Keywords: environmental modelling, GIS application, non-point pollution, nutrients, water quality management, water framework directive.

The EU Water Framework Directive (WFD, 2000/60/EC) was established as a framework for Community action in the field of water policy. The main aim of the Directive is to improve the overall state of the chemical and ecological quality of European surface and ground waters. Within the characterization of water bodies according to Article 5 of the WFD anthropogenic impacts should be identified. In case of surface waters it means, that emission should be estimated for each watercourse, which belongs to larger than 10 km² watershed.

Emission estimates, especially for diffuse nutrient sources are of high uncertainty. Losses of nutrients in groundwater and river systems are poorly understood and monitoring in river systems was not designed to calculate total transported loads, but to detect critical concentrations in the river, and is thus insufficient to calculate total transported nutrient loads in a river. Therefore, much innovation was needed in order to develop effective tools that support strategic planning for improved nutrient and water quality management.

This paper introduces an example of a simplified methodology to estimate diffuse nutrient loads to surface waters. The method was applied for 1100 sub-catchments of Hungary (total area is 93 000 km²). Nutrient emissions via different pathways were calculated by semi empirical model [1], which was developed for large German watersheds. The distribution of emissions for small sub-catchments was based on the development of a spatially distributed sensitivity factor. Calculations were performed in ArcView 3.2 environment. Results were validated for the outflow sections of about sixty sub-catchments, where flow and concentration measurements were available. In order to compare calculated loads with measured ones, nutrient emissions from point sources were also estimated. Instream retention was considered based on an empirical function. The approach presented here was directly utilized for the risk assessment under the implementation of the WFD to calculate river nutrient concentrations [2]. Furthermore results can also contribute to the improvement of process-understanding of the nutrient balance of river catchments.

1

Behrendt, H., Huber, P., Kornmilch, M, Opitz, D., Schmoll, O., Scholz, G. and Uebe, R.: Modelling Nutrient Emissions in River Systems (Theoretical Documentation). Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, 1999.

2

National Report about the Hungarian territory of the Danube Water District along with the Water Framework Directive: Impact and Pressures and Economic Analyses of Water Uses. Ministry for Environment and Water Management, Budapest, 2005.

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