In situ biodegradation, photooxidation and dissolution of petroleum compounds in Arctic seawater and sea ice

Abstract

In pristine sea ice-covered Arctic waters the potential of natural attenuation of oil spills has yet to be uncovered, but increasing shipping and oil exploitation may bring along unprecedented risks of oil spills. We deployed adsorbents coated with thin oil films for up to 2.5 month in ice-covered seawater and sea ice in Godthaab Fjord, SW Greenland, to simulate and investigate in situ biodegradation and photooxidation of dispersed oil. GC-MS-based chemometric methods for oil fingerprinting were used to identify characteristic signatures for dissolution, biodegradation and photooxidation. In sub-zero temperature seawater, fast degradation of n-alkanes was observed with estimated half-life times of~7 days. PCR amplicon sequencing and qPCR quantification of bacterial genes showed that a biofilm with a diverse microbial community colonised the oil films, yet a population related to the psychrophilic hydrocarbonoclastic gammaproteobacterium Oleispira antarctica seemed to play a key role in n-alkane degradation. Although Oleispira populations were also present in sea ice, we found that biofilms in sea ice had 25 to 100 times lower bacterial densities than in seawater, which explained the non-detectable n-alkane degradation in sea ice. Fingerprinting revealed that photooxidation, but not biodegradation, transformed polycyclic aromatic compounds through 50 cm-thick sea ice and in the upper water column with removal rates up to~1% per day. Overall, our results showed a fast biodegradation of n-alkanes in sea ice-covered seawater, but suggested that oils spills will expose the Arctic ecosystem to bio-recalcitrant PACs over prolonged periods of time.

Microbial Community Dynamics during Biodegradation of Crude Oil and Its Response to Biostimulation in Svalbard Seawater at Low Temperature

“…A growing body of Arctic marine microbiology research is characterizing microbial communities using data from either amplicon-based or shotgun metagenomic sequencing [11,[13][14][15]42], and the latter is also used for functional profiling. For the taxonomic assignment of shotgun metagenomic data, numerous classifiers and reference databases are available that fall into several categories: (i) DNA-to-DNA methods, where perfect matches between sequence stretches and reference sequences (k-mers) are sought (e.g., Kraken2, Bracken, and PathSeq); (ii) DNA-to-protein methods, where sequence reads are compared with protein-coding sequences (e.g., Kaiju and DIAMOND); and (iii) DNA-tomarker methods, including only specific marker gene families in reference databases (e.g., MetaPhlAn2) [43,44].…”

“…In recent years, the rapid development of microbial analysis tools, especially whole DNA metagenomics-based approaches enabling simultaneous retrieval of both taxonomic and functional information, has provided unprecedented amounts of information for use in bioremediation strategy development [12]. Knowledge of the diversity and structure of microbial communities in oil-contaminated Arctic seawater has expanded with several amplicon-or metagenome-based community sequencing studies using different taxonomic classification methods and reference databases [10,11,[13][14][15]. The determination of microbiome structure and diversity is based on the assignment of individual reads to taxa by comparing them to reference databases [12], but a "gold standard" method has yet to be established.…”

Crude oil exposure reduces ice algal growth in a sea-ice mesocosm experiment

“…Longer experimental studies would also be needed to include the potential role of photooxidation and biodegradation for removal of oil spills as indicated in a 2.5 month long study in a first year ice area in Greenland, where removal rates were in the order of 1% per day (Vergeynst et al 2019).…”

“…The fate of released oil in the marine environment is largely controlled through processes like evaporation, dispersion, sedimentation, oxidation and bioremineralization, best understood in lower latitudes. A long term in situ study (2.5 months) in first-year ice covered waters revealed a 1% per day removal rate for polycyclic aromatic compounds, mainly due to photooxidation and not biological processes, while removal of alkanes was much lower (Vergeynst et al 2019). Turbulent weather conditions or high current velocities may naturally disperse oil in the upper water column (Tkalich and Chan 2002).…”

Maker Buoy Variants for Water Level Monitoring and Tracking Drifting Objects in Remote Areas of Greenland

“…The data were retrieved using the methods described in Section 2.4. Additionally, microbial oil degradation experiments [42] were attached to the iceberg and to a freely drifting mooring, both of which needed to be retrieved before the completion of the research cruise. Thus, a second drifting buoy variant of the Maker Buoy was attached to the drifting buoy (Figure 6B) and the data were also retrieved in near-real-time from the ship.…”