DENITRIFICATION BELOW THE ROOT ZONE Vibeke Ernstsen Geological Survey of Denmark and Greenland (GEUS) Plantekongres 2006, Herning, 10. januar 2006
Jan 05, 2016
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.