Study of N and C dynamics in aquatic ecosystems

Dr Natacha Brion, Dr Marc Elskens, Dr Steven Bouillon, Dr Frank Dehairs, DrS Emilie Chevalier, DrS Sandra De Galan, DrS Perrine

Mangion, Dr Willy Baeyens

Why ?

• Living organisms = C, N, H, O, P + trace elements

• Life or dead of all organisms depends on the availability and usefulness of C and N holding material.

• Eg: plant: CO2 and NH4 or NO3 and PO4

• Eg: animal: proteins, sugars, lipids

N and C cycles

NH4 PN

DON

N2NO3

DIC POC

DOC

Subdivised by molecule, size, biodegradability, origin etc…

Detritus

Living

autrotrophe

Heterotrophe

SpeciesSizeEtc..

INCREASING COMPLEXITY

Methodological tool I: Study the natural variations of 13C and

15N in various C and N pools• Considered pools:

– Dissolved inorganic (DIN-DIC)– Dissolved organic (DOC-DON)– Particulate organic (SPOM, living organisms)– Particulate inorganic (carbonates)

• Allows to highlight:– Origin of material– Major transformation pathways– Foodweb chain pathways (who eats who)

• Type of information: – qualitative – quantitative when combined with a modelling approach

Methodological tool II: Perform incubation experiments with

enriched 15N or 13C tracers• Tracers : dissolved inorganic or organic N and C• Incubation: one tracer is added per incubation

bottle or a combination of one N and one C tracer in one bottle

• After incubation: measure the 15N and/or 13C in different N and C pools– DIN – DIC pools– DON – DOC pools– PON – POC pools

• Use an isotopic mass balance model to compute transformation rates

• Type of transformation rates that can be measured:

NH4 PN

DON

N2NO3

DIC POC

DOC

Study of N and C cycle in Northern Tanganyika Lake

Rainy season: Nitrite + Nitrate (µM)

0

20

40

60

80

100

120

0 2 4 6 8 10

de

pth

(m

)

Relative role of macrophytes, phytoplankton and sediments in the uptake and release of

inorganic nitrogen in a small river

23-23015-180

3-40

0.1-

0.2

0-2

N-NH4 kg N / day

N cycling in the Southern Bight of the North Sea

1.00 2.00 3.00 4.00

51.00

52.00

February 2004

1.00 2.00 3.00 4.00

51.00

52.00

M ay 2004

51.00

52.00

0

7

14

21

28

35

O ctober 2004

Nitr

ate

+ N

itrite

µM

N cycling in the Scheldt estuary

0

10

20

30

40

50

60

70

80

Nov-01

Dec-01

Dec-01

Jan-02

Mar-02

Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02

Sep-02

Oct-02

Nov-02

Dec-02

d15

NH

4+ (‰

)

TN/day

N dynamics in the Zenne river in Brussels

Z2 (km 0)

Z4 (km 4.0) Brussels-South WWTP

Paruck sewerMolenbeek sewer

Marly sewerHoofdmoerriool sewer

Haren sewer Woluwe sewer

Z5 (km 13.7)

Z6 (km 17.9)

Z8 (km 19.6)

IN

OUT

SEDWAT

WASTE

1

1

1410

4

The fate of mangrove carbon and nitrogen in different mangrove ecosystems

Studied by looking at natural variations of 15N and 13C in different compartments of the ecosystem

• And…

• N and C cyling oin Southern Ocean

• N and C cycling in Pacific Ocean

• N and C cycling in Atlantic Ocean

• …. And many others