Tying Together Iron and Carbon Cycling in the Arctic

Methane production is sensitive to soil acidity. Many Arctic soils are rich in iron, which some soil microorganisms can use instead of oxygen for respiration through iron reduction. This produces carbon dioxide while decreasing soil acidity. Computer models that currently predict greenhouse gas emissions from thawing Arctic soils do not include iron or acidity changes. This study used a chemical reaction network model to simulate interactions of iron reduction, methane production, and organic matter decomposition in permafrost soils. The model was compared to measurements of carbon dioxide and methane production as well as soil acidity from a series of laboratory incubation experiments. The model then simulated cycles of waterlogged and aerated conditions to test how iron affected production of greenhouse gases over multiple cycles. Iron reduction occurred during waterlogged periods, producing carbon dioxide and reducing soil acidity, while iron was recycled during aerated periods. Because methane-producing microorganisms prefer less acidic soil conditions, iron reduction enhanced methane production when there was enough available organic matter to support both processes. When easily decomposed organic matter was more limited, iron reducers competed with methane producers, leading to lower methane production.