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Article
Iron and carbon dynamics during aging and reductive transformation of biogenic ferrihydrite A. Cristina Cismasu, Kenneth H. Williams, and Peter S. Nico Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b03021 • Publication Date (Web): 25 Nov 2015 Downloaded from http://pubs.acs.org on November 29, 2015
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 32
Environmental Science & Technology
1 2 3 4 5
Iron and carbon dynamics during aging and
6
reductive transformation of biogenic ferrihydrite
7 8 9
A. Cristina Cismasu1*, Kenneth H. Williams1 and Peter S. Nico1 1
Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA, USA
10 11
*correspondence
12
Lawrence Berkeley National Laboratory
13
1 Cyclotron Rd, Berkeley, CA 94720, USA
14
MS 47R316C
15
[email protected]
16
650-644-8588
17 18 19 20 21 22 1
ACS Paragon Plus Environment
Environmental Science & Technology
23
Abstract
24
Natural organic matter is often associated with Fe(III) oxyhydroxides, and may be
25
stabilized as a result of co-precipitation or sorption to their surfaces. However, the
26
significance of this association in relation to Fe and C dynamics and biogeochemical cycling,
27
and the mechanisms responsible for organic matter stabilization as a result of interaction with
28
minerals under various environmental conditions (e.g., pH, Eh, etc.) are not entirely
29
understood. The preservation of mineral-bound OM may be affected by OM structure and
30
mineral identity, and bond types between OM and minerals may be central to influencing the
31
stability, transformation and composition of both organic and mineral components under
32
changing environmental conditions. Here we use bulk and submicron-scale spectroscopic
33
synchrotron methods to examine in situ transformation of OM-bearing, biogenic ferrihydrite
34
stalks (Gallionella ferruginea-like), which formed following injection of oxygenated
35
groundwater into a saturated alluvial aquifer at the Rifle, CO field site. A progression from
36
oxidizing to reducing conditions during an eight-month period triggered the aging and
37
reductive transformation of Gallionella-like ferrihydrite stalks to Fe (hydroxy)carbonates and
38
Fe sulfides, as well as alteration of the composition and amount of OM. Spectromicroscopic
39
measurements showed a gradual decrease in reduced carbon forms (aromatic/alkene, aliphatic
40
C), a relative increase in amide/carboxyl functional groups and a significant increase in
41
carbonate in the stalk structures, and the appearance of organic globules not associated with
42
stalk structures. Biogenic stalks lost ~30% of their initial organic carbon content. Conversely,
43
a significant increase in bulk organic matter accompanied these transformations. The
44
character of bulk OM changed in parallel with mineralogical transformations, showing an
45
increase in aliphatic, aromatic and amide functional groups. These changes likely occurred as
46
a result of an increase in microbial activity, or biomass production under anoxic conditions.
2
ACS Paragon Plus Environment
Page 2 of 32
Page 3 of 32
Environmental Science & Technology
47
By the end of this experiment, a substantial fraction of organic matter remained in identifiable
48
Fe containing stalks, but carbon was also present in additional pools e.g., organic matter
49
globules and iron carbonate minerals.
50 51
Introduction
52
The association of organic matter (OM) with ferric iron oxyhydroxides is recognized
53
as a key process in the stabilization of OM in surface environments [1-5]. Owing to the ubiquity
54
of iron and organic carbon in soils, surface waters, and aquifers, and to the high specific
55
surface area and reactivity of Fe(III) oxyhydroxides, this association may have a substantial
56
impact on OM stabilization. Occlusion of organic matter within mineral co-precipitates, as
57
well as OM chemical structure and bond strength between OM and minerals may impact its
58
preservation [1,2,6,7]. Alternatively, Fe(III) oxyhydroxide sorbent types may also play key roles
59
in OM preservation
60
understanding of the processes involved in the formation and stabilization of Fe(III)
61
oxyhydroxide-OM associations is currently lacking, particularly regarding sorbed OM
62
structure, localization, conformation
63
environmental drivers that govern both C and Fe biogeochemical cycles (changes in pH,
64
redox conditions, microbial community composition, etc.).
