Mechanisms Leading to Carbon Sequestration in Disturbed Soils Restored with Biosolids.

Many studies have shown that the incorporation of organic amendments to restore disturbed sites and soils following mining to prompts natural revegetation and restoration of soil function. We studied a restoration chronosequence (0, 0.5, 3, 6, 9 and 14 years) to investigate the effect of biosolids amendment and plant species invasion on mined sites of central Brazil. Without biosolids treatment the mined areas lack vegetation cover regardless of time since overburden removal. However, the incorporation of biosolids increased soil C to 4 times above pre-disturbance levels (~2%) and prompted spontaneous revegetation. Isotopic and elemental analyses showed the increase in soil C was mainly from new C inputs from revegetation suggesting the biosolids promoted C stabilization beyond the capacity of the original soil. A clear association between pyrophosphate-extractable iron and occluded C reflected the role of iron-coordinated compounds influencing aggregate formation. Since total iron was abundant, it is hypothesized that amorphous iron added with the biosolids exchanged with new carbon inputs to stable carbon beyond the potential of the native ecosystem. Mechanisms leading to the excahnge of old and new carbon will be discussed. Iron-bound compounds represented most of total soil C (>100 Mg C ha^-1; 0-20cm) despite its origin (biosolid or plant) showing the benefits of iron containing biosolids in carbon stabilization. The single addition of iron-rich biosolids prompted long-term stabilization of new organic inputs, showing promise for the restoration approach for degraded lands.