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PROBLEM: N DEPOSITION INCREASES
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Historical and future trends in N deposition
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Cheasepeake Bay N runoff Greater the N dep; greater amount of N that goes into the ocean, causing pollution.
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N CYCLE OVERVIEW
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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
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NITROGEN: OXIDATION STATES Minimum oxidation number is –3 Maximum oxidation number is +5
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Oxidation States NH 3 ammonia-3 NH 4 - ammonium-3 N 2 H 4 hydrazine-2 NH 2 0HHydroxylamine-1 N 2 Dinitrogen 0 N 2 ONitrogen (I) oxide+1 (nitrous oxide) NONitrogen (II) oxide+2 (nitric oxide) HNO 2 Nitrous Acid+3 NO 2 - Nitrite+3 NO 2 Nitrogen (IV) oxide+4 (nitrogen dioxide) HNO 3 Nitric Acid+5 NO 3 - Nitrate+5
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Assimilation (algae + bacteria) Assimilation -3+5+4+3+2+1 0 -2 Oxidation state Assimilation Denitrification NO 2 N2ON2O N2N2 NH 4 + NO 2 - Mineralization Org-N Main N-cycle transformations N 2 - Fixation - Soil bacteria - Cyanobacteria - Industrial activity - Sulfur bacteria Denitrification (anoxic bacteria) Nitrification 1 (oxic bacteria) Nitrification 2NO 3 - Ammonification gases
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Important N Species NH 3 ammoniagas, volitization NH 4 - ammoniumatmospheric form of NH3, nutrient N 2 H 4 hydrazinecarcinogenic, rocket fuel NH 2 0HHydroxylamineamines, opiotes N 2 dinitrogen atmospheric N N 2 Onitrous oxidebrown cloud, greenhouse gas, denitrification NOnitric oxidetailpipe emissions, smog HNO 3 nitric Acidenergy emissions NO 3 - nitratenutrient, acidification
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AMMONIUM FATE Assimilated by plants and microbes Adsorbed on CEC Occluded Quinone-NH 2 Volatilized as NH 3 Nitrified
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Problems With NH 3 Volatilization 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
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Sources of NH 3 on Livestock Farms Manure Application Animal Housing Manure Storage Grazing Fertilizer Application Crops Descending Order of Importance Bussink & Oenema, 1998
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CO(NH2)2 + H2O + urease 2NH3 +CO2
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Nitrification: another look 2NH 4 + + 3O 2 --> 2NO 2 - + 2H 2 O + 4H + Nitrosomanous 2NO 2 - + O 2 --> 2NO 3 - + energy Nitrobacter
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NITRIFICATION C:N ratio less than 20 Ammonium oxidation Nitrite oxidation
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NITRATE FATE Assimilation Dentrification Leaching Erosion
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Denitrification Conversion of NO 3 to N 2 O or N 2 by facultative anaerobic heterotrophs 2NO 3 + H 2 O N 2 O + 2O 2 + 2OH +
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Greenhouse Gas
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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 CO 2
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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.
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Excess NH4; pushes system to net nitrification
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Heavily N-limited; usually no NO3 produced
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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
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ABER SPAGHETTI DIAGRAM
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NITRATE LOSSES Increasing N deposition increases net nitrification Nitrate mobile Nitrate export to surface waters increases as N deposition increases
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