E stu aries
Vol. 23, No. 5, p. 6 6 9 -6 8 2
O ctober 2000
Distribution of Nitrifying Activity in the Seine River (France) from
Paris to the Estuary
N a t a c h a B r io n 1
Groupe de Microbiologie des M ilieux Aquatiques
Un iversité Libre de Bruxelles
CP 221, Campus Plaine
Boulevard du Triomphe
1050 Brussels, Belgium
G i l l e s B il l e n
Unité M ixte de Recherche Centre N ational de Recherche Scientifique Sisyphe
Un iversité Paris 6
Place Jussieu 4
75005 Paris, Fran ce
Loïc
G uézennec
Agence de l'Eau Seine Normandie
51 rue Salvador-Allende
92 0 27 Nanterre
Cedex, Fran ce
A n d r é F ic h t
Service de la Navigation de la Seine
Cellule de lutte contre la polution
6 6 Av. J. Chastellain
Ile Lacroix
76000 Rouen, Fran ce
ABSTRACT: T h e d istribution o f nitrification has b e en m easu red w ith the 111'( ( ) ; in co rp o ra tio n m eth o d in the Seine
River a n d its estuary during sum m er conditions. T h e Seine R iver below Paris receives large am ounts o f am m onium
th ro u g h w astew ater discharge. In the river itself, this am m onium is only slowly nitrified, while in the estuary nitrification
is ra p id a n d com plete. We show th a t this contrasting behavior is re la te d to the d iffere n t hydrosedim entary conditions o f
the two system s, as nitrifying b acteria are associated w ith su sp en d ed particles. In the river, particles and th eir attached
bacteria e ith e r rapidly settle o r have a sestonic behavior. B ecause o f the sh o rt residence tim es o f the w ater m asses, the
slow growing nitrifying pop u latio n has no tim e to develop sufficiently to nitrify the available am m onium . T h e estuary is
characterized by strong tidal dynam ics. Particles settle and are re su sp e n d ed continuously w ith the strong c u rre n t inver­
sions o f ebb and flood. As a result o f these dynam ics, particles a n d th e ir attach ed nitrifying bacteria experience longer
residence tim es in a tem p o rary su sp en d ed state th an the w ater m asses them selves, providing to slow growing nitrifying
bacteria the oppo rtu n ity to develop a large pop u latio n capable o f nitrifying all the available am m onium .
ers w h ich receive d irectly o r in d irectly (th ro u g h o r­
g an ic N m in e ra liz a tio n ) la rg e a m o u n ts o f a m m o ­
n iu m fav o rab le to th e d e v e lo p m e n t o f n itrific a tio n .
In rivers, a m m o n iu m can b e n itrifie d in th e sedi­
m e n ts a n d th e w ate r co lu m n , th e relative signifi­
c an c e o f e a c h b e in g a fu n c tio n o f th e su rfac e to
v o lu m e (S : V) ra tio o f th e river. In sm all rivers, am ­
m o n iu m is m ostly n itrifie d by th e b e n th ic co m ­
m u n ity (C o o p e r 1984). In la rg e r rivers, b eca u se o f
th e sm aller S : V ratio , b e n th ic n itrific a tio n is insig­
Introduction
In riv er systems, n itrific a tio n plays a n im p o rta n t
ro le in th e n itro g e n cycle b u t is also a n im p o r ta n t
oxygen c o n su m in g p ro c e ss (e.g., D éri 1991). T his
is p a rtic u la rly tr u e in w astew ater c o n ta m in a te d riv1 C orresp o n d in g author: c u rre n t address: Vrije U niversiteit
Brussels, Faculteit W etenschappen Analytische C hem ie (WE
A N C H ), Pleinlaan 2, 1050 Brussels, Belgium : tele: 32 2 /6 2 9 32
64: fax: 32 2 /6 2 9 32 74: e-mail: nnbrion@ vub.ac.be.
© 2000 E stuarine R ese arch Federation
669
670
N. Brion e t al.
n ific a n t a n d m o st o f th e o x id a tio n o f a m m o n iu m
tak es p la c e in th e w a te r c o lu m n (B illen 1975; Lipschultz e t al. 1986; C h e sté rik o ff e t al. 1992; Bero u n sk y a n d N ix o n 1993).
T h e capacity o f la rg e stream s to o x id ize a m m o ­
n iu m is stro n gly re la te d to th e ir capacity to m a in ­
ta in a la rg e n itrify in g p o p u la tio n . N itrify ing b ac ­
te ria a re c h a ra c te riz e d by th e ir v ery slow g row th
(m a x im u m g ro w th ra te b e tw e e n 0.035 a n d 0.06
h _1, G o u ld a n d L ees 1960; S k in n e r a n d W alker
1961; B o o n a n d L a u d e lo u t 1962; H e ld e r a n d D e
Vries 1983; B rio n a n d B illen 1998); th ey n e e d lo n g
re s id e n c e tim es to d ev elo p a sig n ifican t b iom ass in
tile w a te r c o lu m n . It is c o m m o n ly k n o w n th a t n i­
trifying b a c te ria h av e th e capacity to a tta c h to sur­
faces a n d th is capacity is largely u se d in w astew ater
tr e a tm e n t te c h n o lo g ie s (B o v e n d e u r e t al. 1990). In
a q u a tic systems, th is can r e p r e s e n t a n ad v an tag e
fo r th o se slow g ro w in g o rg a n ism s by allow ing th e m
to stay lo n g e r a t o n e site w ith o u t b e in g flu sh e d o ut.
D éri (1991) sho w ed th a t in th e H u n g a ria n stre tc h
o f th e R iver D a n u b e , very ra p id a n d f r e q u e n t dis­
c h a rg e v a ria tio n s le d to a lte rn a te re s u sp e n sio n a n d
se ttlin g p e rio d s, w ith th e p e rio d s o f m a x im u m tu r­
b idity c o in c id in g w ith th e m a x im u m n itrify in g ac­
tivity. In th e sam e way, A d m ira a l a n d B o tte rm a n s
(1989) sho w ed th a t in th e th r e e b ra n c h e s o f th e
R h in e estuary, th e m o st tu r b u le n t a n d tu rb id
stre tc h c h a ra c te riz e d by th e m o st in te n s e s h ip p in g
was also th e site o f th e m o st in te n s e n itrifica tio n .
Finally, O w ens (1986) c o m p a re d th e fu n c tio n in g
o f th e n itrify in g T a m a r e stu a ry to a flu id iz ed b e d
reacto r, w ith th e tid al m o v e m e n ts m a in ta in in g at­
ta c h e d b a c te ria in su sp en sio n .
F o r th e S ein e R iver b elo w Paris, C h e sté rik o ff et
al. (1992) sho w ed th a t th e v ery la rg e a m o u n ts o f
a m m o n iu m b r o u g h t by th e w astew ater tr e a tm e n t
p la n t o f P aris (10 m illio n in h a b ita n ts ) w ere only
slowly n itrifie d even in s u m m e r low w a te r c o n d i­
tio n s b e c a u se o f th e slow g ro w th o f n itrify in g o r­
ganism s. T h e n itrify in g p o p u la tio n re q u ire s several
days (m o re th a n th e re s id e n c e tim e) to re a c h d e n ­
sities ab le to in d u c e a m e a su ra b le a m m o n iu m d e ­
p le tio n in th e river. In c o n tra st, w h e n e n te rin g th e
estuary, s e p a ra te d fro m th e u p s tre a m se ctio n o f
tile riv er by a n av ig atio n d am , a m m o n iu m is alm o st
totally n itrifie d u n d e r fav o rab le su m m e r te m p e ra ­
tu re c o n d itio n s.
