The years afterwards , are characterized by a steady decline in TE concentrations to levels slowly approaching those before 1925 (Fig. ). For the years 1990 until present, this is supported by national monitoring data of air emissions in Germany (UBA 2020), as well as bioaccumulation data of the national moss surveys , and is accredited mostly to ash and SO2 reduction measures which are part of the legislative and technology measures to reduce air pollutants on an European level since the 1970s . It remains to be seen, however, if those pre-industrial levels are reached in the future. Soils have been accumulating TEs for a very long time and are slowly releasing them, as several studies have shown , so that fluxes to the lakes can remain positive despite emission reductions.