Bernhard Wehrli ([email protected]) thanks to Andreas Brand ...
Transcript of Bernhard Wehrli ([email protected]) thanks to Andreas Brand ...
Old and new sinks in the global nitrogen cycle
Bernhard Wehrli ([email protected])
thanks to Andreas Brand, Martin Maerki, Miriam Reinhardt, Cristian Teodoru, Christian Dinkel, Beat Müller, Carsten Schubert, Alfred Wüest
Eawag: Swiss Federal Institute of Aquatic Science and Technology
03/04/2008 2
Gobal nitrogen cycle and aquatic systems
- how fertilizing the planet affects surface waters - cycling of N and changing surface hydrology
– damming the rivers – constructing new wetlands
- processing N via biogeochemical pathways– denitrification in eutrophic, seiche-driven lakes– elimination of reactive N at aquatic redox boundaries
- conclusions
03/04/2008 4
Global trends in reactive nitrogen sources
0
50
100
150
200
250
300
350
1 11 21 31 41 51 61 71 81 91
fossil fuellegume cropsHaber-Boschlightningnatural fixation
modified afterVitousek et al. (1993) and Gruber & GallowayNature, 451, 293 (2008)
1900 10 20 30 40 50 60 70 80 90 2000
Tg N
year
03/04/2008 6
NO3- concentrations increased by a
factor of 2.5 from 1960 to 2000
McIsaac et al.Nature, 414, 166 (2001)
03/04/2008 8
Efficiency of denitrification in river reaches decreases exponentially with [NO3
-]
Mulholland et al.Nature, 452, 202 (2008)
03/04/2008 9
elimination of Nreactiv in freshwater systems
- only 20-25% of the anthropogenic nitrogen is exported to the sea
- 50% of the global terrestrial denitrification occurs in freshwater
- denitrification capacity in rivers is limited by primary production
- factors controlling N elimination processes – residence time,
– productivity,
– supply of O2 and Corg,
– microbial pathways
03/04/2008 10
Old and new N sinks along the aquatic continuum from land to ocean:
45‘000 large dams managed wetlands
anammoxeutrophic lakes
03/04/2008 11
- 800’000 dams and 45’000 large dams > 15 m
- 0.5 Mio. km2 land inundated (> Caspian Sea)- irrigation > 15% of global food production- hydroelectricity ~20% of total
- rate of dam construction 360 to 170 dams yr-1
- investments 30-45 109 US $ yr-1
2 Understanding the effect ofdams, artificial wetlands
03/04/2008 14
Is the Iron Gate I Reservoir on the Lower Danube a nutrient sink ?
Iron Gates in Romania / Serbia
length 200 kmsurface area 156 km2
volume 2.7 km3
residence time 5.5 d
03/04/2008 16
Danube runoff at Irong Gates Reservoir
net sink
net source
Teodoru & Wehrli (2005) Biogeochemistry 76, 539-565
03/04/2008 18
Does damming reduce the global nitrate export to the ocean?
- Iron Gates ≠ strong nutrient sink
- extrapolated denitrification = 3 10-5 cm s-1 translates to about 1% denitrification along 200 km
- methods for large low-land rivers needed!
