FOOTPRINT Project papers cont.

Stenemo F. and Jarvis N.J. (2007). Accounting for uncertainty in pedotransfer functions in vulnerability assessments of pesticide leaching to groundwater. Pest Management Science, 63(9): 867-875.

A simulation tool for site-specific vulnerability assessments of pesticide leaching to groundwater was developed, based on the pesticide fate and transport model MACRO, parameterized using pedotransfer functions and reasonable worst-case parameter values. The effects of uncertainty in the pedotransfer functions on simulation results were examined for 48 combinations of soils, pesticides and application timings, by sampling pedotransfer function regression errors and propagating them through the simulation model in a Monte Carlo analysis. An uncertainty factor, fu, was derived, defined as the ratio between the concentration simulated with no errors, csim, and the 80th percentile concentration for the scenario. The pedotransfer function errors caused a large variation in simulation results, with fu ranging from 1.14 to 1440, with a median of 2.8. A non-linear relationship was found between fu and csim, which can be used to account for parameter uncertainty by correcting the simulated concentration, csim, to an estimated 80th percentile value. For fine-textured soils, the predictions were most sensitive to errors in the pedotransfer functions for two parameters regulating macropore flow (the saturated matrix hydraulic conductivity, Kb, and the effective diffusion pathlength, d) and two water retention function parameters (van Genuchtenҳ N and a parameters). For coarse-textured soils, the model was also sensitive to errors in the exponent in the degradation water response function and the dispersivity, in addition to Kb, but showed little sensitivity to d. To reduce uncertainty in model predictions, improved pedotransfer functions for Kb, d,N and a would therefore be most useful.

Contact:

Professor Nick Jarvis
Department of Soil Sciences
Swedish University of Agricultural Sciences
Box 7014
75007 Uppsala
Sweden

Email: Nick.Jarvis@Mark.SLU.SE