Salt in the wound: The interfering effect of road salt on acidified forest catchments.

Atmospheric acidic depositions have strongly altered the functioning and biodiversity of Central European forest ecosystems. Most impacts occurred until the end of the 20(th) century but the situation substantially improved thereafter caused by legal regulations in the late 1980's to reduce acidifying atmospheric pollution. Since then slow recovery from acidification has been observed in forested catchments and adjacent waters. However, trends of recovery are inconsistent and underlying mechanisms diminishing recovery are still poorly understood. We propose that the input of road salt can significantly affect acidity regime and acidification recovery of forest ecosystems. By comparing the discharge hydro-chemistry and plant community composition of springs fed by forested catchments with and without high levels of salt input over two decades we observed a significant suppression of recovery and elevated levels of nutrient leaching (K(+), Ca(2+) and Mg(2+)) in highly salt contaminated catchments. We show that the pollution of near-surface groundwater (interflow) by road salt application can have lasting effects on ecosystem processes over distances of several hundred metres apart from the salt emitting road.