i

OCS Study MMS 2004-061

Final Report

Petroleum Hydrocarbon–Degrading Microbial Communities

in Beaufort–Chukchi Sea Sediments

by

Joan F. Braddock*

Principal Investigator

Kathleen A. Gannon

Brian T. Rasley

Institute of Arctic Biology

University of Alaska Fairbanks

Fairbanks, AK 99775-7000

October 2004

*Corresponding author

e-mail: ffjfb@uaf.edu
ii

Project Organization

Report authors

JOAN BRADDOCK – Principal Investigator

Final report oversight. Designed or assisted with design of all experiments.

KATHLEEN GANNON – Master’s degree student

Responsible for sample collection, laboratory experiments and analyses.

BRIAN RASLEY

Final report preparation.

Acknowledgement

We would like to thank Antoinette Roberts for completing

bioavailability experiments in summer 2003.

Contact information

e-mail: cmi@sfos.uaf.edu

phone: 907.474.7707

fax: 907.474.7204

postal: Coastal Marine Institute

School of Fisheries and Ocean Sciences

University of Alaska Fairbanks

Fairbanks, AK 99775-7220
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Table of Contents

List of Tables ..................................................................................................................... iv

List of Figures ..................................................................................................................... v

Abstract .............................................................................................................................. 1

Introduction ........................................................................................................................ 1

Materials and Methods ........................................................................................................ 3

Sampling ...................................................................................................................... 3

Initial dilutions of samples ............................................................................................ 5

Total microscopic direct counts of microorganisms ...................................................... 7

Most probable number of crude oil emulsifiers ............................................................. 9

Most probable number of heterotrophic and substrate-specific microorganisms .......... 10

Mineralization potentials ............................................................................................ 10

Particle analysis and organic carbon content ............................................................... 10

Preparation of sediment slurries for isotherm assays ................................................... 12

Isotherm assays .......................................................................................................... 12

Preparation of phenanthrene-degrading cultures for bioavailability assays .................. 12

Bioavailability assays ................................................................................................. 13

Comparison of chemical and biological data ............................................................... 13

Results .............................................................................................................................. 15

Enumerations ............................................................................................................. 15

Mineralization potentials ............................................................................................ 21

Isotherm assays .......................................................................................................... 21

Bioavailability assays ................................................................................................. 24

Comparison of chemical and biological data ............................................................... 29

Discussion ........................................................................................................................ 32

Conclusions ...................................................................................................................... 35

Study Products .................................................................................................................. 36

References ........................................................................................................................ 37
iv

List of Tables

Table 1. Locations and water depths for samples collected in August 1999

in the vicinity of Barrow ..................................................................................................... 6

Table 2. Percent dry weight for sediment samples collected in the vicinity of Barrow

during August 1999 ............................................................................................................ 7

Table 3. Locations and water depths for sediment samples collected in the vicinity

of Prudhoe Bay during August 2000 .................................................................................. 8

Table 4. Percent dry weight for sediment samples collected in the vicinity

of Prudhoe Bay during August 2000 .................................................................................. 9

Table 5. Particle size analysis of sediment samples collected in the vicinity

of Barrow during August 1999 ......................................................................................... 11

Table 6. Percent organic carbon content of sediment samples used for isotherm

and bioavailability assays ................................................................................................. 12

Table 7. Chemical [Brown et al. 2002] and biological data from sampling sites

visited during 2000 in the vicinity of Prudhoe Bay ......................................................... 14

Table 8. Mineralization potentials in 96-hour assays of substrate-specific

degrading microorganisms in sediment samples collected in the vicinity

of Barrow during August 1999 ......................................................................................... 21

Table 9. Mineralization potentials in 96-hour assays of substrate-specific

degrading microorganisms in sediment samples collected in the vicinity

of Prudhoe Bay during August 2000 ................................................................................ 22

Table 10. Partition coefficients obtained from isotherm assays ...................................................... 24

Table 11. Total percent phenanthrene recovered from mineralization and supernatant ................. 29

Table 12. Coefficients of determination (r2

) for pairwise linear regressions of

chemical [Brown et al. 2002] and biological data ........................................................... 31

Table 13. Microbial population estimates from previous studies .................................................... 33
v

List of Figures

Figure 1. Sampling sites in the Barrow and Prudhoe Bay regions ................................................... 4

Figure 2. Log of total bacteria by location as estimated by microscopic direct count ................... 16

Figure 3. Log of heterotrophic most probable number of microorganisms by location ................ 17

Figure 4. Log of phenanthrene-degrading most probable number of microorganisms

by location ......................................................................................................................... 18

Figure 5. Log of hexadecane-degrading most probable number of microorganisms

by location ......................................................................................................................... 19

Figure 6. Log of oil-degrading (sheen screen) most probable number of microorganisms

by location ......................................................................................................................... 20

Figure 7. Isotherms for 1% and 2% sediment slurries for sediments collected from:

(a) offshore Barrow, (b) offshore NARL, and (c) Elson Lagoon .................................... 23

Figure 8. Phenanthrene mineralized from bioavailability assays of sediment samples

from: (a) offshore Barrow, (b) offshore NARL, and (c) Elson Lagoon ......................... 25

Figure 9. Phenanthrene mineralized from 2003 bioavailability assays of unaged

sediment samples from: (a) offshore NARL and (b) Elson Lagoon ............................... 26

Figure 10. Phenanthrene mineralized from 2003 bioavailability assays of sediment

samples aged 1 month from: (a) offshore NARL and (b) Elson Lagoon ........................ 27

Figure 11. Phenanthrene mineralized from 2003 bioavailability assays of sediment

samples aged 2 months from: (a) offshore NARL and (b) Elson Lagoon ...................... 28

Figure 12. Scores and loadings plots from principle component analysis

of chemical and biological data collected in 2000 ........................................................... 30
1

Abstract

Despite large-scale development on the North Slope, no recent studies examining arctic marine

sediment microbial communities and their ability to metabolize petroleum compounds have been

published. Microbial populations are of interest since biodegradation of petroleum hydrocarbons

is a major removal mechanism of these compounds from the environment. We conducted a survey

(near Barrow and near Prudhoe Bay) of marine sediment microbial populations to determine what

microorganisms are present and what their metabolic capability is for degradation of model petroleum

hydrocarbons. We also examined the effect of sediment on bioavailability of a polycyclic aromatic

hydrocarbon (phenanthrene) to hydrocarbon-degrading bacteria. In our survey we found high total

numbers of microorganisms (about 1010 cells • g dry wt–1 sediment). Interestingly the total numbers

were higher than have been reported for more temperate locations such as Prince William Sound.

Most probable numbers of culturable phenanthrene and hexadecane degraders were fairly high (about

104 cells • g dry wt–1 sediment each) and numbers were significantly higher near Prudhoe Bay than

offshore Barrow. Culturable crude oil degraders were also significantly greater offshore Prudhoe Bay

than Barrow. There was no evidence that these differences are due to anthropogenic contaminants.

Mineralization potentials were low for both hexadecane and phenanthrene at both geographic

locations, indicating that microbial populations are not acclimated to readily use these compounds.

Despite the low organic carbon content of these sediments (1.5%), substantial and rapid adsorption

to particles occurred. Unexpectedly, the presence of sediment in bioavailability assays had no effect

or enhanced mineralization of phenanthrene, even when the sediment was aged with phenanthrene

for up to two months before adding microorganisms. Overall, biodegradation will likely be a slow

removal mechanism of contaminants from the arctic marine environment but adsorption to sediments

may not contribute substantially to persistence of these compounds in the environment.

Introduction

Oil development on the North Slope of Alaska has been active since the construction of the Trans

Alaska Pipeline, which began in 1975. Unfortunately, oil spills resulting from oil field development

and associated activities can lead to petroleum hydrocarbon (PHC) contamination of the arctic

environment. Biodegradation, the breakdown of petroleum hydrocarbons by microbes, is a major

removal mechanism for petroleum hydrocarbons released into the environment [Bartha and

Atlas 1987]. It is therefore useful to acquire baseline data on microbial populations and their

hydrocarbon-degrading potential before an oil spill occurs. This baseline data can help improve

emergency response plans by establishing the size and metabolic potentials of microbial populations

that are native to the region and available to breakdown contaminants. In the event of an oil spill,

microbial populations can serve as an indicator of the extent of contamination and, after cleanup of

the spill, can be used to help establish whether the environment is similar to the original,

uncontaminated state.

