Mercury in Soils of Seabird Nesting Islands in West Iceland

Seabirds are globally recognized vectors of marine-derived materials, which get deposited on land at their breeding colonies, potentially altering local soil chemistry. We studied mercury (Hg) in soil cores on two islands in west Iceland that host thousands of nesting seabirds, predicting that Hg subsidies from nesting birds would result in elevated Hg in local soils. However, despite clear evidence from nitrogen isotopes of marine influence (seabird faeces) on coastal soil cores, O horizon Hg concentrations averaged 223 nanograms per gram (ng/g), were similar between reference and seabird-nesting sites, and were within the range of soils elsewhere in Europe and the Arctic. The concentration of Hg declined for samples deeper in the core, mirroring declines in organic content and concomitant increases in stable isotopes of nitrogen. A more detailed analysis of local pedogenic processes is required to determine the relative contribution of lithogenic, atmospheric, and anthropogenic Hg, but our data do not suggest that seabirds are markedly increasing local soil Hg through ornithogenic subsidies.