Role and Place in FOCUS scenarios calculation Additional model assumptions include first-order kinetics for degradation in each of four `pools' of pesticide in the soil (micro- and macropores, solid/liquid phases), together with an instantaneous sorption equilibrium and a Freundlich sorption isotherm in each pore domain. Exchange between the flow domains is calculated using approximate, physically-based, expressions based on an effective aggregate half-width. Richards' equation and the convection-dispersion equation are used to model soil water flow and solute transport in the soil micropores, while a simplified capacitance type-approach is used to calculate fluxes in the macropores. The model accounts for macropore flow, with the soil porosity divided into two flow systems or domains (macropores and micropores) each characterized by a flow rate and solute concentration. The model calculates coupled unsaturated-saturated water flow in cropped soil, including the location and extent of perched water tables, and can also deal with saturated flow to field drainage systems. Note: FOCUS materials related to MACRO cannot be downloaded from the SLU MACRO homepage. Earlier FOCUS_MACRO packages used Version 4.3 of the MACRO model. Version 5.2 of the MACRO model is used for the FOCUS scenarios in the FOCUS_MACRO 5.5.3 and FOCUS_MACRO 5.5.4 packages. Technical support: Fredrik Stenemo ( : SWECO, Sweden. Responsibility for model: Nick Jarvis (SLU, CKB) MACRO is a physically-based one-dimensional numerical model of water flow and reactive solute transport in field soils (Jarvis, 1994).
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