Multidecadal Trajectory of Riverine Nitrogen and Phosphorus Dynamics in Rural Catchments

The long‐term evolution of nutrient dynamics in rivers under changing external forcings, termed hereafter trajectory, is influenced by local human activities and regional climatic variations. Here we investigate nitrogen (N) and phosphorus (P) dynamics in seven mesoscale agricultural catchments (med...

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Bibliographic Details
Published in:Water resources research 2018-08, Vol.54 (8), p.5327-5340
Main Authors: Dupas, Rémi, Minaudo, Camille, Gruau, Gérard, Ruiz, Laurent, Gascuel‐Odoux, Chantal
Format: Article
Language:English
Subjects:
Agricultural watersheds
agriculture
Atmospheric forcing
Capacity
catchment
Catchment area
Catchments
Climate
Climate and human activity
Climate effects
Climate variations
Denitrification
Dynamics
Earth Sciences
Evolution
Geochemistry
Groundwater
Hydrology
legacy
long term
Mineral nutrients
Mitigation
Nitrogen
North Atlantic Oscillation
nutrient
Nutrient dynamics
Ocean-atmosphere system
Phosphorus
Quality assessment
Quality control
Rivers
Rural catchments
Sciences of the Universe
Storage
Trajectories
Transport processes
Variation
Water pollution
Water quality
Water quality assessments
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Summary:The long‐term evolution of nutrient dynamics in rivers under changing external forcings, termed hereafter trajectory, is influenced by local human activities and regional climatic variations. Here we investigate nitrogen (N) and phosphorus (P) dynamics in seven mesoscale agricultural catchments (median size 800 km2) of western France from seasonal to multidecadal time scales (1970–2016). Results show that, in these catchments dominated by shallow groundwater, long‐term nitrate exports responded to variations of the agricultural N surplus with time lags of approximately 10 years. Presence of legacy N storage, related to the catchments' denitrification capacity, was found to increase response times. In contrast, P trends were predominantly controlled by decreasing point source emissions during the study period, and P dynamics were influenced by in‐stream retention/remobilization processes that hampered precise quantification of land‐to‐river diffuse transport processes. Occurrence of interannual climate variations during three 5‐ to 10‐year dry‐wet cycles, influenced by the North Atlantic Oscillation, affected N and P dynamics with persistent interannual hysteresis patterns among catchment and years. Thus, water quality assessment programs should cover at least five years to decipher the effect of mitigation measures from climate variations. Key Points Long‐term N and P trends disentangled from effect of interannual climate variability N and P trends responded to changes in agricultural N surplus and point source P inputs, respectively Time lags in N load response to variations in inputs influenced by legacy storage in catchments
ISSN:0043-1397
1944-7973
DOI:10.1029/2018WR022905