Microbial succession and mineral leaching in an artificial coal spoil.

An artificial pyritic coal spoil was prepared and examined over a period of 1.5 years for changes in the population of various physiological varieties of bacteria and also for mineral leaching. Heterotrophic bacteria were the first to dominate the spoil, acquiring a population of 10(7) cells per g within 2 weeks. Bacteria capable of utilizing choline sulfate as the sole source of energy comprised approximately 1% of the total heterotrophic bacteria. Sulfur-oxidizing autotrophic bacteria (Thiobacillus) and finally iron-oxidizing bacteria (Thiobacillus ferrooxidans) increased in the population, the latter becoming the dominant species where acidity was greatest. Partition of species paralleled partition of acidity in the spoil. Maximum acidity (pH 2.6) and maximum population of T. ferrooxidans (greater than 10(7) cells per g) occurred at the summit. Molds (notably, Aspergillus), algae (Chlorococcales, Oscillatoria, Navicula), cilliated and flagellated protozoa, an arthropod (Podura aquatica), and a moss (aberrant Physcomitrium pyriforme) were observed. The mineral salts leached from the spoil, in decreasing order, were the sulfates of magnesium (predominantly hexahydrite), calcium (gypsum), sodium, aluminum (alunogenite), and iron.