.. _doc.module.substance.intro:

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

 * Advected substances in MARS may have different behavior (:ref:`definition_substance`) :

   * dissoved passive tracers (conservative)
   * particulate passive tracers (conservative with settling velocity)
   * particulate passive tracers whith a sediment compartment and erosion/deposition fluxes (using module of **SEDIMENT**)(:ref:`doc.module.sedim`) 
   * non conservative substances
       * first order degradation : T90
       * Biological variables    (using module of **BIOLOGY**)(:ref:`doc.module.biolo`) 
       * Contaminant variables (using module **MET&OR**)(:ref:`doc.module.meteor`) 

 * Forcings of substances dynamics (or Tracer dynamics)
    * concentrations in river discharges 
    * fluxes issued from outfalls
    * concentrations in rainfalls (wet settling)
    * fluxes of dry atmospheric settling

 * The implementation of this module (:ref:`implementation_substance`) requires to complete :

   * a new namelist file (:ref:`doc.parasubs`), 
   * a new data file (:ref:`doc_variabledat`), where each substance is defined with its type (:ref:`definition_substance`)
   * if necessary files defining the (:ref:`boundaries_substance`) and (:ref:`initial_substance`) 
   * if necessary concentrations in inputs 
       * :ref:`river_substance` 
       * and :ref:`atmospheric_substance`

 * **Additional functionalities** :

   *  automatic calculation flow across borders defined by the user and balances calculation (stocks and flows) in areas defined by the user.(:ref:`budget_substance`)
   *  ability to save at certain points model results a time step smaller than the one chosen to save overall results.(:ref:`tracking_substance`)
   *  Adding diagnostic variables. The definition and the calculation is done by user