Nitrogen Deposition Impacts: Historical Trends, Future Projections, and N-Cycle Overview

1. PROBLEM:N DEPOSITION INCREASES

3. Historical and future trends in N deposition

5. Cheasepeake Bay N runoff Greater the N dep; greater amount of N that goes into the ocean, causing pollution.

8. N CYCLE OVERVIEW

10. 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

11. NITROGEN: OXIDATION STATES • Minimum oxidation number is –3 • Maximum oxidation number is +5

12. Oxidation States NH3 ammonia -3 NH4- ammonium -3 N2H4 hydrazine -2 NH20H Hydroxylamine -1 N2 Dinitrogen 0 N2O Nitrogen (I) oxide +1 (nitrous oxide) NO Nitrogen (II) oxide +2 (nitric oxide) HNO2 Nitrous Acid +3 NO2- Nitrite +3 NO2 Nitrogen (IV) oxide +4 (nitrogen dioxide) HNO3 Nitric Acid +5 NO3- Nitrate +5

13. Main N-cycle transformations Assimilation Org-N NO2- NO3- NH4+ Nitrification 1 (oxic bacteria) Nitrification 2 Ammonification N2 N2O NO2 • gases Oxidation state -3 -2 -1 +1 +2 +3 +4 +5 0 Assimilation (algae + bacteria) Assimilation Denitrification Mineralization Denitrification (anoxic bacteria) N2 - Fixation - Soil bacteria - Cyanobacteria - Industrial activity - Sulfur bacteria

14. 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

21. AMMONIUM FATE • Assimilated by plants and microbes • Adsorbed on CEC • Occluded • Quinone-NH2 • Volatilized as NH3 • Nitrified

23. 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

24. Sources of NH3 on Livestock Farms • Manure Application • Animal Housing • Manure Storage • Grazing • Fertilizer Application • Crops Descending Order of Importance Bussink & Oenema, 1998

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

30. Nitrification: another look 2NH4+ + 3O2 --> 2NO2 - + 2H2O + 4H+ Nitrosomanous • 2NO2 - + O2 --> 2NO3 - + energy Nitrobacter

31. NITRIFICATION • C:N ratio less than 20 • Ammonium oxidation • Nitrite oxidation

32. NITRATE FATE • Assimilation • Dentrification • Leaching • Erosion

34. Denitrification • Conversion of NO3 to N2O or N2 by facultative anaerobic heterotrophs • 2NO3 + H2O N2O + 2O2 + 2OH+

35. Greenhouse Gas

36. 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

44. 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.

46. Excess NH4; pushes system to net nitrification

48. Heavily N-limited; usually no NO3 produced

49. 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

50. ABER SPAGHETTI DIAGRAM