Assigning Confidence Limits to Outputs from a Nitrate Leaching Model: A Case Study from the River Ure Catchment, UK

Paulette Posen1, Andrew Lovett1, Michael Hutchins2, Helen Davies2

1. School of Environmental Sciences,University of East Anglia,Norwich, UK 2. Centre for Ecology and Hydrology,Crowmarsh Gifford,Wallingford, UK 1. {p.posen, a.lovett}; 2. {mihu,hnd}

Abstract: Diffuse pollution from agriculture is a major concern for surface water management under the EU Water Framework Directive, and water quality models are frequently used as decision support tools for policy implementation to achieve water quality objectives. The current study uses uncertainty analysis techniques to assign confidence limits to outputs from a nitrate leaching model. A sensitivity analysis determines which input variables require most detailed attention in terms of limiting output error. The issue is illustrated through application of a nitrate leaching model to the River Ure catchment in northern England. Implications for predicting possible outcomes of future, policy-driven, land use change are examined, and recommendations are made regarding the use of such models as decision support tools.

Keywords: diffuse pollution, nitrates, SLIMMER, uncertainty analysis, Water Framework Directive

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