Reconstruction of Long-term Trajectories of Soil Nitrogen Surplus Across Europe
Résumé
Worldwide surface waters suffer from the presence of nitrogen (N) compounds causing eutrophication and water quality deterioration. Despite many Europe-wide legislations, we still observe high N levels across many water bodies in Europe. Information on long-term annual soil N surplus is needed to better understand these N levels and inform future management strategies. The goal of this study is to characterize the spatial and temporal pattern of the N surplus across Europe at different spatial scales (i.e., national, subnational or river basin level). To achieve this goal, we constructed a long-term (1850-2019) annual N soil surface budget for both agricultural and non-agricultural soils across Europe at a 5 arcmin spatial resolution. This dataset combines information at different levels (in particular country and grid level) to construct the different N surplus components using publicly available information (e.g., FAOSTAT, EUROSTAT, published literature and reports) for different time periods (i.e., for the periods 1850 – 1960 and 1961 – 2019, and for the year 2000), at different frequencies (i.e., yearly, decadal, snapshots). Furthermore, we account for the underlying uncertainties resulting from both input data sources and methodological choices in major components of the N surplus (i.e., fertilizer, manure and N removal rates). We demonstrate the consistency and plausibility of our estimates by comparing them with previous studies. The reconstructed long-term N surplus provides insights into the trends and spatial distribution of excess N into the soil systems across Europe, highlighting agricultural areas across Central Europe being the hotspot of N surplus. These areas have experienced a drastic change over the last 150 years. For example, N surplus over the EU-28 region exhibited a three-fold increase during 1850-1960 (from 6 ± 0.7 to 20 ± 2.6 kg ha-1 yr-1), further increased by nearly two times between 1960-1990 (36 ± 1.4 kg ha-1 yr-1 in 1990), and then reduced by around 30% during 1990-2019 (28 ± 1.2 kg ha-1 yr-1 in 2019). We highlight the importance of N surplus over non-agricultural soils that amounts up to 30% on average across the Europe. Finally, we show that N surplus estimates have large uncertainties, which calls for their explicit consideration in analysis of past N surplus trajectories.