Update on the Environmental Effects of Wind farms in Belgian Waters

Report Environmental impacts of offshore wind farms
17/03/2017
Update on the Environmental Effects of Wind farms in Belgian Waters
post by
Sigrid Maebe

In Belgian waters, three wind farms are now operational, one is under construction, and five more will be constructed in the near future. By 2019, the number of wind farms constructed will have doubled with the realisation of the Nobelwind, Rentel and Norther projects that will have the largest individual turbines in our waters (up to 8.4 MW – reaching at 187 m above mean sea level!). The Operational Directorate Natural Environment (OD Nature) of RBINS coordinates the monitoring of the environmental effects of these wind farms on the marine environment. The monitoring program targets physical, biological, and socio-economical aspects of the marine environment. New research results are now presented in the Monitoring Report 2016.

Results: OPERATIONAL UNDERWATER SOUND EMISSION

Previous reports analysed the underwater impulsive sound produced during construction activities. In the current report, the continuous underwater sound emitted by steel jacket and monopile foundation wind turbines is measured. The underwater sound increases with wind speed with a rate dependent on the type of foundation. For a mean wind speed of 10 m/s, a steel monopile will emit some 10 dB more than a jacket foundation.

Results: CHANGES IN MACROBENTHIC COMMUNITY

Changes in hydrodynamics, presence of epifaunal coverage along the turbine and fisheries exclusion are expected to be the main causes influencing the macrobenthic community inside a wind farm. We investigated whether previously observed changes in sediment characteristics and macrobenthic community can also be observed at larger distances from the turbines. Stations in the close vicinity of the turbines (50 m distance) and further away (350-500 m distance) were sampled. No significant differences in abiotic factors are observed between the two distances: all samples are characterised by coarse sediments, with a low mud and total organic matter contents. Macrobenthic densities on the other hand differ significantly between the two distances: there were higher densities and more species for the far samples compared to the close samples. It remains unclear what underlying ecological processes are responsible for the difference in community structure between both distances as the current results are not consistent with results from previous studies.

Results: EFFECT ON THE EPIBENTHOS AND FISH OF THE SOFT SEDIMENTS

Many studies have demonstrated the reef effects on epibenthos and fish in the immediate vicinity of the turbine foundations, but the influence on demersal fish in the wider wind farm area is less clear. In Belgian wind farms, there were indications of several wider wind farm effects, including an increase in epibenthos and a possible ‘refugium effect’. Earlier observed positive short-term effects seem to have disappeared, and should be seen as a short-term reaction of opportunistic species directly after construction. These earlier reported signals of a ‘refugium effect’ are no longer observed. Long-lived species are not yet encountered but may get a chance to establish and recover when the ongoing expansion of the wind farm area extends to one large continuous no-fishing area.

To investigate the effect of wind farms on the feeding behaviour of demersal fish, stomach content analyses were performed for lesser weever (Echiichthys vipera) and dab (Limanda limanda) in and around the C-Power wind farm. For both species there are no significant differences in stomach fullness inside or outside the wind farm. However, since the presence of the wind turbine foundations, both fish species consume more prey species that are directly associated with hard substrates, both inside and in the direct vicinity of the wind farm. This demonstrates the expanding reef effect into the surrounding soft sediments.

Results: THE EFFECTS OF SOUND ON YOUNG EUROPEAN SEA BASS

Pile driving generates strong impulsive noise that can affect the health and wellbeing of marine life. The impact of pile driving on young European sea bass (Dicentrarchus labrax), more specifically, the acute and delayed mortality, acute and chronic physiological stress responses and the impact of lower intensity impulsive sound on the fish behaviour were assessed through field and laboratory experiments. A field experiment at 45 m from the pile driving activity revealed no acute or delayed mortality but the fish showed strong acute secondary stress responses, a 50% decrease in oxygen consumption rate, in addition to behavioural responses as could be observed in laboratory experiments. Juvenile fish reduced their swimming activity and ceased all behavioural aggressive actions towards conspecifics at the onset of the impulsive sound, but they showed behavioural recovery within 25 minutes. The results also showed that the initial response changes under repeated exposure.

