Abstract
Since the 1970s, there has been a need to describe and assess the effects of human activities on natural ecosystems. In the 1980s, it was realised that it was not enough to describe and assess the effects of specific proposals and activities. It is also necessary to examine whether the effects of various activities can accumulate to produce ecological or environmental negative impacts. Despite the difficulties, addressing, describing and acknowledging the cumulative effect issue resulted in the incorporation into nature conservation legislation. These directives require that the ecological values, in terms of natural habitat types, species habitats and species, should not only be protected from the possible negative effects of each particular human activity but also from the cumulative effects of all human activities. In the Netherlands, the implementation of these directives in national law has created an explicit requirement under the 1998 Nature Conservation Act (Natuurbeschermingswet (Nbw)) and later on in the renewed Nature Conservation Act (Wet Natuurbescherming (Wnb)). The requirement states that in addition to the potentially significant negative effects on ecological values of individual initiatives, the cumulative effects in combination with other plans and projects in the area provisions of the Act should be assessed. The Nature Conservation Act also considers cumulative effects in the provisions relating to species. However, it does so more implicitly by assessing effects regarding favourable conservation status at various spatial scales.
Since 2005, the Dutch government has received development consent applications for offshore wind farms (OWFs) that require a decision about how to assess the effects on the marine ecosystem of the separate wind, the cumulative effects with other wind farms and wind farms in combination with other activities. Given several issues, including knowledge gaps about the cause-effect relationships, the presence of marine species and the resulting mandatory application of the precautionary principle, the assessment led to the imposition of restrictions on the development of offshore wind power and several mitigation measures.
The identified knowledge gaps led to the establishment of research programmes (for example, in the Netherlands, the Offshore Wind Energy Ecological Programme (Wozep1). Other countries have also recognised the problem of identifying and assessing the effects (cumulative and otherwise) of OWFs and have completed extensive research in recent years.