Distribution of mercury isotope signatures in Yundang Lagoon, Xiamen, China, after long-term interventions

Isotope signatures of mercury (Hg) were determined for Hg fractions in seawater, sediments, porewaters, core sediments and fish from the Yundang Lagoon, Xiamen, China. Sequential extraction was used to extract Hg fractions in sediments and the purge-trap method was used to preconcentrate Hg in seawater. A large variation in mass dependent fractionation (delta Hg-202: -2.50 parts per thousand to -0.36 parts per thousand) was observed in the lagoon. Seawater and fish samples showed positive mass-independent fractionation (Delta Hg-199: -0.06 parts per thousand -0.45 parts per thousand), while most of sediment and porewater samples displayed insignificant mass-independent fractionation (D199Hg: -0.10 parts per thousand-0.07 parts per thousand). Ancillary parameters (total organic carbon, sulfide, pH, Eh, water content and grain size) were also measured in the sediments to investigate correlations with Hg isotopes. Three sources (domestic sewage, sediments and atmospheric deposition) were identified as the main sources of Hg in the lagoon seawater. Photochemical reaction was the main process causing isotope fractionation in seawater. Through Hg partitioning and deposition, light isotopes were enriched from dissolved Hg to particulate Hg, then to sediments, and then to porewaters. Finally, Hg isotope signatures were used to identify the Hg sources and fractionation processes in core sediments from different depths. Our results demonstrate that Hg isotopes are powerful tools for tracing Hg sources and arriving at a better understanding of Hg biogeochemical cycling in the lagoon after long-term interventions. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Isotope signatures of mercury (Hg) in various fractions from Yundang Lagoon, Xiamen, China showed significant variations in mass-dependent and mass-independent fractionations. Three main sources of Hg in the lagoon seawater were identified, with photochemical reactions being the main process causing isotope fractionation. Mercury isotopes were found to be powerful tools for tracing Hg sources and understanding Hg biogeochemical cycling, demonstrating the importance of long-term interventions in the lagoon.