T h is p a p e r shows th a t th e c o n tra s tin g ex p re ssio n
o f n itrific a tio n in th e riv e rin e a n d e s tu a rin e p a rts
o f th e S ein e is re la te d to th e d iffe re n t h y d ro lo g ical
c o n d itio n s p re v a ilin g in th o se two system s. W hile
tile h y d ro d y n a m ic b e h a v io r o f th e riv er is c h a ra c ­
te riz e d by th e u n id ire c tio n a l riv er d isc h a rg e , th e
e stu a ry is also in flu e n c e d by s tro n g tid a l dynam ics.
We in v estig ated th e in te ra c tio n s b e tw e e n n itrify in g
b a c te ria a n d su sp e n d e d p articles, a n d th e ir im p li­
catio n s o n tile n itrify in g p o p u la tio n dynam ics.
S ite D e s c rip tio n
T h e study a re a c o rre s p o n d s to th e d o w n stre am
p a r t o f tile S eine R iver a n d its e stu a ry (Fig. l a ) . It
e x te n d s over 355 km fro m P aris to H o n fle u r. T h e
sam p lin g sites a lo n g th e stre am a re r e fe re n c e d as
d istan ce (km ) fro m th e M arie b rid g e , lo c a te d in
tile c e n te r o f th e city o f Paris, a n d in c re a sin g dow n­
strea m a c c o rd in g to a c o n v e n tio n o f th e Service d e
la N av ig atio n d e la S eine (SN S). T h e S ein e River
below P aris is a la rg e re g u la te d 7 th o r d e r riv er ac­
c o rd in g to tile S tra h le r (1957) classification (th e
c o n flu e n c e o f two rivers o f o r d e r n gives a river o f
o rd e r n + 1, w ith n > 1). A few k ilo m e te rs dow n­
strea m fro m Paris, th e river receives th e e fflu e n ts
o f th e w astew ater tre a tm e n t p la n t o f A chères, tre a t­
in g th e sewage o f th e 1 0 m illio n in h a b ita n ts o f th e
P arisian m e tro p o lita n areas. T h e c o n flu e n c e w ith
River O ise co m es im m e d iate ly a fte r th is w astew ater
d isch arg e. T h e m e a n d isc h a rg e o f th e riv er is 420
m 3 s 1. T h e riv er r u n s over 100 km to Poses, th e
b e g in n in g o f th e estuary, w h e re a n av ig atio n dam
p re v e n ts th e tid a l wave fro m p e n e tra tin g fa rth e r
u p stre a m . T h e e stu a ry e x te n d s over 150 km a n d is
strongly c h a n n e lle d , w ith a w id th o f a few h u n d r e d
m e te rs a n d a m e a n d e p th o f a b o u t 4 m fro m Poses
to R o u e n , a n d 10 m d o w n strea m fro m R o u e n . It
h as a m e a n re sid e n c e tim e o f a b o u t 8 d. T h e m ac ro tid a l h y d ro d y n a m ic b e h a v io r o f th e e stu a ry is
c o n tro lle d by th e c o m b in a tio n o f riv er d isc h arg e
a n d tide, w h ich can successively jo in o r b e o p p o se d
d u rin g e b b a n d flo o d . D u rin g a lu n a r cycle, th e
tid al a m p litu d e varies w ith th e a lte rn a tio n o f n e a p
a n d sp rin g tides. T h e m a x im u m tid e a m p litu d e at
tile m o u th o f th e e stu ary is 7.5 m , a n d th e tidal
wave is g rad u a lly d a m p e n e d a n d d is to rte d w h en
e n te rin g th e estuary, re a c h in g only 30 cm in th e
fr o n t o f th e Poses d am . T h e in tru s io n o f salinity
n e v e r e x te n d s b e y o n d C a u d e b ec , 40 km fro m th e
river m o u th in th e S ein e Bay. In th e larg est p a r t o f
tile estuary, th e re is n o d ilu tio n o f fre sh w a te r w ith
m a rin e w aters.
Methods
P h y s ic a l, C h e m ic a l, a n d B i o lo g i c a l
M e a s u re m e n ts
A m m o n iu m (N H 4), n itra te ( N 0 3), a n d n itrite
(NOo) analyses w ere c a rrie d o u t o n 0.45-|j,m fil­
te re d w ater, d irectly a fte r co lle ctio n . N H 4 was m e a ­
su re d w ith th e in d o p h e n o l b lu e m e th o d a c c o rd in g
to Slawyk a n d M clsaac (1972). N O s was m e a su re d
a fte r ca d m iu m re d u c tio n in N O a. N O , was m e a ­
su re d w ith th e su lp h a n ila m id e m e th o d a c c o rd in g
to J o n e s (1984). R iver d isc h arg e s (Q ) w ere given
daily a t th e Poses d a m (198 km ) by th e SNS. Ox-
671
Nitrification in the S e in e River and Estuary
FRA N CE
i—> 310.5 km Caudebec
—> 251.5 km Dock
r-> 249 km wastewater Rouen
278 km
Le Havre
337lun
Rouen
207.5 km
355 km Honfleur
202 km Poses
■>
219km
198 km POSES DAM: Beginning o f the estuary
> 186.5 km Vernon
—> 85 km Oise-Seine confluence
229.5 km Oissel
^
a* Oise
258 km Moulineaux
ff
150.5 km
►75 km wastewater Achères
62 km Maison-Laffitte
Paris
Marne
^
Left Bank
Right Bank
15km
114.5 km Porcheville
0 km Marie Bridge
Fig. 1. A) Schem atic re p re se n tatio n o f th e Seine River below Paris. Black circles are th e sam pling stations; th e n am e o f th e stations
a n d th e ir position (distance fro m th e M arie B ridge in Paris) are p o in te d o u t w ith arrows. WWTP: W astewater tre a tm e n t p la n t o f
A chères (75 km ). B) Schem atic re p re se n ta tio n o f th e cross section o f th e estuary a t station M oulineaux (258 km ). Circles re p re se n t
th e sam pling sites.
TABLE 1. H ydrologie a n d clim atic characteristics o f th e 10 cruises a n d lin e a r regression o f p o ten tial nitrifying activity (pNA, jjimol
I-1 h -1) versus su sp en d ed m a tte r (SM, m g I-1) c o n cen tratio n s fo r 7 tidal profiles. Q = river discharge (m 3 s-1). tc = tide coefficient
(relative tidal ran g e in % o f th e m ea n spring eq u in o x tidal ran g e, 6.7 m , given fo r th e B rest H a rb o u r o n th e F ren ch A tlantic coast).
T = te m p e ra tu re (°C). A a n d B are coefficients o f th e lin e a r regression pN A = A X SM + B. R is th e regression coefficient, p is the
probability th a t th e regression coefficient R is zero, n = n u m b e r o f observations, ns = n o significant c o rre latio n betw een pN A a n d
SM (p > 0.05).
