Modelling the effect of the spatial distribution of agricultural practiceson nitrogen fluxes in rural catchments

An integrated, hydrology and nitrogen dynamics model was developed to study the spatial interactions between soil and groundwater that can affect the nitrogen delivery to streamwater in rural catchments. The hydrological mode l TNT is based on TOPMODEL hypotheses but is it fully distributed according to a regular square grid. A subsurface flow component was distinguished to account for the supply of groundwater and nitrate to downslope soils. The crop growth and nitrogen biotransformations were simulated using an existin g generic crop model, STICS. Both models are process-based, but kept as sim ple as possible. The integrated model was applied to theoretical catchments to analyze the combined effects of geomorphology and crop distribution on the whole catchment nitrogen budget. The catchments differed both in the sl ope profile and in the pattern of water pathways. The results suggest that placing crops acting as nitrogen sinks downslope potentially polluting crop s could reduce significantly the streamwater contamination by nitrate. This effect is the highest for catchments with parallel water pathways and a wi de concave bottomland. Nitrogen uptake by sink crops was quantitatively mor e important than denitrification to reduce nitrogen output. It is concluded that this model, although still in development, may prove an interesting w orking tool to investigate the effect of the landscape structure on nutrien t budgets in ecosystems. (C) 2001 Elsevier Science B.V. All rights reserved .