title: Nitrate reduction in geologically heterogeneous catchments--a framework for assessing the scale of predictive capability of hydrological models.
abstract: In order to fulfil the requirements of the EU Water Framework Directive nitrate load from agricultural areas to surface water in Denmark needs to be reduced by about 40%. The regulations imposed until now have been uniform, i.e. the same restrictions for all areas independent of the subsurface conditions. Studies have shown that on a national basis about 2/3 of the nitrate leaching from the root zone is reduced naturally, through denitrification, in the subsurface before reaching the streams. Therefore, it is more cost-effective to identify robust areas, where nitrate leaching through the root zone is reduced in the saturated zone before reaching the streams, and vulnerable areas, where no subsurface reduction takes place, and then only impose regulations/restrictions on the vulnerable areas. Distributed hydrological models can make predictions at grid scale, i.e. at much smaller scale than the entire catchment. However, as distributed models often do not include local scale hydrogeological heterogeneities, they are typically not able to make accurate predictions at scales smaller than they are calibrated. We present a framework for assessing nitrate reduction in the subsurface and for assessing at which spatial scales modelling tools have predictive capabilities. A new instrument has been developed for airborne geophysical measurements, Mini-SkyTEM, dedicated to identifying geological structures and heterogeneities with horizontal and lateral resolutions of 30-50 m and 2m, respectively, in the upper 30 m. The geological heterogeneity and uncertainty are further analysed by use of the geostatistical software TProGS by generating stochastic geological realisations that are soft conditioned against the geophysical data. Finally, the flow paths within the catchment are simulated by use of the MIKE SHE hydrological modelling system for each of the geological models generated by TProGS and the prediction uncertainty is characterised by the variance between the predictions of the different models.
authors: Geological Survey of Denmark and Greenland (GEUS), Denmark. Electronic address: jcr@geus.dk.
authors: Jens Christian
authors: JC
authors: Refsgaard
authors: Esben
authors: E
authors: Auken
authors: Charlotte A
authors: CA
authors: Bamberg
authors: Britt S B
authors: BS
authors: Christensen
authors: Thomas
authors: T
authors: Clausen
authors: Esben
authors: E
authors: Dalgaard
authors: Flemming
authors: F
authors: Effersø
authors: Vibeke
authors: V
authors: Ernstsen
authors: Flemming
authors: F
authors: Gertz
authors: Anne Lausten
authors: AL
authors: Hansen
authors: Xin
authors: X
authors: He
authors: Brian H
authors: BH
authors: Jacobsen
authors: Karsten Høgh
authors: KH
authors: Jensen
authors: Flemming
authors: F
authors: Jørgensen
authors: Lisbeth Flindt
authors: LF
authors: Jørgensen
authors: Julian
authors: J
authors: Koch
authors: Bertel
authors: B
authors: Nilsson
authors: Christian
authors: C
authors: Petersen
authors: Guillaume
authors: G
authors: De Schepper
authors: Cyril
authors: C
authors: Schamper
authors: Kurt I
authors: KI
authors: Sørensen
authors: Rene
authors: R
authors: Therrien
authors: Christian
authors: C
authors: Thirup
authors: Andrea
authors: A
authors: Viezzoli
mesh_terms: D003718:Denmark; D058735:Environmental Policy / Q000331:legislation & jurisprudence*; D005544:Forecasting / Q000379:methods; D055593:Geological Phenomena; D008962:Models, Theoretical; D009566:Nitrates / Q000032:analysis*; D058998:Remote Sensing Technology / Q000379:methods; D045483:Rivers / Q000737:chemistry*; D035501:Uncertainty; D014872:Water Movements; D014877:Water Pollution, Chemical / Q000331:legislation & jurisprudence / Q000517:prevention & control*
chemical_list: D009566:Nitrates
keywords: Airborne geophysics; Hydrological modelling; Nitrate; Redox interface; Stochastic geology; TProGS