Predicting nitrate leaching from alpine areas

Abstract

We investigated the effects of changes in atmospheric deposition of inorganic nitrogen (IN = NO₃⁻ + NH₄⁺) and climate change on NO₃⁻ leaching from N-saturated alpine catchments in the Tatra Mountains. This Central European mountain region provided a unique opportunity to assess the impact of the steep increase in atmospheric deposition of IN between the 1930s and 1980s, its largest global decline since the 1990s, and the recent acceleration of warming on long-term trends of NO₃⁻ concentrations in lake water. We analysed data on NO₃⁻ concentrations in 29 alpine lakes, together with observed and modelled trends in IN deposition and climate characteristics for the period 1937–2024. The results show progressive N saturation and NO₃⁻ leaching with increasing IN deposition until the late 1980s. Then NO₃⁻ leaching decreased, but at a slower rate than IN deposition in the 1990s–2000s, and finally reached a steeper trend than IN deposition in the last two decades, probably due to increasing air temperature. We hypothesise that longer and warmer growing seasons have partially mitigated catchment N saturation due to increased vegetation production and the input of plant biomass with high C:N ratios into the soil (i.e., increased organic carbon availability), which increases its ability to immobilise IN. Our results suggest that warming of alpine ecosystems has the potential to reduce their degree of N saturation and terrestrial NO₃⁻ export. Similar effects of climate change on the fate of deposited IN can be expected in other N-saturated alpine ecosystems worldwide.