title: Disentangling the influence of hydroclimatic patterns and agricultural management on river nitrate dynamics from sub-hourly to decadal time scales.
abstract: Despite extensive efforts to reduce nitrate transfer in agricultural areas, limited response is often observed in the nitrate concentration in rivers. To investigate the reasons for this limited response, nitrate dynamics in a 100km(2) agricultural catchment in eastern Germany was analysed from sub-hourly to decadal time-scales. Sub-hourly analysis of storm event dynamics during a typical hydrological year (2005-2006) was performed to identify periods of the year with high leaching risk and to link the latter to agricultural management practices in the catchment. Dynamic Harmonic Regression analysis of a 32-year (1982-2014) record of nitrate and discharge revealed that i) the long-term trend in nitrate concentration was closely related to that in discharge, suggesting that large-scale weather and climate patterns were masking the effect of improved nitrogen management on nitrate trends; ii) a persistent seasonal pattern with winter concentration maxima and summer minima could be observed, which was interpreted in terms of a dynamic nitrate concentration profile in the soil and subsoil; and iii) the catchment progressively changed from chemodynamic to more chemostatic behaviour over the three decades of study, which is a sign of long-term homogenisation of nitrate concentrations distribution over depth. This study shows that detailed physical understanding of nitrate dynamics across time scales can be obtained only through combined analysis of long-term records and high-resolution sensor data. Hence, a joint effort is advocated between environmental authorities, who usually perform long-term monitoring, and scientific programmes, which usually perform high-resolution monitoring.
authors.affiliation: Department Aquatic Ecosystem Analysis and Management (ASAM), Helmholtz Centre for Environmental Research (UFZ), Brückstr. 3a, 39114 Magdeburg, Germany. Electronic address: remi.dupas@ufz.de.
authors.forename: Rémi
authors.initials: R
authors.lastname: Dupas
authors.affiliation: Department Aquatic Ecosystem Analysis and Management (ASAM), Helmholtz Centre for Environmental Research (UFZ), Brückstr. 3a, 39114 Magdeburg, Germany.
authors.forename: Seifeddine
authors.initials: S
authors.lastname: Jomaa
authors.affiliation: Department Hydrogeology, Helmholtz Centre for Environmental Research (UFZ), Permoserstr. 15, 04318 Leipzig, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Musolff
authors.affiliation: Department Aquatic Ecosystem Analysis and Management (ASAM), Helmholtz Centre for Environmental Research (UFZ), Brückstr. 3a, 39114 Magdeburg, Germany.
authors.forename: Dietrich
authors.initials: D
authors.lastname: Borchardt
authors.affiliation: Department Aquatic Ecosystem Analysis and Management (ASAM), Helmholtz Centre for Environmental Research (UFZ), Brückstr. 3a, 39114 Magdeburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Rode
mesh_terms: D000383:Agriculture / Q000379:methods*; D002980:Climate; D004784:Environmental Monitoring; D005858:Germany; D057446:Hydrodynamics; D009566:Nitrates / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical
keywords: Agriculture; Catchment; Climate; Diffuse pollution; High-frequency; Long-term