Mussel farming as a large-scale bioengineering tool: a numerical modelling case study in Rødsand lagoon, Denmark

TY - ABST

T1 - Mussel farming as a large-scale bioengineering tool: a numerical modelling case study in Rødsand lagoon, Denmark

AU - Forsberg, Pernille Louise

AU - Ernstsen, Verner Brandbyge

AU - Lumborg, Ulrik

AU - Bundgaard, Klavs

AU - Kroon, Aart

PY - 2015

Y1 - 2015

N2 - Rødsand lagoon in southeast Denmark is a non-tidal coastal lagoon, which is home to a wide range of marine flora and fauna and is protected under Natura 2000. An increase in turbidity within the lagoon may reduce the ecosystem health due to hindered light penetration. A threat to the lagoonal ecosystem is related to future increasing storm intensities (Olesen et al., 2014), which are presumed to increase the suspended sediment concentration (SSC) within the lagoon. Furthermore the planned construction of a tunnel between Germany and Denmark may propose a threat to the lagoon due to a possible spill of sediment, which could increase the longshore sediment influx to Rødsand lagoon. Mussels can reduce the SSC in marine environments (Schröder et al., 2014), why the implementation of a mussel farm has been considered as a management option. In the present study we developed a module to include mussels as a bioengineering measure in a numerical sediment transport model and investigated how the implementation of an exterior mussel farm affect the sediment dynamics within Rødsand lagoon. On the basis of 2D modelling (MIKE21 by DHI) and field measurements, the flow and sediment dynamics to and from Rødsand lagoon were simulated during a one year period. A mussel farm was numerically modelled through a module extension. The sediments that passed the mussel farm were filtered according to a selected filtration capacity and regenerated as biodeposits with an optional settling velocity estimated based on literature reviews. The model simulations showed that gale-force wind conditions generated a larger sediment transport to Rødsand lagoon than fair weather conditions, and thus typically generated a higher SSC within the lagoon. The SSC within Rødsand lagoon was reduced by 18% with the implementation of a mussel farm within the modelled year. The generated bio-deposits settled within a fan of approximately 400m from the mussel farm, and thereby reduced the sediment transport through the inlets to Rødsand lagoon. The reduction in sediment transport was greatest at the inlet closest to the mussel farm. The effects of the mussel farm on the sediment dynamics were persistent during both fair- and gale-force wind conditions. This suggests that the implementation of a mussel farm has the potential to reduce the sediment transport to Rødsand lagoon and thereby reduce the turbidity caused by suspended sediments. Apart from bioengineering purposes, the mussel module extension can be utilized to improve and develop sediment transport models where known natural patches of mussels are present. Acknowledgements This study is part of the research project “SEDILINK – Flow circulation and sediment dynamics in a nontidal coastal lagoonal system – Rødsand lagoon, Denmark” co-funded by Femern A/S and DHI. References Olesen M., et al. (2014). Fremtidige klimaforandringer i Danmark. Danmarks Klimacenter rapport. Danmarks Meteorologiske Institut. www.dmi.dk/klimaforandringer. Schröder T., Stank J., Schernewski G. and Krost P. (2014). The impact of a mussel farm on water transparency in the Kiel Fjord. Ocean & Coastal Management, 101:42-52.

AB - Rødsand lagoon in southeast Denmark is a non-tidal coastal lagoon, which is home to a wide range of marine flora and fauna and is protected under Natura 2000. An increase in turbidity within the lagoon may reduce the ecosystem health due to hindered light penetration. A threat to the lagoonal ecosystem is related to future increasing storm intensities (Olesen et al., 2014), which are presumed to increase the suspended sediment concentration (SSC) within the lagoon. Furthermore the planned construction of a tunnel between Germany and Denmark may propose a threat to the lagoon due to a possible spill of sediment, which could increase the longshore sediment influx to Rødsand lagoon. Mussels can reduce the SSC in marine environments (Schröder et al., 2014), why the implementation of a mussel farm has been considered as a management option. In the present study we developed a module to include mussels as a bioengineering measure in a numerical sediment transport model and investigated how the implementation of an exterior mussel farm affect the sediment dynamics within Rødsand lagoon. On the basis of 2D modelling (MIKE21 by DHI) and field measurements, the flow and sediment dynamics to and from Rødsand lagoon were simulated during a one year period. A mussel farm was numerically modelled through a module extension. The sediments that passed the mussel farm were filtered according to a selected filtration capacity and regenerated as biodeposits with an optional settling velocity estimated based on literature reviews. The model simulations showed that gale-force wind conditions generated a larger sediment transport to Rødsand lagoon than fair weather conditions, and thus typically generated a higher SSC within the lagoon. The SSC within Rødsand lagoon was reduced by 18% with the implementation of a mussel farm within the modelled year. The generated bio-deposits settled within a fan of approximately 400m from the mussel farm, and thereby reduced the sediment transport through the inlets to Rødsand lagoon. The reduction in sediment transport was greatest at the inlet closest to the mussel farm. The effects of the mussel farm on the sediment dynamics were persistent during both fair- and gale-force wind conditions. This suggests that the implementation of a mussel farm has the potential to reduce the sediment transport to Rødsand lagoon and thereby reduce the turbidity caused by suspended sediments. Apart from bioengineering purposes, the mussel module extension can be utilized to improve and develop sediment transport models where known natural patches of mussels are present. Acknowledgements This study is part of the research project “SEDILINK – Flow circulation and sediment dynamics in a nontidal coastal lagoonal system – Rødsand lagoon, Denmark” co-funded by Femern A/S and DHI. References Olesen M., et al. (2014). Fremtidige klimaforandringer i Danmark. Danmarks Klimacenter rapport. Danmarks Meteorologiske Institut. www.dmi.dk/klimaforandringer. Schröder T., Stank J., Schernewski G. and Krost P. (2014). The impact of a mussel farm on water transparency in the Kiel Fjord. Ocean & Coastal Management, 101:42-52.

UR - http://havforsk2015.geus.dk/xpdf/18_havforsk_abstracts.pdf

M3 - Conference abstract for conference

T2 - 18. Danske Havforskermøde

Y2 - 28 January 2015 through 30 January 2015

ER -