Iodine speciation and cycling in fresh waters: A case study from a humic rich headwater lake (Mummelsee)

Iodine is a vital micronutrient for all mammals, including humans. Despite iodine s listing by the WHO as the worlds most easily preventable cause of train damage, there is very little known about iodine cycling in terrestrial fresh waters, particularly regarding temporal changes in speciation. This study presents iodine speciation (measured by IC-ICP-MS) data from one year of monthly sampling of a dimictic humic lake in the Black Forest (Mummelsee). Total soluble iodine (TSI) levels in the Mummelsee s water column averaged 1.9 +/- 0.3 mu g L-1. Soluble organically bound iodine (SOI) accounted for the majority of TSI in the lake (85 7,16) and inflow (76 6 ). SOI showed few changes throughout the year, despite stratification, anoxia in;he hypolimnion and ice cover. Iodide was lost from the epilimnion during the summer, autumn and winter, which may be related to (micro)biological uptake and sedimentation of dead organic matter. Efficient biological uptake was also suggested by a sediment core, where we found high total iodine concentrations (av. 11.8 +/- 1.7 mg kg(-1)) and a significant correlation with organic carbon content (p