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

N-13; 10 minutes

N-14; Stable

N-15; Stable

N-16; seconds

N-14 is 272 times more abundant than N-
15

Atomic wt is 14.0067

NITROGEN: OXIDATION
STATES

Minimum oxidation number is –3

Maximum oxidation number is +5

NH
3
NH
4
-
N
2
H
4
NH
2
0H
N
2
N
2
O
NO
HNO
2
NO
2
-
NO
2
HNO
3
NO
3
-
Oxidation States ammonia ammonium hydrazine
Hydroxylamine
Dinitrogen
Nitrogen (I) oxide +1
(nitrous oxide)
Nitrogen (II) oxide +2
(nitric oxide)
-3
-3
-2
-1
0
Nitrous Acid
Nitrite
+3
+3
Nitrogen (IV) oxide +4
(nitrogen dioxide)
Nitric Acid +5
Nitrate +5

Main N-cycle transformations
Mineralization
Org-N
NH
4
+
Assimilation
(algae + bacteria)
Assimilation
Nitrification 1
(oxic bacteria)
Ammonification
Assimilation
Denitrification
NO
2
-
NO
3
-
Nitrification 2
Denitrification
(anoxic bacteria)
N
2
- Fixation
- Soil bacteria
- Cyanobacteria
- Industrial activity
- Sulfur bacteria
N
2
N
2
O
NO
2
• gases
Oxidation state
-3 -2 -1 0 +1 +2 +3 +4 +5

Important N Species
NH
3
NH
4
ammonia ammonium gas, volitization atmospheric form of NH3, nutrient
N
2
H
4
NH
2
0H
N
2 hydrazine dinitrogen carcinogenic, rocket fuel
Hydroxylamine amines, opiotes atmospheric N
N
2
O nitrous oxide brown cloud, greenhouse gas, denitrification
NO nitric oxide tailpipe emissions, smog
HNO
3
NO
3
nitric Acid nitrate energy emissions nutrient, acidification

AMMONIUM FATE

Assimilated by plants and microbes

Adsorbed on CEC

Occluded

Quinone-NH
2

Volatilized as NH
3

Nitrified

Problems With NH
Volatilization
3
 Acid Atmospheric Deposition

 raises pH of rainwater, more SO
2 dissolves ammonium sulfate forms - oxidizes soil
 releases sulfuric & nitric acid
 Eutrophication
 water and land
 Loss of N to farmers
 Lowers N:P

Sources of NH
3 on Livestock Farms
 Manure Application
 Animal Housing
 Manure Storage
 Grazing
 Fertilizer Application
 Crops
Descending
Order of
Importance
Bussink & Oenema, 1998

CO(NH2)2 + H2O + urease
2NH3 +CO2

Nitrification: another look
2NH
4
+ + 3O
2
--> 2NO
2
- + 2H
Nitrosomanous
2
O + 4H +

2NO
2
- + O
2
--> 2NO
3
- + energy
Nitrobacter

NITRIFICATION

C:N ratio less than 20

Ammonium oxidation

Nitrite oxidation

NITRATE FATE

Assimilation

Dentrification

Leaching

Erosion

Denitrification

Conversion of NO
3 to N
2
O or N
2 facultative anaerobic heterotrophs by

2NO
3
+ H
2
O

N
2
O + 2O
2
+ 2OH +

Greenhouse Gas

300x more active than CO
2
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