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Table 1 Overview of processes included in SMART2

From: Modelling impacts of acid deposition and groundwater level on habitat quality and plant species diversity

Process Element Process description
Inputs:
 Total deposition \( {\mathrm{SO}}_4^{2-} \), \( {\mathrm{NO}}_3^{-} \), \( {\mathrm{NH}}_4^{+} \), Inputs; total (wet and dry) deposition fluxes
  BC2+ a, Na+, K+ Element- and vegetation-dependent filtering factorb
 Upward seepage \( {\mathrm{SO}}_4^{2-} \), \( {\mathrm{NO}}_3^{-} \), \( {\mathrm{NH}}_4^{+} \), Inputs
  BC2+ a, Na+, K+  
 Water Balance Inputs: precipitation, upward seepage, evapotranspiration
Rate-limited reactions:
 Foliar uptake \( {\mathrm{NH}}_4^{+} \) Linear function of total deposition
 Foliar exudation BC2+ a, K+ Equals foliar uptake
 Litterfall BC2+ a, K+, Logistic growth
  \( {\mathrm{NH}}_4^{+} \), NO3 -  
 Root decay BC2+ a, K+, Linear function of litterfall
  \( {\mathrm{NH}}_4^{+} \), \( {\mathrm{NO}}_3^{-} \)  
 Mineralisation BC2+ a, K+, First-order reaction and a function of pH, mean spring water level (MSW) and C/N ratio of the litter
  \( {\mathrm{NH}}_4^{+} \), \( {\mathrm{NO}}_3^{-} \)  
 N immobilisation \( {\mathrm{NH}}_4^{+} \), \( {\mathrm{NO}}_3^{-} \) Proportional to N deposition and a function of the C/N ratio soil organic matter
 Growth uptake BC2+ a, K+, Logistic growth
  \( {\mathrm{NH}}_4^{+} \), \( {\mathrm{NO}}_3^{-} \)  
 Nitrification \( {\mathrm{NH}}_4^{+} \), \( {\mathrm{NO}}_3^{-} \) Proportional to net \( {\mathrm{NH}}_4^{+} \) input and a function of pH, mean spring water level (MSW) and C/N ratio
 Denitrification \( {\mathrm{NO}}_3^{-} \) Proportional to net NO3 input and a function of pH, mean spring water level (MSW) and C/N ratio
 Silicate weathering Al3+, BC2+ a, Na+, K+ Zero-order reaction
Equilibrium reactions:
 Dissociation/association \( {\mathrm{HCO}}_3^{-} \) CO2 equilibrium
 Carbonate weathering BC2+ a Carbonate equilibrium
 Al hydroxide weathering Al3+ Gibbsite equilibrium
 Cation exchange H+ b, Al3+, BC2+ a Gaines–Thomas equations
 Sulphate sorption H+ b, \( {\mathrm{SO}}_4^{2-} \) Langmuir equation
  1. aBC2+ stands for the sum of divalent base cations (Ca2+, Mg2+)
  2. bImplicitly, H+ is affected by all processes. This is accounted for by the charge balance