Drought resistance of native pioneer species indicates potential suitability for restoration of post-mining areas

In order to test whether invasive exotic species, predominantly used for restoring post-mining areas in north-eastern Vietnam, may be replaced by ecologically superior native pioneer species, we conducted a drought stress experiment in a greenhouse. We hypothesized that juvenile individuals of four native pioneer tree and two native pioneer grass species have a drought resistance comparable to two exotic reference species. Our results confirm this hypothesis: even under drought, native trees had a higher biomass and root : shoot ratio than exotic trees, although their maximum relative elongation rate and biomass were reduced more strongly than for exotic trees with respect to well-watered conditions. Native grasses had a higher root length density and a similar drought-induced reduction of stomatal conductance compared to exotic trees. In spite of a higher biomass reduction, native grasses produced more biomass under drought in absolute terms. Notwithstanding that further investigations of other adverse environmental factors need to be performed, our results indicate with respect to drought resistance that native pioneer species are a potential alternative to exotic species for the ecological restoration of subtropical post-mining areas, which may accelerate secondary succession

Assessing the ecotoxicity of gold mine tailings utilizing earthworm and microbial assays

Problems associated with mining are the disposal of wastes on tailing disposal facilities (TDFs). The aim of this study was to determine the ecotoxicity of gold mine tailings by using earthworm bioassays, earthworm biomarkers and enzymatic analyses. End points included changes in biomass, reproduction, lysosomal membrane stability, tissue metal concentrations, and selected enzymatic activities. Results indicated high concentrations of Ni in the material as well as bioaccumulation of lead and arsenic in the earthworm body tissue after exposure. Enzymatic activity was higher in revegetated tailings than in unrehabilitated tailings. It was concluded that TDF and surrounding areas have an acidic pH which affects earthworms and metal bioavailability. Soil enzymatic activities were a sensitive indicator of metal pollution in mining areas. Growth, reproduction and lysosomal membrane stability of earthworms have also been shown to be sensitive end points to assess the ecotoxic effects of gold TD