Transcript IMPORTANCE OF NITROGEN IN THE ENVIRONMENT

IMPORTANCE OF NITROGEN IN THE
ENVIRONMENT
• N2 comprises 80% of the atmosphere
– N2 can not be used by most organisms
– N2 is not a problem until its in a reactive form like NH3 or
NO3 and is out of balance in nature
• N is the major component of proteins and nucleic
acids
– Often the most limiting nutrient for plant growth
• When out of balance, N can have both direct and
indirect negative impacts on the environment
THE NITROGEN CYCLE
N CYCLE
• N enters the cycle through:
– N fixation
– Fertilization
• N fixation
– Non-biological
Lightning
Burning fossil fuels
N2 + O2
2 NO
2NO + O2
2 N O2
2 N O2 + H2O
HNO3 + HNO2
HNO3
H+ + NO3- (Nitrate; Readily
used by plants)
– Biological N fixation
Microorganisms
Nitrogenase
N2 + 6 e- + 8H+
2NH3 (Ammonia)+ H2
Fe, Mo
• Biological N fixation
– Symbiotic N fixers
• Responsible 70% of all N fixation
• Microorganisms
– Rhizobium bacteria
» Infect roots of legume plants
– Frankia bacteria
» Infect the roots of certain trees
• Process
– Bacteria reduce N2 to NH3
– Plants take up NH3 and combine it with Carbon skeletons to produce amino
acids
– Other plants only have access to this fixed N by the plant dying and
becoming part of the soil organic matter-N pool
– High levels of N will reduce biological N fixation
– Free living N fixers
• Responsible for 30% of world N fixation
• Microrganisms
– Cyanobacteria
» Found in rice paddies
– Azospirrilium, Azobacter, and Clostridium bacteria
» Found in soil
• Generate NH3 for their own use.
N fertilizer
• Produced by the HaberBosch process
• Developed in 1913
• Process
High pressure High temperature
N2 + 3H2
NH3
Fe catalyst
• Primarily responsible for the
green revolution, but also
responsible to large increase
of reactive N in our
environment
Ammonification (Mineralization)
• N in plant protein may become part of the soil’s OM
nitrogen pool by microbial degradation of:
– Dead plant litter
– Undigested protein in animal feces
• OM-nitrogen converted to ammonia by soil bacteria
– Process
R-NH2
NH3 + R
– Done by both aerobic and anerobic bacteria
– Increased by:
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•
•
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Increased soil OM-N pool
Increased soil temperatures
Soil pH > 7
High soil moisture
– NH3 rapidly converted to NH4+ at pH < 7.5
• NH4+ is relatively stable
• N is digested by animals is excreted as urea
(mammals) or uric acid (poultry)
O
H2N – C – NH2
Urea
Urease
2NH3 + CO2
O
H
N
C
H
N
C
C
O
C
C
N
H
Uric acid
N
H
5 steps w/
Urease
O
4NH3 + 5CO2
FATE OF AMMONIA RELEASED BY
MINERALIZATION
• Use by plants
• Immobilization
– Bacteria incorporate N into their own cells and contribute to
soil OM-N pool
– Occurs in soils containing high C:N ratios
• Leaching
– Occurs in sandy soils
• Have a low capacity for binding NH4+
• Ammonium cations may leach into ground water as
precipitation infiltrates soils
– Soils that are high in clay or organic matter can bind NH4+
which can only be lost with erosion
• Nitrification
– Highest proportion of NH4+ is converted to NO3 by aerobic
bacteria
Nitrosomas
Nitrobacter
O2
4H
O2
NH4
NO2
NO3
– Rapid under conditions of:
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•
•
•
•
Warm temperatures
Well aerated soils
Neutral pH
Moist soils
High fertility
– Slow under conditions of:
• Cold temperatures
• Saturated soils
• Low pH
– During nitrification, soil pH may decrease as NH4 is converted to
NO3
• Volatilization
– NH4+ is not volatile
– In soils with high pH (> 7.0), NH4+ is converted to NH3 which
can volatize into the atmosphere as a gas
– NH3 is also released when the urea (in mammals) or uric
acid (in poultry) excreted in urine mixes with the urease or
uricase enzymes produced by the bacteria in the feces in in
manure in barns, outdoor lots, manure storage structures,
and in fields after application
– Amounts of NH3 volatilized
• 20 to 70% of the N in manure
• Ammonia losses from animal agriculture represents 75% of all
NH3 emitted in the U.S.
