Variations in concentrations of dissolved sugars were studied along the salinity gradient of a small estuary (Elorn, Bay of Brest, France) from February 1985 to January 1986. Total dissolved carbohydrate (TDCHO) and dissolved monosaccharides (MCHO) were measured by the methods of Burney and Sieburth and Johnson and Sieburth respectively. It must be noted that these methods cannot distinguish between carbohydrates and carbohydrate-like substances; consequently, these methods probably do not closely reflect biologically available pools of carbohydrates. In the river, TDCHO and MCHO values ranged from 230 to 970 /ig C 1"' and from 75 to 450 ngC\-^ respectively. In the estuary, TDCHO and MCHO were usually lower; they varied respectively from 20 to 570 /zg C 1~' and from 0 to 180/ig C1 '. In June, some TDCHO values were much higher, probably because some polysaccharide was produced at this time by phytoplankton excretion or lysis. The relationship between Cl%o and TDCHO was dependent on the seasons. TDCHO was conservative in autumn, winter and early spring. TDCHO and DOC concentrations were fairly well correlated during the same period. Similar results have been previously reported by various workers. MCHO and TDCHO concentrations were well correlated throughout this study except in June. From these results, it was concluded that most dissolved carbohydrates were linked to a conservative fraction of the organic matter in periods of low biological activity, whereas newly biosynthesised carbohydrates were responsible for non-conservative behaviour.

1. Marine Chemistry, 32 (1991) 19-35
Elsevier Science Publishers B.V., Amsterdam
19
Studies o f dissolved carbohydrates
( o r c a r b o h y d r a t e - l i k e substances) i n a n estuarine
e n v i r o n m e n t *
W i l l i a m Senior** and Lionel Chevolot***
Laboratoire d'Oceanographie Chimique, URA CNRS 322, Universite de Bretagne Occidentale, 6,
avenue le Gorgeu, 29287Brest Cedex (France)
(Received February 13, 1989; revision accepted May 28, 1990)
ABSTRACT
Senior, W. and Chevolot, L., 1991. Studies of dissolved carbohydrates (or carbohydrate-like sub-
stances) in an estuarine environment. Mar. Chem., 32: 19-35.
Variations in concentrations of dissolved sugars were studied along the salinity gradient of a small
estuary (Elorn, Bay of Brest, France) from February 1985 to January 1986. Total dissolved carbo-
hydrate (TDCHO) and dissolved monosaccharides (MCHO) were measured by the methods of Bur-
ney and Sieburth and Johnson and Sieburth respectively. It must be noted that these methods cannot
distinguish between carbohydrates and carbohydrate-like substances; consequently, these methods
probably do not closely reflect biologically available pools of carbohydrates. In the river, TDCHO and
MCHO values ranged from 230 to 970 /ig C 1"' and from 75 to 450 ngC-^ respectively. In the
estuary, TDCHO and MCHO were usually lower; they varied respectively from 20 to 570 /zg C 1~'
and from 0 to 180/ig C1 '. In June, some TDCHO values were much higher, probably because some
polysaccharide was produced at this time by phytoplankton excretion or lysis.
The relationship between Cl%o and TDCHO was dependent on the seasons. TDCHO was conserv-
ative in autumn, winter and early spring. TDCHO and DOC concentrations were fairly well correlated
during the same period. Similar results have been previously reported by various workers. MCHO
and TDCHO concentrations were well correlated throughout this study except in June. From these
results, it was concluded that most dissolved carbohydrates were linked to a conservative fraction of
the organic matter in periods of low biological activity, whereas newly biosynthesised carbohydrates
were responsible for non-conservative behaviour.
INTRODUCTION -
T h e r e is a g r o w i n g interest i n the study o f dissolved organic m a t t e r ( D O M )
i n seawater as i t becomes increasingly obvious that D O M interacts w i t h m a n y
biological a n d chemical phenomena.
