Intensive sampling of iodine and nutrient speciation in naturally eutrophicated anchialine pond (Rogoznica Lake) during spring and summer seasons

Abstract

A study of inorganic iodine speciation in the water column of a naturally eutrophicated anchialine pond (Rogoznica Lake, East Adriatic Coast) was conducted in a period between April and July 2004 to obtain information how close the inorganic iodine system is to that of inorganic nutrients during spring, when phytoplankton activity is at maximum, and how the system changes up to summer, when highly reducible redox-conditions prevail in deep water. Iodate and iodide concentrations were determined by differential pulse voltammetry and cathodic stripping square wave voltammetry, respectively. In addition, total iodine concentrations were determined by ICP-MS in May. The hydrographic and nutrient profiles indicate that the system was greatly affected by photosynthesis and demonstrate strong seasonal change in predominant phytoplankton assemblages. The hypolimnion depths were dominated by regeneration processes and benthic influence, with anoxic and sulphidic conditions at maximum sampling depth in July. The iodine profiles show no clear direct relationship between the iodine and nutrient system regarding to the phytoplankton production. Meanwhile, the results demonstrate temporal matching between high iodate and high regenerated nitrate concentrations in the surface layers, and close spatial matching of iodate production and nitrification at mid-depths of hypolimnion. The key role of nitrifers is discussed and the implication of these findings is explored.