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N2N2. Cosmic abundance of the elements Mass number.

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Presentation on theme: "N2N2. Cosmic abundance of the elements Mass number."— Presentation transcript:

1 N2N2

2 Cosmic abundance of the elements Mass number

3 14.0 N -3,0,3,5

4 Nitrogen species nitrateNO 3 – N +V stable oxide of N, highly soluble as an anion nitriteNO 2 – N +III intermediate between NO 3 – and NH 4 + nitrous oxideN 2 O N +I from lightning and internal combustion engines nitrogen N 2 N 0 elemental nitrogen gas hydroxylamineNH 2 OH N –I intermediate species during oxidation of NH 4 + ammonia NH 3 N –III un-ionized ammonia gas ammonium NH 4 + N –III ionized ammonia (dominates below pH 9.23) ureaCO(NH 2 ) 2 N –III common fertilizer amino NR–NH 2 N –III organic nitrogen as amine, measured as TKN

5 Nitrogen redox

6 C 106 H 263 O 110 N 16 P(S) Elemental composition of algae Protein Essential nutrient

7 Fixing nitrogen for photosynthesis C 106 H 263 O 110 N 16 P(S) :NN::NN:

8 Natural N 2 fixation by Rhizobia and the nitrogenase enzyme (Fe and Fe-Mo proteins) N 2 + 8H + + 8e − + 16ATP → 2NH 3 + H ADP + 16 P adenosine triphosphate (ATP) adenosine diphosphate (ATP)

9 And organic N scavenged from biodegradation R–NH 2 + 2H +  NH 3 NH 3 + O 2  NO 3 – It’s all about getting NH 3 and NO 3 –.

10 NH 3 Human intervention into the nitrogen cycle

11 Urea from animal waste, urine CO(NH 2 ) 2 + H 2 O  2NH 3 + CO 2

12 Guano from Chile and the Pacific islands

13 NO 3 –

14 Nitroglycerine 4 C 3 H 5 (ONO 2 ) 3  12 CO 2 (g) + 10 H 2 O(g) + 6 N 2 (g) + O 2 (g)

15 Saltpetre KNO 3 from India

16 Haber-Bosch, ½N 2 (g) + 3 / 2 H 2 (g) ⇌ 2NH 3 (g) CH 4 (g) + 2H 2 O(g) → CO 2 (g) + 4H 2 (g) N 2 and H 2 are reacted over a ferric iron catalyst with Al 2 O 3 & K 2 O at 250 atm and °C. ΔG = –16.5 kJ/mol

17 Essential nitrogen reactions Degradation of organic N:–NH 2 + H +  NH 3 Organically-bound nitrogen is a component of all proteins and plant biomass. Aerobic and anaerobic degradation of such carbon compounds releases this reduced nitrogen in the form of ammonia. Where this occurs in unsaturated materials such as soils or manure, the ammonia can volatilize, or dissolve into water.

18 Essential nitrogen reactions Degradation of organic N:–NH 2 + H +  NH 3 Organically-bound nitrogen is a component of all proteins and plant biomass. Aerobic and anaerobic degradation of such carbon compounds releases this reduced nitrogen in the form of ammonia. Where this occurs in unsaturated materials such as soils or manure, the ammonia can volatilize, or dissolve into water. Decomposition of urea:CO(NH 2 ) 2 + H 2 O  2NH 3 + CO 2 Urea is a common form of organic nitrogen that is produced naturally in animals and industrially. It is often applied as fertilizer in granulated form, and breaks down by a bacterially mediated reaction (urease enzyme) to release ammonia for plants.

19 Ionization of ammonia: NH 3 + H +  NH 4 + K T = 10 –9.23 high solubility of ammonia in water at neutral pH at high pH NH 3 represents a large fraction of the total ammonia NH 3 = NH 4 + at pH Ammonia transformations

20 Ionization of ammonia: NH 3 + H +  NH 4 + K T = 10 –9.23 high solubility of ammonia in water at neutral pH at high pH NH 3 represents a large fraction of the total ammonia NH 3 = NH 4 + at pH Volatilization of ammonia:NH 3(aq)  NH 3(g) K H = high Henry’s Law constant for ammonia un-ionized NH 3 = 246 mg/L at 25˚C for a NH 3 partial pressure of one atmosphere volatilization from manure, soils and surface waters loss from groundwater below the water table is minimal Ammonia transformations

21 Ionization of ammonia: NH 3 + H +  NH 4 + K T = 10 –9.23 high solubility of ammonia in water at neutral pH at high pH NH 3 represents a large fraction of the total ammonia NH 3 = NH 4 + at pH Volatilization of ammonia:NH 3(aq)  NH 3(g) K H = high Henry’s Law constant for ammonia un-ionized NH 3 = 246 mg/L at 25˚C for a NH 3 partial pressure of one atmosphere volatilization from manure, soils and surface waters loss from groundwater below the water table is minimal Sorption of ammonium:Na–clay + NH 4 +  NH 4 –clay + Na + cation exchange of ammonium onto clay minerals in soils and aquifers erosion of NH 4 -bearing soils is a major sources of contamination in surface waters selectivity coefficient for ammonium varies with the clays and competing cations transport of NH 4 + in groundwater is retarded. Ammonia transformations

