ACCESS NUMBER: TO-15175

STUDY TITLE: Petroleum Hydrocarbon–Degrading Microbial Communities in Beaufort Sea Sediments 

REPORT TITLE: Petroleum Hydrocarbon–Degrading Microbial Communities in Beaufort–Chukchi Sea 

Sediments 

CONTRACT NUMBER: 1435-01-98-CA-30909; TASK ORDER (TO): 15175 

SPONSORING OCS REGION: Alaska 

APPLICABLE PLANNING AREA: Beaufort–Chukchi Sea 

FISCAL YEAR OF PROJECT FUNDING: 1999 

COMPLETION DATE OF REPORT: November 2004 

COSTS: FY 1999: $49,922, FY 2000: $31,139, FY 2002: $25,849 

CUMULATIVE PROJECT COST: $106,910 

PROJECT MANAGER: Joan F. Braddock 

AFFILIATION: University of Alaska Fairbanks 

ADDRESS: Institute of Arctic Biology; University of Alaska Fairbanks; Fairbanks, AK 99775-7000 

PRINCIPAL INVESTIGATOR*: Joan F. Braddock 

KEY WORDS: biodegradation, microbial populations, marine sediment, arctic 

BACKGROUND: 

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

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

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

mechanism for petroleum hydrocarbons released into the environment. 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 break down 

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. 

OBJECTIVES: 

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 (ANIMIDA Project). 

DESCRIPTION: 

We conducted surveys (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 used direct microscopic methods to determine the total numbers of 

bacteria, and most probable number methods to determine populations of crude oil degraders, culturable 
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heterotrophs, and hexadecane and phenanthrene degraders in marine sediment samples. We also used 

radiorespirometry to examine the effect of sediment on bioavailability of a polycyclic aromatic 

hydrocarbon (phenanthrene) to hydrocarbon-degrading bacteria in the presence and absence of 

sediment.

SIGNIFICANT CONCLUSIONS: 

The surveys of the native microbial communities in sediments collected in this study 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 phenanthrenedegrading 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. 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. 

STUDY RESULTS: 

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 also 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. 

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. 
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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. 

*P.I.’s affiliation may be different than that listed for Project Manager. 
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Sampling sites in the Barrow and Prudhoe Bay regions. The Colville River lies to the west of the Prudhoe 

Bay Region. 
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Applicable planning area: Beaufort–Chukchi Sea area of the Arctic Subregion.