Results: SEABIRD MONITORING

The seabird monitoring program showed significant avoidance by northern gannet (Morus bassanus) and common guillemot (Uria aalge) and attraction by great black-backed gull (Larus marinus) at the first two Belgian wind farms. Lesser black-backed gull (Larus fuscus), herring gull (Larus argentatus) and Sandwich tern (Thalasseus sandvicensis) appear to be attracted to only one wind farm. While the avoidance of common guillemot and northern gannet seems readily interpretable from a disturbance perspective, it is still difficult to pinpoint the observed increases in seabird numbers.

Results: PATTERNS IN THE PRESENCE OF HARBOUR PORPOISES IN BELGIAN WATERS

Passive acoustic monitoring data of harbour porpoise from the period 2010 and 2015 reveal a significant seasonal trend in detections with peaks in late winter - early spring and late summer, consistent with both results of aerial surveys and stranding data.

ANTICIPATING FUTURE DEVELOPMENTS:
UNDERWATER NOISE REGULATIONS FOR PILING NOISE

From 2017 onwards, new regulations with regard to impulsive underwater noise will make it necessary to use noise mitigation measures during piling in the Belgian (and Dutch) wind farm zone. Wind farm developers are already developing strategies for cost-effective piling noise reduction but uncertainty remains with regards to both the level of underwater noise produced during piling as well as with the effectiveness of the noise mitigation measures being applied.

RECREATIONAL FISHING AND WIND FARMS

The closure of offshore wind farms for commercial fisheries combined with the installation of artificial hard substrates has favourably affected fish in the wind farm zones and could thus, in theory, provide opportunities for recreational fishermen. However, in Belgium, recreational fishermen are not allowed in the wind farm area and have to keep a minimum distance of 500 m from the turbines. As a result, less than 2% of Belgian recreational fishermen reported to go fishing in the larger wind farm area, even when 30% to 40% of the respondents either expected more fish, bigger fish or other fish species inside the wind farms. 40% of the respondents would consider fishing inside wind farms if it were allowed. This is a clear indication that the enforcement of wind farm closure for fisheries and shipping is vital when aiming at the creation and restoration of nursing grounds in the area.

INFLUENCE ON THE OCCURRENCE OF ICHTYOPLANKTON AND SQUID LARVAE

The expected large scale increase in wind farms is expected to influence both fish and cephalopod egg deposition by modifying the sea floor and providing additional egg deposition opportunities respectively. We expected higher densities of eggs and early life stages at the hard substrates and larvae in the water column at the wind farms. This was investigated at the Thornton bank wind farm by sampling on impact stations and reference stations from 2010 to 2013. The results do not show significant effects of the wind farm on fish eggs, fish larvae and squid larvae. However, the data provide good baseline information about ichthyoplankton and squid larvae at offshore stations that can be used in future monitoring.

DO WIND FARMS FAVOUR INTRODUCED HARD SUBSTRATA SPECIES?

Offshore wind farms and other artificial structures at sea, are hypothesised to favour introduced species and as such pose a threat to the native fauna. Previous reports described the colonisation of this new habitat and the emerging prominence of introduced species in the intertidal zone. Now we investigated introduced species on Belgian offshore wind farms. In the subtidal zone, the offshore wind farms will only marginally contribute to the further spread of introduced species given the vast amount of both natural and artificial hard substrata already available in the North Sea. However, for the intertidal zone, the wind farms may have the potential to substantially increase the risk of the further spreading of introduced species. It is however expected that offshore wind farms may significantly contribute only to the spread of clear water, intertidal introduced species, as such nuancing the introduction and invasion risk posed by offshore wind farms.

BIRD RADAR STUDY

Dedicated bird radars are used in ornithological studies: they provide continuous data on a large scale for many years. However, the recorded radar data have a low taxonomic resolution and contain a lot of clutter i.e. records of objects other than birds (e.g. sea surface, ships, rain). A filter to remove this clutter was developed and will be finetuned. This will result in more accurate bird fluxes and an improved outcome of bird collision models.

BATS

To evaluate and quantify the risk of offshore wind farms to bat populations we need first to determine the distribution of bats in Belgian waters. During two full bat migration periods an automated acoustic recorder was installed on the Belgian research vessel ‘Belgica’ to record bats while the vessel is at sea at night. Over a hundred call sequences belonging to four different species were registered, although calls were limited to only a few nights In 2015 and 2016, an expanded network of nine Batcorders was collecting data in the Dutch and Belgian part of the North Sea and along the coastline. These detectors will increase our knowledge about the impact of wind farms on bats.

More information on wind farms in Belgian waters.

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