sorbed concentration on soil

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Srilert
Posts: 98
Joined: Fri Aug 19, 2005 2:27 am
Location: Thailand

sorbed concentration on soil

Post by Srilert » Thu Jul 14, 2011 10:37 am

Dear Sir,

After running the solute transport (with sorption isotherm), I don't see the sorbed concentration in soil. Actually, we should get the sorbed concentrations on soils, but I cannot get it.

Please let me know

Srilert

Srilert
Posts: 98
Joined: Fri Aug 19, 2005 2:27 am
Location: Thailand

Post by Srilert » Thu Jul 14, 2011 1:55 pm

Dear all,

I would like to clearify further the previous question: I have run the water and pesticide transport through unsaturated soil with hydraulic properties and solute transport parameters(sorption isotherm and degradation), but the output has showed only pesticide concentration in water. However, I didn't see the output of pesticide concentration in soils. How should I do to get such results.

Please suggest me

Thank in advance

Srilert

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Post by Jirka » Thu Jul 14, 2011 4:39 pm

Srilert,

HYDRUS-1D does not report (print to the output) the equilibrium sorbed concentration, since you can very easily calculate it directly from the liquid phase concentration (e.g., s=Kd*c). HYDRUS-1D reports only nonequilibrium sorbed concentration (when kinetic sorption is considered), since this value can not be calculated directly from the liquid phase concentrations.

Note that into the new version of 2 of HYDRUS (2D/3D), we have added graphs for all sorts of concentrations (including equilibrium and nonequilibrium sorbed, liquid, total, etc). However, in this case we calculate these concentrations in the GUI during the postprocessing.

There is simply no reason to write equilibrium sorbed concentration to the output, since it can be so easily calculated directly from the other output.

Jirka

ThomasG
Posts: 2
Joined: Tue Sep 29, 2020 8:10 am
Location: Netherlands

Re: sorbed concentration on soil

Post by ThomasG » Thu Jan 07, 2021 8:39 am

Hi Forum, i have a question relating to this subject.

Hydrus-1d does not report sorbed values. I'm running a model in which I simulate PFAS deposition over 43 years of atmospheric data. The precipitation has a certain concentration of PFAS in ng/cm3. PFAS mostly adsorbs to soil that is rich in organic matter. I can tune this with the Kd value for sorption. My question is as follows: I'm interested in sorption so i use the concentration/depth profiles to calculate 'sorbed concentration' with S=Kd*C. Does this mean that I now have the 'sorbed concentration' of that cm3 soil, excluding the cumulative content of PFAS in the soil moisture?

In other words: If i want to know the cumulative amount of PFAS in my 1cm3, do I have to sum 'sorbed concentration' and 'concentration*water content' to calculate the total amount of PFAS in the 1cm3 volume?

Cheers and thanks in advance,
Thomas

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: sorbed concentration on soil

Post by Jirka » Thu Jan 07, 2021 5:32 pm

To limit the size of output files, I try not to print things that can be easily calculated from existing output.

Indeed, the sorbed concentration can be easily calculated using the adsorption isotherm, e.g., s=Kd*c.

Note that s is in units of [Mass_contaminant/Mass_soil] and thus to get the mass for volume of soil you need to do the following:

ro*s+theta*c (units: [mass_soil/volume_soil * mass_contaminant/mass_soil + volume_water/volume_soil * mass_contaminant/ volume_water = mass_contaminant/ volume_soil].

This should be obvious from the governing CD equation.

Jirka

ThomasG
Posts: 2
Joined: Tue Sep 29, 2020 8:10 am
Location: Netherlands

Re: sorbed concentration on soil

Post by ThomasG » Fri Jan 08, 2021 10:21 am

Thank you kindly for your answer, it makes a lot of sense.

I have taken samples from the field and analyzed them. The PFAS content of these samples is in Mass_contaminant/Mass_soil (ug/kg soil). The samples were dried before analyzing them, so any dissolved FPAS in de residual moister of those samples is trapped in the soil. Analyzing them gives me the results in PFAS content/mass_soil (=adsorbed PFAS+the amount that was dissolved in the initially wetted soil!)

Now I want to know the same in Hydrus. My question is thus: if I want to know PFAS content in 1kg of dry soil, do I have to calculate 's' (from s=Kd*c) and add to that whatever moisture there is in that kg of soil (so Theta*mass_contaminant/ volume_soil (in the case of water, 1kg=1L=1000cm3))?

In profile information, we get the concentration in mass_contaminant/volume_water. If my soil has a porosity of 0,35 and is fully saturated (theta =0,35) it means I have to multiply my concentration*theta to get my content in 1cm3 soil right?

Thanks in advance for the help with this likely 'common sense' problem. It has me puzzled.

Thomas

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: sorbed concentration on soil

Post by Jirka » Fri Jan 08, 2021 5:39 pm

You should be able to figure this out yourself based on the information that I provided in my previous answer. J.

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