ACCESS NUMBER: M14AC00020

STUDY TITLE: Biodegradation and Transport of Crude Oil in Sand and Gravel Beaches of 

Arctic Alaska

REPORT TITLE: Technical Summary

CONTRACT NUMBER: M14AC00020

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA(S): Chukchi and Beaufort Seas

FISCAL YEAR(S) OF PROJECT FUNDING: 2014-16

COMPLETION DATE OF REPORT: July 2015

COSTS: $56,310

PROJECT MANAGER(S): 

LEAD AUTHOR OF REPORT: Dr. Silke Schiewer

AFFILIATION: University of Alaska Fairbanks

ADDRESS: Department of Civil & Environmental Eng., PO Box 755900, Fairbanks, AK, 99775

PRINCIPAL INVESTIGATOR(S): Dr. Silke Schiewer

KEY WORDS: crude oil, bioremediation, fate and transport, volatilization, TPH, beach sediment

BACKGROUND:

Offshore oil production along Alaska’s arctic coast is expected to increase in coming years. 

While this will create economic benefits for the state, crude oil spills may occur which could 

cause adverse ecological effects, particularly at the shoreline. Therefore is important to remove 

spilled oil; however, remediation strategies have to be tailored to the specific environmental 

conditions present at the contaminated site, such as the sediment type, salinity, and 

temperature. Biodegradation by microbes can contribute to hydrocarbon removal, but this 

process can be nutrient-limited. Mass transfer processes also play an important role in

determining the fate of crude oil along shorelines. Biodegradation and mass transfer processes 

are both strongly dependent on temperature and sediment material. It is, therefore, necessary to 

study how the beach matrix, salinity, temperature, and nutrient addition affect the fate of 

hydrocarbons in sediments.

OBJECTIVES:

1) Investigate the combined effects of varying sediment types, temperatures, crude oil 

concentrations and salinities on the fate of crude oil in laboratory experiments 

simulating environmental conditions along Alaska’s arctic shore. 

2) Quantify to what extent crude oil is mineralized, volatilized or remaining in the sediment.

3) Understand the transport of crude oil within different types of beach matrix over time.

4) Evaluate the potential for bioremediation as part of an oil spill response along Arctic 

shorelines.

DESCRIPTION:

Biodegradation was studied in laboratory microcosms as a proxy for actual oil spill 

bioremediation on the Arctic shoreline. Typical sand/gravel beach sediments obtained from 

Barrow, AK, were spiked with a known volume of crude oil as the contaminant, amended with 

nutrients, and incubated. Microcosm experiments were designed to investigate the effect of 

varying temperature (3°C vs. 20°C), crude oil dosage (1 mL vs 5 mL) and salinity (30 g/L vs 35 

g/L) on the fate of crude oil. CO2 production (respiration) was quantified to determine the 

amount of hydrocarbons mineralized. Volatilization was measured by capturing volatiles in 

activated carbon followed by analysis via GC/MS. Hydrocarbons remaining in the sediments 

were extracted and quantified by GC/FID. The MPN method was used to quantify numbers of 

hydrocarbon degraders. Mini-columns were used to study mass transfer, simulating conditions 

of the Chukchi and Beaufort Seas shorelines, respectively, where pebble vs. sandy-gravel

sediment was predominant. The effectiveness of fertilizer addition (both solid and liquid) was 

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examined to determine if nutrient addition had a significant impact on CO2 production. Studies 

were performed at two different temperatures (3°C and 20°C). Crude oil fate was determined by 

tracking its movement through the sediment profile (top, middle, and bottom) for two different 

sediment types using GC/FID. The objective was to determine whether petroleum hydrocarbons 

were washed out, converted to CO2 or volatilized.

STUDY RESULTS: 

Microcosm Experiments. While increased salinity had a small positive effect on respiration, 

there was no clear effect of crude oil dosage on CO2 production. CO2 production was clearly 

higher at 20°C than at 3°C. However, even at 20°C, only a small percentage of the initially 

present hydrocarbons (less than 10 % in most cases) was mineralized to CO2. A larger 

percentage (40 % on average) of initially present hydrocarbons was volatilized and captured by 

activated carbon in the head space. Most of the volatilization took place during the first week. 

Surprisingly, volatilization at 20°C and 3°C was similar. Larger quantities (but smaller 

percentages) of hydrocarbons were volatilized at the higher crude oil dosage. On average, 

approximately 70% of hydrocarbons remained in the sediment after six weeks. The average 

recovery of hydrocarbons, calculated as CO2 + volatiles captured in activated carbon + TPH 

remaining in the sediment, was 114%. This over-recovery can be explained by organic carbon 

initially present in the sediment, which lead to substantial CO2 production even in the absence 

of crude oil.

Mini-column Experiments. In pebble sediment, TPH concentrations were initially highest at the 

top of the column but hydrocarbons quickly moved through the column; after 3-6 days the 

highest concentrations were observed at the bottom of the column. After 18 days, 

concentrations across the columns containing pebble sediment were at low background levels. 

In sandy-gravel, on the other hand, the highest TPH concentrations were observed in the middle 

of the column. In both sediments, TPH levels tended to decrease over time, however with 

considerably higher hydrocarbon levels remaining in sandy-gravel. While respiration was initially 

slightly higher in pebble sediment, CO2 production in sandy-gravel over time surpasses that in 

pebble. TPH levels at 3°C and 20°C were overall generally similar; in sandy-gravel, TPH tended 

to be higher at 20°C; in pebble sediment TPH tended to be higher at 3°C. While CO2 production 

was initially similar for both temperatures, respiration values at 20°C clearly exceeded those 

observed at 3°C by the end of the 18-day experiment. Fertilizer addition had little impact on the 

TPH levels or the amount of CO2 released.

SIGNIFICANT CONCLUSIONS:

Microcosm experiment showed that approximately 40% of hydrocarbons were removed from the 

sediment after six weeks, most of that by volatilization, which occurred quickly even at the lower 

temperature. However, the remaining longer chain hydrocarbons cannot be removed as easily. 

While CO2 production increased with increasing temperature, only a small percentage of the 

crude oil was mineralized to CO2 after six weeks. This implies that bioremediation would have 

very limited success over the studied period. However, more biodegradation would likely occur 

over longer time frames. In mini-columns, hydrocarbons were easily transported through the 

pebble sediment, effectively being washed out from the mini-columns after 18 days. Due to 

smaller pore sizes, hydrocarbons did not move as easily through the sandy-gravel, pooling in 

the middle of the column. This indicates that wash-out by tidal and wave action may contribute 

to hydrocarbon removal from pebbly beaches but less so for sandy beaches. Overall, 

considerably higher TPH levels remained in sandy-gravel than in pebble sediment, indicating 

that the former presents a greater clean-up challenge. Apparently biodegradation was not the 

main factor in hydrocarbon removal since sandy-gravel showed higher remaining TPH levels in 

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spite of higher mineralization. Fertilizer addition does not appear necessary since it had very 

limited impact on TPH levels and respiration.

STUDY PRODUCT(S): 

The results of this project have been presented at several venues including: Alaska Oil Spill 

Technology Symposium 2014 and 2015; American Water Resources Association Conference

2014; Outreach presentation at Ilisagvik College, Barrow, 2015; and CMI Annual Research 

Review, Anchorage, 2015. This research supported the MS thesis work of Anna Iverson 

(Assessing the fate of crude oil in arctic coastline sediments: effect of exposure time and 

sediment structure, UAF, 2015) and Priyamvada Sharma (Crude oil bioremediation in arctic 

seashore sediments, UAF, 2015). Manuscripts for peer-reviewed journals are in preparation.

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