Ecosystem recovery following post environmental change near an aluminium smelter in Žiar nad Hronom, Slovakia

As a result of aluminium production that started in 1953, the surroundings of the aluminium smelter and foundry in Žiar nad Hronom are among the most polluted areas in Slovakia. Following the introduction of a new technology in 1996, emissions from the plant have decreased significantly, but it is not clear to what extent the ecosystems in the area have recovered and whether they still carry traces of pollution. We have evaluated the recovery process 23 years after the change in technology by analysing the current contamination of the ecosystem around the factory. In 2019, we sampled the soil, herbaceous plants (Arrhenatherum elatius and Artemisia vulgaris), and woody plants (Salix euxina, Alnus glutinosa, and Carpinus betulus) along three transects running in different directions from the smelter and compared our results with those of a study conducted in 1971. Our data indicate that the concentrations of elements differ depending on the plant life form. Some elements accumulated more in trees (light elements, Sr, Ca, Zn, and Mn) whereas others accumulated more in herbs (K, P, Cl, Si, and Cu). A resurvey of vegetation data has shown clear signs of ecosystem recovery. Over the past ∼50 years, soil fluoride contamination has decreased several-fold and the slope of the distance–decay relationship has flattened. As regards plant leaf biomass, the distance–decay relation has faded out or even reversed, but the concentrations of fluorine in leaves further from the source of pollution remain as high as, or even exceed, values measured ∼50 years ago. Although the ecosystem around the plant is recovering from the past pollution, the revitalization process is still ongoing. Most importantly, concentrations of fluorine in plant biomass continue to exceed the health risk limit, and the meadows adjacent to the smelter are still unsuitable for agricultural purposes. Our study shows that ecosystem recovery will be a long-term process.