Land Reclamation Effects On Soil Nutrient Distribution in a Surface Mine Chronosequence in East Texas.

A problem in reclaiming surface mines to native conditions is the poor soil quality that impedes revegetation in post-mined soils. Our objectives were to measure the chemical characteristics distribution of nutrients in the soil profile to 1 m over a chronosequence of 40 years to determine when a reclaimed soil returned to premined conditions. In addition, we compared mine soils subjected to two different reclamation practices (crosspit spreader and mixed overburden) at 20 years of age at Big Brown lignite mine in East Texas. Soil quality indicators, including soil organic carbon, were 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 stratification was observed. N maintained premined levels and profile distribution after 15 years of reclamation, while P was able to stratify after 5 years but not reach premined conditions. Other nutrients were able to exceed premined conditions and develop native profile distribution 10-15 years (K and Ca), while Mg, S, and Fe displayed an increase in depth. When comparing the two reclamation practices at 20 years of age, the crosspit spreader showed better stratification between 0-15 and soil deeper than 15cm, but lower concentrations of nutrients compared to the mixed overburden treatment. The stratification of soil nutrients in post-mined soils indicate a return of biological activity, which is strongly influenced by the processes used to regrade the disturbed landscape and the timing of revegetation. Changes in soil textural classification appear to correlate with the increase of nutrients during site rehabilitation. We conclude that the more recent implementation of crosspit spreading served as a better method to return mined soils to premined conditions, but more research should be conducted to determine how aggregates and biological activity from the soil microbial community are influencing the accumulation of soil organic carbon over surface mine reclamation age.