Exposure to oil causes changes in populations and activity of the microbial community [Pfaender and

Buckley 1984; Braddock and Richter 1998]. Hydrocarbon contamination can also lead to an increase

in populations of microorganisms that utilize the intermediate products of hydrocarbon metabolism

[Bartha and Atlas 1987]. Increases in microbial populations after hydrocarbon contamination can be

found in different environments, including marine sediment [Atlas et al. 1978; Horowitz et al. 1978;

Pfaender and Buckley 1984; Bartha and Atlas 1987]. While the overall microbial community often

grows, specific population shifts also occur within the community [Horowitz and Atlas 1977; Atlas

et al. 1978; Pfaender and Buckley 1984]. Several studies have reported increases in the culturable

heterotrophic population [Horowitz and Atlas 1977; Atlas et al. 1978; Pfaender and Buckley 1984],
2

but not in the same proportion as the hydrocarbon-utilizing microorganisms [Atlas et al. 1978;

Pfaender and Buckley 1984].

Hydrocarbon-degrading microorganisms are present in many environments, even when the

environment is pristine [Atlas et al. 1978; Pfaender and Buckley 1984; Bartha and Atlas 1987; Leahy

and Colwell 1990]. However, environmental conditions and prior exposure to hydrocarbons greatly

influence the abundance of hydrocarbon-degrading microorganisms in marine systems. Along oceanic

shipping lanes and in oil-contaminated coastal areas, the hydrocarbon-degrading microbial population

is considerably higher than in marine regions with no prior exposure to crude oil [Bartha and Atlas

1987]. The hydrocarbon-utilizing microorganism population can still be elevated a year after a spill.

However, as the concentration of oil decreases in marine sediment, the population of hydrocarbonutilizing microorganisms declines until it reaches levels similar to those at uncontaminated sites

[Pfaender and Buckley 1984].

Crude oil is composed of a mixture of hydrocarbons, which requires a consortium of microorganisms

in order to be degraded completely [Cerniglia 1984; Pfaender and Buckley 1984; Leahy and Colwell

1990]. Fresh Prudhoe Bay crude oil consists of about 80% linear alkanes, 17% aromatic hydrocarbons,

and 2% asphaltic hydrocarbons [Atlas 1975]. Degradation of the different hydrocarbon species in

crude oil can occur simultaneously by different microorganisms within the consortium, but complete

removal of each species occurs at a different rate [Bartha and Atlas 1987; Leahy and Colwell 1990].

Therefore, it is of interest to determine the populations capable of degrading specific petroleum

hydrocarbon species. Normal alkanes ranging from C10 to C22 are the most readily utilized compounds

degraded by microorganisms [Bartha and Atlas 1987]. The rapid degradation of alkanes may be due

to the high numbers of microorganisms that have enzymes capable of degrading n-alkanes or the fact

that the structures of the compounds are unhindered, causing them to be easily metabolized [Atlas

1981; Bartha and Atlas 1987; Leahy and Colwell 1990; Baker and Herson 1994].

Bartha and Atlas [1987] described several factors affecting the more slowly degraded group of

compounds classified as polycyclic aromatic hydrocarbons (PAH) along with the degradation of

other hydrocarbons. Condensed PAH with 2–4 aromatic rings are somewhat less toxic than the 1-ring

aromatic hydrocarbons and the rate of biodegradation decreases with the level of condensation. The

n-alkane utilizers might also slow the degradation of other compounds by competing with other

microbes for limited resources such as mineral nutrients or oxygen.

The fate of hydrophobic contaminants such as PAH is greatly influenced by bioavailability to marine

microorganisms. However, it is known that PAH may be reintroduced into the water column by

desorption from sediment surfaces into the aqueous solution surrounding the sediment. The result of

the desorption process is an extended exposure of marine organisms to petroleum hydrocarbons [Chin

and Gschwend 1992].

It is generally thought that sorption of hydrocarbons decreases the availability of PAH for microbial

degradation [Manilal and Alexander 1991; Weissenfels et al. 1992]. However, a few studies have

provided evidence that sorbed compounds may be metabolized by some microorganisms [Fu and

Alexander 1992; Guerin and Boyd 1992; Knaebel et al. 1994] or that sediments have no effect on

biodegradation [Larson and Vashon 1983]. The mechanism by which sorbed organic matter becomes

available for metabolism is not well understood, but clearly the substrate must be removed from the

surface before it can be transported into the cell. The use of a substrate by a bacterial cell in aqueous

environments can be conceptualized to consist of three processes: 1) diffusion of substrate molecules

to the cell surface; 2) movement of substrate molecules across the cell wall, periplasmic space, and

cell membranes; and 3) movement and metabolism of the substrate within the cell. The rates of
3

substrate uptake and metabolism are ultimately dependent upon, and cannot exceed, the rate of

substrate diffusion to the cell surface [Schmidt et al. 1985].

It is not known whether sorption per se renders PAH inaccessible for uptake by microbes. Since

bacteria themselves may be sorbed, it is conceivable that bacteria and PAH may be sorbed to adjacent

locations on the soil or sediment surface, thereby facilitating scavenging of substrate by the bacteria.

For natural environments, it has been reported that surfaces are the major site of microbial activity

[van Loosdrecht et al. 1990]. Surfaces may influence the degradability of organic chemicals by

sorbing the molecules to make them less available or by increasing the microbial density at surfaces

as compared to that in solution [Subba-Rao and Alexander 1982]. Another positive influence of

surfaces on bacterial activity may be related to the accumulation of nutrients at the surface. The

increased nutrient and substrate concentration is thought to stimulate bacterial growth or increase

the cell yield.

The overall objectives of this project were to: 1) acquire baseline microbial population data for

selected areas in the Beaufort–Chukchi Seas, 2) compare microbial population data obtained from

this study to similar data collected in the 1970s and 1980s, 3) evaluate the current degree of microbial

community acclimation to hydrocarbons, 4) determine the effects of fine-grained sediments on

bioavailability of petroleum hydrocarbons to acclimated microbes, and 5) compare biological data

obtained in this study with corresponding chemical data collected near Prudhoe Bay by ICF

Consulting [Brown et al. 2002].

Materials and Methods

Sampling

Eleven locations were sampled: three near Barrow and eight near Prudhoe Bay (Figure 1). The three

locations accessed from Barrow were separated into two groups, Elson Lagoon and “near Barrow.”

Near Barrow includes offshore of Barrow and offshore of the former Naval Arctic Research

Laboratory (NARL; the site of the present Barrow Arctic Science Consortium facilities). Elson

Lagoon is mostly enclosed by land with only a small opening allowing water exchange between the

lagoon and open ocean water. In contrast, both locations within the near Barrow region are in the

open ocean. The eight locations accessed from Prudhoe Bay were classified by open ocean versus

fresh water locations. The three rivers (the Colville, the Kuparuk, and the Sagavanirktok Rivers)

contain fresh water but are spatially separate. Therefore, each river was designated as a different

group. The other five locations (Northstar, Liberty, Between Northstar and Liberty, East of Liberty,

and the Boulder Patch) were all located in the open ocean and therefore were classified as one group

referred to as “near Prudhoe Bay.”
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Figure 1. Sampling sites in the Barrow and Prudhoe Bay regions. The

Colville River lies to the west of the Prudhoe Bay Region.
5

Near Barrow and Elson Lagoon sediment samples were collected on 24–25 August 1999 from a skiff

using a hand operated van Veen grab. Locations (Table 1) were estimated using a global positioning

system receiver (GPS) and a depth sounder. Using a sterile spoon, about 200–300 g of sediment was

collected from the surface (aerobic portion) of each grab and transferred to a sterile Whirl-Pak bag.

The sediment was separated into 2 samples (A and B). The A samples were from the uppermost

sediment and the B samples were from the next few centimeters down. Triplicate grabs were taken

at each site and the sediment was placed in separate bags. The same sampling spoon was used for

each site but was cleaned with 70% methanol between grabs. The samples were stored at ~4°C

during transportation back to the laboratory at the University of Alaska Fairbanks. To determine the

dry weights of each sediment sample (Table 2), wet sediment was added to a pre-weighed aluminum

weigh boat and weighed (~50 g for the 1999 samples and ~10 g for the 2000 samples). The sediment

was dried overnight at 100°C and the samples were reweighed the following day.

Arthur D. Little, Inc. collected the sediment samples from the sites near Prudhoe Bay, and the

Colville, the Kuparuk, and the Sagavanirktok Rivers on 19–25 August 2000. Locations (Table 3)

were obtained using a Furuno 12-channel differential global positioning system (DGPS), with an

accuracy of 3–5 meters. The depths were estimated using a Furuno fathometer. Sampling and sample

storage were similar to 1999 except that only one grab was made at each site. However, the number

of sampling sites was substantially greater in 2000 than in 1999. In both years, samples were

processed for microbial assays as soon as possible (within six days). Sediment dry weights for

samples collected during 2000 (Table 4) were determined as described above.

