Abstract
Kentish Flats Ltd (KFL) developed a Wind Farm within the outer Thames Estuary and offshore of north Kent. The site occupies an area of 10km2 and lies approximately 8.5km north of Herne Bay. The scheme is in response to authoritative licensing of Wind Farm developments, which are necessary to fulfil government commitments to the increased exploitation of renewable energy resources. As part of the application process for permission to develop the Kentish Flats site, a full Environmental Impact Assessment (EIA) was required. A baseline ecological survey was conducted prior to commencing the work in order to provide baseline data on the physical and biological conditions of the development site. A series of post construction benthic surveys are required as part of Food and Environment Protection Act 1985 (FEPA) licence No. 31780/03/0 in order to detect if any changes have occurred within the benthic environment following commencement of work. The 2007 macrobenthic ecology survey within Kentish Flats is the third in a series of studies following the development of the Wind Farm. The data generated from the survey were analysed and compared with those obtained from previous surveys, including the 2002 baseline study and the 2005 and 2006 post-construction studies. The aim was to investigate if any significant changes have occurred with respect to the physical characteristics and associated biological communities of the benthic environment that might be attributable to the construction or operation of the Kentish Flats Offshore Wind Farm. Results from the 2007 survey showed that sand was the main sediment fraction across the survey area, with sorting coefficients ranging from very well-sorted to extremely poorly-sorted. A spatial pattern of sediment distribution was identified within the survey area. Specifically, the most offshore sites comprised homogeneous sediments, characterised by relatively well-sorted sands. These stations included the majority of sites within the secondary impact and the northern reference areas. These sites are the most exposed within the survey area and as such subjected to high variable hydrodynamic regimes. As a result, the habitats are more dynamic with greater sediment transport. The more central stations within the survey area comprised more heterogeneous sediments, with higher percentages of gravel and mud. These sites comprised the majority of the stations within the development site, the southern reference area and selected sites within the scour assessment area. Samples from these stations showed higher levels of intra-samples variability, indicating heterogeneity of the sediment on a small scale. Finally, the most inshore sites comprised mixed sediment with the highest percentage of mud. These sites comprised the majority of stations within the cable corridor. These sites are the most sheltered within the survey area with little influence from wave action. Consequently, little sediment transport can take place and levels of mud accumulate increasing the sediment compactness. Comparisons with previous years’ surveys showed that this pattern of sediment distribution across the survey area has been maintained over time. Temporal variations of the sediment composition within the different areas were considered to be not significantly different, each area retaining a high degree of similarity of the sediment composition over time. Spatial variations between the different areas were significant and consistent over time.
Results of the macrobenthic analyses revealed a macrofauna broadly associated with the substrate type. As such the macrofauna distribution across the survey area also showed a pattern. Specifically, mobile sands, typical of the offshore sites (i.e. the majority of sites within the secondary impact and the northern reference areas) supported an impoverished macrofaunal community, characterised by more actively swimming crustacean amphipods and robust polychaetes worms which are characterised by flexible body structures and the ability of rapid burrowing if exposed to physical perturbation. These stations supported little epifauna represented by selected species of bryozoans.