The synergistic effect of calcium on organic carbon sequestration to ferrihydrite

Abstract

Sequestration of organic carbon (OC) in environmental systems is critical to mitigating climate change. Organo-mineral associations, especially those with iron (Fe) oxides, drive the chemistry of OC sequestration and stability in soils. Short-range-ordered Fe oxides, such as ferrihydrite, demonstrate a high affinity for OC in binary systems. Calcium commonly co-associates with OC and Fe oxides in soils, though the bonding mechanism (e.g., cation bridging) and implications of the co-association for OC sequestration remain unresolved. We explored the effect of calcium (Ca2+) on the sorption of dissolved OC to 2-line ferrihydrite. Sorption experiments were conducted between leaf litter-extractable OC and ferrihydrite at pH 4 to 9 with different initial C/Fe molar ratios and Ca2+ concentrations. The extent of OC sorption to ferrihydrite in the presence of Ca2+ increased across all tested pH values, especially at pH ≥ 7. Sorbed OC concentration at pH 9 increased from 8.72 ± 0.16 to 13.3 ± 0.20 mmol OC g−1 ferrihydrite between treatments of no added Ca2+ and 30 mM Ca2+ addition. Batch experiments were paired with spectroscopic studies to probe the speciation of sorbed OC and elucidate the sorption mechanism. ATR-FTIR spectroscopy analysis revealed that carboxylic functional moieties were the primary sorbed OC species that were preferentially bound to ferrihydrite and suggested an increase in Fe-carboxylate ligand exchange in the presence of Ca at pH 9. Results from batch to spectroscopic experiments provide significant evidence for the enhancement of dissolved OC sequestration to 2-line ferrihydrite and suggest the formation of Fe–Ca-OC ternary complexes. Findings of this research will inform modeling of environmental C cycling and have the potential to influence strategies for managing land to minimize OM stabilization.Electronic supplementary materialThe online version of this article (10.1186/s12932-018-0049-4) contains supplementary material, which is available to authorized users.

Multi-element effects on arsenate accumulation in a geochemical matrix determined using µ-XRF, µ-XANES and spatial statistics

“…and natural geochemical systems containing similar components, this connection is not straightforward. For example, research on simple binary mixtures of model components of Fe and Al (hydr)oxides (Antelo et al, 2015;Khare et al, 2005;Murray & Hesterberg, 2006), minerals and organic matter (Alcacio et al, 2001;Chen & Sparks, 2018;Davis, 1984;Hu et al, 2018;Mikutta & Kretzschmar, 2011;Otero-Fariñ a et al, 2017;Sowers et al, 2018), and minerals and microbes (Du et al, 2017;Gadd, 2010) all show non-additive effects on the binding of phosphate or arsenate. Such nonadditive effects could limit the transferability of trace-element binding mechanisms from model systems to soils and other multicomponent geochemical matrices, and confound our ability to measure specific matrix components that are responsible for trace-element binding, redox transformations and other reactions.…”

Conventional analysis methods underestimate the plant-available pools of calcium, magnesium and potassium in forest soils

“…Iron and aluminium (hydr)oxides are thus likely to be the support of a geochemically reactive HNO 3 pool of Ca which is not extracted by conventional exchangeable cation methods. This may be explained by possible temporary occlusion of Ca in these soil phases: occluded in supramolecular aggregates where various large organic molecules are held together by van der Waals forces, hydrogen bonds and metal bridging involving Ca and Fe-hydr(oxides) 59 – 61 . These amorphous minerals are known to very dynamically precipitate and dissolve over time as a result of changes in the physical and chemical properties of the soil solution 31 and under the influence of microbial and plant activity 32 .…”

Frontiers and advances in environmental soil chemistry: a special issue in honor of Prof. Donald L. Sparks

“…By experimental analysis and density functional theory (DFT) calculations, Kubicki et al simulate interactions between chromate and a ferrihydrate nanoparticle [4]. Then, several articles by Sowers et al [5], Stuckey et al [6], Sundman et al [7], and Zhu et al [8] discuss how iron and manganese (hydr)oxides interact with organic compounds undergoing redox reactions and dissolution. In addition, Cade-Menun et al [9] and Hamilton et al [10] investigate the fate and transport of phosphate as a nutrient in soil systems by using inductively coupled plasma spectroscopy, P-nuclear magnetic resonance, and X-ray absorption spectroscopy.…”