•This paper forms part of the thesis (These de Doctoral) of W. Senior.
"Present address: Nucleo de Sucre, Institute Oceanografico Universidad de Oriente, AP 245,
Cerro Colorado, Cumana, Venezuela.
***Author to whom correspondence should be addressed at: Laboratoire de Biologie Marine,
Universite de Nantes, 2 rue de la Houssiniere, 44072 Nantes, France.
0304-4203/91/$03.50 © 1991 — Elsevier Science Publishers B.V.

2. 20 W . S E N I O R A N D L. C H E V O L O T
A l t h o u g h carbohydrates are i m p o r t a n t constituents o f D O M (usually 1 0 -
2 0 % ) , relatively little is k n o w n about t h e m , especially i n estuarine and coastal
ecosystems, m a i n l y because analytical techniques cannot be used i n r o u t i n e
w o r k . S o m e m e t h o d s have been used t o d e t e r m i n e either the total carbohy-
drate content or the m o n o m e r i c sugar c o m p o s i t i o n o f seawater, but these
m e t h o d s are difficult a n d t i m e c o n s u m i n g . ( F u r t h e r i n f o r m a t i o n is given i n
the following reviews: M o p p e r ( 1 9 8 0 ) , D a w s o n and Liebezeit ( 1 9 8 1 a,b) a n d
Liebezeit a n d D a w s o n ( 1 9 8 2 ) . )
Sugars, i n the total dissolved carbohydrate ( T D C H O ) p o o l , are present as
monosaccharides ( M C H O ) or polysaccharides ( P C H O ) ; the latter should be
divided between biogenic polysaccharides a n d carbohydrates b o u n d t o h u m i c
substances ( H S ) . H o w e v e r , i t is n o t easy t o distinguish between these last
fractions a n d they are usually measured together as P C H O .
F r o m the data collected i n various earlier studies, the following features
appear:
( 1 ) T D C H O and M C H O concentrations vary, i n seawaters a n d brackish
waters, f r o m 30 t o 1300 //g C 1 " ' and f r o m 2 t o 300 /ig C 1 " ' respectively. A
few higher values have also been reported ( S u m i t r a et al., 1 9 7 2 ) .
( 2 ) T h e M C H O fraction usually accounts for a significant part o f T D C H O
( B u r n e y a n d S i e b u r t h , 1977; I t t e k k o t et al., 1 9 8 1 ; Sakugawa a n d H a n d a ,
1 9 8 5 ) ; s o m e t i m e s for m o r e t h a n h a l f ( B u r n e y e t a l . , 1979; H a r v e y , 1 9 8 3 ) .
( 3 ) D i u r n a l fluctuations o f T D C H O m a y occur i n periods o f biological
activity ( W a l s h , 1965; B u r n e y et al., 1981a,b); H a r v e y , 1983; E b e r l e i n et al.,
1 9 8 3 ) , but the M C H O concentrations are fairly constant over a 24-h p e r i o d
( B u r n e y e t a l . , 1981a,b; B u r n e y , 1 9 8 6 a ) .
( 4 ) I n o n l y a few studies have attempts been m a d e t o establish a relation-
ship between sugar c o m p o s i t i o n a n d other chemical, physical a n d biological
parameters.
W e report here results obtained f r o m a study p e r f o r m e d i n a s m a l l estuary
located i n B r i t t a n y ( E l o m Estuary, B a y o f Brest, France; see F i g . 1.). S o m e
p r e l i m i n a r y results have been published elsewhere ( S e n i o r et al., 1 9 8 7 ) . T o
our knowledge, this is one o f the few studies p e r f o r m e d over such a l o n g pe-
r i o d o f t i m e i n the same area. Seasonal v a r i a t i o n s a n d origins are studied; the
nature o f dissolved carbohydrates is discussed i n the light o f present a n d pub-
lished data.
