31 Aug 2022
31 Aug 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Endogenic methylmercury in a eutrophic lake during the formation and decay of seston

Laura Balzer1, Carluvy Baptista-Salazar2, Sofi Jonsson2, and Harald Biester1 Laura Balzer et al.
  • 1Institute for Geoecology, Environmental Geochemistry Group, Technische Universität Braunschweig, 38106 Braunschweig, Germany
  • 2Department of Environmental Science, Stockholm University, 106 91 Stockholm, Sweden

Abstract. Anoxic microniches in sinking particles in lakes have been identified as important water phase production zones of monomethylmercury (MeHg) (endogenic MeHg). However, the production and decay of MeHg during organic matter (OM) decomposition in the water column and its relation to the total Hg concentration in seston are poorly understood. We investigated Hg speciation and chemical changes in sinking seston in a small and shallow (12-m-deep) eutrophic lake during phytoplankton blooms from April to November 2019. The results show that MeHg proportions are high in seston at the water surface (up to 22 %) and at the oxic-suboxic redox boundary (up to 26 %). During suboxic OM decomposition, and with decreasing redox-potential, the concentration and proportion of MeHg in seston strongly decrease (< 0.5 %) as the water depth increases. Under these conditions, total Hg concentrations show a 3.8 to 26-fold increase. In the hypolimnion environment, changes in MeHg proportions were minimal in sinking seston, and samples collected by sediment traps had MeHg values similar to those measured at the sediment-water interface, though higher MeHg concentrations were found deeper in the sediment. Our results indicate that cycling of MeHg and total Hg (THg) in seston within small productive lakes is largely controlled by the decomposition processes of settling seston and that the endogenic MeHg pool appears to be largely disconnected from the sedimentary MeHg pool.

Laura Balzer et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-170', Anonymous Referee #1, 29 Sep 2022
    • AC1: 'Reply on RC1', Laura Balzer, 18 Nov 2022
  • RC2: 'Comment on bg-2022-170', Anonymous Referee #2, 03 Nov 2022
    • AC2: 'Reply on RC2', Laura Balzer, 18 Nov 2022

Laura Balzer et al.

Laura Balzer et al.


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Short summary
Toxic methylmercury (MeHg) in lakes can be enriched in fish and is harmful for humans. Phytoplankton is the entry point for MeHg into the aquatic food chain. We investigated seasonal MeHg concentrations in plankton of a productive lake. Our results show that high amounts of MeHg is occurring in algae and suspended matter in lakes and that productive lakes are hot spots of MeHg formation mainly controlled by decomposition of algae organic matter and water phase redox conditions.