[1]
due to their variable surface areas and reactivities. A mechanistic
[1]
, and potential stages of OM degradation as a result of
65
Ferrihydrite is among the most widespread Fe(III) oxyhydroxides at the earth’s
66
surface, often forming at redox boundaries as a result of rapid Fe(II) oxidation. It is known for
67
its nanoparticulate nature, poor crystallinity, high surface area and reactivity. It is commonly
68
associated with organic carbon in soils, sediments
69
hydrothermal settings
70
as a result of biomineralization by Fe(II) oxidizing microorganisms
[10,11]
[8]
, as well as freshwater, marine
[5,9]
and
, with frequent organic matter-ferrihydrite associations occurring
3
ACS Paragon Plus Environment
[11-16]
. The exposure of
Environmental Science & Technology
Page 4 of 32
71
ferrihydrite to fluctuating redox conditions triggers recrystallization or mineralogical
72
transformations that impact the chemical speciation, mobility and bioavailability of associated
73
major or trace elements
74
the types of secondary minerals depend on phase purity, e.g., sorption/incorporation of Al, Si,
75
P, or organic matter. [11, 18-23]. It is anticipated that mineral transformations will also affect the
76
speciation of ferrihydrite-bound natural organic matter; OM can exchange or shuttle electrons
77
[23, 24]
[17]
. Ferrihydrite aging and (a)biotic transformation rates, as well as
but it may also oxidize or desorb selectively.
78
The objective of this work is to present an example of Fe and C dynamics during the
79
aging and reductive transformation of a biogenic ferrihydrite precipitated in situ within the
80
saturated aquifer at the U.S. Department of Energy (DOE) Rifle, CO test site [23]. OM-bearing
81
precipitates dominated by Gallionella-like ferrihydrite stalks formed during a forced
82
oxidation event (injection of oxygenated water into the subsurface); the aging and reductive
83
transformation of the precipitate was monitored for a period of eight months (between August
84
2012 and April 2013) as groundwater reverted to reducing conditions. Iron speciation and
85
mineralogy, organic matter character, as well as the likelihood for release or preservation of
86
mineral-bound organic matter were evaluated using evidence derived from X-ray diffraction,
87
submicron scale elemental mapping and X-ray absorption spectroscopy.
88 89
Materials and Methods
90
Field site and experimental design
91
The DOE Rifle field site is located in northwestern Colorado on a floodplain adjacent
92
to the Colorado River at the site of a former uranium and vanadium mill that operated
93
between 1924 and 1958 (see Williams et al., 2011
94
comprehensive descriptions of the site). Currently, the site supports research activities 4
[25]
; Yabusaki et al., 2007
ACS Paragon Plus Environment
[26]
for more
Page 5 of 32
Environmental Science & Technology
95
associated with the Lawrence Berkeley National Laboratory Sustainable Systems Scientific
96
Focus Area (SFA), whose central aim is to develop a predictive understanding of climate-
97
induced impacts on biogeochemical functioning and carbon cycling at the watershed scale.
