A new study from Erik Björn’s research group demonstrates how the input of terrestrial organic matter influences methylmercury accumulation in coastal planktonic food webs through two opposing processes: (1) increased concentration of thiol functional groups associated with the terrestrial organic matter suppresses methylmercury incorporation at the base of the food web, through the formation of thermodynamically stable methylmercury-thiol complexes with low bioavailability; (2) brownification of the water phase enhances methylmercury biomagnification, through enhanced heterotrophic bacteria production causing a longer food web. Understanding the net outcome of these two processes is essential for predicting methylmercury concentrations in coastal food webs under changing inputs of terrestrial organic matter.

The new documentary Fjords Frontiers: Digging into the Future of Climate Change, presents recent mercury and climate research by the teams of Eric Capo and Erik Björn at Umeå University. The documentary shows field research conducted at the Norwegian fjord Rossfjordsvatnet. The water mass in this fjord is redox-stratified with declining oxygen, and increasing hydrogen sulfide, concentrations at increasing depth. The research aims to understand how the expansion of oxygen deficiency in coastal seas may impact mercury biogeochemistry and microbial metabolisms.

The research is funded by the Swedish Research Council, The Swedish research council FORMAS and the Kempe Foundations.

Research in Björn’s group show how the availability of methylmercury for incorporation at the base of the aquatic food web (by phytoplankton cellular uptake) is controlled by the concentration of thiol functional groups in dissolved organic matter. The research further shows how the concentration of DOM-thiols systematically decreases across the terrestrial-marine aquatic continuum.