METHODS AND MATERIAL
Study area ,,
Figure 1 shows the E l o m E s t u a r y ( B r i t t a n y , F r a n c e ) a n d the l o c a t i o n o f
the seven s a m p h n g sites. Sites E i a n d E j are low-salinity sites, a n d they are

3. D I S S O L V E D C A R B O H Y D R A T E S I N E S T U A R I N E E N V I R O N M E N T S 21
Fig. 1. Location of sampling sites in the Elorn Estuary.
considered t o be located i n the river. E l o m is a 12-km-long estuary. T h e depth
ranges f r o m 3.5 m at L a n d e m e a u t o 12.5 m at A l b e r t L o u p p e bridge.
D u r i n g this study, the flow o f the r i v e r varied between 1.3 a n d 18 m ^ s " ' .
A detailed record has been published earlier ( N o u r e d d i n et al., 1 9 8 7 ) , to-
gether w i t h the rainfall record. T h i s estuary is strongly influenced by tide pat-
tems; the renewal t i m e o f the water is between 2 a n d 4 days ( L ' Y a v a n c , 1 9 8 4 ) .
L a n d e r n e a u (see F i g . 1 ) is a m e d i u m - s i z e d city o f 2 0 0 0 0 inhabitants. T w o
sewers discharge Landerneau's waste-water, after cleaning by a sewage-treat-
m e n t system, slightly d o w n s t r e a m f r o m site E2 ( m e a n accumulated flux: 5000
m ^ d a y " ' , m e a n D O C value 2 0 m g C 1 " ' ) . I n the same area (between sites E2
and E 3 ) there is also a seaweed-processing factory w h i c h extracts alginate f r o m
b r o w n seaweeds ( 3 0 0 0 0 t y e a r " ' ) . Waste-water f r o m this factory is dis-
charged i n t o the estuary i n a n erratic m a n n e r . Site E3 is about 3 k m d o w n -
stream f r o m this plant. I n a d d i t i o n , upstream f r o m site E j , there is also a
milk-processing factory, but its waste-water is treated. Lastly, at d o w n s t r e a m
sites Eg and E7, some organic m a t t e r m a y c o m e f r o m the m a i n sewer that
collects Brest waste-water w h i c h is discharged (after t r e a t m e n t ) close t o
M o u l i n Blanc B a y (see F i g . 1 ) .
Sampling -'
W a t e r samples were collected f r o m F e b r u a r y 1 1 , 1985, t o January 8, 1986
(see Table 1 ) . Samples were collected d u r i n g the 2 - 3 - h p e r i o d a r o u n d h i g h

4. 22 W . S E N I O R A N D L. C H E V O L O T
water; tide coefficients were i n the range o f 7 0 - 8 0 except o n M a r c h 11 ( 9 8 ) .
It was n o t possible, for each cruise, t o sample d u r i n g the same period o f the
day.
T h e samples can also be grouped according t o the season i n w h i c h they were
collected: spring ( M a r c h 11-June 7 ) o r early spring ( M a r c h 1 1 - A p r i l 2 4 ) ,
s u m m e r ( J u l y a n d September) a n d a u t u m n - w i n t e r ( F e b r u a r y 1985 and Oc-
tober 11-January 8, 1 9 8 6 ) .
A t stations E3-E7, water sampling was carried o u t using an electrical p u m p
( L e n z e D i s c o v e r t e l l Getriebe T y p e 11602, F . R . G . ) . T h i s p u m p is a peristaltic
p u m p w i t h a synthetic p o l y m e r tube; consequently, there is n o contact be-
tween mechanical parts and water, a n d n o possibility o f c o n t a m i n a t i o n b y
biogenic molecules; D O C measurements have also s h o w n that there is n o sig-
nificant increase o f D O C . A t stations E i a n d E2, a clean glass bottle was used.
A l l samples were t a k e n j u s t below the surface a n d were filtered i m m e d i a t e l y
t h r o u g h a 1 0 0 - / i m screen. T h e y were kept for several hours at 5°C before
being filtered t h r o u g h a G F / C precombusted (450°C, 4 h ) glass fiber fiher.
