Long-term ecological effects of the red mud disaster in Hungary: Regeneration of red mud flooded areas in a contaminated industrial region.

As one of the most severe ecological disasters ever to take place in Europe, the 2010 red mud accident has left behind long-term environmental impact, prompting the need for monitoring of soil biodiversity. Red mud (wet storage solution) can be regarded as a complex mixture of contaminants due to its extreme alkalinity and the presence of potentially toxic trace elements. After-effect investigations on soil properties and soil microarthropods were carried out in three distinct habitat types (agricultural land, grassland, woodland) in the red mud affected area. Soils in the red mud affected area were moderately to strongly alkaline (pH 7.5 to 8.5). Total content of trace metals Cd, Ni, Cr exceeded threshold concentrations for soil. Acari and Collembola were by far the most abundant taxa, while important groups like Pauropoda, Protura and Symphyla were completely absent from the samples of red mud affected plots. These observations were also reflected by the low values of the soil biological quality (QBS-ar) index. Independently of habitat types, total collembolan abundance tended to be lower in the contaminated area when compared with nearby control samples. Typical species distribution of Collembola communities in the contaminated area generally included one or two very common and abundant species and more, relatively rare species of low abundance. In the red mud affected open habitats, a distinct eudominance of Brachystomella parvula and Parisotoma notabilis was observed; whereas in contaminated woodland Parisotoma notabilis formed the bulk of the community with Sphaeridia pumilis, Folsomia manolachei and F. quadrioculata being subdominant. Species sensitive to alkalinity and red mud components (e.g. Hypogastrura vernalis, Lepidocyrtus tomosvaryi) were completely absent or were present only in limited numbers in the contaminated samples.