Initial dilutions of samples

An initial 1:10 (wt:vol) dilution was prepared for each sediment sample before setting up the

microbial assays. This was done to assure that the sediment-associated microbes were as evenly

distributed as possible for all assays. Fifteen grams of wet sediment was added to 135 mL of marine

BH medium (Bushnell-Haas modified by adding 1/10 of the FeCl3 and amended with 2.5% NaCl)

[p. 174 in Atlas 1993]. The initial dilution bottles were shaken for 2 min then stored at 10°C until

further dilution series were performed. Subsequent dilutions were always performed within 3 h of

the initial dilution. All assays were set up for each grab before proceeding to the next grab to maintain

consistency among populations in all of the assays.
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Table 1. Locations and water depths for samples collected in August 1999 in

the vicinity of Barrow. The first number after the letter represents

the site. The second number (if present) represents the grab.

Sampling Sites

Grouped by

Location

Latitude Longitude Approximate

Depth (m)

Offshore Barrow

B 1-1 71° 18.109 N 156° 46.089 W3

B 1-2 71° 18.110 N 156° 46.084 W3

B 1-3 71° 18.111 N 156° 46.074 W3

B 2-1 71° 18.175 N 156° 46.494 W4

B 2-2 71° 18.174 N 156° 46.502 W4

B 2-3 71° 18.174 N 156° 46.502 W4

B 3-1 71° 18.305 N 156° 47.042 W7

B 3-2 71° 18.279 N 156° 47.164 W7

B 3-3 71° 18.274 N 156° 47.162 W7

B 4-1 71° 18.067 N 156° 47.419 W7

B 4-2 71° 18.067 N 156° 47.419 W7

B 4-3 71° 18.067 N 156° 47.420 W7

B 5-1 71° 18.260 N 156° 47.992 W 14

B 5-2 71° 18.118 N 156° 47.880 W 10

B 5-3 71° 18.102 N 156° 47.904 W 14

Offshore NARL

N 1-1 71° 20.000 N 156° 42.878 W 10

N 1-2 71° 19.957 N 156° 42.973 W 10

N 1-3 71° 19.942 N 156° 42.986 W 10

N 2-1 71° 20.025 N 156° 42.356 W8

N 2-2 71° 19.944 N 156° 42.523 W8

N 2-3 71° 20.006 N 156° 42.689 W8

N 3-1 71° 19.976 N 156° 41.519 W6

N 3-2 71° 19.986 N 156° 41.572 W6

N 3-3 71° 19.986 N 156° 41.572 W6

N 4-1 71° 19.880 N 156° 40.975 W5

N 4-2 71° 19.871 N 156° 41.009 W5

N 4-3 71° 19.863 N 156° 41.031 W5

N 5-1 71° 19.811 N 156° 40.606 W5

N 5-2 71° 19.811 N 156° 40.634 W5

N 5-3 71° 19.808 N 156° 40.634 W5

Elson Lagoon

E 1 71° 20.035 N 156° 33.584 W 1.8

E 2 71° 19.176 N 156° 32.473 W2

E 3 71° 17.529 N 156° 24.707 W 3–4

E 4 71° 22.824 N 156° 26.775 W3

E 5 71° 21.176 N 156° 30.889 W 2–3
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Table 2. Percent dry weight for sediment samples collected in the vicinity

of Barrow during August 1999.

% Dry Weight

Location Site Grab 1 Grab 2 Grab 3

Offshore Barrow 1 84.48 81.84 82.18

2 79.92 85.58 80.88

3 81.08 76.84 67.00

4 46.89 68.94 75.93

5 70.04 73.51 63.11

Offshore NARL 1 55.14 52.11 70.20

2 67.15 62.92 52.64

3 82.02 80.81 80.39

4 79.42 79.83 80.35

5 80.22 80.18 79.58

Elson Lagoon 1 78.15 79.64 78.67

2 77.29 80.28 78.20

3 61.23 60.13 56.27

4 46.88 46.68 45.79

5 70.92 65.60 69.01

Total microscopic direct counts of microorganisms

Total microscopic direct counts [Braddock et al. 1990] were used to determine the populations of

total microorganisms associated with the sediment. To prevent the cells from multiplying and to

preserve them for direct counts, 100 mL of each initially diluted sample was added to 900 mL

of 37% formaldehyde. When preparing for the direct counts, each formalin-preserved sample

was sonicated (VWR Aquasonic 50T ultrasonic cleaner) for 20 s. Then 0.1 mL of 50 mg mL–1

4-6-diamidino-2-phenylindole dihydrochloride (DAPI) stain was added to a 1-mL diluted sample

(usually 50 mL sample:950 mL water) in a 1.8 mL centrifuge vial (Fisher Scientific, Federal Way,

WA). The samples were incubated at room temperature for 1–2 h before being filtered onto a black

polycarbonate filter (0.2 mm, 25-mm diameter) (Poretics Corporation, Livermore, CA). Each vial

was then rinsed 3 times with 1 mL of filtered deionized water (18 MW-cm) and the rinse water

passed through the same filter as the sample. The cells were counted using an epifluorescence

microscope (Olympus BH2-RFCA, Lake Success, NY) at 1000magnification. Dilutions were

prepared so that each field contained >10 and <500 cells. Three slides were prepared from each

site (1 each per replicate sample for the 1999 samples and 3 each per sample for the 2000 samples).

Ten microscope fields were counted for each slide. A final cell population was then estimated by

multiplying by the appropriate dilution factors.
8

Table 3. Locations and water depths for sediment samples collected in the

vicinity of Prudhoe Bay during August 2000.

Sampling Sites

Grouped by

Location

Latitude Longitude Approximate

Depth (m)

Northstar

NS 12 70° 27.321 N 148° 42.078 W6

NS 13 70° 27.004 N 148° 43.552 W5

NS 14 70° 25.978 N 148° 40.459 W4

NS 15 70° 26.710 N 148° 44.570 W2

NS 18 70° 29.082 N 148° 42.151 W 11

NS 21 70° 26.819 N 148° 40.587 W5

NS 22 70° 29.340 N 148° 41.868 W9

NS 23 70° 29.340 N 148° 41.868 W 11

5 F 70° 26.486 N 148° 49.550 W2

Between Northstar

& Liberty

4 C 70° 26.144 N 147° 42.957 W9

5 D 70° 24.488 N 148° 33.605 W2

5 H 70° 22.210 N 147° 47.744 W7

5 (0) 70° 22.210 N 148° 47.744 W5

5 (1) 70° 25.024 N 148° 03.569 W6

5 (5) 70° 26.106 N 148° 18.127 W7

5 (10) 70° 27.323 N 148° 29.980 W8

Boulder Patch

4 A 70° 18.460 N 147° 40.289 W5

4 B 70° 21.034 N 147° 40.007 W7

Liberty

L 01 70° 18.930 N 147° 27.130 W7

L 04 70° 17.032 N 147° 39.897 W5

L 06 70° 16.881 N 147° 33.978 W7

L 07 70° 16.789 N 147° 31.966 W7

L 08 70° 16.701 N 147° 30.298 W6

L 09 70° 16.568 N 147° 27.130 W7

East of Liberty

3 A 70° 16.988 N 147° 05.470 W 7

3 B 70° 17.917 N 147° 02.549 W 5

Colville River

COL-01 70° 15.96 N 150° 49.29 W N/A

COL-02 70° 11.36 N 150° 52.12 W N/A

Kuparuk River

KUP-01 70° 17.70 N 148° 59.37 W N/A

KUP-02 70° 17.70 N 148° 59.37 W N/A

Sagavanirktok River

SAG-01 70° 01.68 N 148° 33.77 W N/A
9

Table 4. Percent dry weight for sediment samples collected

in the vicinity of Prudhoe Bay during August 2000.

Location Site % Dry Weight

Northstar NS 12 47.24

NS 13 50.51

NS 14 46.31

NS 15 78.70

NS 18 68.44

NS 21 44.42

NS 22 88.05

NS 23 57.69

5 F ND

Between Northstar 4 C 61.44

& Liberty 5 D 54.72

5 H 71.24

5 (0) 64.43

5 (1) 61.39

5 (5) 67.91

5 (10) 65.74

Boulder Patch 4 A 73.73

4 B 40.33

Liberty L 01 48.74

L 04 63.14

L 06 51.44

L 07 68.33

L 08 67.16

L 09 73.28

East of Liberty 3 A 60.15

3 B 64.95

Colville River COL-01 80.30

COL-02 70.44

Kuparuk River KUP-01 70.59

KUP-02 77.27

Sagavanirktok River SAG-01 75.21

ND = no data

Most probable number of crude oil emulsifiers

The populations of culturable microorganisms capable of emulsifying crude oil were estimated

using the sheen screen most probable number (MPN) technique [Brown and Braddock 1990].

