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Test of STONE version 2.0. Summary and main results

Toets van STONE versie 2.0. Samenvatting en belangrijkste resultaten


The STONE model for nitrogen and phosphorus emission to the groundwater and surface waters has been developed to evaluate the environmental consequences of policies regarding manure and agriculture. In 2000, an advisory body ('The Spiertz Commission') explicitly asked for validation of the Dutch eutrophication models. This report summarises the most important findings of the so-called 'STONE test'. STONE results were compared with monitoring data at different spatial scales from the field scale up to the national scale. At the field scale, conclusions were drawn on process descriptions and temporal dynamics. At the national scale, spatial patterns and frequency distributions were investigated. Here, STONE slightly underestimated the median nitrate concentrations in the upper groundwater. Also, the correlation between measured and simulated concentrations of nitrogen in the groundwater was good. Large differences were, however, found at the regional scale. These differences might be attributed to errors in the manure transport and application module. This suggests that STONE is not yet suitable for applications at the regional scale. The predicted concentration of nitrate and phosphorus in drain water was higher than the actual concentration of these compounds in surface waters. This was expected, because riparian retention and loss processes in surface waters were not modelled. Future research should be directed towards (i) improving the model performance at the regional scale, and (ii) further validation of the surface water component of STONE by combining the model with a surface water model.

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