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PSYCHIC - A process-based model of phosphorus and sediment transfers within agricultural catchments. Part 2. A preliminary evaluation

Strömqvist, J., Collins, A.L., Davison, P.S., Lord, E.I.
Journal of hydrology 2008 v.350 no.3-4 pp. 303-316
agricultural watersheds, agricultural runoff, nonpoint source pollution, phosphorus, sediment yield, water erosion, watersheds, hydrologic models, environmental models, soil erosion models, losses from soil, fertilizers, animal manures, crop production, animal production, slope, England
This paper describes the preliminary evaluation of the PSYCHIC catchment scale (Tier 1) model for predicting the mobilisation and delivery of phosphorus (P) and suspended sediment (SS) in the Hampshire Avon (1715km²) and Herefordshire Wye (4017km²) drainage basins, in the UK, using empirical data. Phosphorus and SS transfers to watercourses in the Wye were predicted to be greater than corresponding delivery in the Avon; SS, 249 vs 33kgha⁻¹ yr⁻¹; DP, 2.57 vs 1.26kgha⁻¹ yr⁻¹; PP, 2.20 vs 0.56kgha⁻¹ yr⁻¹. The spatial pattern of the predicted transfers was relatively uniform across the Wye drainage basin, whilst in the Avon, delivery to watercourses was largely confined to the river corridors and small areas of drained land. Statistical performance in relation to predicted exports of P and SS, using criteria for relative error (RE) and root mean square error (RMSE), reflected the potential shortcomings associated with using longer-term climate data for predicting shorter-term (2002-2004) catchment response and the need to refine calculations of point source contributions and to incorporate additional river basin processes such as channel bank erosion and in-stream geochemical processing. PSYCHIC is therefore best suited to characterising longer-term catchment response.