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sulfate reduction rate calculation from given pore water sulfate profile
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Topic: sulfate reduction rate calculation from given pore water sulfate profile (Read 921 times)
Gst932364
Contributor
Posts: 2
sulfate reduction rate calculation from given pore water sulfate profile
«
on:
December 16, 2019, 07:30:42 PM »
Hi, I started studying Phreeqc with the aim of getting the most out of my pore water datasets.
Es. I have a SO4 concentration profile for a sediment core and I want to calculate the sulfate reduction rate. Given sedimentation rate of 0.01 cm/yr
How would you do that on Phreeqc?
Example:
Depth (cm) SO4 (ppm)
10 2800
20 2600
30 2400
40 2200
50 1900
60 1400
70 900
80 400
90 0
thank you for your help
«
Last Edit: May 08, 2021, 04:17:29 PM by Gst932364
»
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dlparkhurst
Top Contributor
Posts: 3086
Re: sulfate reduction rate calculation from given pore water sulfate profile
«
Reply #1 on:
December 17, 2019, 03:18:22 AM »
The sedimentation rate is pretty slow relative to diffusion and reaction, so I think you can ignore sedimentation. You may need to consider the change in porosity over a meter, but I'm going to ignore it.
A simple model is diffusion with first-order reaction of sulfate, as given below. Eventually, it reaches steady state. However, your sulfate profile is more linear than exponential, so you will have to consider why. Does steady state apply? Is the reactive matter evenly distributed or are there layers of reactive matter?
SOLUTION 0-20 SEAWATER
units ppm
pH 8.22
pe 8.451
temp 25.0
Ca 412.3
Mg 1291.8
Na 10768.0
K 399.1
Cl 19353.0
Alkalinity 141.682 as HCO3
S(6) 2712.0
O(0) 1.0 O2(g) -0.7
END
KINETICS 1-20
CH2O
-formula CH2O 2
-m0 1
-tol 1e-008
-steps 3.15e7
END
RATES
CH2O
10 m_so4 = TOT("S(6)")
20 k = .3/(3.17e7) # per year
30 rate = k*m_so4
40 moles = rate * TIME
50 SAVE moles
END
TRANSPORT
-cells 20
-shifts 4
-time_step 25 y 1 # seconds
-flow_direction diffusion_only
-boundary_conditions constant closed
-lengths 0.1
-punch_frequency 1
USER_GRAPH 1
-axis_titles "Depth, m" "Sulfate, mg/kgw" ""
-initial_solutions false
-connect_simulations false
-plot_concentration_vs x
-start
10 GRAPH_X dist
20 GRAPH_Y TOT("S(6)")*GFW("SO4")*1000
-end
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Gst932364
Contributor
Posts: 2
Re: sulfate reduction rate calculation from given pore water sulfate profile
«
Reply #2 on:
December 20, 2019, 06:07:25 PM »
Thank you so much for your reply dlparkhurst, I will run some tests and adjust the script to my case studies.
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sulfate reduction rate calculation from given pore water sulfate profile