Evaluation of Polycyclic Aromatic Hydrocarbon Pollution From the HMS Royal Oak Shipwreck and Effects on Sediment Microbial Community Structure

Abstract

Despite many shipwrecks containing oil there is a paucity of studies investigating their impact on surrounding environments. This study evaluates any potential effect the World War II shipwreck HMS Royal Oak is having on surrounding benthic sediments in Scapa Flow, Scotland. HMS (Her Majesty’s Ship) Royal Oak sank in 1939, subsequently leaked oil in the 1960s and 1990s, and is estimated to still hold 697 tonnes of fuel oil. In this study, sediments were analysed, over a 17.5 cm depth profile, along a 50–950 m cruciform transect away from the shipwreck. Analysis of polycyclic aromatic hydrocarbons (PAHs) revealed low concentrations (205.91 ± 50.15 μg kg–1 of dry sediment), which did not significantly differ with either distance from the shipwreck or sediment depth. PAH concentrations were well below the effects-range low (ERL) for the OSPAR (Oslo/Paris convention for the Protection of the Marine Environment of the North-East Atlantic) maritime area. The average Pyrogenic Index, in sediments around HMS Royal Oak, was 1.06 (±0.34), indicating PAHs were pyrogenic rather than petrogenic. Moreover, analysis of sediment microbiomes revealed no significant differences in bacterial community structure with distance from the shipwreck, with extremely low levels of obligate hydrocarbonoclastic bacteria (OHCB; 0.21% ± 0.54%). Both lines of evidence suggest that sampled sediments are not currently being impacted by petrogenic hydrocarbons and show no long-term impact by previous oil-spills from HMS Royal Oak.

80 years later: Marine sediments still influenced by an old war ship

“…The effects of the shipwreck on both chemical and microbial composition of the sediment are in contrast with the study performed by Thomas et al (2021) on sediments surrounding the HMS Royal Oak. Although similar in time spent on/in the sediment (John Mahn: sank in 1942 vs. Royal Oak: sank in 1939), similar in depth (21-35 m vs. 12-33 m), similar in climate (both in between 50-60°N and between 3°W and 3°E, both in a sheltered Sea (BPNS vs. Scapa Flow), and similar in how far the samples were taken from the ship (40 m vs. 50 m), Thomas et al (2021) found no leaching nor any clear bacterial enrichment due to PAH's. The bacterial composition of sediment samples of the HMS Royal Oak showed similar higher taxonomic groups as reported here.…”

“…In comparison to the total PAH concentrations found around the s/s Stuttgart of the Polish coast in the Baltic Sea (Rogowska et al, 2010), i.e. from 16.05 mg/kg to 244.90 mg/kg sediment, the concentrations found around the V-1302 John Mahn are about 100 to 1000 times lower (μg/kg vs. mg/kg), which is in the same range as the concentrations found around the HMS Royal Oak in Scotland (Thomas et al, 2021) (closest samples taken 50 m from the HMS) and within background concentration levels for sediments in the OSPAR (Oslo/Paris convention for the Protection of the Marine Environment of the North-East Atlantic) marine area (Dataset Commission, O, 2017). Our sampling pattern revealed increasing concentrations when approaching the shipwreck (Figures 1C, D).…”

“…However, when looking into a lower taxonomic level, there was a clear difference based on relative abundances of families present, with Flavobacteriaceae, Desulfosarcinaceae, and Sulfurovaceae dominating the Royal Oak sediment while Woeseiaceae, Flavobacteriaceae, and BD-7-8 group dominated the John Mahn sediment. Although similar research aims were pursued, a big difference with the HMS Royal Oak study is that Thomas et al (2021) focused on sediment further from the shipwreck (50 -1000 m), whereas here the samples were taken close to and on the shipwreck (0 to 80 m). This could suggest that the effect of World War II shipwrecks (<50 m deep) in the North Sea sediment are limited to a small area around the wreck due to the dynamic nature of the BPNS, with strong currents from diverse directions.…”

“…The genomic DNA of the samples was then sent out to LGC genomics GmbH (Berlin, Germany) for library preparation and sequencing on an Illumina Miseq platform with V3 chemistry. The microbial data from the HMS Royal Oak sediments were downloaded from the European Nucleotide Archive database under accession number PRJEB37440, these data were obtained by Thomas et al (2021). Sediment (JM xx) samples were taken around the John Mahn shipwreck on the four transects radiating Northeast (four sediment samples and one water sample), Southeast (two sediment samples and one water sample), Southwest (four sediment samples and one water sample) and Northwest (two sediment samples and one water sample) from the ship's centre.…”

“…Historic shipwrecks could also significantly affect the surrounding fauna and flora when leaching heavy metals and metalloids due to (biological) corrosion (Kelly et al, 2012). While wrecks are often considered biodiversity hotspots, the overall environmental impact on the seafloor of historic shipwrecks from the World Wars has only recently sparked interest (Landquist et al, 2013;Thomas et al, 2021).…”