Classification of mercury-labile organic matter relationships in lake sediments

•Relationships between mercury and organic matter are described for 17 Canadian lakes or basins within lakes.•A classification is proposed based on the capacity of a lake system to bind Hg to OM.•This provides a first order screening of lakes to quickly assess them.

This paper synthesizes the sediment geochemistry data for 19 sediment cores from 17 lakes and basins within lakes from various regions of Canada to describe general relationships between mercury (Hg) and the relative amount of labile organic matter (OM) as a proportion of total organic carbon. These relationships form the basis for proposing a general classification scheme of the capacity of a lake system to bind Hg to OM, which provides a first order screening of lakes to quickly assess them before further detailed analytical methods are employed. Mercury is known to have a strong affinity to OM before entering the lakes (binding with soil OM in the watershed) and also within the lakes (scavenging by autochthonous OM). Association of Hg with particulate OM, irrespective of the source, effectively captures available Hg(II) and ultimately sequesters it in bottom sediments. Relationships between total Hg concentration and the relative amount of labile OM in the sediments of a given system reveal important geochemical information; for example, the overall capacity of the system to effectively scavenge and fix available Hg, or its vulnerability to be overwhelmed by excess inputs of Hg in organic-poor or Hg contaminated systems.