Date
Q
tc
T
A
B
R
P
n
L ongitudinal Profiles
July 3-4, 1995
S eptem ber 12-13, 1995
July 3-4, 1996
July 21, 1993
N ovem ber 4, 1993
M arch 17, 1994
May 20, 1994
J u n e 15, 1994
July 17, 1994
S eptem ber 27, 1996
290
296
141
205
450
680
500
500
150
140
68
22
—
89
106
18
19
—
—
—
—
—
—
—
—
—
—
- 0 .3 4
0.21"“
-0 .0 4 " “
0.016
-0 .0 7 0
-1 .1 9
0.11
0.82
-0 .1 3
0.45
0.89
0.84
0.85
0.82
0.003
0.71
0.36
0.003
0.035
0.007
<0.001
10
10
101
68
71
55
67
71
108
T idal Profiles
20
0.037
9
-0 .0 0 3 " “
10
0.0032"“
16.5
0.0055
18
0.0075
22.5
0.043
16
0.015
6
8
6
8
36
672
N. Brion e t al.
Julv 1996
600
400
200
0
0
100
200
300
400
0
100
200
300
400
o
100
200
300
400
20001000
400
Ul
CO
O
300
200
100
I
/
0
0
100
200
300
400
0
100
200
300
400
200
300
400
100
200
300
400
0
100
200
300
400
0
100
200
300
400
0
100
200
300
400
o
100
200
300
400
(B)
8
6
O) 4
CM
O2
0
pNA
v" 2 -
0
100
Distance from Marie Bridge in P aris (km)
Fig. 2. L o ngitudinal variations fro m M aison-Laffitte (62 km ) to H o n fle u r (355 km ) o f A) am m o n iu m (N H 4), n itra te ( N 0 3), total
dissolved in o rg an ic n itro g e n (D IN ), su sp en d ed m a tte r (SM ), chlorinity (Cl ) ; B) oxygen ( 0 2) concen tratio n s a n d p o ten tial nitrifying
activity (pNA) a n d sim ulated in situ nitrifying activity (sNA) fo r Ju ly 1995, S ep tem b er 1995, a n d Ju ly 1996. F or station locations, see
Fig. la.
y gen c o n c e n tra tio n s ( 0 2) w ere d e te r m in e d u sin g
a specific p ro b e (O X Y 96, W T W ). S u sp e n d e d m a t­
te r c o n c e n tra tio n s (SM) w ere d e te r m in e d by filter­
in g 100 to 300 m l o f w a te r im m e d ia te ly a fte r col­
le c tio n th ro u g h a 0.45-|j,m d rie d p re-w eig h ed glass
fib re filte r (GFF, W h a tm a n n ). T h e filte r was th e n
p u t in a d ry in g o ven a t 80°C fo r 4 h , a n d w eig h e d
again. S u s p e n d e d m a tte r c o n c e n tra tio n was d e te r­
m in e d by th e d iffe re n c e.
N itrify in g activities w ere m e a s u re d o n w a te r sam ­
p les im m e d ia te ly a fte r c o lle c tio n w ith th e H 1 4 C 0 3~
in c o rp o ra tio n m e th o d a c c o rd in g to B rio n a n d Bil­
le n (1998). T h e m e th o d involves m e a su rin g th e
d iffe re n c e in d a rk 1 1 1 'CX ) , in c o rp o ra tio n ra te s b e ­
tw een a c o n tro l sam p le a n d a sam p le tre a te d w ith
specific in h ib ito rs o f c h e m o a u to tro p h ic n itrific a­
tion: N -serve ( = 2-chlo ro -6 -trich lo ro m eth y l pyri­
d in e = N itra p y rin e ) a t a fin al c o n c e n tra tio n o f 5
m g I - 1 a n d c h lo ra te at a fin al c o n c e n tra tio n o f 1 0
m m o l I-1. T h e c a rb o n in c o rp o ra tio n rates w ere
c o n v e rte d in to a m m o n iu m o x id a tio n to n itra te
ra te s by u sin g a co n v ersio n fa c to r o f 0 . 1 1 (p m o l
o x id ized N )X (|j,m o l in c o rp o ra te d C ) _ 1 w h ich was
c o n sid e re d to b e c o n s ta n t in th e s ta n d a rd iz e d in-
Nitrification in the S ein e River and Estuary
F lood
- >
c u b a tio n c o n d itio n s (B rio n a n d B illen 1998). P o ­
te n tia l n itrify in g activities (pN A ) w ere m e a s u re d a t
sa tu ra tin g a m m o n iu m ( 2 m m o l I-1) a n d oxygen
(sh ak in g o f th e sam p le o n a ro ta ry tab le) c o n c e n ­
tra tio n s a n d at a c o n s ta n t te m p e ra tu re o f 20°C. U n ­
d e r th e se co n d itio n s, n itrify in g activity is directly
re la te d to n itrify in g b iom ass (B elser a n d Mays
1982). S im u lated in situ nitrify in g activities (sNA)
w ere m e a s u re d by in c u b a tin g th e sam p les in W ink­
le r b o ttle s w ith o u t a h e a d sp a c e a n d at in situ te m ­
p e ra tu re .
Ebb
4-
6.5
f
5.5
5
4.5
4
Sa m p l in g a n d C r u is e s
10
_
12
Longitudinal Profiles
L o n g itu d in a l p ro files o f nitrify in g activity w ere
esta b lish ed d u rin g th re e cru ises c o n d u c te d u n d e r
low river d isc h a rg e c o n d itio n s in Ju ly a n d S e p te m ­
b e r 1995 a n d in Ju ly 1996. E ach sa m p lin g cruise
r a n over 2 d. O n th e first day, u p stre a m statio n s
b etw e e n 62 a n d 230 km w ere sa m p le d fro m b rid g ­
es d u rin g th e ebb. O n th e se c o n d day, d o w n stream
statio n s b etw e en 250 a n d 355 km w ere sa m p le d
fro m a sm all ship o f th e SNS d u rin g th e flo o d ex­
c e p t fo r th e m o st d o w n stre am statio n s at 355 a n d
337 km , w h ich w ere sa m p le d a t th e e n d o f th e ebb.
All sam p les w e re ta k e n in th e m id d le o f th e river
in th e first 3 m o f th e w ate r co lu m n , e ith e r w ith a
b u c k e t (u p stre a m sam ples) o r w ith a p eristaltic
p u m p (d o w n strea m sam p les). T h e riv er d isch arg e,
w ate r te m p e ra tu re , a n d tid e co e ffic ien t o f eac h
cru ise a re given in T ab le 1.
0.5 )
'in
£
>
673
0
o
o
10
.•'4
<D
12
> -0.5 )
-1 J
Time after low tide (h)
Fig. 3. C u rre n t velocity a n d w ater colum n h eight du rin g a
typical tidal cycle m easured at M oulineaux (258 km ).
Tidal Profiles
T h e tid al variability o f p o te n tia l n itrify in g activ­
ities a n d s u sp e n d e d m a tte r c o n c e n tra tio n s w ere as4 N ovember 1993
2 0 July 1993
20 May 1994
40 -
30-
>
O)
3
E
CP'
- 0 .4
10
-
0.2
0.0
0
2
4
6
8
10 12
0
2
4
6
8
10 12
0
2
4
6
8
10 12
Time after low tide (h)
Fig. 4. Typical su sp en d ed m a tte r c o n ce n tra tio n (SM) a n d p o ten tial nitrifying activity (pNA) variations o n surface sam ples a t station
M oulineaux (258 km ) d u rin g 3 tidal cycles.
674
N. Brion e t al.
(A) SM (mg 1-1)
znd of the ebb
Beginning of the flood
Middle of the flood
High tide
Beginning of the ebb
Middle of the ebb
_________L
E?
