Temperature, productivity and sediment characteristics as drivers of seasonal and spatial variations of dissolved methane in the near-shore coastal areas (Belgian coastal zone, North Sea)

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Methane in the Belgian coastal zone (North Sea)

Alberto V. Borges Gaëlle Speeckaert Willy Champenois Mary I. Scranton Nathalie Gypens www.co2.ulg.ac.be

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July 2010

Methane in the Belgian coastal zone (July 2010)

Open Ocean: <4 nmol L

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Coastal Ocean: <100 nmol L

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- Shallow (<30 m) - Highly productive - Permanently mixed B o tt o m C H4 ( n m o l L -1 ) 7 9 11 13 15 17 19 21 7 9 11 13 15 17 19 Surface temperature (°C) 1:1

- Influenced by the Scheldt river

- Study of small scale variability 60 km 120 215 ZG02 330 230 130 780 710 700

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In s h o re In c re a s e o f C H 4 Westward Increase of CH₄ 120 215 ZG02 330 230 130 710 700

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MAX

CH₄ inputs from Scheldt ?

120 215 ZG02 330 230 130 710 700

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CH₄ inputs from Scheldt ? 0 20 40 60 80 100 120 140 160

C

H

4

(

n

m

o

l

L

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)

120 215 ZG02 330 230 130 710 700 WS1

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C

H

4

(

n

m

o

l

L

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)

120 215 ZG02 330 230 130 710 700 WS1

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C

H

4

(

n

m

o

l

L

-1

)

120 215 ZG02 330 230 130 710 700 WS1

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C

H

4

(

n

m

o

l

L

-1

)

120 215 ZG02 330 230 130 710 700 WS1

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C

H

4

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n

m

o

l

L

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Fsed = 103 µmol m-2 _d-1 120 215 ZG02 330 230 130 710 700 WS1

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Drivers of spatial variability of CH₄?

C

H

4

(

n

m

o

l

L

-1

)

120 215 ZG02 330 230 130 780 710 700

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C

H

4

(

n

m

o

l

L

-1

)

120 215 ZG02 330 230 130 780 710 700

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C

H

4

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n

m

o

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L

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Inputs from

gassy sediments

Enhancement benthic methanogenesis with

organic matter availability

120 215 ZG02 330 230 130 780 710 700

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Drivers of spatial variability of CH₄? Inputs from gassy sediments 120 215 ZG02 330 230 130 780 710 700

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Drivers of seasonal variability of CH₄?

Off-shore sandy

Low organic sediments

Phyto = fresh organic inputs

C H4 ( n m o l L -1 ) T e m p e ra tu re (° C ) Near-shore muddy

High organic sediments Temperature controlled 120 215 ZG02 330 230 130 780 710 700

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Drivers of seasonal variability of CH₄? C H4 ( n m o l L -1 ) T e m p e ra tu re ( °C ) C h l-a ( µ g L -1 ) D M S (P t) (n m o l L -1 ) 120 215 ZG02 330 230 130 780 710 700

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Long-term changes in CH₄ ? 1 2 0 2 1 5 3 3 0 7 0 0 7 1 0 C H4 ( n m o l L -1 ) C h l-a ( µ g L -1 ) Decrease of eutrophication Decrease of phyto biomass

Decrease of CH₄ production 120 215 ZG02 330 230 130 780 710 700

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Emissions of CH₄ to the atmosphere 120 215 ZG02 330 230 130 780 710 700 Station CH4 emission (mmol m-2 yr-1) ZG02 8 ± 8 330 12 ± 13 780 66 ± 66 215 17 ± 17 230 23 ± 27 710 88 ± 116 120 42 ± 42 130 152 ± 274 700 184 ± 176 Nearshore stations* 126 ± 200 Offshore stations** 28 ± 47 All stations 66 ± 134 * 120,130,700 ** ZG02, 330, 780

Open ocean 0.1 mmol m-2 _yr-1 _{(Rhee et al. 2009)}

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Borges et al. (in revision) 120 215 ZG02 330 230 130 710 700