Conduits of contamination to contemporary food webs of the Norfolk Broads

Abstract

During the 1960s-1980s antifouling applications containing the organotin tributyltin (TBT) were applied to craft on the Norfolk Broads, leaving a legacy of contaminants in sediments. Previously, no research had been undertaken to investigate the implications that this legacy may have for the ecological integrity of the Norfolk Broads aquatic ecosystem. Eight sites in the Norfolk Broads that represented a gradient of contamination (as measured by sediment TBT concentrations) were selected. Contamination was evident in invertebrates and fish but was lower than sediments, as total organic carbon and species specific metabolic capacity for TBT controlled bioavailability To examine TBT impacts at the community scale, novel metrics were applied to food webs defined by stable isotopes of carbon and nitrogen. Two metrics were reduced in response to increasing TBT contamination, suggesting simplification of food webs along the contaminant gradient; where loss of key food web properties such as trophic diversity and shortened food chain length could reduce resilience to further system perturbations. I hypothesised that chironomids emerging from sites contaminated with organotins would carry with them an organotin burden, which would be reflected in terrestrial predators such as spiders via trophic transfer. A combination of spider and chironomid stable isotopes (principally δ 13C) and isotope mixing models indicated considerable chironomid contribution to spider biomass at all four sites (34-88%). Subsequent organotin analyses revealed consistent low level, butyltin (di-butyltin; DBT) contamination in chironomids and spider predators from the most contaminated site.