Extracting the Essence of Process-Based Models of the Flow of Nitrogen through Catchments

K. Wahlin 1, D. Shahsavani 1, A. Grimvall 1, A. J. Wade 2, D. Butterfield2, and H. P. Jarvie 3
1 Department of Mathematics
Linköping University, SE-58183 Linköping, Sweden
Ph. +46 13 281000; Fax +46 13 100746
E-mail: kawah@mai.liu.se
2 Aquatic Environments Research Centre
School of Human and Environmental Sciences,
The University of Reading, UK, RG6 6AB
3 Centre for Ecology and Hydrology
Wallingford, UK, OX10 8BB

Abstract
The dynamic properties of process-oriented models of the flow of nitrogen through catchments can be very complex. We introduced several types of ensemble runs that can provide informative summaries of meteorologically normalised model outputs and also clarify the extent to which such outputs are related to various model parameters. Specifically, we showed how to assess travel times for nitrogen and water in the unsaturated and saturated zones. Studies of the catchment model INCA-N revealed that the temporal distribution of the modelled water quality  response to changes in fertiliser application was determined primarily by the hydromechanical parameters of the model, whereas the magnitude of the total intervention effect was influenced mainly by the parameters governing the turnover of nitrogen in soil. Furthermore, the travel times in this model were invariably shorter for nitrogen than for water due to preferential removal of the nitrogen exhibiting unusually long residence times.

Keywords: Model reduction; Ensemble runs; Catchment; Nitrogen; Retention.

In: McRoberts, R. et al. (eds).  Proceedings of the joint meeting of The 6th International Symposium On Spatial Accuracy Assessment In Natural Resources and Environmental Sciences and The 15th Annual Conference of The International Environmetrics Society, June 28 – July 1 2004, Portland, Maine, USA.

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