IMPORTANCE OF NITROGEN IN THE ENVIRONMENT N 2 comprises 80% of the atmosphere –N 2 can not be used by most organisms –N 2 is not a problem until its in a reactive form like NH 3 or NO 3 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 N 2 + O 2 2 NO 2NO + O 2 2 N O 2 2 N O 2 + H 2 O HNO 3 + HNO 2 HNO 3 H + + NO 3 - (Nitrate; Readily used by plants) –Biological N fixation Microorganisms Nitrogenase N e - + 8H + 2NH 3 (Ammonia)+ H 2 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 N 2 to NH 3 –Plants take up NH 3 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 NH 3 for their own use.

N fertilizer Produced by the Haber- Bosch process Developed in 1913 Process High pressure High temperature N 2 + 3H 2 NH 3 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-NH 2 NH 3 + R –Done by both aerobic and anerobic bacteria –Increased by: Increased soil OM-N pool Increased soil temperatures Soil pH > 7 High soil moisture –NH 3 rapidly converted to NH 4 + at pH < 7.5 NH 4 + is relatively stable N is digested by animals is excreted as urea (mammals) or uric acid (poultry)

O Urease H 2 N – C – NH 2 2NH 3 + CO 2 Urea O H C N 5 steps w/ H N C Urease C O 4NH 3 + 5CO 2 O C C N N H H Uric acid

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 NH 4 + Ammonium cations may leach into ground water as precipitation infiltrates soils –Soils that are high in clay or organic matter can bind NH 4 + which can only be lost with erosion

Nitrification –Highest proportion of NH 4 + is converted to NO 3 by aerobic bacteria Nitrosomas Nitrobacter O 2 4H O 2 NH 4 NO 2 NO 3 –Rapid under conditions of: 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 NH 4 is converted to NO 3

Volatilization –NH 4 + is not volatile –In soils with high pH (> 7.0), NH 4 + is converted to NH 3 which can volatize into the atmosphere as a gas –NH 3 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 NH 3 volatilized 20 to 70% of the N in manure Ammonia losses from animal agriculture represents 75% of all NH 3 emitted in the U.S. –Rate of NH 3 volatilization is increased by: Soil pH > 7.0 Soil temperatures > 50 F Greater air movement

FATE OF NO 3 PRODUCED DURING NITRIFICATION Use by plants Leaching into groundwater –NO 3 is highly soluble in water and does not bind to soil particles –During periods of excessive precipitation, NO 3 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 NO 3 may be transported to surface waters via tile drainage –Factors that lead to increased leaching in spring Build up on NH 4 + in soil during winter Increased NO 3 in soil as nitrification increases with increased soil temperatures Low utilization of NO 3 by immature plants High soil moisture

Denitrification –Conversion of NO 3 to N 2 in anerobic conditions in soil or manure storage areas –Process C 6 H 12 O NO 3 6CO 2 + 6H 2 O + 2N 2 + NOx NOx = NO, NO 2 or N 2 O –N 2 and NOx are gases released into the environment N 2 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 (NO 3 ) 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: O 2 Hemoglobin in Oxygenated hemoglobin red blood cells Peripheral tissue (Uses O 2 ) Nitrate toxicity: Gut bacteria NO 3 NO 2 O 2 Hemoglobin in Methemoglobin red blood cells Peripheral tissue –Hazardous level: 10 ppm in water

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 Concentration Dilution Neighboring residence < 150 ppb 1:7 Property line < 70 ppb 1:15 –Toxicity in aquatic environments (Manure spills) Most natural water sources –NH 4 -N at 2 ppm is toxic to fish In alkaline waters at high temperatures –NH 4 -N at 0.1 ppm is toxic to fish –Particulate matter less than 2.5 um (PM 2.5 ) Formed when atmospheric NH 3 reacts with SO 2, NOx, and volatile organic compounds (VOCs) –Produce (NH 4 ) 2 SO 4, NH 4 NO 3, and NH 4 HSO 4 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 PM 2.5 –Agriculture –Burning fossil fuels Hazards of PM 2.5 –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 PM 2.5 –Annual average – 15 ug/m 3 –24 hr standard – 65 ug/m 3 –Monitored at 1100 sites across the US

–Acidify soil Process –During nitrification, H + are released that lower pH of soil »NH 4 NO 3 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 PM 2.5 ; NO 2 –Acid rain; NO 2 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; NO 2 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; N 2 O In upper atmosphere, N 2 O triggers reactions that deplete the stratospheric ozone layer which protects the earth from ultraviolet radiation –Human skin cancer –Damages plant foliage –Greenhouse gas; N 2 O N 2 O has 310 x the greenhouse gas effect of CO 2 Contributes to global warming

ADVERSE EFFECTS OF NH 3, NO 3, AND NOx IN AQUATIC AND TERRESTRIAL ENVIRONMENTS In aquatic environments Mobile aquatic Hypoxic communities move zone (Gulf of Increased N Algae bloom Decay of dying Mexico) in marine algae reduce environment dissolved O 2 in Fish kills water Pfisteria Produce toxins Fish lesions (Red tides) Fish and shellfish kills Memory loss, confusion, gastro- intestinal 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