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DENITRIFICATION BELOW THE ROOT ZONE Vibeke Ernstsen Geological Survey of Denmark and Greenland (GEUS) Plantekongres 2006, Herning, 10. januar 2006. Content: Nitrate reduction and the aquatic environment The processes The unsaturated zone - distribution, and potential for reduction - PowerPoint PPT Presentation
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DENITRIFICATION BELOW THE ROOT ZONE
Vibeke ErnstsenGeological Survey of Denmark and
Greenland (GEUS)
Plantekongres 2006, Herning, 10. januar 2006
Content:
• Nitrate reduction and the aquatic environment
• The processes
• The unsaturated zone - distribution, and potential for reduction
• Saturated zone - potentiale for reduction
• The water flowpattern and distribution of nitrate
Reduction by organic matter: 5 C + 4 NO3
- + 2 H2O 2 N2 + 4 HCO3- + CO2
Reduction by pyrite: 5 FeS2 + 14 NO3
- + 4 H+ 7 N2 + 10 SO42- + 5 Fe2+ + 2 H2O
Reduction by ferrous iron - N2: 5 Fe2+ + NO3
- + 12 H2O 5 Fe(OH)3 + 0.5 N2 + 9 H+
Reduction by ferrous iron - NH4: 8 Fe2+ + NO3
- + 21 H2O 8 Fe(OH)3 + NH4+ + 14 H+
Reduction med methane: 5 CH4 + 8 NO3
- + 3 H+ 4 N2 + 5 HCO3- + 9 H2O
Nitratereduction - possible processes
• biological or abiotic process - anoxic environment
Reduce compounds:
• bioavailable organic matter• reduced sulfur (pyrite & hydrogen sulphide)• available ferrous iron (exchangeable/structural)• manganese• methane• ?
SOME ARE USED UP - OTHER ARE RENEWABLE
Nitratreduction - unsaturated zone
• biological or abiotic process - anoxic environment• potential of nitrate reduction relates to the regeneration of reduced compounds - the inherited pools are used up
Vegetation - renewable source of organic matter• leaching from the surface• in the root zone - roots etc.• fauna and flora incl. bacteria
Organic matter retension:• sorption• compleks-binding • used up• precipitate• etc.
Maximum 3 meters
0
5
10
15
0 2 4
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBV
0
5
10
15
0 2 4 6
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBVI
0
5
10
15
0 2 4 6
Nitrate
(mg NO3-N kg-1)
De
pth
(m
)
SBIII
0
5
10
15
0 5 10
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBIV
0
5
10
15
0 1 2
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBXII
0
5
10
15
0 2 4
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBXI
0
5
10
15
0 1 2
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBX
0
5
10
15
0 2 4
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBIX
0
5
10
15
0 8 16
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBVII
0
5
10
15
0 8 16
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBVIII
0
5
10
15
0 8 16
Nitrate (mg NO3-N kg-1)
Dep
th (
m)
SBI
Ramsømagle
Ramsølille
Viby
SBISBIII
SBVIII
SBIX
SBIV
SBVI
SBX
SBXI
SBV
SBXIISBVII
Nitrate reduction - below the usaturated zone
15
20
25
30
0 0,1 0,2
Alkalinity
(meq L-1)
De
pth
(m)
15
20
25
30
0 50 100
Nitrate
(mg NO3 L-1)
De
pth
(m)
15
20
25
30
0 50 100
Sulfate
(mg SO4 L-1)
De
pth
(m)
15
20
25
30
0 5 10
Ferrojus iron
(mg Fe L-1)
De
pth
(m)
15
20
25
30
4 5 6 7
pHD
ep
th (
m)
Kristiansen et al., 1991
GWT
Reduction in anoxic environments by the inherited reduced compundsat different depths. Considerable differences related to geology.
Clayey samples: 15 % clay• Organic matter: 0,05 % C• Pyrite: 0,003 % S• Ferroous iron: 0,9 % Fe
Capacity: 90-110 mol nitrate pr. m3
Pr. meter: 250 - 300 years
Sandy samples: 1-2 % clay• Organic matter: 0,03 % C• Pyrite: 0,005 % S• Ferrous iron: 0 % Fe
Capacity: 30 mol nitrate pr. m3
Pr. meter: 95 years
Clayey samples: 30-40 % clay• Organic matter: 0,10 % C• Pyrite: 0,005 % S• Ferroous iron: 1,2 % Fe
Capacity: 150 -180 mol nitrate pr. m3
Pr. meter: 420 - 500 years
Sandy samples: 1-2 % clay• Organic matter: 0,15 % C• Pyrite: 0,012 % S• Ferrous iron: 0 % Fe
Capacity: 160 mol nitrate pr. m3
Pr. meter: 465 years
Calculation of redox capacity - exsamples
THIS KIND OF CALCULATION DOES NOT TAKEINTO ACCOUNT THE REACTIVITY OF THE COMPOUNDS
LITERATURE:
• Miljøstyrelsen. 2001. Arbejdsrapport nr. 24 • Miljøstyrelsen. 2005. Miljøprojekt nr. 1023, 1024 og 1025
• Ernstsen, V., H.J. Henriksen og F. von Platen. 2001. Principper for beregning af nitratreduktion i jordlagene under rodzonen. Arbejdsrapport nr. 24.
• Ernstsen, V. 2005. Nitratreduktion i den umættede zone. Miljøprojekt 1023.
• Ernstsen, V., Jørgensen, N., og Lynge, C.R. 2005. Metode til analyse af reducerende stoffer i sedimenter. Miljøprojekt 1024.
• Ernstsen, V. 2005. Undersøgelse af reaktiviteten af reducerende stoffer i nogle
danske sedimenter - et pilotstudie. Miljøprojekt 1025.
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