.. _doc.module.substance:

**Module Substance** 
=====================
 * This module is activated with the key : **key_substance** (in MARS) and **SUBSTANCE** (in CROCO)


 * Advected substances 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.MUSTANG`) 
   * non conservative substances
       * first order degradation : T90
       * Biological variables    (using module of **BIOLOGY**) 
       * Contaminant variables (using module **MET&OR**)

 * 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