Microbial biomass, microbial respiration and organic carbon indicates nutrient cycling in a chronosequence coal mine overburden spoil

Soil microbial biomass and microbial respiration have an important influence on nutrient cycling. The spatial distribution of soil microbial biomass, microbial respiration and organic carbon were examined along a chronosequence coal mine overburden spoil to assess the impact of different soil parameters on nutrient cycling over time. Effects of mining activities are markedly adverse, because many beneficial soil characteristics may require a long span of time to develop through pedogenesis, which evaluates the degree of functional microbial processes for ecosystem recovery and used as an index of the progress of soil genesis in mine overburden spoils. The organic carbon, total nitrogen and extractable phosphorous in spoil samples collected from six different age series coal mine overburdens in chronosequence exhibited progressive improvement. The net annual accumulation rate for carbon, nitrogen and phosphorous amounted to 255 kgC/ha/yr, 20 kgN/ha/yr and 1 kgP/ha/yr respectively. Greater proliferation of MB-C over MB-N and MB-P with age of mine spoil was significant MB-C (r=0.955, p<0.001); MB-N (r=0.951, p<0.001); MB-P (r=0.909, p<0.01), which indicated microbial carbon immobilization. The MB-C:OC ratio is proved to be a reliable measure for describing reclamation process. Microbial basal spoil respiration rate showed consistent improvement from 0.132 μg CO₂-C/g spoil/h (OB₀) to 0.348μg CO₂-C/g spoil/h (OB₁₀), which is statistically significant (r=0.981, p<0.001). Stepwise multiple regression analysis suggested that 94.57% of the variability in microbial basal respiration was explained by OC, and an additional 4.5% by MB-C. Further, the decline trend of microbial metabolic quotient with respect to six different coal mine overburden spoil revealed the progression of spoil to soil recovery over time.