The redox speciation of iron in two lakes

Abstract

The redox speciation of iron was determined by voltammetry in two lakes (Blelham Tarn, a lowland lake, and Gossenköllesee (GKS), a mountain lake). The reactive iron (Fe_R) concentration was ~40 nM in the epilimnion of Blelham Tarn, and up to 37% of this occurred as iron(II). In contrast, the Fe_R concentration in GKS was much lower at ~1 nM, similar to concentrations found in the open ocean. Under ice cover the iron(II) concentration peaked in GKS just below the Chl-a maximum, amounting to 50% of Fe_R. In July, the Chl-a concentration was lower, and iron(II) was present throughout the water column at ~30% of Fe_R. This work has demonstrated that iron occurs to a large extent as iron(II) in lake waters, of greatly differing conditions, in spite of the presence of oxygen; the main cause for this is not clear because the iron(II) may have been produced biologically or photochemically (or both). This, and the unexpectedly low reactive-iron concentrations in the transparent mountain-lake waters, warrant further work to evaluate their importance to the microorganisms in the lakes.