Transcript NITROGEN ATOM ISOTOPES

PROBLEM:
N DEPOSITION INCREASES
Historical and future
trends in N deposition
Cheasepeake Bay N runoff
Greater the N dep;
greater amount of N
that goes into the ocean,
causing pollution.
N CYCLE OVERVIEW
NITROGEN ATOM
ISOTOPES
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N-13; 10 minutes
N-14; Stable
N-15; Stable
N-16; seconds
N-14 is 272 times
more abundant than N15
 Atomic wt is 14.0067
NITROGEN: OXIDATION
STATES
 Minimum oxidation
number is –3
 Maximum oxidation
number is +5
Oxidation States
NH3
NH4N2H4
NH20H
N2
N2O
NO
HNO2
NO2NO2
HNO3
NO3-
ammonia
ammonium
hydrazine
Hydroxylamine
Dinitrogen
Nitrogen (I) oxide
(nitrous oxide)
Nitrogen (II) oxide
(nitric oxide)
Nitrous Acid
Nitrite
Nitrogen (IV) oxide
(nitrogen dioxide)
Nitric Acid
Nitrate
-3
-3
-2
-1
0
+1
+2
+3
+3
+4
+5
+5
Main N-cycle transformations
Assimilation
Assimilation
Denitrification
Mineralization
(algae + bacteria)
Org-N
NO2-
Assimilation
NH4+
NO3-
Nitrification 2
Nitrification 1
(oxic bacteria)
Ammonification
Denitrification
N2 - Fixation
(anoxic bacteria)
- Soil bacteria
- Cyanobacteria
- Industrial activity
- Sulfur bacteria
N2
N2O
NO2
0
+1
+2
•gases
Oxidation state
-3
-2
-1
+3
+4
+5
Important N Species
NH3 ammonia
gas, volitization
NH4- ammonium atmospheric form of NH3, nutrient
N2H4 hydrazine
carcinogenic, rocket fuel
NH20H
Hydroxylamine
amines, opiotes
N2
dinitrogen
atmospheric N
N2O nitrous oxide brown cloud, greenhouse gas, denitrification
NO
nitric oxide tailpipe emissions, smog
HNO3 nitric Acid
energy emissions
NO3- nitrate
nutrient, acidification
AMMONIUM FATE
 Assimilated by plants
and microbes
 Adsorbed on CEC
 Occluded
 Quinone-NH2
 Volatilized as NH3
 Nitrified
Problems With NH3
Volatilization
 Acid Atmospheric Deposition
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raises pH of rainwater, more SO2 dissolves
ammonium sulfate forms - oxidizes soil
releases sulfuric & nitric acid
 Eutrophication
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water and land
 Loss of N to farmers
 Lowers N:P
Sources of NH3 on Livestock Farms
 Manure Application
 Animal Housing
 Manure Storage
 Grazing
 Fertilizer Application
 Crops
Descending
Order of
Importance
Bussink & Oenema, 19
CO(NH2)2 + H2O + urease
2NH3 +CO2
Nitrification: another look
2NH4+ + 3O2 --> 2NO2 - + 2H2O + 4H+
Nitrosomanous
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2NO2 - + O2 --> 2NO3 - + energy
Nitrobacter
NITRIFICATION
 C:N ratio less than 20
 Ammonium oxidation
 Nitrite oxidation
NITRATE FATE
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Assimilation
Dentrification
Leaching
Erosion
Denitrification
 Conversion of NO3 to N2O or N2 by
facultative anaerobic heterotrophs
 2NO3 + H2O N2O + 2O2 + 2OH+
Greenhouse Gas
300x more active
than CO2
Relative to carbon dioxide the other greenhouse gases together
comprise about 27.63% of the greenhouse effect (ignoring water vapor)
but only about 0.56% of total greenhouse gas concentrations. Put
another way, as a group methane, nitrous oxide (N2O), and CFC's and
other miscellaneous gases are about 50 times more potent than CO2
Immobilization/Assimilation
 Incorporation of inorganic N to organic N
 Plants/microbes can use only inorganic N
(NH4 and N O3) to produce organic matter
 However, new evidence suggests “tasty”
organic N (primarily amino acids) can be
utilized by plants/microbes.
Excess NH4; pushes system to net nitrification
Heavily N-limited; usually no NO3 produced
LEAKY FAUCET
HYPOTHESIS
 Persistent “leak” of DON from
catchments
 DON is decoupled from
microbial demand for N.
 DON export coupled to soil
standing stock of C, N
 Lag between N inputs and DON
export
ABER SPAGHETTI DIAGRAM
NITRATE LOSSES
 Increasing N
deposition increases
net nitrification
 Nitrate mobile
 Nitrate export to
surface waters
increases as N
deposition increases