Infilling wetlands with construction and demolition (C&D) waste: Influence on land use, plant/dipteran communities and metal contamination
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Construction and demolition (C&D) waste, comprised of sand, stone, concrete, bitumen and other wastes from building sites, is one of the largest fractions of waste produced internationally. It frequently ends up being used for land reclamation (infilling) under specially granted permits in wetlands. This happens despite the instrumental value of wetlands to society, both environmentally and financially, in that they provide a plethora of vital ecosystem services including habitat provision, water regulation and filtration. This study which assessed the distribution of C&D waste infill sites at a local scale, found that sites are primarily wetlands located adjacent to urban areas and major road networks. Wetlands in these areas are, therefore, likely to be at a higher risk of loss. Infill sites were also found to be concentrated around designated conservation sites (SACs), a point of concern as these habitats may be sensitive to any contamination and hydrological changes caused by the waste. The study also found that non-compliance with permit conditions is common, with many sites having excessive or contaminated waste; poor or absent perimeter fencing; infilling activities taking place prior to the granting of permits or after permits have expired. Undocumented infilling which was also found to be a major problem had a similar distribution pattern as legal infilling sites. Resources available to local authorities should be increased to allow better policing of proposed and current sites. The ecological impacts of infilling wetlands with C&D waste were also assessed. It was found that plant species composition was different on the waste compared to the wetland, with an increase in common ruderal species and fewer wetland specialist species on the infill. This is most likely as a result of changed soil parameters where the pH increased and both soil moisture and organic content decreased. Dipteran communities were also found to differ, with a decrease in wetland specialist, gall-forming, parasitic and haematophagous groups. Both the abundance and species-richness of Marsh Flies (Sciomyzidae) were lower on the C&D waste infill than the adjacent wetland. In addition, slugs (Deroceras reticulatum) collected on C&D waste had significantly higher concentrations of priority pollutants Antimony, Arsenic, Barium, Cadmium, Cobalt, Selenium and Thalium than those from control sites. This suggests that the metal in the C&D waste is in a bioavailable form, increasing the potential risk of such infill sites to adjacent wetland habitats, including those with European designations. Challenges faced through the study are discussed, and recommendations are made both for future research and policy makers.