F o r the few hours ( 3 - 4 h ) between collection a n d processing, some bacterial
degradation could n o t be avoided, but f r o m the data published b y B u r n e y
( 1 9 8 6 a , b ) , w e can estimate ( i n s u m m e r a n d i n d a r k ) that the T D C H O deg-
radation rate is usually less t h a n 10 //g C 1 ~ ' h ~ ' . O c h i a i et al. ( 1 9 8 0 ) a n d
O c h i a i a n d N a k a j i m a ( 1 9 8 5 ) gave s i m i l a r o r l o w e r decomposition rates i n
freshwater. A t 5°C, the loss is probably less. E r r o r introduced by keeping the
water for a few hours d i d exist, but was o f the same m a g n i t u d e as the experi-
m e n t a l analytical error (see analytical m e t h o d s ) . F o r M C H O , bacterial u t i -
lization ( f o r the same p e r i o d ) was probably significant. O n the other hand,
filtering w i t h G F / C o n l y partially r e m o v e d bacteria. Consequently, some car-
bohydrates counted as T D C H O were indeed bacterial particulate carbohy-
drates, but probably o n l y t o a slight extent, because w e also analysed 36 sam-
ples by H P L C a n d f o u n d bacterial sugars ( r h a m n o s e , fucose, ribose) o n l y at
l o w percentages (Senior, 1 9 8 6 ) . Filtrates were t h e n kept i n glass bottles after
a d d i t i o n o f 1 m l 1 ~ ' o f a saturated HgCl2 s o l u t i o n . A l l glassware used t h r o u g h -
out the analysis was precombusted (450°C, o v e r n i g h t ) .
Analytical methods
Analyses o f D O C were carried o u t o n a D o h r m a n n D C 80 analyser w h i c h
performs p h o t o - o x i d a t i o n o f samples i n the presence o f persulfate. Results
are expressed i n m g C 1 " C h l o r i n i t y was measured by the K n u d s e n m e t h o d
according t o the procedure described by A m i n o t ( 1 9 8 3 ) . C h l o r o p h y l l a a n d
p h a e o p h y t i n a were d e t e r m i n e d fluorometrically using a T u r n e r I I I fluoro-
meter, according t o L o r e n z e n ( 1 9 6 7 ) , after extraction f r o m the filters b y a n
acetone-water m i x t u r e ( 9 0 : 1 0 , v / v ) . H o w e v e r , w e should p o i n t o u t that re-

5. D I S S O L V E D C A R B O H Y D R A T E S I N E S T U A R I N E E N V I R O N M E N T S 23
suits obtained by this m e t h o d m a y n o t be accurate for estuarine e n v i r o n m e n t s
( M a n t o u r a and L l e w e l l y n , 1 9 8 3 ) .
F o r dissolved monosaccharides ( M C H O ) , the m e t h o d o f J o h n s o n a n d Sie-
b u r t h ( 1 9 7 7 ) was used, f o l l o w i n g the procedure given b y D a w s o n a n d L i e -
bezeit ( 1 9 8 1 a , b ) . M a n n i t o l a n d glucose were used as standards. M o l a r con-
centrations were calculated f r o m the c o n t r o l corrected m e a n absorbance data
using the (glucose-f-mannitol ) / 2 regression line. Results are expressed i n jug
C 1 " ' o f glucose equivalent. I n o u r hands, the precision o f this m e t h o d was
not as h i g h as stated by D a w s o n a n d Liebezeit ( 1 9 8 1 b ) . Measures were m a d e
i n triplicate (three aliquots f r o m the same sample b o t t l e ) ; standard d e v i a t i o n
varied f r o m 10 t o 30 /ig C 1 " ' depending o n the sample. O b v i o u s l y , this m e t h o d
cannot distinguish between true monosaccharides and any substances w h i c h
possess a t e r m i n a l glycol f u n c t i o n ( C H O H - C H j O H ) . Such a f u n c t i o n is ex-
pected t o be present i n h u m i c substances ( H S ) , a n d consequently, interfer-
ence w i t h t h e m cannot be avoided.