22 Aerobic nitrification of ammonium:NH O 2  NO 3 – + H 2 O + 2H +  G° r = –266.5 kJ/mol NH 4 + can be oxidized to NO 3 – by reaction with elemental oxygen (O 2 ) significant energy yield is favorable for bacteria two step reaction of oxidation to nitrite by a Nitrosomonas, Nitrobacter and Nitrosospira, and oxidation of nitrite to nitrate by Nitrobacter Pseudomonas. reaction is restricted to aerobic environments – manure piles, soils and surface waters. Ammonia oxidation

23 Aerobic nitrification of ammonium:NH O 2  NO 3 – + H 2 O + 2H +  G° r = –266.5 kJ/mol NH 4 + can be oxidized to NO 3 – by reaction with elemental oxygen (O 2 ) significant energy yield is favorable for bacteria two step reaction of oxidation to nitrite by a Nitrosomonas, Nitrobacter and Nitrosospira, and oxidation of nitrite to nitrate by Nitrobacter Pseudomonas. reaction is restricted to aerobic environments – manure piles, soils and surface waters. Anaerobic nitrification of ammonium – anammox: 3 NO3– + 5 NH4+ ® 4 N2 + 9 H2O + 2H+  G°r = – kJ/mol-NH 4 + = – kJ mol-NO 3 – Recently discovered (1995) less well-known reaction thermodynamically very favorable for bacteria anaerobic environments with both ammonium and nitrate species are present, such as in waste-water streams, anoxic marine waters and soils. NH 4 + as an electron donor, with NO 3 –, and NO 2 –, as an electron acceptors, producing N 2. only known biologically-mediated reaction for conversion of NH 4 + to N 2. Ammonia oxidation

24 Denitrification:5CH 2 O + 4NO 3 – + 4H +  2N 2 + 5CO 2 + 7H 2 O  G° r = – kJ/mol anaerobic reaction - O 2 – free conditions required low-pe electron donor such as carbon or sulphide nitrate is an electron acceptor with nearly the same energy yield as O 2 Pseudomonas denitrificans reduces NO 3 – to N2 using fixed carbon (biomass) Denitrification can also be mediated by chemotrophs such as Thiobacillus denitrificans, which uses sulfide (H 2 S or pyrite) as a substrate. N 2 from denitrification becomes overpressured in water as dissolved nitrogen gas anaerobic waters with low nitrate concentrations (NO 3 – limited), denitrification to N 2 gas may not be complete, resulting in the production of N 2 O gas. Nitrate reduction back to N 2

25 Nitrate Cycle

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27 UREA HYDROLISIS AND VOLATILIZATION OF AMMONIA NH 3 (gas)  CO (NH 2 )  NH 3  NH 4 +  NO NH NH 4 + (aq)  14 NH 3 (gas) + 15 NH 4 + (aq) Isotope fractionation factor = 1.034

28  15 N NO3-N2 ~ 15 to 20 permil  18 O NO3-H2O ~ 8 permil

29 Isotope Data in Nitrate of Different Origins

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32 Groundwater flow system Ref: Wassenaar, L Applied Geochem. 10:

33 Nitrate distribution in mg/L as NO 3 -

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40 Septic system plume based on Na concentration From Aravena, R., Evans, M.L., and Cherry, J.A Ground Water, 31:

41 Nitrate Concentration in mg/L as NO 3 -

42  15 N data (‰) in Nitrate

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46 Nitrate distribution in mg/L as N Ref:Aravena, R and Robertson, W Ground Water, 36:

47 Oxygen (o) and DOC (  ) concentration profiles

48  15 N (o) and nitrate (  ) concentration profiles

49 Isotope enrichment trend showing denitrification

50 Chemical and Isotope Depth Profiles

51 WHY RIPARIAN ZONES ARE IMPORTANT Nitrate is a major groundwater pollutant in agricultural landscapes Riparian zones act as a buffer zones to attenuate nitrate associated to contaminated groundwater discharging in rivers and lakes

52 Conceptual Groundwater Flow Regimes in Riparian Zones

53 Geological Cross Section of Study Area

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57 Ref: Cey E.E., Rudolph, D.L., Aravena, R., and Parkin, G et al., Journal of Contaminant Hydrology, 37:

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59 Buffer strip Stream

60 Manure Spreading

61 Instrumentation transect perpendicular to the stream

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70 Nitrate vs  15 N Data  15 N vs  18 O data Nitrate vs DOC


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