Since the middle of last century, widespread eutrophication in the marine environment has beenthe primary cause of habitat loss and degradation of habitat quality. Several measures have sincebeen implemented to reduce nutrient discharge to coastal ecosystems, but some habitats havebeen altered to an extend where natural recovery is absent. In these cases, restoration may benecessary to initiate positive feedback mechanisms that can stimulate natural recovery.Policymakers have become aware of the need to restore and protect marine habitats and theEuropean Commission proposed a nature restoration law last year. It is likely, that such aproposition instigates the need for suitable restoration methods and quantification of theecosystem services (ES) of the reestablished habitats. The aim of this dissertation is to expand ourknowledge on habitat restoration of Zostera marina meadows, sediment bottoms and Mytilus edulisbeds and quantify the ES that these habitats provide. Thresholds for growth of transplanted Z.marina was determined to be 2.5 µM average growth season DIN and an annual nitrogen loading of7.9 g N m-2 y-1 (MS 1). Furthermore, it was estimated that the inner 30 % of Danish estuaries are stillunsuitable for Z. marina restoration (MS 1). It was verified that large-scale Z. marina transplantationis possible in Denmark, but that it requires careful site-selection (MS 2). Additionally, it wasconfirmed that the transplanted Z. marina acts as a coastal nutrient filter by retaining nutrientduring the growth season and that carbon and nutrient sequestration had occurred after 2 yrs. (MS2). Moreover, the biodiversity and functional diversity of benthic fauna had improved in thetransplanted meadow compared to bare bottom after approx. 1 yr. and species richness andabundance was positively correlated with eelgrass biomass(MS 3). It was confirmed that large-scalesand-capping is possible in situ and that it contributed to increased erosion threshold whichimproved benthic light from 3% to 22% compared to adjacent muddy sediment (MS 4).Furthermore, biodiversity and functional diversity of benthic fauna improved significantly at thesand-cap compared to mud (MS 4). These improvements where initially more evident in the centralpart of the sand-cap but stabilized across the full range of the capped area after 2.5 yrs. However,epifauna did not show any signs of improvement after sand-capping (MS 5). Lastly, it was verifiedthat M. edulis beds require suitable substrate when they are restored at shallow semi-exposed sitesand that they should have a size >30 mm to reduce initial mortality after relay (MS 6).
|Translated title of the contribution||Anvendelse af multiple marine restaureringstiltag og kvantificering af økosystemtjenester i danske estuarier|
- University of Southern Denmark
- Flindt, Mogens, Principal supervisor
- Quintana, Cintia Organo, Co-supervisor
|Date of defence||21. Jun 2023|
|Publication status||Published - 21. Jun 2023|