1. 하구및 연안생태Coastal management
2015 년 가을학기

2. N2 fixation
Conversion of N2 gas into inorganic N (fixed N, reactive N)
Natural microbial processes
by 20th century, human production of reactive nitrogen via N2 fixation exceeded natural production rates.
~ 40% of the world’s population is fed by crops sustained by the anthropogenic formation of reactive nitrogen.
reactive nitrogen is now accumulating in the atmosphere and hydrosphere with deleterious consequences including eutrophication, hypoxia, harmful algal blooms, smog, acid rain, and loss of stratospheric ozone, all of which lead to habitat degradation and loss of species diversity.

3. Nitrogen fixation N-cycling; complex Fixation: structural synthesis
Energy reaction: use NH4 for fuel : electron doner
Oxidizing agent: use NO3 for electron acceptor
N2: 78 % of air
N-fixation N2 ammonium : by bacteria and blue-green algea
Require large energy: 147 kcal/mole
No O2 condition for nitrogenase : heterocysts of blue-green algae
Trichodesmium: don’t have heterocysts; separate O2 from nitrogenase

4. Recent developments of N cycle
in couple of decades !!!

5. Nitrogen fixation Measurement
Acetylene reduction technique: substitute substrate or nitrogenase; acetylene  ethylene
15N-labelled N2
MIMS (An, 2001)
Lake, freshwater : 30~80 % from N-fixation
Natural N-fixation was enhanced by P addition to lake
Inhibited by high NH4 condition
N-fixation is relatively unimportant in estuaries
Tropical seagrass bed: Epiphytic blue-green and sediments
Why? Not known well: high NH4? : high sulfate inhibit molybdenum (chemically similar) accumulation for nitrogenase synthesis

6. Nitrification and denitrification
NH4 NO3; aerobic
Autotrophs; NH4 for energy
1st step: nitrosomonas: 66 kcal /m
2nd step: nitrobactor: 17.5 kcal /m ; slower
O2 availability is important ; 2
Ks for Nh4 : 25~750 uM; typical 150 uM
Measurement :
increase of NH4 or decrease of NO3 or CO2 in the presence of N-serve
Increase of 15NO3 after 15NH4 addition
NH4 < 5 uM inhibit nitrification
Typical sediments: 50 ug atom m-2h-1; NH4 production is about 100ug atom m-2h-1
High in seagrass bed due to O2 production via root
Two seasonal pattern; high in winter and fall; O2 availability

7. denitrification Use NO3 as electron acceptor to oxidize organic matter
Numerous bacteria; Pseudomonas denitrificans
Facultative anaerobes
N2O production: important for green house gas, break down of ozone
Measurements
N2 production rates
N2O production in the presence of acetyene

8. Global denitrification budget

9. Denitrification measurement techniques
NO3 NO2 N2O N2
Acetylene inhibition technique (Sorensen 1978)
15NO3 dilution technique (Hattori and Koike 1978)
N2 flux after purging (Seitzinger et al. 1980)
Anoxic control (Nowicki 1989)
Direct N2 flux (Devol 1991)
Isotope pairing technique (Nielsen 1992)
N2/Ar using Membrane Inlet Mass Spectrometer
(Kana et al. 1994)
Direct N2 flux (Lamontagne and Valiela 1995)
Ar as an internal standard (An and Joye 1997)

10. Isotope pairing technique
14NO3
15NO3
28N2
29N2
30N2 p q p2
2pq q2
DNF

11. Simultaneous measurement of DNF and NFp2
DNF NF
28N2 p
14NO3
2pq
Organic-N
29N2
15NO3 q2 q
30N2

12. MIMS for labeled N species measurements

13. denitrification NO3 limits denitrification Ks for NO3: 10~50 uM
NO3 sources
Land runoff + nitrification in the water ; large flux into the sediment can be observed
Nitrification in oxic sediments 
move to RDL or
anoxic micro sites
50~100 ug-atom m-2h-1
10 fold OM loading  5 fold denitrification increase
Explains low N/P ratio

14. Major nitrogen-cycle in water column
Open ocean
Oxygen minimum zones
Zehr and Kudela, 2011

15. Major nitrogen-cycle in water column
Major N loss
Expansion of OMZs
Denitrification with N2 fixation
Open ocean
Oxygen minimum zones
Zehr and Kudela, 2011

16. Intensive N loss in OMZs
Oxygen minimum zones (OMZs)
20-40% of Oceanic N loss
Arabian Sea, eastern tropical North and South Pacific,
Paulmier and Ruiz-Pino 2009

17. Synthesis
P: weathering of soil and rock, run off, point source discharge
DIP:
POP
DOP
Remineralization of P occurs in sediments
Redox condition is important: complexing reaction wit metals
Formation of apatite: skeletons
Clay particle; first order kinetics provide buffer action; maintain moderate level of P

18. Synthesis
Dissolved form: silicic acid.