Key parameters and processes affecting the re-establishment of eelgrass in estuaries and coastal water

Research output: ThesisPh.D. thesis

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Abstract

Seagrass are considered engineering species, and as such, provide numerous “ecosystem functions, services and goods”. Among them, seagrass systems offers structural functionality, shelter and food for a diverse trophic chain, high productivity, slow nutrient turnover, reduced hydrodynamic forcing and sediment trapping. In the last decades seagrass, in general and eelgrass (Zostera marina) in particular, have been heavily reduced, primarily due to a generalized euthrophication of the coastal waters. In Denmark, a numerous efforts on nutrient reduction and improvement on coastal water quality have been made in the last 20 years. Nevertheless, eelgrass communities have not yet shown sign of recovery. Little is known about the key parameters and processes involved on the re-establishment of eelgrass, therefore, the REELGRASS project was financed. Whiting the frame of this project, some of the objectives were to gain a further and deeper understanding on eelgrass recolonization processes and to gather all the collected data into a modelling tool which allowing to predict eelgrass reestablishment. Eelgrass re-establishment in Denmark has to be based on seed and seedling success, therefore a series of field activities and laboratory experiments around seed and seedling survival fitting and success rates were planned.
Initially, there were performed pre-screening activities, in a pre-selected study area, Odense fjord (Fyn, Denmark). From the pre-screening basic data on fauna, benthic vegetation and sediment characteristics was collected, in order to map the fjord and select study sites.
Secondly two consecutive field campaigns with one and three stations respectively were performed in Odense fjord. In the field campaigns, it was proven that physical stress in general and macroalgae drift in particular affected negatively seedlings survival. Lugworm (Arenicola marina) sediment rework was also postulated to negatively affect seedling survival.
Laboratory experiments on macroalgae drift and sediment stabilization were performed in annular flumes. The outcome of this study was that unattached macroalgae bedload transport occurred at relative low current velocities and results on high sediment ballistic impacts.
Storage techniques and method to measure EPS (potential indicator for sediment biostability), was put to test within a set of laboratory experiments. Both storage techniques and method resulted in a diverse range of cellular lyses, which will limit the validation on the uses of such techniques for EPS measurements.
A model to simulate bedload resuspension generated by macroalgae drift was created. The aim of the model was to test the influence on such resuspension on light climate. As a result it was proven that macroalgae generated SPM affected the light climate by dampening greatly the light availability at the sea bed in shallow coastal waters.
An agent based model to simulate opportunistic and slower growing macroalgae species transport in Odense fjord was created. In this model, both macroalgae types growing unattached resulted highly mobile in Odense fjord, affecting large areas of sediment, particularly in the shallow areas of the fjord.
Finally, an overall ecological model predicting eelgrass reestablishment in Odense fjord was created. Most existing eelgrass models have their focus on pelagic processes, but within this project, it has been shown, that pelagic processes are not enough to simulate the actual eelgrass dynamics in Denmark. Therefore, stresses affecting eelgrass derivated by macroalgae drift, Arenicola marina and sediment biostabilization were successfully implemented on an existing pelagic based 3D ecological model for Odense fjord.
Original languageEnglish
Supervisors/Advisors
  • Flindt, Mogens, Principal supervisor
  • Rasmussen, Erik Kock, Supervisor, External person
Publisher
Publication statusPublished - 2012

Keywords

  • zostera marina, sediment resuspension, environmental modelling, coastal ecology, Odense fjord

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