Reaction of forest floor organic matter at goethite, birnessite and smectite surfaces

Jon Chorover, Mary Kay Amistadi

Research output: Contribution to journalArticle

230 Citations (Scopus)

Abstract

Experiments were conducted to compare the affinity and reactivity of three different minerals for natural organic matter (NOM) in forest floor leachate (FFL) from hardwood and pine forests. The FFLs were acidic (pH 4) with ionic strengths of 1.4 mM (hardwood) and 1.1 mM (pine), and they contained larger organic molecules (weight average molecular weights [Mw] = 5-6 kDa) than has been reported recently for surface waters using similar methods. A synthetic diluent solution was prepared to match the inorganic chemistry of the FFL and to provide a range of initial dissolved organic carbon (DOC) concentrations (0-140 g C m3) for reaction with goethite (α-FeOOH), birnessite (δ-MnO2) and smectite (montmorillonite, SWy-2) in suspension, and in corresponding blanks. A variety of macroscopic and spectroscopic methods were employed to show that reaction with the three minerals resulted in distinctly different NOM adsorption, fractionation and transformation patterns. Goethite exhibited a steep initial slope in the adsorption isotherm and a maximum retention of 10.5 g C kg1. The isotherm for montmorillonite was more linear, but equal amounts of C were adsorbed to goethite and montmorillonite (per unit sorbent mass) at maximum DOC. Whereas preferential uptake of high Mw, aromatic constituents via ligand exchange was observed for goethite, compounds of lower than average Mw were retained on montmorillonite and no preference for aromatic moieties was observed. Birnessite, which has an isoelectric point of pH < 2, retained low amounts of organic C (<2 g C kg1) but exhibited the highest propensity for oxidative transformation of the NOM. The data indicated that fractionation behaviour of NOM is dependent on mineral surface chemistry in addition to sorbent affinity for organic C. This work also emphasizes the fact that abiotic transformation reactions must be considered in studies of NOM interaction with Fe(III) and Mn(IV) containing solid phases.

Original languageEnglish (US)
Pages (from-to)95-109
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume65
Issue number1
DOIs
StatePublished - 2001
Externally publishedYes

Fingerprint

birnessite
Bentonite
forest floor
goethite
Biological materials
smectite
montmorillonite
organic matter
Minerals
Hardwoods
Molecular weight
Fractionation
Sorbents
Organic carbon
dissolved organic carbon
leachate
isotherm
mineral
fractionation
adsorption

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Reaction of forest floor organic matter at goethite, birnessite and smectite surfaces. / Chorover, Jon; Amistadi, Mary Kay.

In: Geochimica et Cosmochimica Acta, Vol. 65, No. 1, 2001, p. 95-109.

Research output: Contribution to journalArticle

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