Collembolan response to red mud pollution in Western Hungary

Abstract

Effects of red mud pollution on the community structure of Collembola were studied in soils from open grassland and forest habitats following the red mud disaster in Western Hungary. Nearby unpolluted control plots of each habitat types were selected for comparative purposes. Analyses revealed that soil became strongly alkaline and, even nine months after the disaster, pH exceeded a value of 9.0 in the polluted forests. Water soluble Na content found to be 50–160 times greater in the polluted area, and total content of metals (e.g. Fe, Al, Mn, Zn, As, Cr, Cu, Ni, Pb, Zn) also increased considerably. Nevertheless, owing to the high alkalinity and red mud's adsorption capacity, bioavailable forms of heavy metals were lower in comparison to the acid control soils. Collembola species richness was about the same in the polluted and control forests (31 and 32, respectively), but lower in the polluted meadows compared to the control plots (21 and 27, respectively). Total community abundance changed differently in the open habitat and in the forest. Its value dropped by 45% in the polluted meadows, while almost tripled in the polluted forests. Changes in the abundance of individual species involved both decrease/elimination of sensitive species (e.g. Isotomiella minor, Sminthurinus aureus) and displacement of species tolerant to pollution (e.g. Micranurida pygmaea) into higher abundance classes. Certain species (e.g. Folsomia manolachei, Sphaeridia pumilis), following the pollution, showed a reverse pattern of abundance in the two habitat types; increasing in the forest while decreasing in the meadow. This study has suggested that soil alkalinity and salt (Na) toxicity were presumably the two most important factors determining the structure of Collembola communities in the area affected by red mud pollution. Despite the high toxicity risk associated with this accident, no adverse effect has been observed in Collembola abundance. Nevertheless, as a consequence of soil re-acidification, re-mobilisation of fixed metals may occur in the long term, constituting to a potential risk to soil Collembola.