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

Oxidation StatesNH3 ammonia -3NH4

- ammonium -3N2H4 hydrazine -2NH20HHydroxylamine -1N2 Dinitrogen 0N2O Nitrogen (I) oxide +1

(nitrous oxide)NO Nitrogen (II) oxide +2

(nitric oxide)HNO2 Nitrous Acid +3NO2

- Nitrite +3NO2 Nitrogen (IV) oxide +4

(nitrogen dioxide)HNO3 Nitric Acid +5NO3

- Nitrate +5

Assimilation

(algae + bacteria)

Assimilation

-3 +5+4+3+2+10-1-2Oxidation state

AssimilationDenitrification

NO2N2ON2

NH4+

NO2-

Mineralization

Org-N

Main N-cycle transformations

N2 - Fixation- Soil bacteria- Cyanobacteria - Industrial activity- Sulfur bacteria

Denitrification(anoxic bacteria)

Nitrification 1(oxic bacteria)

Nitrification 2

NO3-

Ammonification

•gases

Important N Species

NH3 ammonia gas, volitizationNH4

- ammonium atmospheric form of NH3, nutrientN2H4 hydrazine carcinogenic, rocket fuelNH20HHydroxylamine amines, opiotesN2 dinitrogen atmospheric NN2O nitrous oxide brown cloud, greenhouse gas, denitrificationNO nitric oxide tailpipe emissions, smogHNO3 nitric Acid energy emissionsNO3

- 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 raises pH of rainwater, more SO2 dissolves ammonium sulfate forms - oxidizes soil releases sulfuric & nitric acid

Eutrophication 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

DescendingOrder ofImportance

Bussink & Oenema, 1998

CO(NH2)2 + H2O + urease

2NH3 +CO2

Nitrification: another look

2NH4+ + 3O2 --> 2NO2 - + 2H2O + 4H+ Nitrosomanous

2NO2 - + O2 --> 2NO3 - + energy

Nitrobacter

NITRIFICATION

C:N ratio less than 20 Ammonium oxidation Nitrite oxidation

NITRATE FATE

Assimilation Dentrification Leaching Erosion

Denitrification

Conversion of NO3 to N2O or N2 by facultative anaerobic heterotrophs

2NO3 + H2O N2O + 2O2 + 2OH+

Greenhouse Gas

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

300x more active 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