Aarhus University Seal / Aarhus Universitets segl

No. 180: Nature restoration of rock reefs in Roskilde Fjord

Dahl, K. & Göke, C. 2020. Naturgenopretning af stenrev i Roskilde Fjord. Supplerende forundersøgelser samt designforslag for et rev ved Ægholm. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 22 s. - Teknisk rapport nr. 180. http://dce2.au.dk/pub/TR180.pdf



A transect study at Nørrerev and Selsø Hage have been carried out as a supplement to the previous study “Nature restoration of rock reefs in Roskilde Fjord - Basic study of three selected localities” reported in Dahl et al, 2019. The study showed that these new areas host dense populations of eelgrass at greater depth intervals. The areas studied are therefore not ideal as a site for establishment of boulder reefs. The study was therefore supplemented with a long transect investigation at a new locality at Ægholm in Roskilde Fjord, which was very suitable for a nature restoration project for boulder reefs. The bottom conditions at Ægholm consist of sand-gravel sediments at the surface, which seems able to support the laying of stones up to a depth of 3-3½ meters. Occurrences of mussels and eelgrass covered a maximum of 25% of the bottom but were often sparse.

The report also describes a design proposal for a boulder reef at Ægholm. The design proposal includes a description of the various reef structures proposed. It is estimated that there is a need at app. 4.450 tonnes of boulders for the nature restoration. In addition, it has previously been proposed to establish a reef for educational and information purpose off Veddelev, with a need for app. 300 tonnes boulders (cf. Dahl et al, 2020).