Long-term nitrogen retention and transit time distribution in agricultural catchments in western France

Elevated nitrogen (N) concentrations have detrimental effects on aquatic ecosystems worldwide, calling for effective management practices. However, catchment-scale annual mass-balance estimates often exhibit N deficits and time lags between the trajectory of net N inputs and that of N riverine expor...

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Bibliographic Details
Published inEnvironmental research letters Vol. 15; no. 11; pp. 115011 - 115022
Main Authors Dupas, Rémi, Ehrhardt, Sophie, Musolff, Andreas, Fovet, Ophélie, Durand, Patrick
Format Journal Article
LanguageEnglish
Published Bristol IOP Publishing 01.11.2020
Subjects
Agricultural ecosystems
Agricultural watersheds
Aquatic ecosystems
catchment
Catchment scale
Catchments
Denitrification
Environmental Sciences
Global Changes
Groundwater
legacy
Lithology
Mass balance
Nitrogen
nutrient
Retention
Runoff
Soils
Strategic management
Topsoil
Transit time
transit time distribution
Vadose water
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Summary:Elevated nitrogen (N) concentrations have detrimental effects on aquatic ecosystems worldwide, calling for effective management practices. However, catchment-scale annual mass-balance estimates often exhibit N deficits and time lags between the trajectory of net N inputs and that of N riverine export. Here, we analyzed 40-year time series of N surplus and nitrate-N loads in 16 mesoscale catchments (104-10 135 km2) of a temperate agricultural region, with the aim to (1) investigate the fate of the 'missing N', either still in transit through the soil-vadose zone-groundwater continuum or removed via denitrification, and (2) estimate the transit time distribution of N by convoluting the input signal with a lognormal model. We found that apparent N retention, the 'missing N', ranged from 45%-88% of then N net input, and that topsoil N accumulation alone accounted for ca. two-thirds of this retention. The mode of the nitrate-N transit time distribution ranged from 2-14 years and was negatively correlated with the estimated retention. Apparent retention was controlled primarily by average runoff, while the transit time mode was controlled in part by lithology. We conclude that the fate of the soil 'biogeochemical legacy', which represents much of the catchment-scale 'missing N', is in our hands, since the N accumulated in soils can still be recycled in agroecosystems.
Bibliography:ERL-109223.R2
ISSN:1748-9326
1748-9326
DOI:10.1088/1748-9326/abbe47