Subscriber access provided by - Access paid by the | UCSB Libraries
Article
Evidence of Coupled Carbon and Iron Cycling at a HydrocarbonContaminated Site from Time Lapse Magnetic Susceptibility Anders Lund, Lee Slater, Estella Atekwana, Dimitrios Ntarlagiannis, Isabelle M. Cozzarelli, and Barbara Bekins Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b02155 • Publication Date (Web): 05 Sep 2017 Downloaded from http://pubs.acs.org on September 6, 2017
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 22
Environmental Science & Technology
Evidence of Coupled Carbon and Iron Cycling at a Hydrocarbon-Contaminated Site from Time Lapse Magnetic Susceptibility Anders L. Lund,
∗,†,k
Ntarlagiannis,
†
Lee D. Slater,
Estella A. Atekwana,
Isabelle Cozzarelli,
†Rutgers ‡Oklahoma
∗,†
¶
‡
Dimitrios
and Barbara A. Bekins
§
University, Newark, NJ, United States
State University Main Campus, Stillwater, OK, United States
¶National
Research Program, USGS, Reston, Virginia, United States
§National
Research Program, USGS, Menlo Park, CA, United States
kUniversity
of Aarhus, Aarhus, Denmark
E-mail:
[email protected];
[email protected] 1
Abstract
2
Conventional characterization and monitoring of hydrocarbon (HC) pollution is of-
3
ten expensive and time consuming. Magnetic susceptibility (MS) has been proposed
4
as an inexpensive, longterm monitoring proxy of the degradation of HC. We acquired
5
repeated down hole MS logging data in boreholes at a HC contaminated eld research
6
site in Bemidji, MN, USA. The MS data were analyzed in conjunction with redox con-
7
ditions and iron availability within the source zone in order to better assess whether
8
MS can serve as a proxy for monitoring HC contamination in unconsolidated sediments.
9
The MS response at the site diminished during the sampling period, which was found
10
to coincide with depletion of solid phase iron in the source zone. Previous geochemical 1
ACS Paragon Plus Environment
Environmental Science & Technology
Page 2 of 22
11
observations and modeling at the site suggest that the most likely cause of the decrease
12
in MS is the transformation of magnetite to siderite, coupled with the exhaustion of
13
ferrihydrite. Although the temporal MS response at this site gives valuable eld-scale
14
evidence for changing conditions of iron cycling and stability of iron minerals it does
15
not provide a simple proxy for longterm monitoring biodegradation of hydrocarbons in
16
the smear zone.
17
Introduction
18
Hydrocarbon (HC) contamination is one of the most common types of pollution worldwide,
19
posing a threat to fresh drinking water supplies and natural habitats. Long-term monitor-
20
ing of biogeochemical transformations of these contaminants is essential to protect these
21
resources and habitats. Established methods for mapping and monitoring of HC contami-
22
nation, such as drilling of boreholes for water, soil and pore gas samples are time consuming
23
and expensive, as well as limited in spatial and temporal extent. Monitored natural attenu-
24
ation (MNA) is increasingly the method of choice for many HC contaminated sites because
25
active methods such as excavation and chemical cleanup have been shown to be ine cient
26
in removing widespread contaminants present at low concentrations.
27
inexpensive and rapid technologies for monitoring the progress of the natural attenuation of
28
hydrocarbons is desirable, especially for HC contaminated sites that do not pose an imme-
29
diate threat to drinking water supplies or natural habitats, where MNA is logical. Natural
30
attenuation of HC has previously been linked to iron-reducing bacteria
31
of magnetite,
32
bacteria have been shown to reduce Fe(III) and oxidize Fe(II) and in this process form
33
magnetite.
34
susceptibility (MS) response amongst the iron minerals associated with iron reduction.
3,4
4,5
The development of
1,2
and the formation
as part of the iron cycle at HC contaminated sites. Numerous iron-reducing
Magnetite has been shown to be the strongest contributer to the magnetic
6,7
35 36
Rijal et al.
8
measured the MS response of core samples acquired from the source zone at
2
ACS Paragon Plus Environment
Page 3 of 22
Environmental Science & Technology
37
a HC contaminated site. They found that the top of the groundwater uctuation zone had
38
the highest MS response and that contaminated cores had a higher MS response than cores
39
taken from less contaminated, upgradient zones. Microbial activity was also highest at the
40
top of the groundwater uctuation zone.
