Recovery of Soil Functionality and Quality In a Post-Lignite Surface Mine Chronosequence In East Texas.

A problem in restoring surface mines to native or improved conditions is the inability for soils to sustain nutrient cycling rates, which impedes revegetation in post-mined soils. Our objectives were to measure and compare chemical and biological characteristics over a reclamation chronosequence of 40 years to determine when the functionality of a reclaimed soil returned to premined conditions at The Big Brown Mine in East Texas. In addition, we compared these parameters in mine soils subjected to two different reclamation practices (crosspit spreader [CP] and mixed overburden [MO]) at 20 years of age. We measured different soil quality indicators: soil carbon and nitrogen, mineralization, soil microbial biomass, and functional diversity via BIOLOG®. Soil organic carbon was able to reach and exceed premined concentrations almost immediately after reclamation began, although the distribution through the soil profile required at least 5 years before any stratification was observed. Soil nitrogen returned to premined levels and demonstrated profile distribution after 15 years of reclamation. The C:N ratios were most similar to premined levels at 5 years. Carbon mineralization rates exceeded premined levels after 10 years of reclamation, but were most similar after 15 years. Carbon mineralization rates were highest in MO20 and MO30 soils.  Nitrogen mineralization rates in reclamation sites exhibited a similar pattern to carbon mineralization rates by exceeding premined levels at 10 years. Interestingly, both the CP15 and MO40 sites displayed nitrate production rates most similar to the unmined site. As expected, soil microbial biomass levels also correlated strongly with soil carbon levels and C mineralization rates. To complement this data, a BIOLOG assay was completed, which revealed an increase in metabolic diversity after reclamation began, peaking at 15 years, and then stabilizing. Our data shows that the soil quality of reclaimed surface mines can meet and even exceed from premined conditions shortly after reclamation practices are implemented. The sustainability of nutrient cycling in disturbed lands is important for maintaining nutrient levels for a healthy plant community in the long term.