Eelgrass acts as nursery ground for many fish species, provides food for birds, and protects the shores from resuspension and erosion – making it an important ecological component in coastal waters. After recovering from wasting disease in the 1930s, a large scale decline in eelgrass meadows has occurred since the mid-1970s. This declined has been attributed to increased loads of phosphorus and nitrogen from mainly farmland (70-90%), causing increased eutrophication.
Reductions in the nutrient load from cities and farmland over the last two decades has not prompted a recovery of eelgrass vegetation. An earlier research project entitled Reelgrass* indicated that a major reason why this recovery has not occurred is negative feedback mechanisms – physical or biological disturbances are hindering or delaying the re-establishment of eelgrass. These disturbances include:
- waves and currents uprooting seedlings in soft sediments
- lugworms burying seeds and seedlings
- perennial macroalgae (Fucus) that are attached to stones scouring over the sediment under windy conditions, which damages seedlings
- increased resuspension under windy condition in areas with annual macroalgae
Assisting with eelgrass restoration
Eelgrass produces large quantities of seed, meaning it could potential restore large areas. However, this is currently not happening in areas with reduced loading because of the abovementioned stressors. As such, the five-year long NOVAGRASS (Innovative eelgrass restoration techniques) project, which began in 2013, aims to:
- develop innovative techniques for mechanical harvesting of shoots, optimal storage, and planting under different environmental conditions
- apply and evaluate these tools on a larger scale in the field under different conditions
- provide guidelines for eelgrass restoration, including climatic challenges through modelling
- provide a socio-economic analysis and assessment the ecosystem services gained by restoration
For this project, biologists from DHI Denmark are heading up Work Packet Four (WP4), entitled ‘Predicting eelgrass recovery after implementing restoration action’. Senior biologist Erik K. Rasmussen is the project leader for our part of the project.
Identifying potential eelgrass recovery areas
Using our MIKE Powered by DHI’s modelling software, we will identify potential eelgrass recovery areas in three Danish lagoons: Odense Fjord, Roskilde Fjord and Limfjord. The model will also be used to assess the effect of climate changes on eelgrass vegetation and provide input into the socio-economic analysis and assessment. Using our MIKE Zero and MIKE ECO Lab software, a three-dimensional hydraulic model will be combined with an ecological model able to simulate:
- nutrients
- phytoplankton
- biomass of annual and perennial macroalgae
- eelgrass
- eelgrass seeds
- sediment pools of organic carbon, nitrogen and phosphorus
- fine inorganic sediment
- resuspension and transport of fine sediment (inorganic and organic)
So far, the model system has been used to identify good potential locations for planting seedlings or eelgrass seeds in the three fjords. At a later stage of the project, the model will feed data and information into a comprehensive socio-economic analysis that will be prepared by another partner. During the first two years of the project, we developed techniques for harvesting and storing seeds. In addition, we conducted the first set of controlled experiments involving planting seeds, both with and without protecting measures against uprooting, lugworms, and drifting algae. Depending on the results during the following summers, new restoration experiments will be set up over the next few years of the project.
Project partners
The NOVAGRASS project is funded by a DKK 14.1 million grant from the Danish Council for Strategic Research with an additional DKK 12.8 million coming from project partners. Our portion of the grant is DKK 2.17 million and our total project budget is DKK 2.93 million. Other NOVAGRASS partners include:
- University of Southern Denmark (SDU, Denmark) – grant holder (Professor Erik Kristensen)
- University of Aarhus (Denmark)
- University of Copenhagen (Denmark)
- SEGES, formerly known as the Knowledge Centre for Agriculture (Denmark)
- Grön og Blå Tech (Sweden)
- Multidyk (Denmark)
- KC Denmark (Denmark)
- Danish Nature Agency (Denmark)
- Radboud University Nijmegen (the Netherlands)
- Virginia Institute of Marine Science (United States)
- University of Gothenburg (Sweden)
*Reelgrass (Key parameters and processes affecting the re-establishment of eelgrass in estuaries and coastal water) was a four-year project in which we were a partner. The Danish Council for Strategic Research funded Reelgrass.