F o r t o t a l dissolved carbohydrates ( T D C H O ) , the m e t h o d o f B u r n e y a n d
S i e b u r t h ( 1 9 7 7 ) was used. H o w e v e r , the c o n d i t i o n s o f hydrolysis were differ-
ent ( I t t e k k o t , 1 9 8 2 ) : 5 - m l seawater samples w i t h 1 m l o f H C l ( 3 0 % ) were
hydrolysed a t 100°C for 3.5 h . A f t e r cooling, the acid was neutralized w i t h
concentrated N a O H ( ~ 1 m l ) . p H was checked w i t h p H papers. Concentra-
t i o n s were corrected for d i l u t i o n s . A s for M C H O , H S interference occurs.
H o w e v e r , a good correlation ( r = 0 . 9 7 , « = 36; slope = 1.1) was obtained be-
t w e e n the s u m o f i n d i v i d u a l sugars measured by H P L C (see above; Senior,
1 9 8 6 ) a n d the result g i v e n by the M B T H m e t h o d .
T h e concentration o f dissolved polysaccharides ( P C H O ) is the difference
between t h e concentration i n T D C H O a n d t h e concentration i n M C H O
( B u r n e y a n d Sieburth, 1 9 7 7 ) .
RESULTS AND DISCUSSION
Tables 1 and 2 list respectively the T D C H O a n d M C H O concentrations at
each site d u r i n g the f)eriod studied. T h e T D C H O concentrations were vari-
able in the river a n d ranged f r o m 2 3 0 t o 9 7 0 / i C 1 " ' . T h i s v a r i a b i l i t y could
be cansed by some material being brought b y t i d a l currents ( s a m p l i n g was
f i f c a i J I f y ^ f c • 111 I ) from Landerneau's sewers or f r o m the seaweed fac-
toiv.lBpHlicBfar.11ic970/«CI~' value (100/^C 1~' m o r e t h a n the second-
b l ^ E H v a l a e l wm drmnmjittj h i g h , because the tide coefficient ( 9 8 ) w a s
s i g B f l i c a M l f h i g h e r OB Aisdqrtlian nsoal. Consequently, this value was n o t
i n d n d e d im t k e akaiatkms. For the r e m a i n i n g o v e r a l l measurements, t h e
m e a n value was 5 6 0 « C l ~ ' . In autumn-*inter. the average concentration
i n the r i v e r was higher ( 6 7 5 , u g C l ~ ' ) t h a n i n early spring (420/zg C 1 " ' ) . A t
d o w n s t r e a m stations, the T D C H O concentrations were usually l o w e r ( 2 0 -

6. 24 W . S E N I O R A N D L . C H E V O L O T
TABLE 1
TDCHO concentrations (//g C 1^') in the Elorn Estuary
Date (1985) Site
E, E2 E 3 E 4 E 5 E6 Ev
February 11 860 530 350 340 140 40 20
March 11 970* 440 145 180 155 150 125
April 3 320 430 310 265 220 240 290
April 17 495 750 230 205 280 255 245
April 24 265 265 210 105 165 145 140
June 7 795 785 620 755 470 1080 395
July 1 550 480 325 185 270 265 165
September 20 305 230 395 385 320 195 205
October 11 765 755 330 295 295 305 215
November 25 545 835 120 115 145 90 100
December 9 700 715 400 315 295 265 245
January 8 (1986) 500 545 570 325 315 250 240
*This abnormally high value has been discarded.
