하구및 연안생태Coastal management 2015 년 가을학기

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.

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

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

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

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

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

Global denitrification budget

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)

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

Simultaneous measurement of DNF and NF p2 DNF NF 28N2 p 14NO3 2pq Organic-N 29N2 15NO3 q2 q 30N2

MIMS for labeled N species measurements

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

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

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

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

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

Synthesis Dissolved form: silicic acid.