98 99
Mimicking the short-lived but significant increases in dissolved oxygen (DO) that accompany seasonal excursions in groundwater elevation at the Rifle site
[27]
, injection of
100
oxygenated groundwater into an otherwise anoxic portion of the aquifer was designed to
101
examine the impact of fluctuating redox conditions on biogeochemical pathways relevant to
102
metal and carbon cycling. Aerated groundwater was injected into a formerly biostimulated
103
well field [28] over a period of 125 days from August to December 2012; see Figure SI3.1 for
104
a sketch of the injection setup. Prior to injection, groundwater in the well field was suboxic
105
(DO concentration 3-7µM; ORP from -132 to -196mV) with a neutral pH (7.2-7.5) and
106
elevated ferrous iron and dissolved sulfide concentrations (53-63µM and 0.3-3µM,
107
respectively). The injectate consisted of groundwater pumped from an upgradient, previously
108
un-impacted well having low DO and Fe(II) (
Article
Iron and carbon dynamics during aging and reductive transformation of biogenic ferrihydrite A. Cristina Cismasu, Kenneth H. Williams, and Peter S. Nico Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b03021 • Publication Date (Web): 25 Nov 2015 Downloaded from http://pubs.acs.org on November 29, 2015
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 32
Environmental Science & Technology
1 2 3 4 5
Iron and carbon dynamics during aging and
6
reductive transformation of biogenic ferrihydrite
7 8 9
A. Cristina Cismasu1*, Kenneth H. Williams1 and Peter S. Nico1 1
Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA, USA
10 11
*correspondence
12
Lawrence Berkeley National Laboratory
13
1 Cyclotron Rd, Berkeley, CA 94720, USA
14
MS 47R316C
15
[email protected]
16
650-644-8588
17 18 19 20 21 22 1
ACS Paragon Plus Environment
Environmental Science & Technology
23
Abstract
24
Natural organic matter is often associated with Fe(III) oxyhydroxides, and may be
25
stabilized as a result of co-precipitation or sorption to their surfaces. However, the
26
significance of this association in relation to Fe and C dynamics and biogeochemical cycling,
27
and the mechanisms responsible for organic matter stabilization as a result of interaction with
28
minerals under various environmental conditions (e.g., pH, Eh, etc.) are not entirely
29
understood. The preservation of mineral-bound OM may be affected by OM structure and
30
mineral identity, and bond types between OM and minerals may be central to influencing the
31
stability, transformation and composition of both organic and mineral components under
32
changing environmental conditions. Here we use bulk and submicron-scale spectroscopic
33
synchrotron methods to examine in situ transformation of OM-bearing, biogenic ferrihydrite
34
stalks (Gallionella ferruginea-like), which formed following injection of oxygenated
35
groundwater into a saturated alluvial aquifer at the Rifle, CO field site. A progression from
36
oxidizing to reducing conditions during an eight-month period triggered the aging and
37
reductive transformation of Gallionella-like ferrihydrite stalks to Fe (hydroxy)carbonates and
38
Fe sulfides, as well as alteration of the composition and amount of OM. Spectromicroscopic
39
measurements showed a gradual decrease in reduced carbon forms (aromatic/alkene, aliphatic
40
C), a relative increase in amide/carboxyl functional groups and a significant increase in
41
carbonate in the stalk structures, and the appearance of organic globules not associated with
42
stalk structures. Biogenic stalks lost ~30% of their initial organic carbon content. Conversely,
43
a significant increase in bulk organic matter accompanied these transformations. The
44
character of bulk OM changed in parallel with mineralogical transformations, showing an
45
increase in aliphatic, aromatic and amide functional groups. These changes likely occurred as
46
a result of an increase in microbial activity, or biomass production under anoxic conditions.
2
ACS Paragon Plus Environment
Page 2 of 32
Page 3 of 32
Environmental Science & Technology
47
By the end of this experiment, a substantial fraction of organic matter remained in identifiable
48
Fe containing stalks, but carbon was also present in additional pools e.g., organic matter
49
globules and iron carbonate minerals.
50 51
Introduction
52
The association of organic matter (OM) with ferric iron oxyhydroxides is recognized
53
as a key process in the stabilization of OM in surface environments [1-5]. Owing to the ubiquity
54
of iron and organic carbon in soils, surface waters, and aquifers, and to the high specific
55
surface area and reactivity of Fe(III) oxyhydroxides, this association may have a substantial
56
impact on OM stabilization. Occlusion of organic matter within mineral co-precipitates, as
57
well as OM chemical structure and bond strength between OM and minerals may impact its
58
preservation [1,2,6,7]. Alternatively, Fe(III) oxyhydroxide sorbent types may also play key roles
59
in OM preservation
60
understanding of the processes involved in the formation and stabilization of Fe(III)
61
oxyhydroxide-OM associations is currently lacking, particularly regarding sorbed OM
62
structure, localization, conformation
63
environmental drivers that govern both C and Fe biogeochemical cycles (changes in pH,
64
redox conditions, microbial community composition, etc.).
