Catchment Properties control Mercury Speciation in Streams and Lakes across a Sub-Arctic Climate Gradient

Catchment properties may influence the mercury (Hg) cycle by affecting Hg speciation, transport, and bioavailability, though their role is not fully understood. In aquatic systems, the bioaccumulation of methylmercury (MeHg) poses significant risks to wildlife and human health. Despite its importance, our understanding of the relationships between catchment properties and the concentrations of total Hg and MeHg in the environment and at the base of the aquatic food web remains incomplete.

In this study, we explore how catchment properties relate to Hg concentrations and speciation in high-latitude Swedish catchments encompassing tundra, birch, and boreal forest ecosystems. Sampling was conducted in August 2020 across 18 streams and 8 lakes distributed along a climatic and vegetation gradient (67.5°–68.5°N, 18°–21.5°E). We measured Hg species and over 60 ancillary parameters and employed a PARAFAC model to examine the role of dissolved organic matter (DOM) characteristics in aquatic Hg dynamics.

Using multivariate analysis, we found distinct differences in water type and catchment systems based on the ancillary parameters. Total Hg and MeHg concentrations followed the trend boreal > birch > tundra for both lakes and streams, with lakes generally showing higher MeHg levels and MeHg% compared to streams. Our findings suggest that terrestrial humic-like DOM plays a key role in transporting Hg from terrestrial systems to and within aquatic environments, thereby influencing aquatic Hg concentrations. Microbial and algal DOM, on the other hand, appears to promote Hg methylation processes.