Conversion of organic nitrogen into N 2 in the oceans: where does it happen? and how? Yuan-Hui...
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- Conversion of organic nitrogen into N 2 in the oceans: where
does it happen? and how? Yuan-Hui (Telu) Li Department of
Oceanography University of Hawaii at Manoa
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- Outline 1. Nitrogen cycle in the oceans: 2. Three end-member
mixing model and the aerobic partial nitrification hypothesis. 3.
Nitrate deficits by the aerobic partial nitrification and the
anoxic denitrification. 4. Conclusions 5. Acknowledgement
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- Air
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- 1. Nutrient cycle in the ocean: Redfield Ratios and
Nitrification by nitrifying bacteria [oxic]: 138 O 2 + (CH 2 O) 106
(NH 3 ) 16 (H 3 PO 4 ) H 2 PO 4 + 16 NO 3 + 106 CO 2 + 17 H + + 122
H 2 O P\ N\ C org \- O 2 = 1\16\106\138 or r p = - O 2 / P = 138 r
n = - O 2 / N = 8.63 r c = - O 2 / C org = 1.30 phytoplankton
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- Denitrification by denitrifying bacteria [anoxic and suboxic]
phytoplankton 94.4 NO 3 - + 93.4 H + + (CH 2 O) 106 (NH 3 ) 16 (H 3
PO 4 ) H 2 PO 4 + 55.2 N 2 + 106 CO 2 + 177.2 H 2 O P\- N\ C org \
N 2 = 1\94.4\106\55.2 Anaerobic ammonia oxidation (anammox) by
anammox bacteria: NH 4 + + NO 2 - N 2 + 2 H 2 O
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- 2. Three end member mixing model (Li and Peng, 2002) 1 = f 1 +
f 2 + f 3 (1) = f 1 1 + f 2 2 + f 3 3 (2) S = f 1 S 1 + f 2 S 2 + f
3 S 3 (3) O 2 + r n NO 3 = (NO) = f 1 (NO) 1 + f 2 (NO) 2 +f 3 (NO)
3 (4) O 2 = 0 + 1 + 2 S - r n NO 3 (4a) where, r n = - O 2 / NO 3
Similarly O 2 = A 0 + A 1 + A 2 S r p PO 4 (5a) where, r p = - O 2
/ PO 4 Also: DA = 0 + 1 + 2 S + 3 O 2 (6a) where, r c = 1/( 3 0.5/r
n ); r c = - O 2 / C org DA = (DIC Alk/2)
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- 2a. Aerobic Partial nitrification hypothesis: Unidentified
bacteria have evolved in a low oxygen (but oxic) and high nitrate
environment (such as in oxycline, marine snow and fecal pellets,
sediments) to utilize both oxygen and nitrate as terminal electron
acceptors during oxidation of organic matter, and convert some
organic nitrogen into N 2, N 2 O, and NO.
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- 3. Nitrate deficit by partial nitrification (dN) and
denitrification (dN) N a = 16(P - 0.16) N b = -3.223 + 16.772 P +
0.574 P 2 - 0.465 P 3 When N b N N a dN = N a - N ; When N < N b
dN = N a - N b dN = N b - N ; N* by Deutsch et al (2001): N* = (N -
N a ) N a = 16(P - 0.181) -N* dN + dN
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- i7n ( mol/kg)
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- Additional support for the aerobic partial nitrification
hypothesis: 1. Schmidt et al (2004) showed that a wild-type of
Nitrosomonas europaea in chemostat cell cultures can produce
nitrogen gases (N 2, NO, and N 2 O) during aerobic (O 2 ~ 125 M)
oxidation of ammonia, using genes encoding reduction enzymes such
as nitrite reductase, nitric oxide reductase etc. For example, NH 4
+ (ammonia monooxygenase) NH 2 OH (hydroxylamine oxidoreductase) NO
2 (nitrite reductase) NO (nitric oxide reductase) N 2 O (not yet
identified nitrous oxide reductase) N 2. 2. Aerobic and anaerobic
ammonia oxidizing bacteria are coupled in suspended organic
particles in a low-oxygen (O 2 ~ 5 M) CANON reactor (Nielsen et
al., 2005) to produce N 2
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- 3. Codispoti et al. (2001) estimated the excess N 2 in the
water column of the Arabian Sea, using the Ar/N 2 ratio in the
water column and in the air. They found that the excess N 2 is
substantially greater than the N 2 produced by the denitrification
process.
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- Acknowledgement: Ms Lauren Kaupp patiently showed me how to use
the Ocean Data View program, which was provided by Dr. Reiner
Schlitzer. Discussions with Drs. James Cowen, David Karl, Marcel
Kuypers, Fred Mackenzie, Hiroaki Yamagichi and Wajih Naqvi were
most fruitful. Many thanks to Professor Yoshiki Sohrin for kindly
inviting me here. This work is supported by a NOAA grant to Y.H. Li
and T.H. Peng.
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- -dN\O2 =(6 1)\130
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- r p = -O 2 /P; r n = -O 2 /N; r p /r n = N/P
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- Redfield ratios: P\N\C org \-O 2 = 1\16\106\138; (CH 2 O) 106
(NH 3 ) 16 (H 3 PO 4 ) Antarctic Indian Ocean: P\N\C org \-O 2 =
1\(15 1)\(83 2)\(134 9) Deep equatorial Indian Ocean: P\N\C org \-O
2 = 1\(10 1)\(94 5)\(130 7) Average remineralization ratios for the
warm water mass: P\N\C org \-O 2 = 1\(15.6 0.7)\(110 9)\(159 8)
Andersons (1995) remineralization ratios and phytoplankton formula:
P\N\C org \-O 2 = 1\16\106\150; (C 106 H 48 )(H 2 O) 38 (NH 3 ) 16
(H 3 PO 4 )
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- 1. The remineralization ratios (P\N\C org \-O 2 ) of organic
matter in the oxygenated regions of Indian Ocean change
systematically with latitude and depth. 2. The average
remineralization ratios for the Indian warm water masses (potential
temperature ~ 10) are P\N\C org \-O 2 = 1\(15.6 0.7)\(110 9)\(159
8). These are comparable to the traditional Redfield ratios P\N\C
org \-O 2 = 1\16\106\138, and are in good agreement with Andersons
(1995) values of P\N\C org \-O 2 = 1\16\106\150 within the given
uncertainties. 5. Conclusions