The influence of light and nutrient addition upon the sediment chemistry of iron in an arctic lake

The geochemical response of sediments to increased nutrient input to an Alaskan, arctic lake was examined using direct measurements of sediment-water chemical fluxes. An unexpected increase in Fe flux occurred when sediments were exposed to high incident radiation and nutrient concentrations. Correlation between light and acid-soluble Fe concentrations suggests that photoreduction of Fe(III) oxides may occur, but nutrient addition enhanced the effect indicating that primary productivity was also important. The processes controlling the flux of Fe from sediments in this lake were complex and included the redox potential (dissolved oxygen concentration) of the water, quality of organic matter present in the sediment, light, and nutrients supplied from the sediments and/or water column. These four factors together with the possibility of direct uptake of Fe by phytoplankton and the possible release of algal reductants may contribute to Fe cycling in this lake.