The Impact of Afforestation on Seepage Water Formation on Post-mining Spoil Heaps and Dumps - Results of Water Balance Modeling

Abstract

Mining sites like spoil heaps and dumps often have a geochemical composition that causes harmful effects on the environment - especially on ground and surface water. Water collection and treatment require elaborate technologies and high expenditures. The reduction of seepage water by afforestation, which leads to high evapotranspiration rates, offers an alternative to mitigate negative environmental impacts. To estimate such effects, we investigate the water regime of different post-mining tips and dumps in Germany: potash tailings piles with high salt contents in Thuringia, a slagheap of hard coal mining with heavy metal leaching in Saxony and a dump in the Lusatian lignite mining district, causing the discharge of iron sulfates. We simulate the seepage water formation with the Bowahald and LWFBrook90 software. Up to now, only 10% of the surface area of the potash tailings piles are covered by woody plants. Complete afforestation of the five potash tailings piles would reduce seepage water by 44%. On the sites in Saxony and Lusatia we modeled the water regime for different forest types. The results show differences between the sites characterized in terms of soil properties and between the selected tree species compositions. Hence, we recommend a mixture of tree species to keep a stable forest on spoil heaps and dumps and protect the groundwater at once.