Sterile Prudhoe Bay crude oil was added to the surface of each well as the carbon source for the

microorganisms. The plates were incubated at 10°C for 5 weeks before they were scored. Plates that

exhibited no growth after the initial 5-week period were then incubated at 25°C for 4 more weeks

(samples receiving additional incubation time exhibited no additional growth). Growth was indicated

via emulsification of the sheen produced from the application of oil to the surface of the liquid in the

cell wells.
10

Most probable number of heterotrophic and substrate-specific microorganisms

Heterotrophic microorganisms, and hexadecane and phenanthrene degraders were estimated using

a miniaturized most probable number method [Braddock and Catterall 1999]. For heterotroph

enumerations, the initially diluted sample was further diluted 100-fold before beginning a dilution

series in a 24-well plate and then inoculating into 96-well plates containing Marine Broth 2216

(Difco, Franklin Lakes, NJ) for culturing. For hexadecane and phenanthrene degraders, the initially

diluted sample was directly diluted in a 24-well plate then inoculated into a 96-well plate containing

marine BH with 0.025g L–1 Tetrazoleum Violet (Sigma Chemical Company, St. Louis, MO; BH-TV)

and either phenanthrene or hexadecane. For phenanthrene plates, phenanthrene was dissolved in

methanol (13 g L–1), then 10 mL of the solution was added to each well and the methanol allowed

to evaporate before adding the BH-TV medium. For hexadecane plates, 1 drop of filter-sterilized

hexadecane was added after the wells were filled with the BH-TV medium and inoculated with

sample. All plates were incubated at 10°C for 6 weeks before being scored for turbidity or a change

from clear to violet. The plates were then incubated at 25°C for 3 weeks before being scored again.

Only August 2000 heterotroph samples exhibited additional growth after additional room temperature

incubation.

Mineralization potentials

Mineralization potentials for phenanthrene and hexadecane were determined for each site using

14C-labeled substrates. The substrates used were [9-14C] phenanthrene (10.0 mCi mmol–1, 98% purity)

and [1-14C] hexadecane (5.0 mCi mmol–1) (Sigma Chemical Company). Substrate solutions were

prepared in acetone by combining 14C-labeled substrate and unlabeled substrate to yield solutions

containing 2 g substrate L–1 with activities of about 50,000 disintegrations per minute (dpm) per

50 mL of solution. Microcosms were set up [Brown et al. 1991] using the initial dilutions of the

1:10 (wt:vol) sediment slurry. Each microcosm was set up by pipetting 10 mL of diluted sample into

a 40-mL septa-capped I-Chem (Rochester, NY) vial. The microcosms were then spiked with 50 mL

of substrate solution. For each sample, triplicate vials were prepared for the 2000 samples and

5 replicate vials were prepared for the 1999 samples. The vials were incubated at 10°C for 96 hours

before adding 1 mL of 10 M NaOH to fix CO2 in solution and stop microbial activity. To determine

the amount of substrate mineralized to CO2, the vials were first acidified with 1 mL of 12 M HCl, the

carbon dioxide stripped into a CO2-sorbing scintillation cocktail containing 7.5 mL Cytoscint (ICN,

Costa Mesa, CA):2.5 mL -phenylethyl-amine (Sigma Chemical Company), and then counted in a

Beckman LS 6000SE liquid scintillation counter with automatic quench correction.

Particle analysis and organic carbon content

One sample (of triplicates) from the offshore Barrow and offshore NARL locations (see Figure 1)

and three replicates from the Elson Lagoon location were sent to the University of Washington for

particle size analysis. Results of the particle size analysis are shown in Table 5. Three sediment

samples (B1-3A, N 2-3A, and E1-3A) from three locations and with different textures were further

analyzed for percent organic carbon (Table 6). The inorganic carbon was removed from the samples

before analysis as follows: In a 40-mL glass vial (I-Chem), 0.25 mL concentrated HCl was added to

4.75 mL water followed by addition of 1 mL sediment (the sediment had a high water content which

allowed pipetting) and mixed thoroughly with a vortex mixer before storing overnight at room

temperature. The next day the vials were centrifuged (Sorvall RC-2 superspeed automatic refrigerated

centrifuge) at 3000 g for 30 s, then 4000 g for 30 s and the supernatant was removed. A pH meter

was used to measure the pH in the middle of each sample. All samples were adjusted to a final pH of 2.

The samples were then taken to the Institute of Marine Science chemical oceanography laboratory at

the University of Alaska Fairbanks for carbon analysis using infrared mass spectrometry (IRMS).
11

Table 5. Particle size analysis of sediment samples collected in the vicinity of Barrow during August

1999.

Size Class (%)

Sampling

Location

Gravel

>2 mm

Sand

2–0.05 mm

Silt

0.05–0.002 mm

Clay

<0.002 mm

Textural

Classes

Offshore Barrow

Site 1 9.22 79.36 2.27 9.07 loamy sand

Site 2 X 86.2 5.05 8.75 loamy sand

Site 3* X 83.75 3.75 12.5 loamy sand, sandy

X 70.0 10.0 20.0 sandy clay loam

X 58.0 20.0 22.0 loam

Site 4 22.6 26.3 18.6 32.5 sandy clay loam

Site 5 X 50.0 24.0 26.0 sandy clay loam

Offshore NARL

Site 1 X 14.0 54.0 32.0 silty clay loam

Site 2 X 26.0 52.0 22.0 silty loam

Site 3 X 74.0 10.0 16.0 sandy loam

Site 4 X 93.75 2.50 3.75 sand

Site 5 X 96.25 2.50 1.25 sand

Elson Lagoon

Site 1 X 92.5 1.25 6.25 sand

Site 2 X 55.0 20.75 16.25 sandy loam

Site 3 X 54.0 10.0 36.0 sandy clay

Site 4 X 3.75 43.75 52.5 silty clay

Site 5 X 46.25 27.5 26.25 sandy clay loam

*Five samples (grabs) were collected at each site. Only one sample was analyzed for particle size except at

Offshore Barrow Site 3, where three different samples were analyzed to assess variability at a given site.

Xs indicate no gravel present.
12

Table 6. Percent organic carbon content of sediment samples used for isotherm

and bioavailability assays.

% Organic Carbon Sampling Location Replicate 1 Replicate 2 Average Value

Elson Lagoon Site 1 (E1) 0.044 0.044 0.044

Offshore NARL Site 2 (N2) 1.590 1.500 1.545

Elson Lagoon Site 1 (E1) 0.088 0.093 0.091

Preparation of sediment slurries for isotherm assays

Sediment slurries were prepared via the following procedure: The sediment (~15 g) was dried

overnight at 110°C in a drying oven. Two sediment slurry solutions were prepared, one at 1% wt:vol

and one at 2% wt:vol. The appropriate amount of sediment was weighed out into tared 40-mL

I-Chem vials then capped with Teflon septa and autoclaved to sterilize both the vial and sediment.

Ten milliliters of filter sterilized (0.2 mm polyether sulfone membrane; PES) marine BH media was

added to each vial just before starting the assays.

Isotherm assays

After preparing the sediment slurries, isotherm assays (experiments to evaluate the partitioning of a

compound between sediment and aqueous phases) were set up by adding 50 mL of the appropriate

14C-phenanthrene solution (250, 500, 750 and 1000 mg L–1) and shaking for 10 s so all of the

sediment was exposed to the solution. One-milliliter aliquots were removed from the total volume

of 10 mL at 0 min, 1 min, 2 h, and 2 d (and 4 d for 2% samples). Each aliquot was filtered through a

pre-combusted (450°F for 16 h) glass fiber filter (Gelman Sciences, Ann Arbor, MI; type A/E 47)

into a sterile I-Chem vial. The filtered solution was then placed into a vial containing 10 mL Cytoscint

and the activity counted in a Beckman LS 6000SE liquid scintillation counter. The offshore NARL

slurry samples were centrifuged for 1 min at 3000  g to further separate the sediment and solution

phases since the sediment in these samples was too fine to be efficiently filtered by the Gelman filters.

Preparation of phenanthrene-degrading cultures for bioavailability assays

All phenanthrene bioavailability assays were carried out using a marine phenanthrene degrader, BIOS

2, obtained from Julia Foght at the University of Alberta, Edmonton, Canada. To prepare BIOS 2 for

experiments, it was first grown in Marine Broth 2216 (Difco) for 2 d. After 2 days, 10 vials of the

culture were prepared for storage by adding 0.8 mL of 1:1 glycerol:water to 0.8 mL culture in a

1.8-mL cryovial and freezing the vials at –10°C. Cultures were prepared for use in the bioavailability

assays by adding 1 vial of BIOS 2 to a flask containing 250 mL filtered Marine Broth 2216 and

placing it on a shaker at room temperature for 3 d. After incubation, cultures were centrifuged and

rinsed with marine BH media 3 times. The optical density was measured for each sample as an

estimate of the cell population. Samples were diluted until the absorbance was about 0.42 for each

sample to control for variance in the bioavailability assays.
13

Bioavailability assays

Solutions for bioavailability experiments were prepared to yield final solution concentrations of 250,

500, 750, and 1000 mg L–1 phenanthrene, with activities of about 50,000 dpm 50 mL–1 solution. Three

assays (0%, 1%, and 2% sediment) were set up in triplicate in 40-mL VOA (volatile organic analysis)

vials (I-Chem) with 5 concentrations of phenanthrene. Vials, sediment, and filters were prepared the

same way as for the isotherm assay. In these initial experiments, phenanthrene was added just prior

to adding the culture, thus no “aging” occurred prior to the addition of the phenanthrene degraders.

