Monitoring in the Grenland fjords 2012. Sediments and soft bottom fauna

Sammendrag

The report describes the results from monitoring of sediment contamination and macrofauna in the Grenland fjords in 2012. Field work was conducted May 29 – 31 2012 from RV ”Trygve Braarud" and comprised sediment profile imaging (SPI), grab sampling of benthic fauna, and core sampling of sediments. A transect across Frierfjorden from Versvika in SE to Balsøya in NE was covered by 17 single grab stations. In addition one station from the deepest part of Eidangerfjorden, Langesundsfjorden and Håøyfjorden was covered, each with four replicate grab samples. Core sampling was made at two stations in Frierfjorden (30 and 93 m depth) and at the fauna station in Langesundsfjorden. The sediment analyses covered dioxins (PCDD and PCDF) and non-orto PCBs, HCB, OCS, DCB and organotin compounds, both in the upper 0-2 cm and in a vertical profile to 20 cm sediment depth. The SPI photos were used to calculate the BHQ environmental index and the fauna data to calculate various indices of fauna diversity and sensitivity. The highest level of sum PCDD/PCDF was found in the upper 2 cm at 30 m depth in Frierfjorden (Station Ø30, cf. Figure 1 for station positions). Station V93 at 93 m depth had far lower levels than both the samples from Station Ø30. The concentrations at the deepest part of Langesundsfjorden (Station F8) were far less than in Frierfjorden and the data indicated an improvement over time. Comparison with earlier data shows a gradual improvement in dioxin contamination in the upper 2 cm at the two sites in Frierfjorden since 1989 and in Langesundsfjorden at least since 1997 (no survey in 1989). Still the dioxin levels are far above the limit for environmental status class V (Extremely polluted). HCB, OCS, and DCB showed essentially the same vertical distribution in the sediments. Highest levels were found in 5-10 cm depth at Station Ø30. A strong decline for all compounds was seen below this. The levels at Station V93 were a factor 4 less than at Station Ø30 and showed no vertical change. At Station F8 the levels were the same as (DCB) or slightly lower than (HCB and OCS) at Station V93. In the deepest part of Frierfjorden the levels of all the compounds at 0-2 cm had decreased since 1989. In the shallow area south of Herøya an improvement had occurred between 1989 and 1997, but not after that. In the deeper area of Langesundsfjorden only OCs showed improvement over time. These patterns are very uncertain due to differences in station positions, analytical strategy and analytical uncertainty. The highest TBT level (Norwegian Environmental Agency Quality Class V) was found in the 2-5 cm layer at Station V93, and the levels at 10-20 cm were in Class III. Stations Ø30 and F8 had similar vertical distribution patterns (improvement with depth) and levels (Class II – III). The levels at Station F8 were higher than at Station Ø30, and the difference increased with increasing sediment depth. There are no available data to assess trends in TBT contamination over time. The sediment fauna of the areas studied has shown a weak but unanimous improvement over time. In Frierfjorden the vertical depth range of the fauna had increased by 10 m since 2001, i.e. from 50-60 m to about 70 m depth. The depth extent was the same on both sides of the fjord. The survey in 2012 showed a slight worsening of the fauna conditions compared to 2008, in particular on the western side. The fauna of the deepest part in Eidangerfjorden and Langesundsfjorden also showed an improvement after year 2000. The fauna condition in the deep part of Håøyfjorden was worse than in these fjords, and showed no change since 1987. The index values have decreased slightly from 2008 to 2012, but not sufficiently to change the classification of the ecological condition.