'cu
15
10
03
'o
5
O
jC
05
'03
50
100 150 200 250
50
100 150 200 250
width (m)
width (m)
O ^ ^ C O O l M C O O I W O
o o o o o o o o o
Fig. 5. T idal variation o f (A) suspended m atter concentration (SM) a n d (B) potential nitrifying activity (pNA) on a cross-section at
station M oulineaux (258 km ). D iam onds re p re se n t the m easurem ents. C oncentrations were extrapolated from the m easurem ents over
the entire river section using th e Kriging m eth o d (Surfer version 4 R eference m anual) o f com puter p rogram SURFER (G olden Software).
sessed fo r seven cru ises c o n d u c te d a t a sta tio n lo­
c a te d a r o u n d th e m id d le o f th e estuary: M ouli­
n e a u x , 258 km (Fig. l a ) . C ru ises follow ed 12 h tid ­
al cycles a n d co v e re d d iffe re n t seaso n al a n d tidal
situ atio n s. W ater te m p e ra tu re , riv er d isc h a rg e , a n d
tid e co efficien ts o f e a c h c ru ise a re s u m m a riz e d in
T able 1. B etw een Ju ly 1993 a n d Ju ly 1994 (six cru is­
es), sam p les w ere ta k e n o f th e su rface w ate r w ith
a b u c k e t fro m a sm all p ie r o n th e le ft b a n k (Fig.
l b ) . O n S e p te m b e r 27, 1996, sam p les w ere ta k e n
fro m a ship (C ôte d ’A q u itain e, C.N.R.S.) w ith 5-1
N isk in ’s b o ttle s a t th re e d e p th s (b o tto m , cen ter,
a n d su rface o f th e w a te r co lu m n ) a n d a t th re e sta­
tio n s across th e riv er (left b an k , m id d le , a n d rig h t
b a n k ) (Fig. l b ) .
S e d im e n t a t io n o f
pNA
a n d
SM
To illu stra te th e in te r-re la tio n sh ip b e tw e e n sus­
p e n d e d p a rtic le s a n d nitrify in g b a c te ria in estria­
rm e w aters, th e s e ttle m e n t o f pN A a n d SM w ere
Nitrification in the S ein e River and Estuary
(B )
675
p N A ((jm o l 1-1 h -1 )
End of the ebb
Beginning of the flood
Middle of the flood
High tide
Beginning of the ebb
Middle of the ebb
E
15
n
T----
10
5
0
0
50
100 150 200 250
width (m)
width (m)
Fig. 5.
fo llo w ed in p a ra lle l o v er tim e in a m eso co sm ex­
p e rim e n t. A t sta tio n M o u lin e a u x (258 k m ), o n July
23, 1997, seven plastic cy lin d e r tu b e s w ere gently
im m e rs e d side to side in a v ertical p o sitio n u n d e r
th e w a te r su rface, clo sed a t th e ir b o tto m e n d , a n d
carefully b r o u g h t u p to th e riv er b a n k w h e re they
w ere p la c e d w ith m in im a l d is tu rb a n c e in a n in c u ­
b a to r a t in situ te m p e ra tu re . Im m ed iately, th e u p ­
p e r 2 0 cm o f th e first cy lin d e r w ere s ip h o n e d a n d
h o m o g e n ise d . T h e o th e rs w ere allow ed to settle fo r
5, 15, 30, 60, 120, a n d 240 m in u te s respectively
b e fo re b e in g s ip h o n e d a n d h o m o g e n ise d . pN A
C o ntinued
a n d SM w ere d e te rm in e d o n e a c h c o lle c te d sam ­
ple.
Results
L o n g itu d in a l P ro file s
T h e 3 sets o f lo n g itu d in a l p ro files cover su m m e r
situations; a situ a tio n w ith a river d isc h arg e o f
a b o u t 300 m 3 s a n d a m e a n w ater te m p e ra tu re s
o f 18°C (S e p te m b e r 1995) a n d 22°C (July 1995),
a n d a situ a tio n w ith a low er riv er d isc h a rg e (141
m 3 s 1 ) a n d a m e a n w ate r te m p e ra tu re o f 19.5°C
(July 1996) (T able 1). S u sp e n d e d m a tte r co n ce n -
676
N. Brion e t al.
tra tio n s a re r a th e r low a n d c o n s ta n t in th e river
( 1 0
to 2 0 m g I-1), w hile in th e u p p e r p a r t o f th e
estuary, th ey a re m o re v ariab le a n d g e n e ra lly h ig h ­
e r (40 to 50 m g I-1) (Fig. 2 a). T h e d o w n strea m
p a r t o f th e e stu a ry is c h a ra c te riz e d by th e p re se n c e
o f a tu rb id ity m a x im u m (u p to 2 g I - 1 o f SM) as
previously d e sc rib e d by A voine e t al. (1981). T his
tu rb id ity m a x im u m is p a rtic u la rly e v id e n t in S ep­
te m b e r 1995 a n d Ju ly 1996.
A m m o n iu m c o n c e n tra tio n s vary b e tw e e n 0 a n d
350 |j.mol I - 1 (Fig. 2 a). T h e d isc h a rg e o f th e A ch­
è re s w astew ater tr e a tm e n t p la n t a t 75 km causes a
su d d e n in c re a se . B etw een 75 a n d 202 km , c o n c e n ­
tra tio n d e c re a ses in Ju ly 1995 w hile it in c re ases in
S e p te m b e r 1995 a fte r th e d ilu tio n w ith th e River
O ise (85 k m ). F ro m 202 km a n d d o w n stre am , in
tile estuary, a m m o n iu m c o n c e n tra tio n s d e cre ase
u n til th ey re a c h u n d e te c ta b le lim its. N itra te c o n ­
c e n tra tio n s vary b e tw e e n 200 a n d 500 p m o l I - 1 a n d
in c re a se d o w n stre a m (Fig. 2a). T otal dissolved in ­
o rg a n ic N c o n c e n tra tio n s (D IN = N H 4 + N O , +
N O 3 ) vary b e tw e e n 300 a n d 650 p m o l I - 1 (Fig. 2a).
A n in c re a se follow s th e d isc h a rg e o f w astew ater at
75 k m (A chères) a n d is im m e d ia te ly fo llo w ed by a
slig h t d e c re a se at 85 km a fte r th e d ilu tio n w ith th e
River O ise. A fter th is c o n flu e n c e , D IN in crea se s
d o w n stre a m u n til 202 k m (P oses), show ing a n in ­
flu x c o m in g fro m o rg a n ic N m in e ra liz a tio n . B e­
tw een 202 k m a n d 243 km (R o u e n ), D IN d ec rea ses
slightly. Below 340 km , th e c o n c e n tra tio n s o f all
D IN species d e c re a se su d d e n ly d u e to d ilu tio n o f
riv er w ith seaw ater, as show n o n th e c h lo rin ity p ro ­
files (Fig. 2a).
O xy g en c o n c e n tra tio n s d e c re a se drastically ju s t
below th e w astew ater d isc h a rg e o f A c h è re s (75 km )
(Fig. 2 b ) . A lo n g its travel to th e estuary, th e w ater
is th e n re -o x y g e n a ted by m ix in g w ith th e River
O ise (85 km ) a n d by th e w aterfalls a t several nav­
ig a tio n dam s. In th e estuary, a s e c o n d severe oxy­
g e n d e c re a se is o b se rv e d , w ith m in im u m v alues b e ­
low 1 m g R 1 lo c a te d a r o u n d 300 k m (Fig. 2 b ). R e­
o x y g e n a tio n o f th e w a te r m asses only o c c u rs a t th e
m o st d o w n stre a m statio n s by th e m ix in g w ith m a ­
rin e w aters.