The samples were then incubated for 96 h before injecting 1 mL of 10 N NaOH to stop respiration.

The CO2 evolved from the mineralization of phenanthrene was then determined as previously

described [Brown et al. 1991]. Once the CO2 had been recovered, the radiolabeled isotopes remaining

in the aqueous phase were measured using a similar method to that described for isotherm assays.

Additional experiments were conducted in 2003 in which sediments were “unaged” or “aged” with

phenanthrene for approximately 1 or 2 months before adding BIOS 2. For the 2003 experiments,

5 replicates were run for each treatment; some mineralization potential data was rejected on the basis

of Q-tests (90% confidence level).

Comparison of chemical and biological data

Year 2000 chemical data [Brown et al. 2002] and biological data collected in this study (Table 7)

were compared using principle component analysis (PCA) and linear regression techniques. PCA

analysis was performed using The Unscrambler software (CAMO Technologies Inc., Woodbridge,

NJ) with 1/standard deviation weighting of variables. PCA modeling is used to visualize trends in

tabulated data that may be difficult to observe directly. In PCA modeling, scores plots describe the

properties of samples while loadings plots describe the relationships between variables. Linear

regression analysis was performed using Microsoft Excel software (Redmond, WA).
14

Table 7. Chemical [Brown et al. 2002] and biological data from sampling sites visited during 2000 in the vicinity of Prudhoe 

Station PAH (g kg–1) PHC (mg kg–1) S/T (g kg–1) TOC (%) Silt & Clay (%) Al (%) Ba (ppm) Hg (ppm) Pb (ppm) Cd (ppm) Hex MP Phen MP Log Total Pop Log Hetero NorthstarNS 12 1500 24.0 150 1.6 90 6.2 654 0.078 17.7 0.35 65 35 9.88 6.21 

NS 13 1100 17.0 99 1.9 91 6.69 465 0.065 11.6 0.25 103 38 9.79 7.46 NS 14 1100 24.0 150 4.4 88 5.85 555 0.087 17.3 0.45 122 48 9.82 6.02 NS 15 29 1.0 3 0.1 2.2 1.44 172 0.006 2.8 0.06 45 14 9.49 4.32 NS 18 870 12.0 77 0.5 61 3.78 271 0.033 5.2 0.16 71 27 9.91 7.1 NS 21 170 27.0 180 2.3 94 6.64 609 0.084 17.3 0.37 157 53 10.22 7.06 NS 23 540 10.0 68 1.8 99 6.25 625 0.075 20.3 0.43 81 33 6.54 5 F 420 7.8 48 0.51 49 3.43 349 0.029 8.2 0.18 97 32 9.78 4.74 Between Northstar & Liberty4 C 300 6.1 23 0.5 42 3.69 226 0.03 4.9 0.12 55 31 8.23 5 D 630 17.0 100 2 54 4.03 380 0.049 9.8 0.33 81 36 7.19 5 H 180 4.1 29 0.4 25 2.74 285 0.024 6.6 0.21 50 26 9.63 6.63 5 (0) 380 6.5 25 0.96 26 4.2 367 0.049 9.9 0.24 72 30 9.74 7.4 5 (1) 510 6.5 36 0.96 31 4.33 388 0.035 11.5 0.17 73 31 7.28 5 (5) 440 5.6 31 1.1 29 4.17 372 0.039 9.9 0.22 59 30 6.71 5 (10) 270 4.7 23 0.91 33 3.85 349 0.037 8.9 0.21 27 21 9.83 4.54 Boulder Patch4 A 630 8.1 32 0.59 85 4.48 285 0.041 6 0.18 64 27 9.93 6.85 4 B 420 16.0 55 1.2 49 5.43 305 0.058 8.9 0.17 99 52 9.72 8.4 LibertyL 01 610 12.0 62 1 66 6.18 370 0.067 10.7 0.18 63 40 9.72 7.97 L 04 400 7.7 51 0.47 60 3.66 353 0.03 9 0.26 53 20 9.76 7.03 L 06 400 11.0 51 0.9 94 4.16 252 0.039 5.7 0.19 84 30 10.27 7.05 L 07 220 6.9 20 1.5 36 3.56 233 0.045 5.5 0.19 61 27 9.91 6.83 L 08 280 12.0 41 0.24 31 2.53 343 0.025 6.4 0.15 42 38 9.83 6.83 L 09 99 1.9 11 0.49 5.3 2.64 269 0.025 9.5 0.13 62 19 9.75 6.76 East of Liberty3 A 340 7.4 36 0.29 70 3.99 400 0.044 9.6 0.26 81 34 9.9 6.89 3 B 320 6.4 28 0.58 73 4.14 288 0.038 6.3 0.17 67 28 9.69 6.58 

PAH = polycyclic aromatic hydrocarbons; PHC = petroleum hydrocarbons; S/T = sterane/triterpane ratio; TOC = total organic carbon; Hmineralization potential; Phen MP = phenanthrene mineralization potential; Total Pop = total bacterial population as estimated by direct mHetero = heterotroph populations as estimated by MPN techniques; Phen Deg = phenanthrene degrader populations as estimated by MPN hexadecane degrader populations as estimated by MPN techniques; Sheen Screen = oil degrader populations as estimated by MPN techni

14
15

Results

Enumerations

The populations of total direct counts of marine bacteria, viable heterotrophs, oil-degrading microbes,

hexadecane-degrading microbes, and phenanthrene-degrading microbes were determined. The

Prudhoe Bay samples collected in 2000 were compared to the Barrow samples collected in 1999. The

populations were compared by aggregating the sampling sites into five groups and then using oneway analysis of variance (ANOVA) to determine if there was a significant difference between groups

( = 0.05). The groups examined were: “near Barrow” (Offshore NARL and Offshore Barrow), Elson

Lagoon, “near Prudhoe Bay” (Northstar, Liberty, Between Northstar and Liberty, East of Liberty, and

the Boulder Patch), Colville River, Kuparuk River, and Sagavanirktok River. Significant differences

among groups were determined by performing Bonferroni pairwise comparisons ( = 0.05).

The mean log cell number of microorganisms per gram of sediment for the various enumeration

assays are shown in Figures 2–6. Total direct counts of bacteria (Figure 2) and the most probable

number of heterotrophs (Figure 3) showed no significant differences among any of the groups

examined. For phenanthrene degraders (Figure 4) and hexadecane degraders (Figure 5), there was

a significant difference between the near Barrow and near Prudhoe Bay groups. However, Elson

Lagoon and the three river regions had phenanthrene- and hexadecane-degrader populations that were

not significantly different from either the near Barrow or near Prudhoe Bay groups. For oil-degrader

populations (Figure 6) there were many differences among groups. In general however, the groups

in the Barrow region were significantly different from the groups in the Prudhoe Bay region.
16

Figure 2. Log of total bacteria by location as estimated by microscopic

direct count. There were no significant ( = 0.05) differences

among groups.
17

Figure 3. Log of heterotrophic most probable number of microorganisms by

location. There were no significant ( = 0.05) differences among

groups.
18

Figure 4. Log of phenanthrene-degrading most probable number of

microorganisms by location. Significant ( = 0.05) differences

among groups are indicated by letters above sample locations.
19

Figure 5. Log of hexadecane-degrading most probable number of

microorganisms by location. Significant ( = 0.05) differences

among groups are indicated by letters above sample locations.
20

Figure 6. Log of oil-degrading (sheen screen) most probable number of

microorganisms by location. Significant ( = 0.05) differences

among groups are indicated by letters above sample locations.
21

Mineralization potentials

Tables 8 and 9 summarize the mineralization potential results for samples collected during 1999

and 2000. There were no significant differences among groups for the hexadecane mineralization

potentials using Bonferroni pairwise comparisons ( = 0.05). Phenanthrene mineralization potentials

showed significant differences among the Barrow region groups and the near Prudhoe Bay group.

However, all phenanthrene mineralization potentials measured were very low.

Table 8. Mineralization potentials in 96-hour assays of substrate-specific

degrading microorganisms in sediment samples collected in the

vicinity of Barrow during August 1999.

