frequent wet-dry cycles common to the unsaturated zone, particularly in semi-arid regions. To test for an effect of wetdry cycles on DOM interaction and stabilization in subsoils, samples were collected from subsurface (Bw) horizons of an Entisol and an Alfisol from the Catalina-Jemez Critical Zone Observatory and sequentially reacted (four batch steps) with DOM extracted from the corresponding soil litter layers. Between each reaction step, soils either were allowed to air dry ("wet-dry" treatment) before introduction of the following DOM solution or were maintained under constant wetness ("continually wet" treatment). Microbial degradation was the dominant mechanism of DOM loss from solution for the Entisol subsoil, which had higher initial organic C content, whereas sorptive retention predominated in the lower C Alfisol subsoil. For a given soil, bulk dissolved organic C losses from solution were similar across treatments. However, a combination of Fourier transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopic analyses revealed that wet-dry treatments enhanced the interactions between carboxyl functional groups and soil particle surfaces. Scanning transmission X-ray microscopy (STXM) data suggested that cation bridging by Ca 2+ was the primary mechanism for carboxyl association with soil surfaces. STXM data also showed that spatial fractionation of adsorbed OM on soil organo-mineral surfaces was diminished relative to what might be inferred from previously published observations pertaining to DOM fractionation on reaction with specimen mineral phases. This study provides direct evidence of the role of wet-dry cycles in affecting sorption reactions of DOM to a complex soil matrix. In the soil environment, where wet-dry cycles occur at different frequencies from site to site and along the soil profile, different interactions between DOM and soil surfaces are expected and need to be considered for the overall assessment of carbon dynamics.

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Properties of Fe-Organic Matter Associations via Coprecipitation versus Adsorption

Cited by 465 publications

References 51 publications

Enhanced terrestrial carbon preservation promoted by reactive iron in deltaic sediments

Enhanced terrestrial carbon preservation promoted by reactive iron in deltaic sediments

Iron-mediated soil carbon response to water-table decline in an alpine wetland

Wet–dry cycles impact DOM retention in subsurface soils

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