P o te n tia l n itrify in g activity varies fro m 0.05 to
2.75 p m o l R 1 h - 1 a n d p ro file s show a slow b u t re g ­
u la r in c re a se o f th e n itrify in g p o p u la tio n fro m 75
(A chères) to 202 km (Poses) (Fig. 2 b ). In th e es­
tuary, pN A re a c h e s v ery h ig h v alues e x c e p t in Ju ly
1995. S im u la te d in situ n itrify in g activity m e a su re ­
m e n ts vary fro m 0 to 0.7 p m o l R 1 h - 1 w ith o n e
valu e o f 1.4 p in o i R 1 h
a n d show th e sam e vari­
a tio n p a tte r n as pNA, w ith a lm o st n o d iffe re n c e in
tile u p s tre a m p a r t o f th e riv er b e fo re 202 km . In
tile estuary, sNA v alues a re lo w er th a n pN A values,
especially in th e d o w n stre a m p a r t o f th e estu a ry
w h e re low a m m o n iu m a n d oxygen c o n c e n tra tio n
strongly lim it th e activity o f th e n itrify in g p o p u la ­
tio n . Spatial p a tte r n s in sNA a n d pN A a t th e m o st
d o w n strea m statio n s in d ic a te th e d ilu tio n o f river
w ith m a rin e w aters.
T id a l P r o f il e s
A typical e x a m p le o f th e tid al wave is show n in
Fig. 3 (258 km , M o u lin e a u x ). It p re se n ts th e suc­
cession o f e b b a n d flo o d . D u rin g th e 4 h o f flood,
tile w a ter c o lu m n h e ig h t in cre ases rap id ly to a
m a x im u m d e p e n d in g o n th e tid e co efficien t, a n d
d u rin g th e 8.5 h o f ebb, it d e c re a ses slowly to a
m in im u m . A very ra p id flow in v ersio n follow s th e
eb b -flo o d succession a n d a m u c h m o re progressive
in v ersio n follow s th e flo o d -e b b succession as seen
o n th e velocity p ro files (Fig. 3).
O n su rfa ce sam ples, s u sp e n d e d m a tte r c o n c e n ­
tra tio n s (Fig. 4) m e a s u re d a t 258 km (M o u lin eau x )
d u rin g several tid al cycles vary strongly d u rin g th e
tid e. In g e n e ra l, c o n c e n tra tio n s a re m a x im u m in
tile first 2 h o f th e flo o d , follow ing th e c u r r e n t
in v ersio n (t = 0 h ) a n d th e n d e c re a se d u rin g th e
flo o d a n d a t h ig h tid e to g e th e r w ith c u r r e n t veloc­
ity ( 2 h < t < 4 h ) . D e p e n d in g o n th e situ atio n ,
SM starts to in c re a se fro m th e e b b c u r r e n t inver­
sion (t = 4 h ) w h e n c u r r e n t velocity in creases, a n d
re a c h e s a sm a lle r m a x im u m 2 to 4 h la te r ( 6 h <
t < 8 h ). It is follow ed ag ain by a d e cre ase a t th e
e n d o f tile e b b (/ > 8 h ). P o te n tia l n itrify in g activ­
ity p ro file s m e a s u re d d u rin g th e sam e tid a l cycles
show a sim ilar v a riatio n p a tte r n as s u s p e n d e d m a t­
te r p ro file s (Fig. 4).
O n a cross section, m e a su re m e n ts o f SM a n d
pN A as d e te r m in e d in S e p te m b e r 1996, show a
stro n g sp atial a n d tid al variability (Fig. 5a,b) w ith,
again, a sim ilar p a tte rn fo r pN A v ariatio n s as fo r
SM. T h e six cross-section p ro files c o rre s p o n d to 6
ch ara c teristic m o m e n ts o f th e tid a l cycle. A t th e
e n d o f th e ebb, c o n c e n tra tio n s a re relatively h o ­
m o g e n o u s a n d low. A t th e b e g in n in g o f th e flood,
c o n c e n tra tio n s in c rea se, b e g in n in g fro m th e b o t­
tom , as a re su lt o f th e re su sp e n sio n o f p a rticle s
follow ing th e c u r r e n t inversion. A t th e m id d le o f
tile flo o d , a severe stratificatio n resu lts fro m th e
sin k in g o f p a rtic le s fro m su rfac e w aters a n d c o n ­
se q u e n t a c c u m u la tio n o f p a rtic le s in th e b o tto m
layers. A t h ig h tid e a stro n g s e d im e n ta tio n o f SM
a n d pN A in all p a rts o f th e w ater c o lu m n follows
tile z e ro flow velocity. A t th e b e g in n in g o f th e ebb,
SM c o n c e n tra tio n s in c re a se b e g in n in g fro m th e
b o tto m as a re su lt o f th e se c o n d c u r r e n t inversion,
a lth o u g h to a lesser e x te n t th a n fo r th e flo o d in ­
v ersion. Finally, at th e m id d le o f th e eb b , c o n c e n ­
tra tio n s b e c o m e ag ain relatively h o m o g e n o u s a n d
low a fte r se d im e n ta tio n . T h e re is also a stro n g
asym m etry b e tw ee n th e left b a n k a n d th e rig h t
b an k . T h is is re la te d to th e fa ct th a t th e riv er at
Nitrification in the S e in e River and Estuary
•
£
pNA
0 .6 -
S 0 .4 -
0 .2 -
0.0
50
0
100
150
Sedimentation time (min)
200
250
Fig. 6. S edim entation kinetics o f su sp en d ed m a tte r (SM)
a n d p o ten tial nitrifying activity (pNA).
th is sta tio n (258 km ) fo rm s a lo o p (see Fig. la )
w ith tile le ft b a n k at th e o u te r side. P articles ac­
c u m u la te m o re a t th e in n e r side o f th e lo o p (rig h t
b a n k ) , w h e re c u r r e n t velo cities d u rin g th e e b b are
m o re re d u c e d .
S e d im e n t a t io n
o f pN
A
and
SM
R esults o f th is e x p e rim e n t (Fig. 6 ) show th a t SM
a n d pN A have a very sim ilar s e d im e n ta tio n p ro file
w ith a 3 0 -4 0 % fra c tio n n o n -d e c a n ta b le a fte r 90
m in .
Discussion
D
is s o l v e d
In o r g a n ic N
it r o g e n
B udget
D IN flu x es in th e riv er a n d e stu a ry a re p re s e n t­
e d in Fig. 7, in five successive stretch es: 6 2 -1 1 4 km ,
w h e re th e S ein e receiv es th e w astew ater d isch a rg e
o f A c h è re s (75 km ) a n d th e R iver O ise (85 km );
114—186 km , tile last riv er stre tc h b e fo re th e estu ­
ary; 1 8 6 -2 3 0 km , th e u p s tre a m p a r t o f th e estu a ry
(w ith a little p o r tio n o f th e riv er as n o sam ples
w ere ta k e n j u s t at th e e n d o f th e riv e rin e section,
198 k m ); 2 30-251 km , w h e re th e S ein e receives th e
w astew ater o f th e city o f R o u e n (249 k m ); a n d 2 5 1 310 km , th e d o w n stre a m p a r t o f th e e stu ary b e fo re
th e d ilu tio n w ith seaw ater. T h e in c o m in g , o u tg o ­
ing, a n d in te rn a l N -fluxes in e a c h stre tc h a re cal­
c u la te d fro m th e m e a s u re d D IN , N H 4, a n d N O s a t
its u p stre a m a n d d o w n stre a m lim its, a n d fro m th e
riv er d isch arg e. O u r ca lc u la tio n s assum e steadystate c o n d itio n s a n d n e g le c t p h y to p la n k to n ic N u p ­
tak e as b lo o m s in th is seaso n only o c c u r in th e
u p s tre a m p a r t o f th e riv er n e tw o rk (G a rn ie r e t al.
1995). In d e e d , a re c e n t review by N ed w ell e t al.
(1999) c a m e to th e co n c lu sio n th a t p h y to p la n k to n ­
ic N -u p tak e in estu a rie s receiv in g h ig h lo ad s o f n i­
tro g e n is o f lim ite d im p o rta n c e as a sin k fo r n itro ­
677
g e n . In tile lo n g stre tc h e s w ith o u t trib u ta rie s o r
w astew ater in p u ts (stre tc h e s 2, 3, a n d 5 ), w e c o n ­
sid e r th a t an in c re a se o f D IN only co m es fro m an
a p p a re n t m in e ra liz a tio n o f o rg a n ic N in N H 4 a n d
th a t a d e c re a se o f D IN is only th e re su lt o f an ap ­
p a r e n t N O 3 d e n itrific a tio n . In th e se stretch es, ap ­
p a r e n t n itrific a tio n is c a lc u la ted by c o m p a rin g th e
in p u t a n d o u tp u t c o n c e n tra tio n s o f a m m o n iu m
a n d ta k in g in to a c c o u n t th e c o n trib u tio n o f N H 4
fro m a p p a re n t m in e ra liz a tio n . In th e s h o rt stre tc h ­
es w ith e x te rn a l in p u ts (stretch es 1 a n d 4), we c o n ­
sid e r th a t a D IN in c re a se is only th e re su lt o f this
p o in t so u rce ta k in g in to a c c o u n t th e w a ter dis­
c h a rg e o f th e trib u ta ry a n d / o r w astew ater. By d e ­
sign, stre tc h e s su b m itte d to e x te rn a l N in p u ts w ere
d e fin e d as s h o rt as possible. In th is way, bio lo g ical
p ro ce ss flu x es ca n b e n e g le c te d b ec au se o f th e
s h o rt re sid e n c e tim es.
C a lc u la te d fluxes show th a t D IN dynam ics in th e
riv er itse lf a re d o m in a te d by th e in p u ts o f a m m o ­
n iu m fro m w astew ater d isch arg e a n d fro m o rg a n ic
m a tte r m in e ra liz a tio n . S om e n itrific a tio n also oc­
cu rs b u t th e m a jo r p a r t (63% to 90% ) o f th e initial
+ b r o u g h t + p ro d u c e d a m m o n iu m is d eliv e re d to
th e estu a ry w ith o u t tra n sfo rm a tio n s. In th e estuary,
th e d o m in a n t p ro c ess affe ctin g D IN dynam ics is
clearly n itrific a tio n w ith all th e a m m o n iu m e n te r­
in g th e system b e in g oxidized. S om e d e n itrific a ­
tio n also o ccu rs in th e m o st d o w n stream p a r t o f
th e system. In te n se n itrific a tio n in e stu aries o f
la rg e rivers receiv in g im p o rta n t N H 4 in p u ts is a
g e n e ra l o b se rv a tio n . C aspers (1981) id e n tifie d a
la rg e z o n e o f th e fre sh w a te r sec tio n in th e E lbe
e stu ary w h e re in te n se n itrific a tio n was c o rre la te d
w ith a d e p le tio n o f th e oxygen c o n c e n tra tio n . In
a n e a rlie r study, B illen (1975) also show ed th a t,
w h e n oxygen c o n c e n tra tio n s w ere n o t lim itin g , n i­
trifica tio n was a m a jo r p ro ce ss in th e S c h e ld t es­
tuary. In th e D elaw are R iver estuary, L ip sh u ltz e t
al. (1986, p. 701) also fo u n d th a t “ q u a n tita tiv e as­
sessm en t o f n itro g e n m eta b o lism o f a sew age im ­
p a c te d river clearly id e n tifie d N H 4+-o x id a tio n as
th e m a jo r p ro ce ss affe ctin g o b se rv e d d istrib u tio n s
o f N O T , N O s- a n d N H 4+” .
In a c c o rd a n c e w ith th e o b se rv e d N -dynam ics,
th e n itrify in g activities m e a s u re d in th e S ein e are
relatively low in th e riv er itse lf b u t m u c h h ig h e r in
th e estuary. O u r re c o r d e d sNA values (0.07 to 0.73
|ju n o l\ 1 h ) a re c o m p a ra b le to th o se f o u n d in
su m m e r in th e P ro v id e n c e River e stu a ry (R h o d e
Island, U .S.) (0.17 to 0.46 p m o lN R 1 I r 1) w hich
also receives la rg e a m o u n ts o f tre a te d w astew ater
(B erounsky a n d N ix o n 1993).
C o n s i s t e n c y o f D IN B u d g e t s a n d M e a s u r e d
N i t r if i c a t io n R a te s
We a tte m p te d to c h e c k th e c o rre s p o n d e n c e b e ­
tw een o u r nitrify in g activity m e a su re m e n ts a n d th e
678
N. Brion et al.
Oise
A chères
62
-
Rouen
114
230 \
1S6
-i
i V
T-
251
310 km
—>
ESTU A RY
R IVER
July 1995
NO,‘ 69
NH.
September 1995
no;
74
175
NH.
July 1996
no;
52)
H ill A pparent P oint sources
... I A pparent N itrification
25 A pparent O rganic N m ineralisation
A pparent D enitrification
DIN fluxes in T N day'1
N H / 3g[
Fig. 7. Dissolved inorganic n itro g e n (DIN) flows from 62 km (M aison-Laffitte) to 310 km (C audebec, before th e dilution with
seawater) for th e 3 longitudinal cruises. Flows are calculated as described in th e text in five stretches o f the river: 62-114 km , 114186 km , 186-230 km , 230-251 km , a n d 251-310 km (see Fig. la ).
ab o v e-d escrib ed D IN b u d g e ts. K now ing th e riv e r’s
g e o m e try (w ater sectio n s given every 4 km fo r a
given riv er d isc h a rg e ), it was possib le to calcu late
tile fre sh w a te r v o lu m e o f th e riv er a n d o f th e es­
tuary. F o r th e e stu a ry th e sectio n s w ere in te g ra te d
m e a n s ta k in g in to a c c o u n t th e tid al variability o f
tile w a te r level o v er a n e a p -sp rin g tid e p e rio d . By
m u ltip ly in g th o se v o lu m e s w ith th e c o rre s p o n d in g
n itrify in g activities m e a s u re d u n d e r in situ c o n d i­
tions, w e o b ta in th e N -flux re la te d to n itrific atio n .
T h is flu x d eriv e d fro m o u r sNA m e a su re m e n ts is
c o m p a re d to th e n itrific a tio n flu x d eriv e d fro m
o u r D IN b u d g e t (Fig. 7) in T ab le 2. In th e river
p a r t o f tile S eine, fluxes d e riv ed fro m th e sNA val­
u es a re in g o o d a g re e m e n t w ith c a lc u la te d fluxes
a lth o u g h th e re is an u n d e re s tim a tio n o f th e m e a ­
su re d n itrify in g activities fo r Ju ly 1995. T h is is p r o b ­
ably lin k e d to th e sa m p lin g strategy th a t d id n ’t fol­
low th e re a l w ater m ass travel fo r th e c o n c e n tra tio n
m e a su re m e n ts. C h e sté rik o ff e t al. (1992) w ho d id
Nitrification in the S ein e River and Estuary
TABLE 2. C om parison o f nitrification fluxes derived from sNA
m easurem ents a n d from DIN budgets in th e river a n d estuarine
stretches o f the Seine River. V = volum e o f freshw ater in the
stretch (IO8 m 3). N IT m eas = nitrification flux derived from the
sNA m easurem ents calculated by m ultiplying th e in te g rate d av­
erage o f m easu red in situ nitrifying activity in the stretch by V
(T-N d 1). NITcalc = nitrification flux calculated from the DIN
bu d g e t as in Fig. 7 (T-N cU1)- Ju n e 1989-April 1990 data are
from C hestérikoff et al. (1992).
V
J u n e 1989-April 1990
July 1995
S eptem ber 1995
July 1996
N IT m eas
NITcalc
N IT m eas
NITcalc
N IT m eas
NITcalc
N IT m eas
NITcalc
River
E stuary
1.31
1.90
0.3-0.7
0.3-0.9
10
18
7
8
3
—
—
—
17
78
27
75
25
43
th e ir e x p e rim e n ts follow ing th e sam e w ate r m ass
a lo n g its travel d o w n stre a m fro m P aris to th e Poses
d am , f o u n d a g re e m e n t b e tw e e n sNA v alues (m e a­
s u re d w ith th e sam e m e th o d ) a n d D IN p rofiles. In
th e e stu a ry flu x es d e riv e d fro m th e sNA show a
c le a r d isc re p a n c y w ith th e c a lc u la te d n itrific a tio n .
It is obvious th a t th e r e is an u n d e re s tim a tio n o f
th e n itrify in g activity m e a s u re m e n ts w ith re g a rd s to
th e o b se rv e d a m m o n iu m d e c re a se. To e x p la in this
d iscrepancy, we r e c o n s id e re d o u r sa m p lin g stra te ­
gy. In d e e d , in th e river, as w ell as in th e estuary,
sam p les w ere ta k e n in th e u p p e r p a r t o f th e w ater
c o lu m n . In th e river, as th e w a te r c o lu m n is k now n
to b e w ell m ix e d (C h e sté rik o ff e t al. 1992), surface
sam p les a re re p re s e n ta tiv e a n d sNA m e a su re m e n ts
d o a g re e w ith m e a s u re d D IN p ro files. In th e es­
tu a ry w e saw th a t th e r e was a severe a n d variab le
v ertical stra tific a tio n o f n itrify in g activities, as well
as o f s u s p e n d e d m a tte r. C o n seq u en tly , su rfac e sam ­
p les ta k e n at a given tim e o f th e tid a l cycle a re n o t
likely to b e re p re se n ta tiv e o f th e w a te r c o lu m n .
To q u an tify th is u n re p re s e n ta tiv e n e s s o f o u r sur­
face sam p les in th e e s tu a rin e e n v iro n m e n t, we
have to c o n sid e r th e close re la tio n s h ip b e tw e e n n i­
trifying b a c te ria a n d p a rtic u la te m a te rial. We saw
th a t th ey vary in th e sam e way d u rin g tid al cycles
a n d th a t th ey settle a t sim ilar rates, su g g estin g th a t
m o st o f th e n itrify in g b a c te ria a re n o t free-living,
b u t a tta c h e d to th e p articles. C o rre la tio n s b etw e en
pN A a n d SM w ere esta b lish e d fo r e a c h o f o u r tidal
p ro file s (T able 1 ) by lin e a r re g re ssio n . We see th a t
a g o o d re la tio n g en erally exists as lo n g as th e ra n g e
o f th e SM (a n d pN A ) v a ria tio n is la rg e e n o u g h
(T able 1). T h is is th e case fo r th e cru ises o f July
1993, May, J u n e , a n d Ju ly 1994, a n d S e p te m b e r
1996 w h ich a re c h a ra c te riz e d by a relatively low riv­
e r d isch arg e. In th a t case, th e slo p e o f th e lin e a r
re g re ssio n s gives an in d e x o f c o lo n iz a tio n o f p a r­
679
ticles by n itrify in g b a c te ria . T h is pN A asso ciated to
p a rtic le s vary seasonally fro m 5.5 to 43 p in o lN g
h _1. O w ens (1986) extensively discusses th e sam e
k in d o f c o rre la tio n fo r th e sm all T a m a r estuary. H e
fo u n d a p article-asso cia ted pN A o f 0.4 to 0.9
p m o lN g
h
w h ich is less th a n o u r values b u t
n o t su rp risin g as we c o n sid e r th e sm all size o f th e
T a m a r R iver e stu a ry (34 m 3 s 1, G ra b e m a n n e t al.
1997) in co m p a riso n w ith th e S ein e River estuary.
In e stu a rin e system s w ith fr e q u e n t a n d so m etim es
ra p id c u r r e n t ch an g es, th e re su lt o f th e a tta c h m e n t
o f n itrify in g b a c te ria to p a rtic le s is th a t th e d istri­
b u tio n o f sNA, like SM, is e x tre m e ly h e te ro g e ­
n e o u s w ith in th e w ate r c o lu m n , b u t also w ith in th e
tid al cycle (Figs. 4 a n d 5). T h e re p re se n ta tiv e n e ss
o f su rfac e m e a su re m e n ts in su ch a system is p re ­
s e n te d in Fig. 8 w h ich shows th e spatial variability
o f s u s p e n d e d m a te ria l a n d pN A w ith in a cross sec­
tio n o f th e e stu a ry d u rin g th e tid al cycle o f S ep­
te m b e r 27, 1996.
E x ce p t a t th e e n d o f th e eb b , su rfa ce m e a su re ­
m e n ts a re always at th e e x tre m e low er lim it o f th e
d istrib u tio n . F o r this situ atio n w e can ca lcu la te th a t
su rface m e a su re m e n ts o f SM a n d pN A a re a p p ro x ­
im ately 2 tim es low er th a n th e c o rre s p o n d in g cross
sectio n b a la n c e d m e a n s (ratio 1 to 5 a c c o rd in g to
th e m o m e n t o f th e tid a l cycle). O nly a t th e e n d o f
th e eb b , th e w a ter c o lu m n is h o m o g e n o u s a n d sur­
face sam ples a re re p re se n ta tiv e o f th e w h o le w a ter
co lu m n . So in th is p a rtic u la r case, su rface pN A
m e a su re m e n ts u n d e re s tim a te by a m e a n fa c to r o f
two tile a ctu al cross sectio n average. A lth o u g h it
was only d e te r m in e d at o n e sta tio n a n d fo r o n e
tid al a n d seasonal situ atio n , we see th a t ap p lying
this fa c to r to o u r lo n g itu d in a l sNA m e a su re m e n ts
in th e estuary, resu lts in a b e tte r a g re e m e n t b e ­
tw een n itrify in g activity m e a su re m e n ts a n d D IN
b u d g e ts (T able 2).
C o n seq u en c e o f t h e C o u pled Su spen d ed
P a r t i c l e s - N i t r i f i c a t i o n D y n a m ic s
A c o n se q u e n c e o f th e c o u p le d SM -pNA tid al dy­
n am ics is th a t th e re su sp e n sio n o f p a rtic le s d u rin g
th e f lo o d ’s flow inversion, a n d th e ir u p stre a m
tra n s p o rta tio n by th e flo o d , follow ed by a signifi­
c a n t s e d im e n ta tio n a t h ig h tide, c o u ld le a d to a
n e t a c c u m u la tio n o f p a rtic le s in som e e stu a rin e
seg m e n ts d u rin g low riv er d isc h a rg e c o n d itio n s.
