Chemical and Macrobenthic Monitoring

Since 1978, regular chemical monitoring of the coastal waters, seabed and macrobenthos (organisms living in or on the seabed, larger than 1mm) has taken place.

Between 1978 and 1988, 29 sample sites were surveyed and monitored annually, across Sullom Voe, Garths Voe and Yell sound. Abiotic factors (temperature, salinity and dissolved oxygen in seawater) were all monitored.

In addition to this, seabed sediments are monitored for heavy metals and oil contamination. Oil contamination from the terminal construction has been evident in Orka Voe, where five sites were subsequently set up and closely monitored.

Macrobenthic surveys have been carried out at 12 stations in Sullom Voe and Garths Voe using a technique known as grab sampling. Five biological samples are taken from each station to determine the species present and their abundance, as well as taking a sixth sediment sample at the same site, to characterise the nature of the sediment.

In 1985, the chemical and macrobenthic programmes were amalgamated under a single contractor and have been carried out on a biennial basis since 1990 with a heavy metals sampled every 6 years. This has allowed for the integration of sampling sites and has enabled comparisons to be made regarding the health of organisms on the seabed and the type and condition of their habitat.

At Present

As a result of the West of Shetland oil and gas development activities there has been construction of new pipeline landfalls coming into and out of the Orka Voe area. SOTEAG continues to intensively monitor Orka Voe on a biennial basis to ensure that the natural health and condition of the area is maintained.

The chemical and macrobenthic programme includes the survey of two soft shore sites in Sullom Voe which are monitored for hydrocarbons, grain size and organic matter, to understand the effect of potential pollution on the environment.

Sediment

From the results of the most recent survey conducted in 2018, the overall sediment character was broadly comparable with that found during recent surveys, with most sediments being classified as slightly gravelly muddy sands. However, most of the stations show some variations in the relative proportions of sand, mud or gravel compared with the characteristics noted in 2016.

The mud contents of the benthic sediments are comparable to the 2016 results with <10% changes, which continues to be noticeably higher than the historic mean result for period 2000-2014.

For some stations there are spikes of higher mud content in the historic data and many of the 2016-2018 results correlate with the levels observed in the 2004 survey.

The methodology for the particle size analysis and mud content have changed in 2016 to the NMBAQC protocols and higher levels of mud are likely to be observed due to differences between the gravimetric and volumetric measurements.

Macrofauna

Overall the total abundance of macrobenthic organisms sampled during 2018 has increased compared to that recorded in 2016 and remains in line with background levels of abundance recorded in previous survey years.

Faunal diversity across the stations at Sullom Voe decreased slightly in 2018 compared to recent survey years though remained within the window of natural variability exhibited by fauna since monitoring began in 2002 under the current programme.

Overall, the macrobenthic communities sampled throughout Sullom Voe in 2018 remained rich, characteristic of the assemblages recorded during historical monitoring of the area.

A number of rare, alien and protected species were recorded in the 2018 faunal samples. These included the OSPAR-listed ocean quahog Arctica islandica, the nationally rare sea slug Calliopaea bellula, the nationally scarce orange-footed sea cucumber Cucumaria frondosa, the IUCN Red-listed edible sea urchin Echinus esculentus, the nationally scarce purple sea urchin Paracentrotus lividus, and the alien soft-shell clam Mya arenaria.

The most recent monitoring reports are available on the website.