Mechanism of dissolved iron production in a watershed and the effect of soil freezing and thawing

Abstract

Iron, one of the essential elements, is a very common element, since the total weight of the iron is ap-proximately 30 % of the weight of the Earth. However, concentration of iron in oceans is less than nmol, which is extremely low. Thus, iron supply from the terrestrial area through air dusts and river flows is significantly im-portant for ocean ecosystems. In this sense, understanding the mechanism of iron behavior on lands is essential. Reviewing published articles on dissolved iron genera-tion mechanisms suggests that soil organic matter and iron in the soil particles are behaving simultaneously. Under the condition that freezing and thawing processes is im-portant, thawing depth might be the key factor to determine dissolved iron concentration. In addition, analysis on ab-normal dissolved iron concentration peak in the late 1990s’ in the Amur River is indicating that the effect of thawing of permafrost have a significant effect on dissolved iron pro-duction mechanisms. Based on this hypothesis, we con-ducted field observations combined with the analysis of long-term evaluation of thawing depths. The result indi-rectly supports the hypothesis. For the further understand-ing, classification of organic matter contributing the chela tion with iron, and the monitoring of iron and dissolved organic matters during freezing and thawing processes are critical.