.. _doc.meteor.intro:

Introduction
------------

 * Module *contaminant* in MARS model is associated with module *subtance* (:ref:`doc.module.substance`). 

 * The module *contaminant* offers a choice of generic reactions already programmed that represent a number of conventional biogeochemical transformations. The reactions take place between the different variables which may for example represent different species of a contaminant. The type of each reaction, the parameters that determine each one and the associated variables are defined in a data file (:ref:`doc.meteor.reactions`)

 * Contaminants speciation is treated by considering the different species which may have different physical behaviors (dissolved/particulate), reactivity, bioavailability or specific toxicity. The main processes involved are sorption processes with respect to dissolved ligands and particulate substrates, transformation processes (degradation, hydrolysis ..), and transfer process (volatilization) 

 * These processes are incorporated in the equations of conservation of mass through terms "sinks and sources". For some very fast or equilibrium reactions, a separate operator is used to a posteriori correct at each time step the concentrations of each chemical species involved. 

 * Process definition, characteristics of the contaminants and parameters required to define the different reactions are read directly into data files, easy to use. 

 * Associated with a module that describes the biological ecosystem, this module allows to study the transfer of contaminants from the abiotic environment to the first link in a food chain (phytoplankton - microzooplankton). It has been used in combination with ECO3M module (developed by M.I.O. - University of the Mediterranean - Baklouti et al, 2006).

 * The implementation of this module (:ref:`doc.meteor.implement`) requires to complete :

   * a new namelist file (:ref:`doc_paraconta`), 
   * a new data file (:ref:`doc_reactiondat`), where each reaction is defined (:ref:`doc.meteor.reactions`)