Effects of heavy metal contamination from an abandoned mine on nematode community structure as an indicator of soil ecosystem health

Soil nematode community structure reflects soil ecosystem health and is influenced by the soil environment directly and/or indirectly by affecting the soil micro-flora and fauna that they graze. In this study, ecological indices for soil nematode community structure and microbial populations in soils contaminated with mine drainage (CS) from an abandoned mine and of a nearby non-contaminated area (NC) were examined during the seven seasons from July 2007 through December 2008 to reveal influences of mine drainage (especially heavy metals) on the soil nematode community structure. Of the soil physicochemical characteristics measured, nutritional properties such as organic matter content, nitrogen content, and soluble cations were not significantly different between CS and NC; however, significant differences were detected in pH, electrical conductivity (EC), available phosphorus (av.P₂O₅), and most strikingly, the concentrations of heavy metals such as Cd, Pb, Zn, and Ni. Nematodes were less abundant in CS than in NC, especially for long-living persistor-type nematodes. Comparison of ecological indices between CS and NC indicates that abundance, maturity, richness, and diversity of the soil nematode community were decreased in CS soil, indicating that soil health and function were adversely affected. Of the weighted-soil food-web indices, the structural index (SI) of the soil nematode community was significantly lower in CS than in NC, while no significant difference in the enrichment index (EI) was observed between CS and NC, suggesting that the heavy metal contamination may have disturbed the soil ecosystem by suppressing biological activity. Seasonal changes in the ecological indices during the study period showed that the discrepancies between CS and NC persisted throughout most of the seasons, suggesting that the effect of mine drainage (heavy metal) contamination on nematode community structure may be little influenced by seasonal changes in environmental conditions.