Nitrate transport and retention in Western European catchments are
shaped by hydroclimate and subsurface properties
Rémi Dupas
INRAE, L'institut Agro, UMR 1069 SAS, 35000 Rennes, France, INRAE, L'institut Agro, UMR 1069 SAS, 35000 Rennes, France, INRAE, L'institut Agro, UMR 1069 SAS, 35000 Rennes, France, INRAE, L'institut Agro, UMR 1069 SAS, 35000 Rennes, France
Author ProfileAbstract
Excess nitrogen (N) from anthropogenic sources deteriorates freshwater
resources. Actions taken to reduce N inputs to the biosphere often show
no or only delayed effects in receiving surface waters hinting at large
legacy N stores built up in the catchments soils and groundwater. Here,
we quantify transport and retention of N in 238 Western European
catchments by analyzing a unique data set of long-term N input and
output time series. We find that half of the catchments exhibited peak
transport times larger than five years with longer times being evident
in catchments with high potential evapotranspiration and low
precipitation seasonality. On average the catchments retained 72% of
the N from diffuse sources with retention efficiency being specifically
high in catchments with low discharge and thick, unconsolidated
aquifers. The estimated transport time scales do not explain the
observed N retention, suggesting a dominant role of biogeochemical
legacy in the catchments’ soils rather than a legacy store in the
groundwater. Future water quality management should account for the
accumulated biogeochemical N legacy to avoid long-term leaching and
water quality deteriorations for decades to come.