Monitoring of the outer Oslofjord. Investigation of benthos in 2013.

Summary

Benthic investigations included in 2013 surveys of soft bottom by grabbing and SPI-sampling (Sediment Profile Imaging) and lower growth-limit measurements of macroalgae on hard bottom by SCUBA diving. The quality of Outer Oslo Fjord soft bottom areas showed considerable variation between surveyed areas, various water bodies and within water bodies. In general, the state of the environment in 2013 was better than earlier in water bodies around Tønsberg (Kanalen, Vestfjorden-nordre, Vestfjordensøndre), somewhat worse in Iddefjord main basin (VERY BAD), but mostly equal status as in previous studies in the inner Drammensfjord (VERY BAD), Frierfjord (MODERATE) and Leira (GOOD). A great deal of variation between individual years can be explained by changes in organic load and irregular replacement of deep-water in fjord areas. Lower growth-limit of a variety of macroalgae was examined by diving at three stations (Småholmane in Østfold, Sandsundholmane and Vågøy in Telemark) in the outer Oslofjord. Lower growth limit index was used to determine the status of the water quality at the three stations. The EQR value (Ecological Quality Ratio) was calculated based on the results. The survey shows that there was Good status at Småholmane, Good status at Sandsundholmane and Very good status at Vågøy.