SEASONAL CHANGES IN BENTHIC FLUXES AND NET ECOSYSTEM METABOLISM IN THE RIA DE VIGO (NW SPAIN)

F. Alonso-Pérez, Carmen G. Castro, Zuñiga, D., B. Arbones y F.G. Figueiras

Instituto de Investigaciones Marinas (CSIC, Vigo)

Rías Baixas at the northern boundary of

the Canary Current upwelling system

Seasonal variation:

Upwelling: April to September

Downwelling: October to March

Ex(103 m3 s-1 Km-1)

-0.6-0.30.00.30.6

ME

S

A

M

F

E

D

N

O

SA

J

J

M

MO

NTH

Upwelling index (1987-2004)

Courtesy of RMS from PML

AVHRR Sea Surface TemperatureAugust 1998

UPWELLING

BACKGROUND

Fate of this high primary production?

NCP 0.84

Respiration0.56

Respiration?

Carbon flux0.18

aphoti

c zo

ne

photi

c zo

ne

sedimentRespiration

?

2-D non stationary box model for the Ria based on temporal variability of nutrient distributions

Units: gC m-2d-1

(Rosón et al. 1999)

BACKGROUND

To study the fate of fixed carbon on a seasonal scale

based on direct measurements of gross primary

production, pelagic and benthic respiration and vertical

export of organic matter in the Ria de Vigo.

OBJECTIVE

RIA DE VIGO: SAMPLING STATION

8 . 9 8 . 8 8 . 7 8 . 6

L o n g i t u d e ( W )

4 2 . 1 5

4 2 . 2 0

4 2 . 2 5

4 2 . 3 0

4 2 . 3 5La

titud

e (

N)

4 0 m 2 0 m1 0 m

V i g o

Reference Site

20 m depthmain ria channel

2 weeks campaign in April-04, July-04, October-04 and January-05.

METHODS

Seawater samples for nutrients and size-fractionated chlorophyll (0.2, 2 & 20 m) (5 depths)

Net Community Production (NCP) and Dark Community Respiration (DCR) by in situ 24 h light-dark bottle oxygen incubations (5 depths).

NCP = O2 (24h)light – O2 (t0)

DCR = O2 (t0) - O2 (24h)dark

Gross Primary Production:

GPP = NCP + DCR

Biogenic particle vertical fluxes by in situ 24 h deployment of a sediment trap

METHODS

Photos: Manuel E. Garci

External frame

Chamber

12 V Motor

Syringe water

sampler

Jet inflow

Outflow - Slotted tube

Lid

SEDIMENT

Rim

Water pump

80 cm

28 c

m

Sensor

Ele

ctro

nics

Chamber

Rim

Lead

Methacrylate base

Reed contact

LAND VERIFICATION ASSEMBLY

SEDIMENT8

cm

80 c

m

65 c

m

20 cm

Home made benthic chamberMeasuring oxygen and nutrient benthic fluxes

Cylindrical chape and incubating volume ~ 140 LStirring by 3 centrifugal pumps

Water samples at prefixed times by syringe sampler (50 mL)

Continuous recording of T, pH, turbidity and oxygen

METHODS

Ferrón et al, 2008

January

14 16 18 20 22 24 26 28

October

4 6 8 10 12 14 16 18

July

4 6 8 10 12 14 16

Upw

elli

ng

In

dex

April

17 19 21 23 25 27 29

-Qx

-4000

-2000

0

2000

4000

Up

wellin

g I

nd

ex

(m3/(

s k

m)

Tem

pera

ture

(ºC

)N

itr a

te(µ

M)

Ch

la(m

g/m

3)

APRIL JULY JANUARYOCTOBER

2004

19- apr 22- apr 26- apr 29- apr20

15

10

5

0

Dep

th (m

)

19- apr 22- apr 26- apr 29- apr20

15

10

5

0

Dep

th (m

)

19- apr 22- apr 26- apr 29- apr20

15

10

5

0

Dep

th (m

)

20046- j ul 8- j ul 12- j ul 15- j ul

20

15

10

5

0

6- j ul 8- j ul 12- j ul 15- j ul20

15

10

5

0

6- j ul 8- j ul 12- j ul 15- j ul20

15

10

5

0

07- oct 11- oct 14- oct 18- oct20

15

10

5

0

07- oct 11- oct 14- oct 18- oct20

15

10

5

0

07- oct 11- oct 14- oct 18- oct20

15

10

5

0

2004

17- j an 20- j an 24- j an 27- j an20

15

10

5

0

17- j an 20- j an 24- j an 27- j an20

15

10

5

0

17- j an 20- j an 24- j an 27- j an20

15

10

5

0

2005

HYDROGRAPHIC CONDITIONS

WATER COLUMN INTEGRATED SIZE-FRACTIONED CHLOROPHYLL-a

Units: mg Chl a m-2

Arbones et al, 2008

SEASONAL AVERAGES VERTICAL CARBON FLUXES

ABR JUL OCT JAN

C m

g m

-2 d

-1D

ata

0

200

400

600

800

1000

1200

1400

1600

1800

2000

ABR JUL OCT JAN

C:

N

0

2

4

6

8

10

12

14

16

ABR JUL OCT JAN

% O

rgC

/Dry

mas

s

0

2

4

6

8

APR JUL OCT JAN

O2

(mm

ol

m-2

d-1

)

-50

-40

-30

-20

-10

0

SEASONAL AVERAGES OF BENTHIC FLUXES

APR JUL OCT JAN

NO

3- (m

mo

l m-2

d-1

)

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

APR JUL OCT JAN

NH

4+ (

mm

ol

m-2

d-1

)

0

1

2

3

4

5

APR JUL OCT JAN

Si(

OH

) 4 (m

mo

l m

-2 d

-1)

0

2

4

6

8

10

SEASONAL AVERAGES OF BENTHIC FLUXES

APR JUL OCT JAN

Alk

co

rr (

mm

ol m

-2 d

-1)

0

10

20

30

APR JUL OCT JAN

Max

Co

x (m

mo

l m

-2 d

-1)

0

10

20

30

40

50

APR JUL OCT JAN

pH

un

its

m-2

d-1

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

APR JUL OCT JAN

Min

Co

x (m

mo

l m

-2 d

-1)

0

10

20

30

40

Using carbonic and boric dissociation constants (Luecker, 2000) TCO2 benthic fluxes =

MaxCoxTCO2 – ½ Alkcorr MinCox

APR JUL OCT JAN

Co

x A

vge

(mm

ol m

-2 d

-1)

0

10

20

30

40

Annual benthic carbon flux : 0.26 g C m-2 d-1 ~ 13 % GPP

NCP 1.00

Respiration1.25

Respiration0.11

Carbon flux0.96

APRIL-04

ap

hoti

c

zon

ep

hoti

c

zon

e

sedimentRespiration

0.30

NCP 4.06

Respiration1.07

Respiration0.32

Carbon flux1.12

JULY-04

sedimentRespiration

0.26

NCP 0.46

Respiration0.60

Respiration0.02

Carbon flux1.05

OCTOBER-04

ap

hoti

c

zon

ep

hoti

c

zon

e

sedimentRespiration

0.28

NCP 0.22

Respiration0.36

Respiration0.01

Carbon flux1.32

JANUARY-05

sedimentRespiration

0.19

44% 79%

43% 38%

56% 21%

56% 62%

5% 6%

2% 1%

27% 14%

23%31%

Su

mm

ary

& C

on

clu

sion

s: 1

D S

EA

SO

NA

L B

UD

GE

TS

Units: g C m-2 d-1