® •
THE MEASUREMENTS OF NUTRIENT FLUXES AT THE
WATER-SEDIMENT INTERFACE: INCUBATION METHODS
(IN LABORATORY AND IN SITU) ; GRADIENT METHOD
(CALCULATED FLUXES) ; BENTHIC ECOSYSTEM TUNNEL
M. FEUILLET-GIRARD(1), D. GOULEAU(1), W. ZURBURG(2),
A.C. SMAAL(3), N. DANKERS(4), M. HERAL(5)
(1) CNRS-IFREMER, Crema L'Houmeau B.P. 5, 17137 L'Houmeau (France). (2) Delta Institute for hydrobiological Research, Vierstraat 28, 4401 EA Yerseke (Netherlands) (3) Ministry of Transport and Public Works, Tidal Waters Division, P.O. Box 8039, 4330. EA Middelburg (Netherlands). (4) mN TEXEL (Netherlands). (5) LABEIM-IFREMER, B.P . 133, 17390 La Tremblade (France).
- 6S -
THE MEASUREMENTS OF NUTRIENT FLUXES AT THE WATERSEDIMENT INTERFACE : INCUBATION ~1ETHODS (IN LABORATORY • " AND IN-SITU ; GRADI ENT METHOD (CALCULATED FLUXES) BENTHIC ECOSYSTEM TUNNEL.
, . ' ' , ' .
M. FEUILLET-GIRARD (1), D. GOULEAU (1), V. ZURBURG (2) , A.C. SMAAL (3), N. DANKERS (4), M.HERAL (5).
(1) CNRS-IFREMER, Crema l'Houmeau B.P. 5 17137, , l'Houmeau FRANCE.
(2) Delta 1 nsti tute for hydrolog ical Research, Vierstraat 28, 4401 EA Yerseke, The NETHERLANDS. (3) Ministry of Transport and Public Works, Tidal Wl\ters Division, P.O. Box 8039, 4330. EA ~liddleburg,
The NETHERLANDS. (4) 1 B N. TEXEL, THE NETHERLANDS.
_ (5) Labeim-IFREMER B.P. 133, 17390 La Tremblade FRANCE.
INTRODUCTION
Many flux measurements methods have been described in the literature. The purpose of our study was to compare results obtained by these different methods : Gradient Method, Incubation ~Iethod (Laboratory and In Si tu), Benthic Ecosystem Tunnel. The field experiment has been performed in the Marennes Ol éron Bay since May 1991 (contrat C.E.E. FAR) .
DIAGRAM OF THE APPARATUS DESIGNED FOR MEASUREMENT OF FLUXES AT SEDIMENT-WATER INTERFACE
1. - GRADIENT METHODS : calculated fluxes w i th F ick' first law
.-
dc ~ = -n D IlM m-2 h-l
dz
~ OVCII,in9 w~ltr ,-__ ~~~ ____ ==-==-____ ~ C, •
NU I,,«"1 conCtnlf~tlon
Lnel 0 ----- ----.. ----~-- '. ~ c, _.· .• . , . , .~ ,~ ~ . . . - .
, ; " " . ".
: ~ . . "
Sêdimenl
O z Oillus,on cocll ,( ,lnl
n: Poros , l y
Port .... .. I tl
t~ll .. cllon t
C"
!Jc~C , ·c.
'luIIHI: n! ( ooccnlr.l,on o 0.5 cm
2.- I NCUUi\T ION ~IETIIOVS
r 6em
6em
l
-66-
Li\BOIIATORY (in the dark)
slirr\! r waler
sedimtnt sUllace : 8.1 en"
sedtme:nlcOfe
•
wat t t - billh wilh 12 COfe5 ., plug TO in situ
Short incubation .J-c. h
ill SITU (in tlle dark)
P,V, C.
j 6,8 em
Sedi ment A'ea : JG,J2crn'
[
- 67 -3. - IlENTIlI C ECOSYSTHI TUNNEL
RESULTS
~
l: N
É ::;: ::l ..,.
l Z
Yzcm
Neopre ne Ski rt ~
Reinforcement bottom surf ace = 8,5 ml
Benthic Ecosystem Tunnel
(BESn
The: BEST struclu re usc:d 10 obt:l.in nUACS of mltCfI:Jh Jeron J.J1 opler retr.
300
200
100
0
· 100
·200
~OO
HOW NEASUREHENTS OF FLUXES ARE FUNCTION OF THE USED HETHODS ?
AMMONIUM FLUXES
642
1.
~ '- L 1 . 1. 1 Il~ .... • .. • 1
1 May 1 1 Oclober 1
13 15 21 23 8 10 22 24
Sampling Dais
1_ Calculated _ LDbOIBIOry _ ln Situ
50
~ a ,
.s:
'" -50
è -100
:; ·150 :J
'" -200 0 Z -250
-300
- 68 -
NITRATE FLUXES
1 Oclober 1
13 15 21 23 B 10 22 24
Sampling Dale
1 D Calculated _ Laooralory _ ln Situ
Pore water concentrations of NH4+ and N03- ranged from about 10 to 120 p~l and 0.42 to 20 pM. Calculated Ammonium Fluxes were higher than the measured ones. This difference could be explained by the decrease of molecular diffusion on ;the sediment surface (see picture 2).
[NCUBA TI ON MErl/OOS
- 69 -
AMMONIUM FLUXES
40
JO
~ 20
1-1-. ~ N la-E 0 ::;: -la :J ..,. -20 I
~ 190 Z -30
1 May 1 1 Oclober -40
-50 13 15 21 23 6 la 22 24
Sampling Date
1_ Labolalory _ ln Silu
Both measurements, in laboratory and in situ ,!(ave weak flux intensities compared with previous measurements. Short incubations in laboratory (4h) showed that ammonium fluxes were dominated by a weak re lease in ~Ia)'. Reverse fluxes were observed in October. In the case of in situ incubation, we fo~nd r everse fluxes in May, and releases in October. Differences in sampling might account for the discrepancies between the results of both techniques.
NITRATE FLUXES
50~--------------------------------------,
-\------r~· ~ -5:-:1-' E -100 ::;: :J cry o z
-150
-200
-250
13 15 21 23 6 10
Sampling Date
1_ Laboralory ~ ln SUu
22 24
In the case of in situ incubation using micro benthic chambers Nit ra te fl ux intensities were hir:;he r than those obtained by the laboratory incubation method . In October differences were l owe r . III almost a IL cns~s. we obsened a reverse flux that could be thE' .-esul t of nutrient uptake by nitrif r in" bacteria u r bv denitrificntion.
I-\IVIIVIUI\lIUIVI rLUI\Cù _ 70 _
Tunnel experiment 13-14.05.-1991 For a tidal cycle. 92-95 caeL
15 16 ,. 2 J 4 5 6 7 Hours
Here 1-Ie anly show results obtained in spring tide over an oyster bed, we cou ld not obtain eithe r uptake o r release wi th the control tunnel. By another way Ammonium flux calcu lated with Ammonium excretion ra te found in ~IIlY in laborato r y, a<:reed wi th fluxes found in the tunnel and r eae hed 400 I.fl m-2 h-1.
il
NH4 EXCRETIOI\j RÂ TE by oysters in laborator y
Moy
2 .3 4 5 6 7 8 9 10 11 12
l,lOIS
•
CONCLUSION - 71 -
The non-ag reement bet" een flu xes estimated t'rom pore water profiles and exchange measurements is apparent for Ammonium fluxes. This disagreement could be explained by the presence of Il biof ilm on the sedimen't surface which hides the diffusion. The fluxes measured by the SEST permitted us to measure an Ammonium release from oyster bed and the mussel bed, but the control tunnel did not take into account the flux coming from the sediment, because the resident time was tao short.