Nitrogen CycleEssential for the growth of plants and animalsSteps:Nitrogen fixation: Reduction of N2 into biologically available form (NH4+ ). It is high energy process. Nitrification: Oxidation of NH4+ into further oxidation states. Denitrification: Reduction of NH4+ and NO3 back into N2. Occur under anaerobic conditions and mostly in soilAmmonification: Conversion of organic nitrogen into NH4+ when plant or animal die. Done by saprotrophs

Disruption of cycleSynthesis of fertilizersFossil fuel burningMunicipal wasteForest fires

FertilizersFertilizers- Haber bach processNitrogenous fertilizers given as ammonium salts, anhydrous or liquid ammonia, nitrate or ureaNitrification- NH4+ (Ammonium) ions are converted to NO3_ (Nitrate) ions by nitrifying bacteria, with H+ ions as byproduct. Thus leading to soil acidificationHeavy metals such as lead zinc and cadmium easily mobilized in acidic soilAcidification of soil results from Inorganic nitrogen fertilizers and acid deposition resulting from urban and industrial pollution.

Nitrate is highly soluble, easily percolate to groundwater.Percolation depend upon the rock type. Slow in limestone and fast in chalk and triassic standstonesNO3- can be leach from the soil, along with positively charged alkaline minerals such as calcium and magnesiumHigh concentration of nitrate causes- methaemoglobina in young children and formation of carcinogenic nitrosamines in the human gutsFertilizers should be applied in appropriate quantity. Use of foliar fertilizers potentially ensures that the nitrogen reaches the plant rather than the microorganisms of the soil.

Possible fates of excess fertilizer nitrogenSource: Janet I. Sprent, The Ecology of the Nitrogen Cycle, Cambridge University Press, New Year, 1988

Form of NitrogenPossible FateNitrate Leaching into groundwater in wet areas. Conversion to N2O/ N2 and loss to atmosphere. Occasionally bound to soilAmmonium /AmmoniaOften complexed with cation-binding sites in soil. May be volatilized and lost to atmosphere especially at high pHUreaUsually rapidly hydrolyzed in soil then subject to same fates as ammonium/ammonia

Eutrophication

Eutrophication arises from the oversupply of nutrients, which induces explosive growth of plants and algae which, when such organisms die, consume the oxygen in the body of water, thereby creating the state of hypoxia.Increase in BODAlong with runoff from agriculture, waste from municiplaities, and other human-related activities increase the flow of both inorganic nutrients and organic substances into ecosystems.Estuariestend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters a confined channel.

Fossil fuel burningNOx enter the atmosphere from anthropogenic sources i.e. combustion of fossil fuels in both stationary and mobile sources. Nitrous oxide is green house gas, leads to global warmingConc. of Nitrous Oxide grew about two times faster from 1960 to 1999 than over any 40 year period of two millennia before 1800 and have continued to grow at the same rate to a 2011 concentration of 324 ppb

Atmospheric concentrations of nitrous oxide over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red lines).

Source: IPCC Fourth Assessment Report: Climate Change 2007

Photochemical smog

Complex mixture of products formed from the interaction of sunlight with major components of automobile exhaust, nitric oxide and hydrocarbons. Harmful effects:Harmful to humans, animals, plants and the nature as a wholeIrritation in the eyeInflammation in the tissues of lungs; giving rise to pain in the chestOther issues or illnesses such as cold and pneumonia are also related to smog

Acid rainAcid rain consists 70 sulphur dioxide and 30 nitrogen compounds giving rise to sulphuric and nitric acids respectivelyAcid rain causes Acidification of lakes and streams Damage of trees at high elevations and sensitive forest soilsAccelerates the decay of building materials and paints, statues, and sculptures

Forest FiresWith high-intensity wildfire, both organic and inorganic nitrogen in the vegetation and the forest floor material is released, both to the atmosphere and in the form of oxidized mineral to the soil.

Waste slurries:Organic nitrogen and ammonium can find their way from animal slurries and municipal waste into rivers and other waterwaysSheep manure is high in nitrogen and potash, while pig manure is relatively low in both.

ReferencesBernhard, A. (2010) the nitrogen cycle: processes, players and human impact. Nature education knowledge 3 (10).25E. P. Odum, G.W. Barrett; Fundamentals of Ecology, 5e, 2005, p(143-149)Janet I. Sprent, The Ecology of the Nitrogen Cycle, Cambridge University Press, New Year, 1988http://www.conserve-energy-future.com/SmogPollution.php#sthash.oRG36ETQ.dpuf