## Science Modules / Tracers

Modellers can use the aed_tracer to simulate a particulate tracer that can be set to also settle and decay. In addition to suspended sediment simulated in this way, the aed_totals module has an option to assign any number of FABM variables (including non-AED variables) to contribute to a turbidity, subject to a transformation coefficient.

Modellers can also use this module to simulate the water retention time. In this case the water retention time is treated as a tracer with a growth rate of 1 with time after enterting the water body, and being mixed and transported with water.

#### aed2_tracer :

The AED2 module tracer contains equations that describe a soluble or particle tracer, including decay, sediment interaction, and & resupension and settling

#### Variable Summary & Setup Options

Variable Name Description Units Variable Type Core/Optional
TRC_ss{x} generic tracer / suspended solid group $$mg\,L^{-1}$$ pelagic optional: set num_tracers >0
TRC_ret water retention time seconds pelagic optional: set retention_time = .true.
Variable Name Description Units Variable Type Core/Optional
TRC_ss{x}_vvel suspended solid group x vertical velocity $$m\,s^{-1}$$ pelagic diagnostic optional: created when settling = XXX
TRC_d_taub bottom shear stress $$N\,m^{-2}$$ benthic diagnostic core
TRC_fs{x} sediment fraction of particle size x $$%$$ benthic diagnostic core
TRC_resus resuspension rate $$g\,m^{-2}\,s^{-1}$$ benthic diagnostic core
Parameter Name Description Units Parameter Type Default Typical Range Comment
retention_time activates the retention time variable - boolean .false. .true./.false. enable if you wish to keep track of the age opf water within the domain
num_tracers number of tracers/ss's to model - integer 0-10 -
decay vector of decay rates for each simulated tracer group $$day^{-1}$$ float -100-100' -
Fsed vector of sediment flux rates for each simulated tracer group $$g\,(m^{2}\, ^{*} s)^{-1}$$ float 0-100 -
Ke_ss vector of specific light attenuation constants for each simulated tracer group $$m^{-1} (g\,m^{-3})^{-1}$$ float 0.01-0.1 -
settling settling sub-model - integer 1,2,3 0 = none; 1 = constant; 2= constant (temp adjusted); 3 = Stokes
w_ss vector of sedimentation velocity $$m\,day^{-1}$$ float -1 0-10 used if settling = 1 or 2
d_ss vector of particle diameter $$m$$ float 1e-06 - used if settling = 3
rho_ss vector of particle density $$kg\,m^{-3}$$ float 1600 - used if settling = 3
resuspension resuspension sub-model - integer - 0 = none; 1 = constant; 2= constant adjusted; 3 = stokes
fs vector of particle fraction within the sediment - float 0-1 vector of length num_tracers be supplied
epsilon vector of resuspension rate coefficient $$g\,m^{-2}\,s^{-1}$$ float 0-0.1 -
tau_0 vector of critical shear stress for resuspension $$N\,m^{-2}$$ float 2e-02 0.005 - 0.05 -
tau_r reference shear stress $$N\,m^{-2}$$ float 1 1 -
Ktau_0 coefficient determining the effect of 'macrophyte_link_var' on 'tau_0' $$N\,m^{-2}\,(mmol C m^{-2})^{-1}$$ float 1e-01 -
macrophyte_link_var AED2 benthic variable on which the critical shear stress depends - string - e.g., 'MAC_ruppia' optional: if resuspension = 2

An example nml block for the tracer module is shown below:

 &aed2_tracer !-- Optional retention time tracer retention_time = .true. !-- Select number of tracers/ss's and their decay/sedflux/light properties num_tracers = 2 decay = 0, 0 Fsed = 0, 0 Ke_ss = 0.06, 0.063 !-- Configure sediment resuspension settling = 3 w_ss = -0.000001 d_ss = 4e-6, 1e-5 rho_ss = 1.5e3, 1.8e3 !-- Configure sediment resuspension resuspension = 1 fs = 0.7 epsilon = 0.0250 tau_0 = 0.03 tau_r = 1.0 Ktau_0 = 0.001 macrophyte_link_var = 'MAC_ruppia' /