A poster presented at the Seagriculture Conference (http://www.seagriculture.eu/) in September 2013 on Deltares' and partners activities on floating seaweed culture installations

1. Helena Hulsman1, Job Schipper 2, Arne van der Hout1, Pieter ‘t Hart3
1 Deltares, Delft, the Netherlands, 2 Hortimare BV, the Netherlands, 3 Koers & Vaart BV, the Netherlands
Environmental Considerations for
Floating Seaweed Culture
Introduction
Environmental impacts of a floating installation
In the context of the Dutch SBIR project ‘Sustainable Seaweedfarm’ (2009-2013,
coordinated by Hortimare B.V.), we examined the most important environmental
considerations for the development and implementation of sustainable floating seaweed
culture installations. Two aspects were evaluated:
• Environmental boundary conditions
• Environmental impacts
Floating seaweed culture installation can potentially have various positive and negative impacts
on their environment during installation, operation, maintenance and decommissioning phases.
Environmental boundary conditions
In designing a floating seaweed culture installation and in selecting an optimal location, the
Potential negative impacts
following environmental aspects should be taken into account:
• Changes in currents, wave attenuation
• Hydrodynamics – waves, currents (forces, drag): flexibility, strength
• Changes in seabed morphology, scour around
• Morphology – water depth, type of sediment: anchoring
• anchors Changes in water quality parameters,
• Water quality – nutrients, CO2, pollutants, turbidity: seaweed productivity and quality
• Ecology – natural predators, competitors: seaweed productivity
microplastics
• Changes in ecosystem composition and
productivity, exotic species introduction,
disturbance and mortality of birds, fish,
mammals, benthic organisms.
Potential positive impacts
• Wave attenuation around offshore structures
• Erosion reduction and protection of sand banks
• Improvement of water quality, reduction of
eutrophication and heavy metals
• Increase in bio-productivity, providing refuge,
nursery function, supporting recovery of
sandmined areas.
Model experiments in flume
Understanding the behaviour of the floating installation is essential for effective design of the
installation. To gain understanding, experiments were conducted in the Atlantic Basin wave/
Mitigating environmental impacts
Mitigating measures can be taken to minimize or avoid negative impacts:
flow flume at Deltares, Delft, the Netherlands.
• Scaled floating installation and seaweed (1:30),
• Various wave + flow regimes and combinations
Location selection can be optimized by taking into account:
• Different exposition of floating structure relative to wave/flow direction
• Sufficient currents to provide constant inflow of nutrients and CO2
• Limited wave forces to reduce risk of damage to installation and seaweed biomass
• Minimum depth of 15m and dynamic wave/flow climates to avoid scour
• Availability of nutrients, ideally in already eutrophied areas
• Maximize distance to other users (including nature reserves) to minimize
disturbance and risks.
Design of floating installation can be optimized by taking into account:
• Structure should be flexible enough to move along with waves / rigid enough to
attenuate waves (depending on demands and location)
• Materials should be durable, low maintenance, prevent or withstand fouling
Lessons from flume experiment
• Method of fixation/ anchoring such that seabed disturbance is minimal
• Orientation of installation relative to dominant current to minimize drag
• Installation retains its shape under all wave and flow circumstances.
• Model experiments emphasize the importance of the behavior of the installation under various
current climates and directions.
• Forces on the model installation were estimated; results indicate that the prototype could
encounter forces.
Culture methods can be optimized by taking into account:
• Density of floating culture elements, density of biomass on lines, taking into
account shading effects and carrying capacity of areas
• Harvesting approach should aim for minimal disturbance.
• Next experiments (in the context of EU FP7 project MERMAID) are to assess drag of 1:1 seaweed
lines, and assess wave attenuation potential.
www.deltares.nl
for more information
Deltares
Helena.Hulsman@deltares.nl