Small-scale field trials identify optimal habitat restoration options on exclosed nuclear sites

Degradation of cliff-top habitats due to industrial activity is infrequent, leading to unique challenges when activity ceases and a site requires remediation. Dounreay, an ex-nuclear power facility on the north coast of Scotland, is currently being decommissioned prior to complete demolition of all buildings. A small area of the site will then be covered in a 1000 mm capping layer to prevent contamination of bioreceptors at the surface from below ground contaminants. Topsoil replacement is frequently used in such instances, however, limited availability of topsoil in the region means that other materials are sought to mitigate against undesirable ecological and economic costs. We tested combinations of differentially graded rocks and topsoil to assess their suitability in supporting re-vegetation. The vegetation response was measured as richness (numbers of species), ground cover, species diversity, and biomass. Wider ecosystem function was assessed by measuring invertebrate numbers and diversity, and comparing these to locally relevant reference site data. Fine crushed rock supported native vegetation establishment and growth, though cover, diversity, and biomass (after three years) were significantly below levels found when topsoil was used instead. Initial establishment on the fine crushed rock may be limited by the low water retention and nutrient availability of the material. We suggest that a rich heterogeneous habitat able to support a wide range of native vegetation and invertebrates may be provided by mixing topsoil with the fine crushed rock in the future. This mosaic combination would also allow for significant ecological and financial cost savings (against topsoil only remediation) and could be tested on larger scales.