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An improved dual-permeability model of solute transport in structured soils

model development and parameter identification in laboratory and field experiments

Larsbo, Mats (2005). An improved dual-permeability model of solute transport in structured soils. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2005:51
ISBN 91-576-6950-3
[Doctoral thesis]

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Preferential flow through macropores is one of the major pathways through which pesticides can leave the root zone and enter ground and surface waters. Dual-permeability models account for preferential flow by including a separate flow domain coupled to the less permeable soil matrix. The exchange of water and solutes between flow domains is usually described by first-order expressions. Key model parameters regulating the degree of preferential flow are difficult or impossible to derive from direct measurements. Therefore, the objective was to evaluate the possibilities of parameter identification through automatic calibration in the dual-permeability model MACRO. An improved version of the model, with implicit numerical solutions introduced to shorten model run times, was first developed. This enabled the use of computationally intensive calibration methods. Generalised likelihood uncertainty estimation (GLUE) and sequential uncertainty domain parameter fitting (SUFI) were applied to a comprehensive field data set containing measurements of soil water contents, drainflow and flux and resident concentrations of bentazone and bromide. All groups of data were needed to get highly conditioned and unbiased parameter estimates. However, the parameter describing mass exchange between pore domains was poorly conditioned even with a very comprehensive data set. SUFI decreased the initial uncertainty domains significantly for all parameters except for the parameter describing mass exchange between pore domains in the subsoil. However, random sampling from SUFI posterior uncertainty domains resulted in larger prediction uncertainty compared to GLUE. This is because these domains contain parameter combinations that are poor simulators, mainly due to parameter correlations. GLUE and a parameter identification method based on the localisation of information (PIMLI) were applied to real and numerically generated data from laboratory microlysimeter experiments. The data contained enough information to reduce the uncertainty of the parameter describing mass exchange between pore domains, the saturated matrix hydraulic conductivity and the macroporosity. Simultaneous identification of the macroporosity, the macropore hydraulic conductivity and the parameter describing macropore tortuosity was not possible, probably because of parameter correlations. Measurements with large information content for parameter identification were generally found during the first irrigations after solute application.

Authors/Creators:Larsbo, Mats
Title:An improved dual-permeability model of solute transport in structured soils
Subtitle:model development and parameter identification in laboratory and field experiments
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :2005
Number of Pages:46
ALLI. Larsbo, M., Roulier, S., Stenemo, F., Kasteel, R. & Jarvis, N. An Improved Dual-Permeability Model of Water Flow and Solute Transport in the Vadose Zone. Vadose Zone Journal, In Press. II. Larsbo, M. and Jarvis, N. Information content of measurements from tracer microlysimeter experiments designed for parameter identification in dual-permeability models. Manuscript. III. Larsbo, M. & Jarvis, N. 2005. Simulating solute transport in a structured field soil: Uncertainty in parameter identification and predictions. Journal of Environmental Quality 34, 621-634.
Place of Publication:Uppsala
ISBN for printed version:91-576-6950-3
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:P Natural resources > P33 Soil chemistry and physics
U Auxiliary disciplines > U10 Mathematical and statistical methods
Subjects:Not in use, please see Agris categories
Agrovoc terms:soil water balance, soil water movement, soil pore system, solutes, pesticides, simulation models, data analysis
Keywords:pesticides, parameter identification, parameter uncertainty, calibration, dual-permeability model, macropore flow, MACRO, GLUE, SUFI, PIMLI
Permanent URL:
ID Code:823
Department:(NL, NJ) > Dept. of Soil Sciences (until 081001)
Deposited By: Mats Larsbo
Deposited On:02 May 2005 00:00
Metadata Last Modified:02 Dec 2014 10:07

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