Bismo, M.

Jensen, B.

Rasmussen, S.

Thorsøe, M.

Wahl, Niels Arne

    Aalborg UniversitetGIS-based modelling of nitrogen loading at the catchment scaleBismo, M.; Rasmussen, S.; Jensen, B.; Thorsøe, M.; Wahl, Niels ArnePublished in:Geophysical Research AbstractsPublication date:2006Document VersionPublisher's PDF, also known as Version of recordLink to publication from Aalborg UniversityCitation for published version (APA):Bismo, M., Rasmussen, S., Jensen, B., Thorsøe, M., & Wahl, N. A. (2006). GIS-based modelling of nitrogenloading at the catchment scale: a case study from the Karup Å catchment, Denmark. In Geophysical ResearchAbstracts European Geosciences Union.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: April 26, 2017Geophysical Research Abstracts, Vol. 8, 00399, 2006SRef-ID: 1607-7962/gra/EGU06-A-00399© European Geosciences Union 2006GIS-based modelling of nitrogen loading at thecatchment scale: a case study from the Karup Åcatchment, DenmarkM. Bismo (1), S. Rasmussen (1) , B. Jensen (1), M. Thorsøe (1) and N.A. Wahl (2)(1) B-study board, Aalborg University, (2) Dept. of Civil Engineering, Aalborg University(wahl@civil.aau.dk)Oxygen depletion in Danish waters has accelerated during the last 20 years and ithas been documented that the human discharge of N plays an important role in thisnegative development. Since the first oxygen depletion case in 1982 it has been apolitical goal to reduce the nitrogen discharge, in order to reduce the frequency ofoxygen depletion. Improper agriculture practice is responsible for approx. 68 % of thenitrogen load in Danish waters. In order to reduce the nitrogen discharge it is thereforenecessary to change some agricultural practices.The object of this paper is N-discharge from the Karup Å catchment. The river KarupÅ feeds Skive Fjord, which is a particular delicate ecosystem, with frequent oxygendepletion happening during the summer months. We used data from soils from 12 sitesin the catchment area, estimations on the nitrate content of soil water, and a GIS basedmodelling of solute fluxes at the catchment scale in order to estimate the agriculturalcontribution to the riverine nitrogen load in the Karup Å catchment. An estimate ofthe amount of leached nitrogen from the root-zone is derived by using the empiricalbased “Viborg-model”. In addition, a distance based model using 1st order kinetics isused to estimate the area based distribution of the denitrification taking place from thesource of emission to the river. The two models combined indicate which areas of thecatchment contribute to the total nitrogen load and were efforts could be implementedin order to reduce nitrogen leaching.On this background, initiatives to reduce nitrogen leaching and discharge in the KarupÅ catchment are considered. This is done by assessing the area-based initiatives putforward by the Danish Action Plan for the Aquatic Environment (Vandmiljøplan III),aiming at a countrywide reduction of nitrogen leaching by a further 13 %. These ini-tiatives are combined with the regional plans set forth by Viborg and RingkøbingCounties for the Karup Å catchment.It was found that the crucial variable determining the amount of leached nitrogen tothe riverine environment is the distance from the source of emission to the river, as thisdistance determines the amount of nitrogen denitrificated during the transport processin the groundwater. After defining the area with the highest proportion of nitrogenemission, four scenarios were put forward, each defined in Vandmiljøplan III: 1. All ofthe defined area is taken out of production. Reduction: 75 %. 2. Creation of 10 m bufferzones around the river. Reduction: 6 %. 3. Agri-environmental measures undertakenin the areas included in the vulnerable agricultural area (SFL) and NATURA 2000-areas. Reduction: 20 %. 4. Application of agri-environmental measures in 11 % of thevulnerable agricultural area (SFL). Reduction: 2 %Based on the results from these four scenarios we conclude that scenario 2 will be themost appropriate.

GIS-based modelling of nitrogen loading at the catchment scale:a case study from the Karup Å catchment, Denmark

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GIS-based modelling of nitrogen loading at the catchment scale:a case study from the Karup Å catchment, Denmark

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