Aggregate and organic matter dynamics in reclaimed soils as indicated by stable carbon isotopes

Recovery of belowground ecosystem processes, such as soil aggregation and organic matter (OM) accumulation, in reconstructed soils is crucial to successful reclamation of disturbed lands. Objectives of this study were to track soil aggregate recovery in combination with aggregate associated OM on a chronosequence of reclaimed surface mine sites and a native, undisturbed reference site. Macroaggregate and micro-within-macroaggregate proportions increased with reclamation age, while microaggregate proportions decreased. Organic carbon (C) and total nitrogen (N) concentrations increased with reclamation age for each aggregate fraction and were higher in the OM fraction observed within soil aggregates than in the free OM fraction found between soil aggregates. Naturally occurring isotopic signatures of 13C decreased rapidly with reclamation age, indicating over 50% of total aggregate C to be new C from predominately C3 plant community inputs after 26 years of reclamation. Soil aggregate size distribution trends of increasing macroaggregation and micro-within-macroaggregates along with rapid rates of OM accumulation with time indicated that reclaimed soils had recovered structurally towards a native soil condition after a period of 10-15 years.