Impact of Swedish peatland rewetting on mercury (Hg) bioaccumulation in downstream ecosystems: process quantification using Hg stable isotopes

Extensive peatland areas in Sweden’s forest landscape have been drained.

Rewetting of these peatlands is currently considered for the enhancement of carbon storage, biodiversity, groundwater storage, and surface water quality.

However, peatland rewetting also causes fundamental changes in soil biogeochemical properties, possibly resulting in undesired effects.

A notable example is the potentially enhanced export of mercury (Hg) from the restored anaerobic environments to downstream lakes. This would increase the threat to the health of wildlife and humans that current Hg levels already pose.

Yet, it is unclear if rewetted peatlands will increase the Hg concentrations in downstream fish.My project will use a novel Hg stable isotope tool to improve the fundamental understanding of three key aspects of the linkages between Hg in peatlands and downstream lake ecosystems: 1) what processes affect Hg release from rewetted peatlands? 2) Does changing peat hydrology alter Hg loads to downstream lakes? 3) How much does Hg in fish originate from the peat soils in the landscape?The project outcomes will improve the ability to assess and mitigate potential risks of rewetting effects on Hg levels in fish by advancing the understanding of ecosystem-scale Hg cycling.

This is of value both for a holistic understanding of the choices society makes in managing boreal landscapes and for supporting the Minamata Convention in its call to reduce the exposure of people and wildlife to Hg.