Mineralization Potential

(ng substrate mineralized • g dry wt–1 sediment) Sampling

Location Hexadecane Phenanthrene

Offshore Barrow

Site 1 57 ± 2 12 ± 1

Site 2 38 ± 4 7 ± 1

Site 3 35 ± 4 11 ± 1

Site 4 134 ± 4 39 ± 2

Site 5 51 ± 4 18 ± 2

Offshore NARL

Site 1 100 ± 15 15 ± 2

Site 2 86 ± 5 15 ± 3

Site 3 62 ± 7 13 ± 1

Site 4 59 ± 4 19 ± 1

Site 5 43 ± 5 10 ± 1

Elson Lagoon

Site 1 46 ± 4 12 ± 1

Site 2 90 ± 5 21 ± 2

Site 3 56 ± 2 15 ± 2

Site 4 127 ± 6 30 ± 4

Site 5 35 ± 4 11 ± 2

Isotherm assays

Isotherm assays were preformed using offshore Barrow, Elson Lagoon and offshore NARL sediment

samples. Apparent partition coefficients (Kp) were determined from the slopes of lines formed when

aqueous phenanthrene concentrations were plotted against sediment phenanthrene concentrations

(Figure 7). In general, Kp values (Table 10) increased with time, indicating that phenanthrene

increased its affinity for sediment over time. Kp values for offshore NARL samples were much

higher than the offshore Barrow or Elson Lagoon samples. This is most likely due to the higher

organic content of the offshore NARL sediment compared to the other two sites (Table 6).
22

Table 9. Mineralization potentials in 96-hour assays of substrate-specific

degrading microorganisms in sediment samples collected in the

vicinity of Prudhoe Bay during August 2000.

Mineralization Potential

(ng substrate mineralized • g dry wt–1 sediment) Sampling

Location Hexadecane Phenanthrene

Northstar

NS 12 65 ± 19 35 ± 5

NS 13 103 ± 19 38 ± 4

NS 14 122 ± 7 48 ± 4

NS 15 45 ± 4 14 ± 1

NS 18 71 ± 13 27 ± 1

NS 21 157 ± 9 53 ± 3

NS 22 44 ± 4 13 ± 0

NS 23 81 ± 11 33 ± 1

5 F 97 ± 9 32 ± 3

Between Northstar

& Liberty

4 C 55 ± 10 31 ± 2

5 D 81 ± 13 36 ± 3

5 H 50 ± 8 26 ± 2

5 (0) 72 ± 8 30 ± 2

5 (1) 73 ± 8 31 ± 2

5 (5) 59 ± 7 30 ± 2

5 (10) 27 ± 8 21 ± 2

Boulder Patch

4 A 64 ± 7 27 ± 2

4 B 99 ± 6 52 ± 5

Liberty

L 01 63 ± 4 40 ± 4

L 04 53 ± 8 20 ± 5

L 06 84 ± 11 30 ± 2

L 07 61 ± 8 27 ± 2

L 08 42 ± 19 38 ± 8

L 09 62 ± 6 19 ± 3

East of Liberty

3 A 81 ± 14 34 ± 2

3 B 67 ± 5 28 ± 2

Colville River

COL-01 35 ± 0 15 ± 1

COL-02 46 ± 4 19 ± 3

Kuparuk River

KUP-01 58 ± 10 19 ± 1

KUP-02 133 ± 10 21 ± 2

Sagavanirktok River

SAG-01 50 ± 4 19 ± 1
23

Figure 7. Isotherms for 1% and 2% sediment slurries for sediments collected from: (a) offshore

Barrow, (b) offshore NARL, and (c) Elson Lagoon. The offshore Barrow and Elson Lagoon

sediments had <1% organic carbon content compared to the offshore NARL sediment with

a 1.5% organic carbon content. Note scale difference on the x-axis in panel b.
24

Table 10. Partition coefficients obtained from isotherm assays.

Apparent Kp (mL g–1) Sampling

Location

Reaction

Time 1% Sediment 2% Sediment

Offshore Barrow 1 minute 35.5 16.8

2 hours 81.4 48.1

2 days 49.2 45.0

4 days ND 58.9

Offshore NARL 15 minutes 170.1 230.6

2 hours 774.2 824.6

2 days 2131.7 1610.5

4 days 2411.1 4592.2

Elson Lagoon 1 minute 26.7 11.9

2 hours 40.1 28.5

2 days 64.2 50.3

4 days ND 74.7

ND = no data

Bioavailability assays

The bioavailability of phenanthrene did not generally appear to be a function of the amount of

sediment added or the sediment composition. Despite differences in sediment composition among

offshore Barrow, offshore NARL, and Elson Lagoon samples, there was no significant difference

in the percent phenanthrene mineralized for the different concentrations of sediment slurries in the

initial set of unaged experiments (Figure 8). In a similar experiment replicated in 2003 using samples

collected from different grabs at two of the same locations as were used in the initial experiments,

similar data were collected (Figure 9). Parallel experiments were set up in which phenanthrene

was aged with sediment for one month (Figure 10) or two months (Figure 11) before adding

phenanthrene-degrading bacteria. Interestingly, the percent phenanthrene mineralized following

aging was greater in all cases than in the unaged experiments. There did not appear to be a significant

difference between the two sediments used in these experiments. However, the one-month incubation

appeared to result in the highest bioavailability of phenanthrene to the microbial culture used. The

data suggest that the bioavailability of phenanthrene increases with time irrespective of the sediment

loading or the amount of phenanthrene added to the samples.

The amount of phenanthrene accounted for via mineralization and in the supernatant was not

significantly different among sediment types, sediment slurry concentration, or concentration of

phenanthrene added. Table 11 shows that even when there was a significant difference between the

amount of phenanthrene in the supernatant or mineralized samples, the total amount of phenanthrene

accounted for is similar no matter what sediment type or sediment concentration was used.
25

Figure 8. Phenanthrene mineralized from bioavailability

assays of sediment samples from: (a) offshore

Barrow, (b) offshore NARL, and (c) Elson

Lagoon.
26

Figure 9. Phenanthrene mineralized from 2003 bioavailability assays of unaged

sediment samples from: (a) offshore NARL and (b) Elson Lagoon.
27

Figure 10. Phenanthrene mineralized from 2003 bioavailability assays of sediment

samples aged 1 month from: (a) offshore NARL and (b) Elson Lagoon.
28

Figure 11. Phenanthrene mineralized from 2003 bioavailability assays of sediment

samples aged 2 months from: (a) offshore NARL and (b) Elson Lagoon.
29

Table 11. Total percent phenanthrene recovered from mineralization and supernatant.

Sampling

Location

Phenanthrene

Concentration

Added

(g L–1)

0% Sediment 1% Sediment 2% Sediment

Offshore Barrow 250 47 ± 22 37 ± 17 51 ± 7

500 52 ± 21 38 ± 18 49 ± 12

750 60 ± 16 55 ± 20 54 ± 10

1000 58 ± 9 62 ± 8 62 ± 8

Offshore NARL 250 66 ± 3 65 ± 9 67 ± 8

500 29 ± 13 60 ± 6 23 ± 22

750 47 ± 23 58 ± 15 70 ± 7

1000 69 ± 3 55 ± 26 49 ± 14

Elson Lagoon 250 62 ± 8 32 ± 19 47 ± 8

500 53 ± 17 54 ± 27 47 ± 18

750 32 ± 15 61 ± 7 65 ± 6

1000 53 ± 14 68 ± 10 65 ± 6

Comparison of chemical and biological data

Results of principle component analysis of the chemical and biological data are shown in Figure 12.

The Scores plot in Figure 12 indicates that sample locations NS12, NS3, NS14, NS15, NS21, NS23

and 5F are likely different than the rest of the samples. The X-loadings plot indicates that the

bacterial enumeration variables behave differently than (and thus will not be good predictors of) the

rest of the variables.

Results of regression analyses are summarized in Table 12. As might be expected, the strongest

correlations are found between similar types of variables (chemical vs. chemical or biological vs.

biological). As predicted by the PCA model, the bacterial enumeration variables are not well

correlated (r2 < 0.50) with any of the chemical variables with one exception. Phenanthrene degraders

are reasonably correlated (r2 = 0.53) with aluminum content in the sediment samples. Phenanthrene

mineralization potentials were most strongly correlated with petroleum hydrocarbons (r2 = 0.66),

mercury levels (r2 = 0.58) and aluminum levels (r2 = 0.52). Hexadecane mineralization potentials were

most strongly correlated with petroleum hydrocarbons (r2 = 0.52) and the sterane/triterpane (S/T) ratio

(r2 = 0.54).
30

Figure 12. Scores and loadings plots from principle component analysis of chemical and biological data collected in 2000.

