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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