To dam, or not to dam? Abolishment of further flooding impedes the natural revegetation processes after long-term fluvial deposition of copper tailings

Long-term potentials and constraints of nature to spontaneously recover after severe degradation by toxic mine waste, and general principles of mutual modifications of spontaneous vegetation and soils during this process, have remained widely unknown. This study investigates the effect of flooding on natural restoration of a model locality in Eastern Serbia, complexly degraded by 70-years fluvial deposition of sulfidic copper (Cu) mine tailings in a floodplain along 80km of the polluted river flow. We analyzed multivariate response of forest vegetation (floristic and structural parameters) together with physical and chemical properties of concomitant soils and sediments. Floods strongly modify the interactions between soil and vegetation. Three very different types of forest vegetation constitute the response of the nature to key soil adverse factors (excessive Cu availability, low nutrients, and low pH); combined with drought, these constraints completely inhibit revegetation. Continual flooding after mine closure, despite the pollution it still brings in, fosters a faster development of highly specialized vegetation and most importantly faster buildup of soil organic matter necessary for phytostabilization of substantial amounts of Cu tailings present in the floodplain. We show that enhanced nutrient fluxes facilitated by natural flooding regime might overrun the constraining effect of deposited Cu also for natural vegetation