Environmental Fate and Transport of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 39

2.4.3 Leaching Estimation and Chemistry Model
Leaching Estimation and Chemistry Model (LEACHM) is a process-based model that
simulates water flow, transformation and transport of solute, and plant uptake in the
unsaturated zone (Jemison et al. 1994). A complete description of this model was given by
Hutson and Wagenet (1992). Specifically, LEACHM-P is designed for simulating dynamics
of pesticides and has shown success in many applications (Kohne et al. 2009). However,
it does not simulate macropore flow of water, unequal depth increments, runoff, erosion,
and management practices and requires a lot of computer run time and data acquisition
time (Smith et al. 1991).
2.4.4 MACRO Model
MACRO model simulates macropore flow processes in agricultural systems (Jarvis 1994;
Larsbo and Jarvis 2005). Its assumptions include that sorption of chemicals on soil is
instantaneous and that adsorption follows the Freundlich isotherm model (Kohne et al.
2009). Brown et al. (1999) applied MACRO 4.0 to simulate isoproturon leaching in a lysim-
eter experiment and noted that a calibration of fraction of sorption is needed to match the
observation curve. In a leaching test of the fungicide iprodione in golf green, MACRO very
well predicted its transport in drainflow (Stromqvist and Jarvis 2005).
2.4.5 Root Zone Water Quality Model
Root Zone Water Quality Model (RZWQM) simulates plant growth in agricultural systems,
and water and chemical movement through macropores (Ahuja et al. 2000a,b; Kohne
et al. 2009). In this model, various physical, chemical, and biological processes, including
degradation and adsorption, were integrated and adjusted according to environmental
parameters such as soil and water content and temperature. It is capable of predicting
water transport by assuming that water radially flows through macropores when rainfall
rate exceeds soil infiltration rates. Chemicals move with water and their transport can be
simulated by assuming instantaneous partitioning of chemicals between water and soil
(Malone et al. 2001). Malone et al. (2004), Wauchope et al. (2004), and Ma et al. (2007) used
RZWQM in their soil column studies to simulate pesticide transport.
2.4.6 Studio of Analytical Models
Studio of Analytical Models (STANMOD) is a windows-based computer software pack-
age for evaluating solute transport in soils using analytical solutions of the convection-
dispersion solute transport equation (Simunek et al. 1999). It contains seven independent
models for predicting fate and transport of chemicals (including pesticides) in soils.
Five of these models (i.e., CXTFIT, CFITM, CFITIM, CHAIN, and SCREEN) are for one-
dimensional transport and the other two (i.e., 3DADE and N3DADE) are for two- and
three-dimensional transport.
2.4.7 Saturated-Unsaturated Transport Model
Saturated-Unsaturated Transport (SUTRA) is a computer model for simulating density-
dependent saturated or unsaturated fluid flow and transport of either a solute or thermal