[1]
due to their variable surface areas and reactivities. A mechanistic
[1]
, and potential stages of OM degradation as a result of
65
Ferrihydrite is among the most widespread Fe(III) oxyhydroxides at the earth’s
66
surface, often forming at redox boundaries as a result of rapid Fe(II) oxidation. It is known for
67
its nanoparticulate nature, poor crystallinity, high surface area and reactivity. It is commonly
68
associated with organic carbon in soils, sediments
69
hydrothermal settings
70
as a result of biomineralization by Fe(II) oxidizing microorganisms
[10,11]
[8]
, as well as freshwater, marine
[5,9]
and
, with frequent organic matter-ferrihydrite associations occurring
3
ACS Paragon Plus Environment
[11-16]
. The exposure of
Environmental Science & Technology
Page 4 of 32
71
ferrihydrite to fluctuating redox conditions triggers recrystallization or mineralogical
72
transformations that impact the chemical speciation, mobility and bioavailability of associated
73
major or trace elements
74
the types of secondary minerals depend on phase purity, e.g., sorption/incorporation of Al, Si,
75
P, or organic matter. [11, 18-23]. It is anticipated that mineral transformations will also affect the
76
speciation of ferrihydrite-bound natural organic matter; OM can exchange or shuttle electrons
77
[23, 24]
[17]
. Ferrihydrite aging and (a)biotic transformation rates, as well as
but it may also oxidize or desorb selectively.
78
The objective of this work is to present an example of Fe and C dynamics during the
79
aging and reductive transformation of a biogenic ferrihydrite precipitated in situ within the
80
saturated aquifer at the U.S. Department of Energy (DOE) Rifle, CO test site [23]. OM-bearing
81
precipitates dominated by Gallionella-like ferrihydrite stalks formed during a forced
82
oxidation event (injection of oxygenated water into the subsurface); the aging and reductive
83
transformation of the precipitate was monitored for a period of eight months (between August
84
2012 and April 2013) as groundwater reverted to reducing conditions. Iron speciation and
85
mineralogy, organic matter character, as well as the likelihood for release or preservation of
86
mineral-bound organic matter were evaluated using evidence derived from X-ray diffraction,
87
submicron scale elemental mapping and X-ray absorption spectroscopy.
88 89
Materials and Methods
90
Field site and experimental design
91
The DOE Rifle field site is located in northwestern Colorado on a floodplain adjacent
92
to the Colorado River at the site of a former uranium and vanadium mill that operated
93
between 1924 and 1958 (see Williams et al., 2011
94
comprehensive descriptions of the site). Currently, the site supports research activities 4
[25]
; Yabusaki et al., 2007
ACS Paragon Plus Environment
[26]
for more
Page 5 of 32
Environmental Science & Technology
95
associated with the Lawrence Berkeley National Laboratory Sustainable Systems Scientific
96
Focus Area (SFA), whose central aim is to develop a predictive understanding of climate-
97
induced impacts on biogeochemical functioning and carbon cycling at the watershed scale.
98 99
Mimicking the short-lived but significant increases in dissolved oxygen (DO) that accompany seasonal excursions in groundwater elevation at the Rifle site
[27]
, injection of
100
oxygenated groundwater into an otherwise anoxic portion of the aquifer was designed to
101
examine the impact of fluctuating redox conditions on biogeochemical pathways relevant to
102
metal and carbon cycling. Aerated groundwater was injected into a formerly biostimulated
103
well field [28] over a period of 125 days from August to December 2012; see Figure SI3.1 for
104
a sketch of the injection setup. Prior to injection, groundwater in the well field was suboxic
105
(DO concentration 3-7µM; ORP from -132 to -196mV) with a neutral pH (7.2-7.5) and
106
elevated ferrous iron and dissolved sulfide concentrations (53-63µM and 0.3-3µM,
107
respectively). The injectate consisted of groundwater pumped from an upgradient, previously
108
un-impacted well having low DO and Fe(II) (
