The transformation and mobility of charcoal in a fire-impacted watershed

Hockaday, William C.; Grannas, A. M.; Kim, Sunghwan; Hatcher, Patrick G.

doi:10.1016/j.gca.2007.02.023

Cited by 244 publications

(206 citation statements)

References 65 publications

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“…9c for low-temperature maturation. Our hypothesis is supported by the fact that even in modern and immature sediments, small amounts of naturally occurring condensed aromatic ring structures can be found that have been linked to wildfires, anthropogenic contamination, and catalytic/enzymatic processes (e.g., Delfourne et al, 2000;Silliman et al, 2001;Finkelstein et al, 2006;Hockaday et al, 2007). It is likely that some of these condensed ring systems contain covalently bonded nitrogen.…”

Section: Increase Of N-c 3 Substituting For Carbon In Condensed Partmentioning

confidence: 52%

Organic nitrogen chemistry during low-grade metamorphism

Boudou

Schimmelmann

Ader

et al. 2008

Geochimica et Cosmochimica Acta

135

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-Most of the organic nitrogen (N org ) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil N org within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of N org and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of N org a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of N org speciation, transformation and elimination before and during metamorphism and advocates the use of XRay Photoelectron Spectroscopy (XPS) to monitor changes in N org speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset N org is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much N org is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for N org elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate N org along a progressing reaction front, without causing nitrogen isotope fractionation in the residual N org in the unreacted core of the carbonaceous matrix. Before the reaction front can reach the core, an increasing part of core N org chemically stabilizes in the form of nitrogen atoms substituting for carbon in condensed, partially aromatic systems forming graphite-like structural domains with delocalized π-electron systems (nitrogen atoms substituting for "graphitic" carbon in natural metamorphic organic matter). Thus, this nitrogen species with a conservative isotopic composition is the dominant form of residual nitrogen at higher metamorphic grade.

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Section: Increase Of N-c 3 Substituting For Carbon In Condensed Partmentioning

confidence: 52%

Organic nitrogen chemistry during low-grade metamorphism

Boudou

Schimmelmann

Ader

et al. 2008

Geochimica et Cosmochimica Acta

135

View full text Add to dashboard Cite

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“…Additionally, the average body-size of a soil protist is between 8 to 100 μm, while the average body size of soil micro-arthropods ranges from 100 μm to 2 mm (Swift et al 1979). In contrast, the pore diameters in a biochar particle can often be smaller than 16 μm in diameter (Kawamoto et al 2005;Glaser 2007;Hockaday et al 2007). Based on the differences in the body sizes across these different organisms, it is clearly possible that many of the pores within a biochar particle are large enough to accommodate soil microorganisms, includ-ing most bacteria and many fungi, to the exclusion of their larger predators.…”

Section: Mechanism 4: Biochar Serves As a Refuge For Colonizing Fungimentioning

confidence: 99%

Mycorrhizal responses to biochar in soil – concepts and mechanisms

et al. 2007

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Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycorrhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycorrhizal associations are subject to management, understanding and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreasing order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant-fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses.

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“…DOM from charcoal leachates had been previously characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS; Hockaday et al, 2007), an ultrahigh resolution analytical technique which allows for the assignment of individual molecular formulae to mass spectral peaks (Kujawinski, 2002;Sleighter and Hatcher, 2007;Dittmar and Paeng, 2009). Details regarding instrumental conditions and assignment of molecular formulas have been previously described by Hockaday et al (2006Hockaday et al ( , 2007.…”

Section: Selection Of Dissolved Black Carbon Molecular Formulaementioning

confidence: 99%

A New Perspective on the Apparent Solubility of Dissolved Black Carbon

2017

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Black carbon (BC), pyrogenic organic matter generated from the incomplete combustion of biomass, is ubiquitous in the environment. The molecular structures which comprise the BC pool of compounds are defined by their condensed aromatic core structures polysubstituted with O-containing functionalities (e.g., carboxyl groups). Despite the apparent hydrophobicity of BC molecules, a considerable portion of BC is translocated from terrestrial to aquatic systems in the form of dissolved BC (DBC). However, the specific biogeochemical mechanisms which control the transfer of BC from the land to the water remain elusive. In the current study, the apparent solubility of DBC was inferred from octanol-water partition coefficients (K ow ) modeled for proposed DBC structures with varying degrees of polycondensation and polar functionality. Modeled K ow values indicated that DBC molecules with small aromatic ring systems and high degrees of hydrophilic functionality may be truly solubilized in the aqueous phase. However, large and highly condensed DBC structures yielded high K ow values, which suggested that a considerable portion of the DBC pool which has been quantified in aquatic environments is not truly dissolved. We hypothesized that other DOM components may act as mediators in the solubilization of condensed aromatic molecules and serve to increase the solubility of DBC via hydrophobic, intermolecular associations. This hypothesis was tested through controlled leaching experiments to determine whether the mobilization of DBC from particulate soils and chars became enhanced in the presence of DOM. However, we observed that characteristics inherent to each sample type had a greater influence than added DOM on the apparent solubility of DBC. In addition, the direct comparison of molecular marker (benzenepolycarboxylic acids) and ultrahigh resolution mass spectral data (FT-ICR/MS) on leachates obtained from the same set of soils and char did not show a clear overlap in DBC quantification or characterization between the two analytical methods. Correlations between FT-ICR/MS results and BPCA were not significant possibly due to differences in the methodological windows and/or small sample size. Our results were unable to provide evidence in support of proposed hydrophobic interactions between DOM and DBC, suggesting that other physical/chemical mechanisms play important roles in the dissolution of BC.

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The transformation and mobility of charcoal in a fire-impacted watershed

Cited by 244 publications

References 65 publications

Organic nitrogen chemistry during low-grade metamorphism

Organic nitrogen chemistry during low-grade metamorphism

Mycorrhizal responses to biochar in soil – concepts and mechanisms

A New Perspective on the Apparent Solubility of Dissolved Black Carbon

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