Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.

Wind farms in the southwestern Baltic Sea: A model study of impacts on oxygen conditions

Offshore wind farm piles are secondary hard substrate and hence an attractive colonisation surface for many species. Especially in marine areas dominated by soft sediments, wind farms may lead to a significant increase of biomass by enlarging habitats from benthos layers into the pelagic column. A concomitant effect is the increase of oxygen consumption through respiration of living biomass and especially through degradation of dead biomass, mainly Mytilus edulis. This leads to impacts on the regional oxygen budget, and local anoxia in the direct vicinity of wind farm piles has been documented in scientific literature. The present study investigates the regional impact of multiple wind farms on oxygen concentration levels and on the appearance of hypoxia.

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The results show that wind farms do not lead to a significant decrease of oxygen on the mesoscale level.

Biomass falling off secondary hard substrate with subsequent bacterial decomposition leads to decreased oxygen concentration in both simulated events in late winter and autumn. However, on a regional scale, impacts are low in general. Hypoxia, defined as water with an oxygen concentration less than 2 mg l-1, and anoxia (no oxygen at all) occur at several stations naturally. The simulation run, however, showed no additionally hypoxia or even anoxia induced by secondary hard substrate.

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However, additional anoxia can occur locally, which may lead to the release of hydrogen sulfide.

Locally occurring anoxia events, as observed during the sampling period, are not fully reproduced by the model. Those events, however, may potentially lead to a domino effect. The southwestern Baltic Sea is currently showing increased biomass values as consequence of eutrophication. At the same time the Baltic Sea is locally quite sensitive to hypoxia. In those cases where insufficient oxygen supply or increased oxygen consumption lead to the release of hydrogen sulfide, a self-perpetuating process may be initiated. Benthos which comes into contact with H2S will die off and its bacterial decomposition may then lead to continuing hydrogen sulfide releases. Such a H2S roller has been observed in the Pomeranian Bight, where an originally limited local release of hydrogen sulfide caused severe mesoscale impacts on the benthos community. Via this roundabout way, wind farms may indirectly lead to mesoscale impacts on oxygen conditions.additional anoxia can occur locally, which may lead to the release of hydrogen sulfide.

Relevance for Policy:
  • Convention on Biological Diversity
  • Directive on Maritime Spatial Planning and Integrated Coastal Management (forthcoming)
  • EU Biodiversity Strategy
  • Habitats and Birds Directive
  • Integrated European Maritime Policy (IMP)
  • Marine Strategy Framework Directive
  • Strategic Environmental Assessment Directive

Lead Author:

Holger Janßen
(holger.janssenospamn@io-warnemuende.de)
Leibniz Institute for Baltic Sea Research (IOW)
Date of research: February 2014

Related articles:

Wind farms and jellyfish distribution 

Bioaccumulation of metals in blue mussels

Ecosystem impacts of non-indigenous species

Effects of macrophyte vegetation on zoobenthos 

Food web change along a nearshore-offshore gradient

Food webs along the European Atlantic coast

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 266445
© Vectors 2015. Coordinated by Plymouth Marine Laboratory.