30
31

Table 12. Coefficients of determination (r2) for pairwise linear regressions of chemical [Brown et al. 2002] and biolog

Biological Chemical

Hex

MP

Phen

MP

Total

Pop Hetero Phen Deg Hex Deg Sheen Screen Al Ba Hg 

ChemicalPAH 0.07 0.12 0.01 0.01 0.13 0.11 0.00 0.39 0.34 0.36 PHC 0.52 0.66 0.23 0.05 0.18 0.17 0.00 0.56 0.53 0.68 S/T 0.54 0.49 0.22 0.01 0.13 0.11 0.00 0.54 0.64 0.66 TOC 0.43 0.39 0.07 0.00 0.18 0.13 0.00 0.44 0.44 0.66 Silt & Clay 0.34 0.27 0.39 0.04 0.34 0.16 0.04 0.61 0.39 0.54 Al 0.41 0.52 0.15 0.14 0.53 0.30 0.08 0.60 0.88 Ba 0.29 0.32 0.11 0.00 0.20 0.12 0.00 0.70 Hg 0.46 0.58 0.16 0.07 0.44 0.28 0.03 Pb 0.30 0.29 0.08 0.00 0.22 0.13 0.01 Cd 0.31 0.26 0.15 0.00 0.22 0.16 0.01BiologicalHex MPPhen MP 0.58Total Pop 0.23 0.13Hetero 0.05 0.20 0.06Phen Deg 0.06 0.21 0.15 0.31Hex Deg 0.02 0.19 0.14 0.48 0.74Sheen Screen 0.00 0.14 0.03 0.11 0.09 0.08

Hex MP = hexadecane mineralization potential; Phen MP = phenanthrene mineralization potential; Total Pop = total bacterial popestimated by direct microscopic counting; Hetero = heterotroph populations as estimated by MPN techniques; Phen Deg = phenanpopulations as estimated by MPN techniques; Hex Deg = hexadecane degrader populations as estimated by MPN techniques; Shedegrader populations as estimated by MPN techniques; PAH = polycyclic aromatic hydrocarbons; PHC = petroleum hydrocarbonssterane/triterpane ratio; TOC = total organic carbon

31
32

Discussion

Microbial population data collected for this study were used in two major ways. First, data from

this study were compared to similar data collected in the 1970s and 1980s. Second, data collected

near a relatively undeveloped area, Barrow, was compared to data collected near a heavily developed

area, Prudhoe Bay. Historical trends in data can provide insight into how specific locations or

environments have changed over time.

The data collected in 1999–2000 indicate that total bacterial numbers estimated by microscopic

direct counts (see Figure 2) were about ten times greater than those measured in the 1970s (Table 13).

It is not clear if this is due to the slightly different methods used for estimating numbers or actual

population increases. However, in both the 1970s and this study, it is interesting to note that the total

numbers estimated in arctic regions are higher than similar data from more temperate regions [see

Kaneko et al. 1978; Braddock et al. 1995 and Table 13]. An ANOVA test ( = 0.05) of the total

bacterial population data (Figure 2) shows no significant differences among the analysis groups.

Therefore, whatever the source of the increased population estimates, the difference is probably not

due to development activities (Barrow, which is “undeveloped”, is no different than a “developed”

area like Prudhoe Bay).

Heterotrophic population estimates for this study are substantially lower than the total microorganism

population (see Figures 2 and 3). A number of factors may account for this difference. First, the total

microbial count does not distinguish between living, dead, or inactive cells. Second, the laboratory

conditions set up to grow these microorganisms are likely not optimal for many members of the

population. Whatever the reason, it is common to find large differences in total direct counts of

microorganisms and heterotroph counts [Kaneko et al. 1978; Atlas and Griffiths 1987]. The range

of log total viable count concentrations reported for summer 1975 and 1976 was 4.7 to 6.9 for sites

in the Beaufort Sea and Elson Lagoon [Kaneko et al. 1978; Atlas and Griffiths 1987 and Table 13].

In this study, heterotroph population estimates range from 6.0 to 7.1 with no significant differences

among groups (Figure 3). Again, development does not appear to have affected heterotrophic

populations.

With regard to phenanthrene- and hexadecane-degrader populations, there is no data for comparison

since previous studies did not look at populations of microorganisms capable of degrading specific

components of petroleum hydrocarbons. For locations near Barrow, phenanthrene- and hexadecanedegrader populations (Figures 4 and 5) were significantly lower than locations near Prudhoe Bay.

However, this is not apparently due to anthropogenic hydrocarbon contamination [Brown et al. 2002].

Elevated populations may be due to variations in sediment composition. However, phenanthrene and

hexadecane degrader populations are not well correlated (Table 12) with any of the physical or

chemical variables with one exception. Phenanthrene degraders are reasonably correlated (r2 = 0.53)

with aluminum content in the sediment samples. However, the linkage between these two variables

is not obvious.

Oil-degrading microorganism populations at locations near Prudhoe Bay were also significantly

greater than for locations near Barrow (Figure 6). The population estimates near Prudhoe Bay

were 1–2 orders of magnitude higher than the near Barrow and Elson Lagoon groups. Haines and

Atlas [1982] found that oil degraders in control sediments never exceeded 100 cells • g dry wt–1,

which corresponds with the Elson Lagoon and near Barrow populations. Braddock et al. [1995]

found that sites unaffected by the Exxon Valdez Oil Spill (EVOS) had populations less than

10,000 cells • g dry wt–1 and used this number as a threshold to distinguish contaminated samples

from uncontaminated samples.
33

All of the sites within the Elson Lagoon, offshore Barrow, and offshore NARL locations had oildegrader populations lower than 100 cells • g dry wt–1 as opposed to all the sites within the near

Prudhoe Bay, Kuparuk River, Colville River, and Sagavanirktok River regions, where populations

were all higher than 100 cells • g dry wt–1 but less than 10,000 cells • g dry wt–1. The population of

oil degraders found in Kuparuk River samples was greater than the population found near Prudhoe

Bay, while the Colville River and Sagavanirktok River samples had populations lower than locations

near Prudhoe Bay. Again, however, these somewhat higher oil-degrader population estimates do not

appear to be related to anthropogenic inputs of hydrocarbons and all are lower than the threshold

value set for uncontaminated sites examined after the EVOS [Braddock et al. 1995].

Table 13. Microbial population estimates from previous studies.

Location Date

Log of

Total

Direct

Counts

Log of

Total

Viable

Organisms

Log of

Concentration

of

Hydrocarbon

Degraders

Reference

Pt. Barrow Sum 78 — — 3.48 Atlas et al. [1978]

Pt. Barrow Sum 75 — 4.72 — Kaneko et al. [1979]

Beaufort Sea Sum 75 7.79 5.00–6.00 — Kaneko et al. [1978]

Beaufort Sea Sum 76 9.32 5.00–6.00 — Kaneko et al. [1978]

Elson Lagoon Sum 75 — 5 — Kaneko et al. [1979]

Elson Lagoon Sum 75 — 5.04 — Kaneko et al. [1979]

Off Oliktok Pt. Sum 75 — 4.94 — Kaneko et al. [1979]

Prudhoe Bay Sum 75 — 5.36 — Kaneko et al. [1979]

Between Northstar

& Liberty Sum 75 — 4.83 — Kaneko et al. [1979]

Between Northstar

& Liberty Sum 75 — 4.99 — Kaneko et al. [1979]

Elson Lagoon Sum 81 8.65–8.791 — 1.48–4.382 Haines & Atlas [1982]

Beaufort Sea Sum 75 8.8 ± 8.0 6.0 ± 6.0 — Atlas & Griffiths [1987]

Beaufort Sea Sum 76 9.3 ± 8.9 6.9 ± 6.8 — Atlas & Griffiths [1987]

Beaufort Sea Sum 78 9.2 ± 8.9 6.72 ± 6.51 4.4 ± 4.3 Atlas & Griffiths [1987]

Norton Sound Sum 79 8.3 ± 8.3 — 3.9 ± 3.9 Atlas & Griffiths [1987]

Prince William

Sound Study Sites Sum 89 6.9–9.0 — <1.3–6.3 Braddock, Lindstrom& Brown [1995]

Prince William

Sound Study Sites Sum 89 7.0–8.9 — — Braddock, Lindstrom& Brown [1995]

Prince William

Sound Study Sites Sum 90 — — <1.3–5.1 Braddock, Lindstrom& Brown [1995]

Prince William

Sound Study Sites Sum 91 — — <1.3–3.2 Braddock, Lindstrom

& Brown [1995]

1 Highest value in range was after four months.

2 Highest value was after two years of exposure.
34

Mineralization potentials for both hexadecane and phenanthrene degraders were quite low.

Mineralization potentials for hexadecane never exceeded 157 ng substrate mineralized • g dry wt–1

sediment (Tables 8 and 9). The mineralization potentials for phenanthrene were even lower, with

the highest value being 53 ng substrate mineralized • g dry wt–1 sediment (Tables 8 and 9). The

values observed in this study are very low when compared to values measured for the EVOS. Unoiled

sites for the EVOS had hexadecane and phenanthrene mineralization potential values ranging from

0 to 400 ng substrate mineralized • g dry wt–1 sediment. Values for EVOS oiled sites ranged as high

as 90,000 ng (hexadecane) and 104,000 ng (phenanthrene) hydrocarbon mineralized • g dry wt–1

sediment [Braddock et al. 1996]. Thus, even the highest mineralization potentials observed in this

study were considerably lower than values observed for unoiled sediments in more temperate

climates. The low mineralization potential values indicate that the native populations of

microorganisms in the study area are not acclimated to mineralize hexadecane or phenanthrene

(and may not readily acclimate to degrade hydrocarbons of any type).

