In response to growing awareness of the causes and effects of climate change, the developed nations agreed at the 1997 Kyoto conference to reduce the emission of greenhouse gases through energy savings and a greater emphasis on renewable energy sources. As a signatory to the Kyoto Protocol the Netherlands is committed to reduce greenhouse gas emissions by 6% of 1990 levels by the year 2012, and by 2020 it is planned that 10% of Dutch energy consumption will be generated by renewable sources (Offshore Wind Energy, 2004). Wind energy is expected to contribute 16% of renewable sources by 2020 and thus represents an important component of the Netherlands energy strategy. Because of space limitations and planning complications the growth of land-based windfarms has been constrained and the development of offshore sites has therefore taken on a greater significance. Even after taking other uses (such as sand/gravel extraction, fishing and hydrocarbon exploration) into account, there is sufficient potential space in the Dutch Exclusive Economic Zone to generate 6000 MW, representing about 20% of the Netherlands’ domestic demand. It is the intention of the Dutch government to facilitate the full exploitation of this resource but in harmony with other marine interests and environmental considerations.
The Near Shore Windfarm (NSW) was commissioned as part of the early stages of offshore wind development. Concieved as a demonstration project, NSW will be used to gain knowledge and experience for use in future projects. The windfarm will be situated about 10 km from the coast west of Egmond aan Zee, will cover an area of 25 km2. It is projected to have a capacity of 100 MW generated by 36 turbines, and a lifespan of 20 years, after which it will be dismantled. There will be a 500 m safety exclusion perimeter zone which will be closed to all shipping.
Although wind generation is pollution-free, the environmental effects of construction and operation must be taken into account. The Dutch authorities have therefore commissioned an environmental assessment to address potential windfarm impacts on demersal and pelagic fish, marine mammals and birds and the benthic, or seafloor fauna. The benthic invertebrates (mainly worms, crabs and bivalve clams) are a vital link in the food chain, re-cyling organic material and making it available as a food source for fish and birds.
This report describes in detail the distribution of the invertebrates and the composition of the seafloor sediments in, and on which they live. Changes arising from windfarm construction may be detected by comparison with the baseline data presented here.
The study employed regularly spaced sampling sites within the proposed windfarm area, the safety zone and two reference areas situated approximately 15 km to the north and 20 km to the south of the windfarm. At each site the sediment and small, abundant species were sampled using a 0.068 m2 box core. At some sites multiple samples were taken to obtain a measure of spatial variablilty. A similar array of sites was used to take larger (100 m2), more deeply penetrating samples with a specially modified dredge. This was designed to sample the larger, more sparsely distributed animals.
This two-tiered sampling strategy using 126 box core sites and 51 dredge sites was successful in sampling the small common invertebrates as well as the less abundant burrowing animals.
- The sediments were sandy throughout all areas with very little organic matter. They were coarser in the south.
- The survey found 115 invertebrate species with total density ranging from 0 to 1349 animals per square metre. Most species were those commonly encountered in high energy, shallow subtidal sands of the North East Atlantic and North Sea realm. The northern reference area had more species and a higher density of animals than the other areas.
- Rare species were represented by individuals normally found more abundantly in different habitats of the southern North Sea and their presence was interpreted as the result of random dispersal events.
- Many species exhibited a patchy distribution. Classification analysis of the species - abundance data revealed two main clusters (species assemblages) of box core samples and four clusters of dredge samples. In each case the clusters appeared to be defined by changes in relative abundance of common species rather than changes in species composition.
- The southern North Sea benthic fauna has been modified throughout a long history of intensive beam trawling. The exclusion area created by the windfarm will provide an opportunity to examine some of the effects of trawling and to study recovery rates using bivalve metrics.
It was recommended that the reference areas be maintained and sampled for comparison with baseline data. Future monitoring should be carried out by sampling at multiple sample sites for sediment characteristics and benthic invertebrates. Dredging should also be carried out to compare species data and collect bivalves for analysis.