41
reducing bacteria associated with the formation of magnetite in the groundwater uctuation
42
zone, indicating that Fe(III)-reducing bacteria likely play an important role in the formation
43
of magnetite.
Ameen et al.
9
noted elevated activity of Fe(III)-
44 45
This association between the natural attenuation of hydrocarbons and the MS response
7
46
led Atekwana et al.
to hypothesize that an increase in the MS response over time would
47
occur as magnetite accumulated in line with the progression of intrinsic bioremediation of the
48
HC plume; they also suggested that borehole MS logging can serve as a proxy for assessing
49
the extent of contamination and for delineating regions where carbon cycling is linked to
50
iron cycling. Our main objective was to build on the work of Atekwana et al.
51
if the MS response over time at a HC contaminated site supports the concept that borehole
52
MS logging can be used as a eld-scale proxy for monitoring the progress of biodegradation.
53
We also investigate how changes in the MS response may be linked to the depletion of solid
54
phase iron in the source zone, aecting the presence of magnetite.
55
Research Site
56
Data were acquired at the United States Geological Survey (USGS) managed Natural Crude
57
Oil Spill Fate and Natural Attenuation Research Site in Bemidji, Minnesota, Figure 1a.
58
A high pressure crude oil pipeline ruptured at this site in 1979, spilling 1.7 million liters
59
of oil.
60
2 and subsequently pooled in low topographical areas, covering around 2000 m , forming the
61
North and South pools.
62
2 an area to the southwest covering approximately 7500 m . After the initial clean up eort
The oil initially covered a total area of 6500 m
2
7
to investigate
to the southwest of the pipeline
The pressure from the pipeline also caused the oil to spray over
3
ACS Paragon Plus Environment
Environmental Science & Technology
Page 4 of 22
63
an estimated 400,000 liters of oil was left in the ground due to oil seepage. Because of the
64
fairly remote location, away from human interference to the aquifer, the USGS adopted the
65
site for longterm research on HC degradation.
66
m layer of moderately calcareous silty sand and outwash glacial deposits overlying clayey
67
till of unknown thickness.
68
the North Pool was situated at the time of the spill, as it has been the focus of intensive
69
geochemical
70
m occurring annually across the site cause smearing of hydrocarbons onto the aquifer solids.
71
The oil saturation at the North Pool has a maximum of 0.74, and the smear zone is more
72
than 2-m-thick in the down-gradient part of the oil body.
73
table below the surface varies from 11 m at the highest point to 0 m at an unnamed lake
74
about 300 m down-gradient to the east of the North Pool.
75
zones have been identi ed at the site of the North Pool as can be seen in Figure 1b.
11
10
The site geology consists of a roughly 20
Our study was located in and around the source zone, where
and microbiological studies.
12,13
Seasonal water table uctuations of around 1
14
The depth of the groundwater
15
Several dierent geochemical
76 77
The site serves as a highly characterized natural laboratory for investigating biogeophys-
78
ical and biogeochemical processes associated with intrinsic bioremediation of a crude oil
79
spill,
80
Mewafy et al.
81
of HC contaminated groundwater in unconsolidated sediments are related to redox cycling
82
at the site, where iron reducing bacteria also present at the site
83
producing, amongst other iron minerals, magnetite. Atekwana et al.
84
hole logs showing an enhanced MS response at the site, with the highest MS response found
85
in the zone of water table uctuation in the source zone. They also observed that the MS
86
response in the vadose zone was higher above the source zone than the vadose zone above
87
the dissolved-phase plume and uncontaminated zones. The blue line in Figure 2 shows the
88
MS pro le acquired in 2011 for borehole G0906 located at the center of the source zone.
89
The MS response increases to as much as
17,18
including the spatial and temporal variability in MS across a mature HC plume.
19
found evidence that changes in MS resulting from water level uctuations
300 × 10−4
20
reduce Fe(III) to Fe(II)
7
reported on MS bore-
SI within the smear zone as compared
4
ACS Paragon Plus Environment
Page 5 of 22
Environmental Science & Technology
Unsaturated zone containing liquid crude oil
Spray Zone
440 Elevation (mamsl)
Pipeline break
435
Land surface
Data point
430
Mean water table
425 420
Land surface una ected by spill
Source Zone
Zone 1
GW ow
415 -250
-200
Oxic
Anoxic DO
