The redox speciation of iron in two lakes

The redox speciation of iron was determined by voltammetry in two lakes (Blelham Tarn, a lowland lake, and Gossenkollesee ( GKS), a mountain lake). The reactive iron (Fe-R) concentration was similar to 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 similar to1 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 similar to 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 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.