Modelling nitrate transport in the Slapton Wood catchment using SHETRAN

摘要

In Birkinshaw and Ewen [Nitrogen transformation component for SHETRAN catchment nitrate transport modelling system, J. Hydrol. 230, 1-17] a detailed nitrogen transformation model was incorporated in the SHETRAN physically based spatially distributed river catchment modelling system. This gives SHETRAN the capability to simulate nitrate generation and leaching and the subsequent subsurface transport through combinations of confined, unconfined and unsaturated systems to seepage points and streams, and transport through stream networks. SHETRAN is applied here to explaining the complicated pattern of nitrate discharge seen at the stream outlet from the Slapton Wood catchment, Devon, UK. The nitrate concentrations simulated by SHETRAN are physically realistic and in agreement with measurements made at the catchment, and since SHETRAN was not calibrated against any of the nitrate measurements made at the catchment this represents a strong validation test of the nitrogen component of SHETRAN. The catchment is clay-loam soil underlain by slate, and the main features of the nitrate concentration at the outlet are low concentrations associated with both low and high flows and high concentrations associated with medium flows. A plume of nitrate develops above and around the loam-slate boundary following fertiliser applications in the spring and early summer, and the high outlet concentration occurs when lateral how develops at the loam-slate boundary during the winter and acts as the main source of flow to the stream. At times when the stream how is low it is fed from the slate below the plume, and when it is high it is fed from surface flow. SHETRAN simulates the above behaviour and there is close agreement between the simulated and measured outlet concentrations. The SHETRAN distributed results for nitrate concentrations and leaching load also agree well with existing measurements. It is concluded that SHETRAN should prove to be a powerful, practical and useful tool for studying nitrate pollution problems. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 32]