IntroductionIn 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

Environmental boundary conditionsIn designing a floating seaweed culture installation and in selecting an optimal location, the

following environmental aspects should be taken into account:

• Hydrodynamics – waves, currents (forces, drag): flexibility, strength

• Morphology – water depth, type of sediment: anchoring

• Water quality – nutrients, CO2, pollutants, turbidity: seaweed productivity and quality

• Ecology – natural predators, competitors: seaweed productivity

Model experiments in flumeUnderstanding 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/

flow flume at Deltares, Delft, the Netherlands.

• Scaled floating installation and seaweed (1:30),

• Various wave + flow regimes and combinations

• Different exposition of floating structure relative to wave/flow direction

Lessons from flume experiment• 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.

• Next experiments (in the context of EU FP7 project MERMAID) are to assess drag of 1:1 seaweed

lines, and assess wave attenuation potential.

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 impacts of a floating installation

Floating seaweed culture installation can potentially have various positive and negative impacts

on their environment during installation, operation, maintenance and decommissioning phases.

Potential negative impacts• Changes in currents, wave attenuation

• Changes in seabed morphology, scour around

• anchors Changes in water quality parameters,

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.

for more information Deltares

Helena.Hulsman@deltares.nlwww.deltares.nl

Environmental Considerations for Floating Seaweed Culture

Location selection can be optimized by taking into account:

• 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

• Method of fixation/ anchoring such that seabed disturbance is minimal

• Orientation of installation relative to dominant current to minimize drag

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.

Mitigating environmental impactsMitigating measures can be taken to minimize or avoid negative impacts: