Mercury in litterfall and sediment using elemental and isotopic composition of carbon and nitrogen in the mangrove of Southeastern Brazil

Abstract

Mercury and elemental and isotopic compositions of carbon and nitrogen were determined in litterfall and sediments from the mangrove of the Paraíba do Sul River, Rio de Janeiro, Brazil. Total mercury (THg) and monomethylmercury (MMHg) concentrations in sediment ranged from 33 to 123 ng g−1 and 0.20–1.38 ng g−1, respectively. The δ13C in sediment varied from −29.4 to −26.5‰ and from 2.4 to 5.8‰ in δ15N. The THg concentration in litterfall and its annual input to the mangrove was 21 ± 2 ng g−1 and 16 ± 4 μg m−2 for the species Laguncularia racemosa, 18 ± 1 ng g−1 and 17 ± 3 μg m−2 for Rhizophora mangle, and 53 ± 4 ng g−1 and 33 ± 4 μg m−2 for Avicennia germinans, respectively. The isotopic composition of leaf litter ranged from −28.6 to −26.9‰ for δ13C and 4.5–7.2‰ for δ15N. Both the highest annual Hg input via litterfall and highest sediment Hg concentration were observed in areas dominated by A. germinans. These results suggest that the rate of litterfall of plant species and the atmospheric deposition have played an important role in the Hg biogeochemical cycle in the mangrove ecosystem.