Does Soil Aggregation Affect Carbon Sequestration in Restored Wetlands?.

Chronosequence studies suggest that soil properties (e.g., number of aggregates) in restored wetlands could take10s-100s of years to reach natural reference levels.  Wetland soils store carbon by incorporating organic matter into soil macro-aggregates.  These larger aggregates (> 2000 μm) will stabilize more carbon; thus, an understanding of how restoration affects aggregate size distribution has implications for estimating wetland carbon sequestration.  We hypothesized that the conversion process of an agricultural field to a wetland would decrease macro-aggregates (> 2000 μm) producing smaller aggregates (250-2000 μm, 53-250 μm, and < 53 μm) due to the physical break down of larger aggregates during intensive earth moving.  Aggregate separation was achieved by wet sieving subsamples of air-dried soil through a series of three sieves (2000 μm, 250 μm, and 53 μm).  Topsoil disturbance during the construction phase resulted in a significant decrease in soil macro-aggregates (by 51%, P < 0.01).  Aggregates in size classes 250-2000 μm, 53-250 μm, and < 53 μm were increased significantly (by 46%, P < 0.01; 33%, P < 0.01; and 67%, P < 0.01 respectively) in the post construction sampling.  Reduced aggregation and increased numbers of smaller aggregates from construction disturbance may alter the pool of stable carbon formerly upheld by macro-aggregates and limit future carbon sequestering potential for restored wetlands.