Acid rain footprint three decades after peak deposition: Long-term recovery from pollutant sulphate in the Uhlirska catchment (Czech Republic)

The granitic Uhlirska headwater catchment with a size of 1.78km² is located in the Jizera Mountains in the northern Czech Republic and received among the highest inputs of anthropogenic acid depositions in Europe. An analysis of sulphate (SO₄^2-) distribution in deposition, soil water, stream water and groundwater compartments allowed to establish a SO₄^2- mass-balance (deposition input minus surface water export) and helped to evaluate which changes occurred since the last evaluation of the catchment in 1997. The determined SO₄^2- concentrations decreased in the following order: wetland groundwater>groundwater from 20m below ground level (bgl)>groundwater from 30m bgl>stream water>groundwater from10m bgl>hillslope soil water>wetland soil water>bulk deposition with median values of 0.24, 0.21, 0.17, 0.15, 0.11, 0.07, 0.03 and 0.01mmolL^-1, respectively. Our results show that average deposition reductions of 62% did not result in equal changes of the sulphate mass-balance, which changed by only 47%. This difference occurs because sulphate originates from internal sources such as the groundwater and soil water. The Uhlirska catchment is subject to delayed recovery from anthropogenic acid depositions and remains a net source of stored sulphur even after three decades of declining inputs. The wetland groundwater and soil water provide environmental memories of legacy pollutant sulphate. Elevated stream water sulphate concentrations after the unusually dry summer 2015 imply importance of weather and climate patterns for future recovery from acidification.