T h e seaso n al v aria tio n s o f SM in th e e stu a ry (sta­
tio n M o u lin ea u x , 258 km ) in c o m p a riso n w ith th e
seasonal v ariatio n s o f SM in th e river (Poses dam ,
198 km ) illu stra te this p o in t (Fig. 9 ). S easonal var­
iatio n s o f SM a t th e e stu a rin e sta tio n (258 km )
show m a x im u m c o n c e n tra tio n s w h en river dis­
c h a rg e is m in im u m . T h e o p p o site p a tte r n is o b ­
serv ed at th e riv erin e sta tio n (198 km ) w h e re m ax ­
im u m c o n c e n tra tio n s usually co in c id e w ith m axi­
680
N. Brion e t al.
800
600 -
ö
2 -
200-
■2
0
2
6
4
0
-2
10
8
2
4
6
10
8
Tim e after low tide (h)
Tim e after low tide (h)
Fig. 8. V ariab ility o f th e s u s p e n d e d m a tte r (SM ) a n d p o te n tia l n itrify in g activity (pN A ) m e a s u re m e n ts o n a cross se c tio n a t sta tio n
M o u lin e a u x (258 k m ) a lo n g a tid a l cycle o n S e p te m b e r 2V, 1996. C rosses r e p r e s e n t th e su rfa c e m e a s u re m e n ts , d o tte d lin e s w ith o p e n
circles a re th e m in im u m a n d m a x im u m values o n th e cross se ctio n , a n d th e full lin e w ith fille d circles is th e in te g r a te d av erag e value
o n th e cross sectio n .
m u m riv er d isch arg es. SM m e a s u re m e n ts p e r­
f o rm e d twice m o n th ly by th e SNS at 198 km a n d
a t 260 km , fro m 1990 to 1995, show th a t d u rin g
h ig h d isc h a rg e p e rio d s, SM c o n c e n tra tio n s in th e
riv er a re h ig h e r th a n a t th e e stu a rin e statio n , w hile
d u rin g p e rio d s o f low d isch arg e, th e o p p o site is
- • —SM Estuary (258 km)
o b se rv e d (Fig. 10). It seem s cle a r th a t th e r e is an
a c c u m u la tio n o f p a rtic le s in th e e stu ary th ro u g h ­
o u t th e low w a te r flow p e rio d , w h e n th e re sid e n c e
tim e o f p a rtic le s in th e e stu ary is p ro b a b ly lo n g e r
th a n th e w ate r re sid e n c e tim e.
A lth o u g h o u r d e sc rip tio n o f th e p a rtic le dynam -
- - 0 - - S M River (198 km)
60-
-
2000
- 1500
T_ 40 -
-
'
0-
-
1000
- 500 “
-2000
2= 4 0 - 1500
3
20
-
-
1000
-5 0 0
035 T>J
O
o
C_
1993
<_
C
3U
T>3
c
1994
O
o
c_
cu
3
T>J
C_
c_
1995
O
C—
03>
■>o
<_
C_
“
O
o
1996
Fig. 9. Seasonal variations o f su sp en d ed m atter co n ce n tra tio n (SM) a t stations Poses dam (198 km , in th e river) a n d M oulineaux
(258 km , in th e estuary), a n d p o ten tial nitrifying activity o n these particles (pNA:SM) a t station M oulineaux (258 km ). M ean surface
suspended m a tte r co n ce n tra tio n is calculated by in te g ratin g th e tidal profiles o f Figs. 4 a n d 5. Som e su p p le m e n tary d ata w ere given
by th e Service de la N avigation de la Seine (SNS) pNA : SM. P otential nitrifying activity associated w ith su sp en d ed m a tte r is calculated
as th e slope o f th e lin e a r regression d u rin g tidal variations o f SM a n d PNA (see Table 1) o r as th e sim ple single pNA divided by SM
m easurem ents. River discharge is p re se n te d as a d o tte d line.
Nitrification in the S e in e River and Estuary
681
th e sm all T a m a r R iver estuary, O w ens (1986) cam e
to th e sam e c o n c lu sio n s by c o m p a rin g e stu a rin e
n itrific a tio n to a flu id iz ed b e d re a c tio n .
Q < 600 m3 s
Q > 600 m3 s '1
A cknow ledgm ents
This work was supported by the French research program s Pro­
gram m e Interdisciplinaire de Recherche sur l’Environnem entSeine (Centre N ational de R echerche Scientifique, Agence de
l’Eau Seine N orm andie) a n d Seine-aval (Region H aute N orm an­
die). At the tim e o f this work N atacha Brion was a d octoral research-fellow o f th e F o n d p o u r la fo rm atio n à la R echerche
p o u r l ’In d u strie e t l’A gronom ie (Belgium ) a n d Gilles B illen was
th e re sear ch-dire eto r o f th e F o n d N ational de R ech erch e Scien­
tifique (B elgium ).
0
50
100
150
200
SM river (mg I"1'
Fig. 10. S uspended m atter (SM) m easu red at M oulineaux
(258 km , in th e estuary) versus su spended m atter m easu red at
Poses dam (198 km , before the estuary) for 2 discharge cate­
gories, betw een 1990 a n d 1995. (Service de la N avigation de la
Seine u n p u b lish ed data).
ics in th e S ein e e stu a ry m ay b e sim plistic, a re c e n t
d e ta ile d h y d ro -se d im e n ta ry study o n p a rtic le tra n s­
p o r t in th e S ein e e stu a ry m a d e by G u é z e n n e c e t
al. (1999) cam e to th e sam e co n clu sio n s. T h e ac­
c u m u la tio n o f p a rtic le s in th e e stu a ry d u rin g sum ­
m e r c o u ld have im p o r ta n t im p lic a tio n s fo r th e
g ro w th o f th e n itrify in g p o p u la tio n . T h e slo p e o f
th e re g re ssio n lin es o f p o te n tia l n itrify in g activity
versus s u s p e n d e d m a tte r given in T able 1 pro v id es
a m e a su re o f th e n itrify in g b io m ass asso ciated to
th o se p articles. A d d itio n a l d a ta w ere o b ta in e d by
d iv id in g sin g le m e a s u re m e n ts o f pN A m a d e a t sta­
tio n M o u lin e a u x (258 km ) w ith SM, m a k in g th e
sim plifying h y p o th e sis th a t all n itrify in g b a c te ria
a re asso ciated w ith all th e p articles. T h e seasonal
v a ria tio n s o f th is pN A :SM ra tio (Fig. 9) show th a t
p a rtic le s a re progressively c o lo n iz e d by n itrify in g
b a c te ria w ith a very sh a rp a n d h ig h p e a k c o rre ­
s p o n d in g to th e s u m m e r m in im u m riv er d isch arg ­
es. T h is m a x im u m also o c c u rs d u rin g p e a k sum ­
m e r te m p e ra tu re s w h ich a re p a rtic u la rly favorable
to th e g ro w th o f n itrify in g b a c te ria , b u t th e sh a rp ­
n ess o f th e p e a k suggests th a t th e lo n g re sid e n c e
tim es o f th e p a rtic le s to w h ich n itrify in g b a c te ria
a re a tta c h e d a re fav o rab le to th e d e v e lo p m e n t o f
im p o r ta n t biom asses. T h e asso ciatio n o f n itrify in g
b a c te ria to p a rtic le s w ith lo n g e r re s id e n c e tim es
th a n w a te r m asses re p re s e n ts th u s a b e n e fit fo r th e
d e v e lo p m e n t o f th e se slow g ro w in g o rg anism s. A
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E m s -D o lla rd e s tu a r y by H e l d e r a n d D e V ries
(1983) also cam e to th e c o n c lu sio n th a t it was only
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So u r c e
of
U n p u b l is h e d M a t e r ia l s
Received fo r consideration, March 23, 1999
Accepted fo r publication, June 12, 2000