Processes controlling manganese distributions and associations in organic-rich freshwater aquatic systems: The example of Loch Bradan, Scotland

►Aqueous phase transfer of Mn from western basin sediments across the loch. ►Terrestrial DOC in streamwater influences the speciation of Mn therein. ►Loch water Mn speciation is partly influenced by that in the main inflows. ►Mn diffusion out of sediments occurs under non-turbulent conditions. ►Mn2+ and/or Mn in large colloidal form are released from loch bottom sediments.