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									 ESM 202

   Human activities alter the N cycle

   N fertilization of aquatic systems leads to

   N2O is a major greenhouse gas

   All of this is linked to our demand for energy
    and food
N: where is it?

  ATMOSPHERE: 3.9E21 g

 LAND: 3.4E17 g
                         WATER: 2.3E19 g
Nitrogen compounds
   Gases
       N2 dinitrogen
       N20 nitrous oxide
       NOx = NO2 + NO nitrogen dioxide + nitric oxide
       NH3 ammonia
   Inorganic
       NH4+ ammonium
       NO2- nitrite (HNO2 nitrous acid)
       NO3- nitrate (HNO3 nitric acid)
   Organic N
       Amino acids, proteins; enzymes
       Uric acid: C5H4N4O3
       Urea: (NH2)2CO (hydrolyzes to CO2 and NH4+)
                   N Reservoirs

Source: Biogeochemistry, Schlesinger, 1991
Global N Cycle

                 Source: Biogeochemistry, Schlesinger, 1997
   N fixation
     N2  reactive N
        (e.g. NH3 , NH4+)
     Mostly biological


free- living bacteria (asymbiotic)
Synthetic fertilizer

            • production is considered
            N fixation

            • takes N2, reacts it with
            natural gas, producing NH3
            and CO2
(Townsend et al. Frontiers Ecol. Environ. 2003)
(Tilman et al. Nature, 2002)
Maximum N uptake

                   Source: Biogeochemistry, Schlesinger, 1997
  Fixed N: what happens to it?
                       N2 (g)
                      N2O (g)         Denitrification
     N Fixation       NO (g)

    NH3/NH4+                             NO-2/NO3-
                  Ammonification       Nitrate
                  (mineralization)    Reduction
Assimilation &
                    Organic N
Ammonia Cycle

                Source: Biogeochemistry, Schlesinger, 1997
Ammonia Cycle

                Source: Biogeochemistry, Schlesinger, 1997
     Ammonia Oxidation

   In the atmosphere:

         NH3 + OH·  NO/NO2 + H2O
   NO and NO2 referred to as NOX

                NO + O  NO2
   NO converts to HNO2  NO2-
   NO2 converts to HNO3  NO3-
   Nitrite and Nitrate deposit as particles or with rain
NOx Cycle: Human N Fixation

                   Source: Biogeochemistry, Schlesinger, 1997
NOx Sources

              Source: Biogeochemistry, Schlesinger, 1997
Spatial location of N Processes


                       Source: Biogeochemistry, Schlesinger, 1997
Factors in Nitrification
   Ammonium
   Bicarbonate (HCO3-) alkalinity
   Oxygen
   Time
   While “specialists”, the bacteria are
    widely distributed…
   Nitrate
   Water soluble, mobile
   Metabolized (gut) into NO2-
      Nitrite inactivates hemoglobin, particularly
      for infants—methemoglobin
   WHO / US health standard: 10 mg/L
   As with SO42-, acid rain

(Townsend et al. Frontiers Ecol. Environ. 2003)
              Percent Increase in Nitrogen Fluxes in Rivers

Source: Millennium Ecosystem Assessment
     Gulf of Mexico Dead Zone

Source: NOAA
Source: Principles Env. Sci. & Eng. (Davis & Masten)
Oceanic N Processes

                      Source: Biogeochemistry, Schlesinger, 1997
Oceanic N Processes

                      Source: Biogeochemistry, Schlesinger, 1997
Nitrification and Denitrification
Factors in Denitrification
   Nitrate
   Organic C
   Lack of dissolved oxygen
   Wide range of bacteria, widely
   120 yr residence time in atmosphere
   Absorbs radiation / greenhouse gas
      4th largest contributor
      more effective than CO2
   Depletes stratospheric O3
      UV degrades N2O to NO; NO is O3 depleter
                   N2O accumulation in atmosphere

Source: Biogeochemistry, Schlesinger, 1997   Source: National Oceanic and Atmospheric Administration,
N2O Budget

             Source: Biogeochemistry, Schlesinger, 1997
(Matson et al. Science 1998)
       Sources of Nitrogen
                                              Fertilizer application

                     Atmospheric Deposition

                                              Groundwater irrigation
   Septic systems

                                               Livestock & manure

Treated wastewater
(Valiela et al. 1997)
Sources of N in catchments

 (Petzoldt & Uhlmann 2006)
   20 to 85 mg/L N untreated (domestic,
   2º trmt for BOD5 and TSS (30/30 mg/L)
      Some N removed to biomass: C5H7NO2
   Nutrient removal
      Nitrification , denitrification
      Total effluent N can be < 5 mg/L
Biological nutrient removal
            Nitrous Oxide (N2O) Is a Greenhouse Gas.
            Nitrous Oxide Depletes Stratospheric Ozone.
            Nitrogen Gases Generate Air Pollution.
            Nitrate Ions in Drinking Water Can Be a Threat to
             Infant Health.
            Nitrogen Oxides Emitted into the Atmosphere
             Contribute to Acid Deposition.
            High Nitrate Concentrations in Aquatic Ecosystems
             Can Lead to Eutrophication.
            Nitrogen Addition to Ecosystems Reduces Biodiversity
             and Loss of Ecosystem Function.

Socolow, 1999, PNAS
“Fertilizer is the fossil fuel of food.”

“The goal of achieving a constant carbon dioxide concentration
in the atmosphere makes future use of fossil fuels hostage to
the combined power of natural and engineered carbon
sequestration. Similarly, the goal of achieving constant stocks
of fixed nitrogen makes future use of nitrogen fertilizer
hostage to the strength of natural plus engineered denitrification
in the corresponding ecosystems. Globally, until nitrogen
fixation is balanced by denitrification, the amount of excess
fixed nitrogen in the world will grow relentlessly, with increasing
consequences for ecosystems and public health.”

“As an alternative to fossil fuel, fast-growing energy crops
may be established on dedicated, fertilized plantations.”
 Socolow, 1999, PNAS
(Townsend et al. Frontiers Ecol. Environ. 2003)
(Townsend et al. Frontiers Ecol. Environ. 2003)
Global N Budget

                  Source: Millennium Ecosystem Assessment

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