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Title: Complexes with Aquatic Organic Matter Suppress Hydrolysis and Precipitation of Fe(III)

Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chem. Geol. 322: 19-27, 2012
Country of Publication:
United States

Citation Formats

Karlsson, Torbjorn, and Persson, Per. Complexes with Aquatic Organic Matter Suppress Hydrolysis and Precipitation of Fe(III). United States: N. p., 2014. Web.
Karlsson, Torbjorn, & Persson, Per. Complexes with Aquatic Organic Matter Suppress Hydrolysis and Precipitation of Fe(III). United States.
Karlsson, Torbjorn, and Persson, Per. Mon . "Complexes with Aquatic Organic Matter Suppress Hydrolysis and Precipitation of Fe(III)". United States. doi:.
title = {Complexes with Aquatic Organic Matter Suppress Hydrolysis and Precipitation of Fe(III)},
author = {Karlsson, Torbjorn and Persson, Per},
abstractNote = {},
doi = {},
journal = {Chem. Geol. 322: 19-27, 2012},
number = ,
volume = ,
place = {United States},
year = {Mon Sep 29 00:00:00 EDT 2014},
month = {Mon Sep 29 00:00:00 EDT 2014}
  • The dynamics of dissolved, colloidal, and deposited iron phases were examined during a forced-gradient field experiment. The experiment involved the injection of oxygenated water containing high levels of natural organic matter (NOM) into a sandy aquifer. The initial redox potential of the aquifer favored Fe(II) in the groundwater. The changes in the concentrations of Fe(II) and Fe(III) were observed in sampling wells. Under the increased dissolved oxygen (DO) conditions, Fe(II) oxygenation was rapid, resulting in the formation of Fe(III) (hydr)oxide colloids. The oxidation follows the rate law as given in Stumm and Morgan (1981). For an averaged pH and DOmore » of the groundwater, the half time of Fe(II) oxidation is 49 h. The NOM was postulated to stabilize the newly formed colloids, thereby increasing the turbidity in the groundwater. The additional increase in the colloidal fraction of Fe(III) oxide suggested that transport of the colloidal particles was occurring. At those locations where DO remained constantly low, the turbidity increase was moderate, and up to 80% of Fe(III) was in the dissolved phase (<3000 mol. wt.). The latter observation was attributed to the presence of NOM, forming Fe(III)-organic complexes. In addition, NOM may play a role in the oxygen consumption through a Fe(II)/Fe(III) catalyzed oxidation of organic matter as outlined by Stumm and Morgan (1981, p. 469). In this mechanism, Fe(II) oxidation is slow, maintaining a near constant Fe(II) concentration, in agreement with field data. The overall increase in Fe(III) under low DO conditions was postulated to be a combination of (1) slow oxidation, (2) ligand-promoted and catalytic dissolution of deposited iron phases, and (3) the transport of newly formed iron oxide colloids along flow paths. 47 refs., 7 figs., 6 tabs.« less
  • Climate warming is projected to increase the frequency and severity of wildfires in boreal forests, and increased wildfire activity may alter the large soil carbon (C) stocks in boreal forests. Changes in boreal soil C stocks that result from increased wildfire activity will be regulated in part by the response of microbial decomposition to fire, but post-fire changes in microbial decomposition are poorly understood. Here, we investigate the response of microbial decomposition to a boreal forest fire in interior Alaska and test the mechanisms that control post-fire changes in microbial decomposition. We used a reciprocal transplant between a recently burnedmore » boreal forest stand and a late successional boreal forest stand to test how post-fire changes in abiotic conditions, soil organic matter (SOM) composition, and soil microbial communities influence microbial decomposition. We found that SOM decomposing at the burned site lost 30.9% less mass over two years than SOM decomposing at the unburned site, indicating that post-fire changes in abiotic conditions suppress microbial decomposition. Our results suggest that moisture availability is one abiotic factor that constrains microbial decomposition in recently burned forests. In addition, we observed that burned SOM decomposed more slowly than unburned SOM, but the exact nature of SOM changes in the recently burned stand are unclear. Finally, we found no evidence that post-fire changes in soil microbial community composition significantly affect decomposition. Taken together, our study has demonstrated that boreal forest fires can suppress microbial decomposition due to post-fire changes in abiotic factors and the composition of SOM. Models that predict the consequences of increased wildfires for C storage in boreal forests may increase their predictive power by incorporating the observed negative response of microbial decomposition to boreal wildfires.« less