Title: Iron and Carbon Dynamics during Aging and Reductive Transformation of Biogenic Ferrihydrite

Abstract

Natural organic matter is often associated with Fe(III) oxyhydroxides, and may be stabilized as a result of coprecipitation or sorption to their surfaces. However, the significance of this association in relation to Fe and C dynamics and biogeochemical cycling, and the mechanisms responsible for organic matter stabilization as a result of interaction with minerals under various environmental conditions (e.g., pH, Eh, etc.) are not entirely understood. The preservation of mineral-bound OM may be affected by OM structure and mineral identity, and bond types between OM and minerals may be central to influencing the stability, transformation and composition of both organic and mineral components under changing environmental conditions. Here we use bulk and submicron-scale spectroscopic synchrotron methods to examine the in situ transformation of OM-bearing, biogenic ferrihydrite stalks (Gallionella ferruginea-like), which formed following injection of oxygenated groundwater into a saturated alluvial aquifer at the Rifle, CO field site. A progression from oxidizing to reducing conditions during an eight-month period triggered the aging and reductive transformation of Gallionella-like ferrihydrite stalks to Fe (hydroxy)carbonates and Fe sulfides, as well as alteration of the composition and amount of OM. Spectromicroscopic measurements showed a gradual decrease in reduced carbon forms (aromatic/alkene, aliphatic C), a relativemore » increase in amide/carboxyl functional groups and a significant increase in carbonate in the stalk structures, and the appearance of organic globules not associated with stalk structures. Biogenic stalks lost ~30% of their initial organic carbon content. Conversely, a significant increase in bulk organic matter accompanied these transformations. The character of bulk OM changed in parallel with mineralogical transformations, showing an increase in aliphatic, aromatic and amide functional groups. These changes likely occurred as a result of an increase in microbial activity, or biomass production under anoxic conditions. By the end of this experiment, a substantial fraction of organic matter remained in identifiable Fe containing stalks, but carbon was also present in additional pools, for example, organic matter globules and iron carbonate minerals.« less

Authors:

Cismasu, A. Cristina ^[1]; Williams, Kenneth H. ^[1]; Nico, Peter S. ^[1]

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+ Show Author Affiliations

1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Publication Date:

Wed Nov 25 00:00:00 EST 2015

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1471002

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Science and Technology

Additional Journal Information:

Journal Volume: 50; Journal Issue: 1; Journal ID: ISSN 0013-936X

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES