Trajectories of nitrate input and output in three nested catchments along a land use gradient 1 2 1,3 2 1 Sophie Ehrhardt , Rohini Kumar , Jan H. Fleckenstein , Sabine Attinger , Andreas Musolff 1Department of Hydrogeology, Helmholtz-Centre for Environmental Research, Leipzig, 04318, Germany 5 2Department Computational Hydrosystems, Helmholtz-Centre for Environmental, Leipzig, 04318, Germany 3 Bayreuth Center of Ecology and Environmental Research, University of Bayreuth, Bayreuth, 95440, Germany Correspondence to: Andreas Musolff (
[email protected]) Abstract. Increased anthropogenic inputs of nitrogen (N) to the biosphere during the last decades have resulted in increased 10 groundwater and surface water concentrations of N (primarily as nitrate) posing a global problem. Although measures have been implemented to reduce N inputs, they have not always led to decreasing riverine nitrate concentrations and loads. This limited response to the measures can either be caused by the accumulation of organic N in the soils (biogeochemical legacy) –or by long travel times (TTs) of inorganic N to the streams (hydrological legacy). Here, we compare atmospheric and agricultural N inputs with long-term observations (1970–2016) of riverine nitrate concentrations and loads in a Central 15 German mesoscale catchment with a three nested sub-catchments arrangement of increasing agricultural land use. Based on a data-driven approach, we assess jointly the N budget and the effective TTs of N through the soil and groundwater compartments. In combination with long-term trajectories of the C–Q relationships, we evaluate the potential for and the characteristics of an N legacy. We show that in the 40-year-long observation period, the catchment (270 km2) with 60 % of agricultural area have received 20 an N input of 53 437 t, while it exported 6 592 t indicating an overall retention of 88 %.