The isotherm studies indicate that adsorption was rapid. Kp values generally decreased with

increasing sediment concentration and increased with time (Table 10). Henrichs et al. [1997] reported

a similar result. The decrease in apparent Kp values with increased sediment concentrations may be

due to the binding of the hydrocarbons by the dissolved or colloidal components of the slurry

[Henrichs et al. 1997]. NARL sediments adsorbed phenanthrene more rapidly and to a greater extent

than did sediments from offshore Barrow or Elson Lagoon. This is most likely related to the higher

organic carbon content of the offshore NARL sediment compared to the other sites (Table 6). Organic

carbon content of sediments is often a factor in adsorption of compounds like phenanthrene [e.g., see

Braddock and Richter 1998]. The question we were ultimately interested in was: “How does

adsorption to these sediments affect the bioavailability of a model PAH, like phenanthrene?”

Unexpectedly, sediment type and sediment concentration did not appear to influence the amount

of phenanthrene mineralized in the bioavailability assays. There are at least two possibilities to

explain why there was no relationship between sediment concentration (or type) and the amount of

phenanthrene mineralized. It is possible that: 1) phenanthrene did not have time to tightly adsorb to

the sediment before significant microbial mineralization occurred, or 2) the phenanthrene degraders

could mineralize phenanthrene both in solution and bound to sediment particles. Since phenanthrene

was adsorbed rapidly in isotherm assays but mineralized to a greater extent in “aged” experiments

compared to “unaged” experiments, it would appear that for this system, phenanthrene degraders

were able to readily use phenanthrene associated with the sediment. A similar result was reported

using Cook Inlet sediments [Braddock and Richter 1998]. The implication of these studies is that

phenanthrene associated with sediments in the environment may not be less bioavailable to

microorganisms. However, naturally occurring populations did not appear to be acclimated to

mineralize phenanthrene and it is not clear how rapidly these populations might respond should

a spill occur.

Overall, the PC1 and PC2 of the PCA model used for the variables examined in this study account for

roughly 69% of the total variance of the samples. As a result, the predictive capability of the model

should be reasonably good in most cases. Principle component analysis of chemical [Brown et al.

2002] and biological variables yielded two main results: First, a subgroup of sampling sites (NS12,

NS3, NS14, NS15, NS21, NS23 and 5F) appear to be different than most of the other sampling sites

(see the Scores plot in Figure 12). The “different” sites are all geographically clustered south of

Northstar. Based on an examination of all the data in Table 7, it seems likely that the high silt and

clay content of these samples is the reason that they appear different in the principle component

analysis. The second interesting result from the PCA is that bacterial enumeration estimators do not

vary systematically in the same way as the other variables examined. As shown in the X-loadings plot
35

of Figure 12, most of the microbial enumeration variables have a significant PC2 axis component

that is not present for the other variables. The X-loadings plot also indicates that there is probably

not a strong correlation between any of the population estimator variables as a result of their wide

distribution along the PC1 axis.

The results of the linear regression analyses (Table 12) support the findings of the principle

component analysis with respect to the microbial enumeration variables. Most of the enumeration

variables are poorly correlated (r2

<0.5) with any of the other variables examined in this study. The

lone exception is the phenanthrene-degrader variable which is reasonably well correlated with the

aluminum content (r2 = 0.53) of the sediment samples and the hexadecane population estimator

variable (r2 < 0.74). The correlation between hexadecane degraders and phenanthrene degraders may

be due to the presence of naturally occurring sources of PAH and straight-chain hydrocarbons which

allows for the growth of both types of organisms. Naturally occurring aluminum concentrations have

been shown to vary “as a function of sediment grain size, organic carbon level and mineralogy”

[Trefry et al. 2003]. Thus the correlation between the population of phenanthrene degraders and

aluminum is likely attributable to particle surface area. Not unexpectedly, petroleum hydrocarbons

and steranes & triterpanes, both of which are sources of straight-chain hydrocarbons, are reasonably

well correlated with hexadecane mineralization potential (an indicator test for straight-chain

hydrocarbon utilization). In general, there are no strong correlations (r2 > 0.7) among any of the

chemical and biological variables. This is probably due to a variety of complex interactions, each of

which accounts for a relatively small amount of total system variance.

Conclusions

The surveys of the native microbial communities associated with the “near Barrow”, Elson Lagoon,

“near Prudhoe Bay” and three rivers’ sediments indicate that: 1) estimates of total microscopic counts

of bacteria and culturable heterotrophs are comparable to estimates obtained in the same region

during studies performed in the 1970s and 1980s; 2) there are population differences of phenanthrene,

hexadecane, and oil degraders between the regions offshore of Barrow and those offshore of Prudhoe

Bay not attributable to petroleum hydrocarbon contamination, particle size or total organic carbon;

3) total microbial populations measured in Arctic Ocean sediments are high compared to those

reported for temperate regions, including Prince William Sound; and 4) mineralization potentials

for both phenanthrene and hexadecane are very low, indicating that the microbial population is not

acclimated to use these model compounds. Laboratory analyses using sediments collected near

Barrow showed that: 1) phenanthrene is rapidly adsorbed to sediments collected in this study; 2) the

extent of adsorption is at least partially related to organic carbon content of the sediments; and

3) unexpectedly, the presence of sediment did not reduce the bioavailability of phenanthrene, even

when phenanthrene/sediment mixtures were “aged” for up to two months before inoculation with

phenanthrene-degrading organisms. Comparison of chemical and biological data yielded only

relatively weak correlations among the variables studied. Although PCA modeling of the data could

account for 69% of the global variance of the system, no single chemical variable could be identified

as a good predictor of any of the biological variables.
36

Study Products

Braddock, J.F., and K.A. Gannon. 2000. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments, p. 69–77. In University of Alaska Coastal Marine Institute Annual

Report No. 7. OCS Study MMS 2000-070, University of Alaska Fairbanks and USDOI, MMS,

Alaska OCS Region.

Braddock, J.F., and K.A. Gannon. 2000. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments. Minerals Management Service Information Transfer Meeting,

February 2000, Anchorage.

Braddock, J.F., and K.A. Gannon. 2000. Petroleum hydrocarbon degrading microbial communities.

University of Alaska Coastal Marine Institute Annual Research Review, March 2000, Fairbanks.

Braddock, J.F., and K.A. Gannon. 2001. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments. University of Alaska Coastal Marine Institute Annual Research

Review, February 2001, Fairbanks.

Braddock, J.F., and K.A. Gannon. 2001. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments. American Society for Microbiology–Alaska Chapter 17th Annual

Meeting, April 2001, Anchorage.

Braddock, J.F., and K.A. Gannon. 2001. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments. Minerals Management Service Information Transfer Meeting, April

2001, Anchorage.

Braddock, J.F., and K.A. Gannon. 2002. Petroleum hydrocarbon degrading microbial communities

in Beaufort–Chukchi Sea sediments, p. 65–72. In University of Alaska Coastal Marine Institute

Annual Report No. 8. OCS Study MMS 2002-001, University of Alaska Fairbanks and USDOI,

MMS, Alaska OCS Region.

Braddock, J.F., and K.A. Gannon. 2003. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments (Phase II) [Outreach perspective]. University of Alaska Coastal Marine

Institute Annual Research Review, February 2003, Fairbanks.

Braddock, J.F., and K.A. Gannon. 2003. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments. Minerals Management Service Information Transfer Meeting, March

2003, Anchorage.

Braddock, J.F., K.A. Gannon and B.T. Rasley. 2004. Petroleum hydrocarbon degrading microbial

communities in Beaufort–Chukchi Sea sediments, p. 9. In University of Alaska Coastal Marine

Institute Annual Report No. 10. OCS Study MMS 2004-002, University of Alaska Fairbanks and

USDOI, MMS, Alaska OCS Region.

Braddock, J.F., K.A. Gannon and B.T. Rasley. 2004. Petroleum hydrocarbon–degrading microbial

communities in Beaufort–Chukchi Sea sediments. Final Report. OCS Study MMS 2004-061,

University of Alaska Coastal Marine Institute, University of Alaska Fairbanks and USDOI,

MMS, Alaska OCS Region, 38 p.

Gannon, K.A. 2002. Petroleum hydrocarbon degrading microbial communities of Arctic Ocean

sediment. M.S. Thesis, University of Alaska Fairbanks, 95 p.

Lindstrom, J.E., and J.F. Braddock. 2000. Petroleum hydrocarbon degrading microbial communities

in Beaufort Sea sediments, p. 81. In University of Alaska Coastal Marine Institute Annual Report

No. 6. OCS Study MMS 2000-046, University of Alaska Fairbanks and USDOI, MMS, Alaska

OCS Region.
37

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