– Rate of NH3 volatilization is increased by:
• Soil pH > 7.0
• Soil temperatures > 50 F
• Greater air movement
FATE OF NO3 PRODUCED DURING
NITRIFICATION
• Use by plants
• Leaching into groundwater
– NO3 is highly soluble in water and does not bind to soil
particles
– During periods of excessive precipitation, NO3 transported
to ground water as water infiltrates the soil
• Carries Ca, Mg, and K cations out of the soil reducing fertility
while leaving Al which is toxic to plants
• NO3 may be transported to surface waters via tile
drainage
– Factors that lead to increased leaching in spring
• Build up on NH4+ in soil during winter
• Increased NO3 in soil as nitrification increases with increased
soil temperatures
• Low utilization of NO3 by immature plants
• High soil moisture
• Denitrification
– Conversion of NO3 to N2 in anerobic conditions in soil or
manure storage areas
– Process
C6H12O6 + 4 NO3
6CO2 + 6H2O + 2N2 + NOx
NOx = NO, NO2 or N2O
– N2 and NOx are gases released into the environment
• N2 is inert in the environment
• NOx has numerous adverse effects on the environment
– Denitrification is increased by:
• High soil N levels
• Anerobic soils
– Flooded soil
– Compacted soil
• Warm temperatures
• High OM in soil
POSITIVE EFFECTS OF INCREASING THE AMOUNTS
OF REACTIVE N IN THE ENVIRONMENT
• Increased yields and nutritional value of feeds
• Increased wealth of the human population
• Increased productivity of N-limited crops and
ecosystems
• Increased yields per acre
– Could reduce cultivation of marginal and forested lands
• Increased carbon sequestration
ADVERSE EFFECTS OF NITROGEN IN THE
ENVIRONMENT
ADVERSE EFFECTS OF NITRATE (NO3) IN THE
ENVIRONMENT
• Enters drinking water supplies
• Hazard (Blue Baby Syndrome)
– Formation of methemoglobin that prevents hemoglobin in
red blood cells from carrying oxygen to peripheral tissues
Normal:
O2
Hemoglobin in
red blood cells
Oxygenated hemoglobin
Peripheral tissue
(Uses O2)
Nitrate toxicity: Gut bacteria
NO3
NO2
O2
Hemoglobin in
red blood cells
Peripheral tissue
– Hazardous level: 10 ppm in water
Methemoglobin
ADVERSE EFFECTS ON AMMONIA IN THE
ENVIRONMENT
• Hazards
– Odor
– Direct toxin
• Physiological effects and amounts
– Livestock (<100 ppm, usually found in livestock facilities)
» Eye irritation
» Respiratory tract irritation
» Reduced disease resistance
– Humans (OSHA limit is 50 ppm)
» 9 ppm
Eye, nose and throat irritation
» 50 – 150 ppm
Severe cough and mucous production
Nasal irritation
» > 150 ppm
Scarring of the upper and lower respiratory tract
Pulmonary edema
Chemical burns of eyes
» 500 ppm
Acute death
• Problem for workers and animals in confinement
• Limited threat to the community
– Recommended limits (One-hour average exposure)
Measurement
Neighboring residence
Property line
Concentration Dilution
< 150 ppb
1:7
< 70 ppb
1:15
– Toxicity in aquatic environments (Manure spills)
• Most natural water sources
– NH4-N at 2 ppm is toxic to fish
• In alkaline waters at high temperatures
– NH4-N at 0.1 ppm is toxic to fish
– Particulate matter less than 2.5 um (PM2.5)
• Formed when atmospheric NH3 reacts with SO2, NOx, and
volatile organic compounds (VOCs)
– Produce (NH4)2SO4, NH4NO3, and NH4HSO4
• Forms in rain clouds and fog
– Dispersed to ground as rainfall and snow (Wet deposition)
– Released in air as aerosols (Dry deposition)
• Sources of components of PM2.5
– Agriculture
– Burning fossil fuels
• Hazards of PM2.5
– Human health
» Penetrate into lungs
» Increased hospital emissions
» Increased respiratory diseases
» Decreased lung function
» Alteration in lung tissue and respiratory defense
mechanisms
» Chronic bronchitis
» Increased risk of myocardiac infarctions
– N deposition in the environment
» Acidifying lakes and streams
» Algae bloom in water sources
» Depletion of minerals in soils
» Decreased biodiversity of ecosystem
• Health-based standard for PM2.5
– Annual average – 15 ug/m3
– 24 hr standard – 65 ug/m3
– Monitored at 1100 sites across the US
– Acidify soil
• Process
– During nitrification, H+ are released that lower pH of soil
» NH4
NO3
4H+
• Reduces ability of plants to uptake nutrients
Total Ammonia Emissions by County
for 1995
ADVERSE EFFECTS ON NOx IN THE
ENVIRONMENT
• Major sources
– Combustion of fossil fuels
– Agriculture
• Hazards
– Component of PM2.5; NO2
– Acid rain; NO2
• NOx + H
HNOx
• Effects
– Damages lung tissue
– Increases acid in waters
» Harms fish population
– Increases acid in soil
» Harms trees
– Damages buildings and statues
– Formation of ground level ozone; NO2
• Formed when volatile organic compounds (VOCs) react with
NOx in the presence of heat and sunlight
• Effects
– Health
» Respiratory infections and diseases
» Premature aging of lungs
– Ecosystems
» Reduced agricultural and forest yields
» Reduced survivability of tree seedlings
» Increased susceptibility of plants to stress and
disease
» Damage to foliage of plants
» Forms smog with PM reducing visibility
– Destruction of stratospheric ozone; N2O
• In upper atmosphere, N2O triggers reactions that deplete the
stratospheric ozone layer which protects the earth from
ultraviolet radiation
– Human skin cancer
– Damages plant foliage
– Greenhouse gas; N2O
• N2O has 310 x the greenhouse gas effect of CO2
• Contributes to global warming
ADVERSE EFFECTS OF NH3, NO3, AND NOx IN
AQUATIC AND TERRESTRIAL ENVIRONMENTS
• In aquatic environments
Mobile aquatic
communities move
Increased N
Algae bloom
in marine
environment
Pfisteria
(Red tides)
Decay of dying
algae reduce
dissolved O2 in
water
Produce toxins
Hypoxic
zone
(Gulf of
Mexico)
Fish kills
Fish lesions
Fish and
shellfish kills
Memory loss,
confusion,
gastrointestinal
problems
(Humans)
• In terrestrial environment
– Increased soil N favors
growth of plants with high N
needs
– Alterations of soil chemistry
• Loss of Ca, Mg and K
• Build up of Al
National Atmospheric Deposition Program 1999 Annual Summary