This study addresses the technological
feasibility of seaweed cultivation in the North Sea in combination with
offshore wind parks and harvesting and conversion of seaweed biomass
to renewable energy carriers and chemicals. The study also identifies
stakeholders and participants for technology development and the ecological
and societal conditions to fit in large-scale seaweed cultivation in
the marine environment, existing marine infrastructure and functions,
and (inter)national regulations and policies for the North Sea.
Three seaweed species that are
native in the North Sea have been selected for potential cultivation:
Ulva sp. (belonging to the green macroalgae), Laminaria sp.
(a brown macroalga) and Palmaria sp. (a red macroalga). Current
commercial seaweed cultivation systems usually consist of (partly) anchored
line structures to which the seaweeds are attached and are generally
located on coastal locations. International research shows that cultivation
systems in the open sea may become easily damaged by wind and wave action.
An experimental ring shaped system has thus far shown the best stability
for the conditions in the North Sea. However the production costs are
high. Considerable system development is therefore required to enable
large-scale, economically attractive cultivation of seaweeds combined
with offshore wind parks. The optimal system design is unknown. This
study proposes a layered system for seaweed cultivation employing the
typical light absorption characteristics of green, brown and red macroalgae
respectively, to enable optimal use of the available sunlight and enhance
areal productivity. Without addition of nutrients the productivity in
the North Sea is estimated at approx. 20 tons dry matter/ha.year. Through
layered cultivation and/or addition of nutrients this can potentially
be increased to ca. 50 tons dry weight /ha.year. Development of precision
nutrient dosage technology is required to prevent eutrophication.
Potential negative environmental
impacts include: sedimentation of seaweed fragments and other organics
with a negative effect on the oxygen budget in the water column, and
possible negative impacts on migration of sea mammals including dolphins,
porpoises and whales. Seaweed cultivation can also have positive impacts
including the uptake of nutrients by the macroalgae (reducing eutrophication)
and an enhancement of marine biodiversity, because the seaweeds and
the cultivation systems offer substrate for attachment, shelter and
feed for molluscs and fish. Indeed, the system could be managed as a
nursery for young fish in order to restore fish populations in the North
Sea. Integration of seaweed cultivation with other types of aquaculture
e.g. cultivation of mussels or fish is a realistic option.
The Dutch government target for
offshore wind in 2020 is 6.000 MW installed turbine capacity. This will
involve a surface area of approx. 1000 km2. The support constructions
for the wind turbines can serve as a structural basis for seaweed cultivation
systems. Designs must take into account the additional load on the turbine
supports due to currents, wind and wave action, and accessibility of
the turbines for maintenance vessels. Potential synergistic effects
of the combination of offshore wind and seaweed cultivation supporting
the profitability of both activities include joint management and maintenance,
alternative employment opportunities for fisheries and ecological benefits.
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