Fig from: Mulholland et al.Nature, 452, 202 (2008)
03/04/2008 19
Reducing the nitrate load with new wetlands
Volume 700 m3
Surface 720 m2
max. depth 3 mCatchment 110 000 m2
Volume 700 m3
Surface 720 m2
max. depth 3 mCatchment 110 000 m2
03/04/2008 21
Nitrogen dynamics in a pond
constant 15NO3- in spring
shift towards lighter valuesin summer
03/04/2008 23
Isotopic Mass Balance for 15N
Reinhardt, Müller, Gächter, Wehrli (2006) Environ. Sci. Technol. 40, 3313-3319
03/04/2008 24
- Spring: high nitrate load, oxic pond- Denitrification at the sediment → no fractionation−δ15NO3
- → manure
- High flux > 10 mmol m-2 d-1
- Summer: low nitrate, anoxic water column- Nitrification >> denitrification- low δ15NO3
- → biomass-N
- overall efficiency of 27% limited by anoxia
Tracing N turnover in artificial wetland
03/04/2008 25
3
EawagKastanienbaum
L. AlpnachL. LucerneL. Zug
Understanding processesdenitrification & anammox
03/04/2008 27
16 LISA deployments in L. Zug 01/02
N
50 m
80 m
120 m
Maerki, Mueller, Dinkel, Wehrli (2008) L&O (submitted)
03/04/2008 28
High-res. pore water profiles L. Zug
March 2002, 50 m water depth
oxygen top 0.5 mmnitrate top 15 mmammonium top + 30 mm
dept
h (m
m)
100 200 3000
O2
100 200 3000 10 20 300
-3-2-101234
-5
5101520
0
2530
-5
5101520
0
2530
NO3-NH4
+
pore water concentration µM
03/04/2008 29
no oxic respiration below 100 m
O2
0
10
20
30
40
50
0 50 100 150 200
DecMarMay/Jun
Depth (m)
O2 -
flux
(- m
mol
m-2
d-1)
flux
[mm
ol m
-2d-1
]
water depth [m]
27.5 mmol m-2 d-1
03/04/2008 30
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
DecMarMay/Jun
Depth (m)
NO3-
NO
3-flu
x [m
mol
m-2
d-1]
depth [m]
constant nitrate flux to 120 m depth
0.65 mmol m-2 d-1
flux chamber &mass balance1.1 mmol/m2 d
Mengis et al.L&O, 1997
03/04/2008 31
NH4+
0.5
1
1.5
2
2.5
3
3.5
4
0 50 100 150 200
DecMarchMay/June
Depths (m)
NH
4+flu
x [m
mol
N m
-2d-1
]
depth [m]
increasing anaerobic mineralizationwith depth
factor 3
03/04/2008 33
benthic denitrification in L. Zug
- O2, NO3- fluxes → no trend with water depth
- O2 and NO3- fluxes quite variable between
deployments sediment → heterogeneity or benthic boundary layer dynamics?
- analyze diffuse boundary layer dynamics!
03/04/2008 34
Boundary layer physics and the daily life of microbes
How can we work withsuch a thick diffusiveboundary layer?
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
0 2 4 6 8 10
DOO
ODJδ
222
∆−=
Oxygen concentration [ mg/l ]
Hei
ght a
bove
sed
imen
t [ m
m ]
δD∆O2
Sediment
Water
Oxygen flux:
03/04/2008 35
10-11
10-10
10-9
10-8
12:00 16:00 20:00 24:00 04:00 08:00 12:000
5
10
15
20
25
30
35
August 13/14 2002
Cur
rent
spe
ed u
[ m
m/s
] u1m
ε
1 m above the sediment
Dissipation rate ε [ W
/kg ]Energy dissipation and current velocities
Lake Alpnach velo
city
[mm
/s]
1m a
bove
sed
imen
t
Dis
sipa
tion
[Wkg
]
03/04/2008 36
10-11
10-10
10-9
10-8
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
12:00 16:00 20:00 24:00 04:00 08:00 12:000
5
10
15
20
25
30
35
August 13/14 2002
Cur
rent
spe
ed u
[ m
m/s
] u1m
ε δDBL
Dissipation rate ε [ W
/kg ]
DBL thickness δ
DBL [ m
m ]
DB
L Th
ickn
ess
[mm
]
Lorke et al. (2003) L&O 48, 2077
Currents control boundary layer dynamics
Lake Alpnach
03/04/2008 42
Anaerobic ammonium oxidation byanammox bacteria in the Black Sea
Kuypers et al. (2003) Nature, 422, 608-611
03/04/2008 43
Significance for Black Sea biogeochemistry
- 0.17 mmol NO3- m-2 d-1 mixed downwards
- 0.12 mmol NH4+ m-2 d-1 transported upwards
- up to 0.4 Tg reactive N could be lost via anammox.
- where else?
Teodoru, Friedl, Friedrich, Roehl, Sturm, Wehrli (2007) Marine Chem. 105, 52-59
03/04/2008 44
Anammox in Lake Tanganyika
Schubert, Durisch-Kaiser, Wehrli, Thamdrup, Lam, Kuypers (2006) Env. Microbiol.doi:10.1111/j.1462-2920.2006.001074.x
03/04/2008 45
Conclusions
large lowland rivers are inefficient N sinks
enormous denitrification potential of oxic wetlands
anammox is a key process at redox boundaries in marine and freshwater systems
eutrophication activates denitrification regardless of DBL dimension
mass balance15N
sensors
molecularmicrobiology
03/04/2008 47
Carbon burial in L. Zug
Meckler et al. L&O, 2004: Higher TOC in anoxic zone butno difference in indicators for decomposition, DI, CI