TABLE 2
MCHO concentrations (/^g C 1"') in the Elom Estuary
Date Site
E, E 3 E 4 E 5 E6 E 7
February 11 290 200 110 130 0 0 0
March 11 390 180 70 60 55 90 40
April 3 245 225 180 165 115 135 170
April 17 450 400 95 80 80 105 75
April 24 165 185 170 100 150 90 95
June 7 105 165 90 75 75 430 130
July 1 325 305 120 60 105 110 35
September 20 105 75 145 100 115 80 90
October 11 325 335 125 105 110 70 65
November 25 260 385 45 30 35 35 10
December 9 285 305 125 130 100 55 65
January 8 185 230 130 95 75 55 40
570 jUg C 1~'), w i t h some notable exceptions i n June ( 1 0 8 0 / / g C 1 " ' at station
Eg, for instance). T h e M C H O values were lower; they ranged f r o m 75 t o 4 5 0
/ig C 1 ~ ' i n t h e r i v e r a n d f r o m 0 t o 180 /zg C 1 " ' at m o r e d o w n s t r e a m stations.
Relationship between chlorinity and TDCHO
T D C H O concentrations showed a relatively poor b u t significant relation-
ship w i t h c h l o r i n i t y ( r = 0 . 5 8 ; « = 83; / ' < 0 . 0 0 1 ) f o r t h e overall measure-

7. D I S S O L V E D C A R B O H Y D R A T E S I N E S T U A R I N E E N V I R O N M E N T S 25
ments. I f the values measured i n June, July a n d September are not t a k e n i n t o
account, a better relationship is obtained (see F i g . 2 a ) .
I f the data are split i n t o early spring values ( M a r c h 1 1 - A p r i l 2 4 ) a n d au-
t u m n - w i n t e r values, t w o different regression lines are obtained (see F i g . 2 ) .
F o r this last period, the y-intercept a n d slope are higher, probably because the
T D C H O i n p u t f r o m the r i v e r was m o r e i m p o r t a n t at this t i m e , w h e n terres-
trial plants were decaying a n d w h e n the l a n d was m o r e efficiently drained. I t
is w o r t h p o i n t i n g out that, w i t h o u t the r i v e r measurements, w e obtained s i m -
ilar regression lines i n early spring ( r = 0 . 7 9 ; « = 20; P<0.001;
[ T D C H O ] = - 1 3 . 5 (±2.5) [Cl%o] + 390 (±40)) as well as i n a u t u m n -
w i n t e r ( r = 0 . 5 9 ; « = 25; P<0.01; [ T D C H O ] = - 2 3 (±6.5) [ C l % o ] - I - 6 0 0
( ± 1 0 0 ) ) . F o r b o t h periods, y-intercepts ( 3 9 0 a n d 600 /zg C 1"') are accept-
ably close t o the T D C H O m e a n values i n the r i v e r ( 4 2 0 a n d 675 /zg C 1 " s e e
a b o v e ) . T h i s result suggests that the T D C H O concentration was w i d e l y vari-
able i n the r i v e r o n a short time-scale, but the T D C H O flux introduced i n t o
the estuary by the r i v e r was m o r e stable. These data also suggest that m o s t o f
the T D C H O was c o m i n g f r o m the r i v e r a n d was conservative i n a u t u m n -
w i n t e r a n d early spring i n this estuary a n d for this study. T o o u r knowledge,
this is the first t i m e that such b e h a v i o u r o f dissolved carbohydrates has been
established. T h i s result is rather surprising, because a p r i o r i , carbohydrates
should be a d y n a m i c part o f the D O M a n d should n o t be conservative.
D u r i n g t h e period o f higher biological activity ( J u n e - S e p t e m b e r ) , t h e
T D C H O vs. Cl%o relationship disappeared, probably because o f some i n situ
production, especially i n June ( m o s t o f the points are above the regression
lioe; see F i g . 2 a ) . Surprisingly, d u r i n g the early spring ( M a r c h 1 1 - A p r i l 2 4 ) ,
the T D C H O vs. Cl%o relationship was fairly strong ( r = 0 . 7 7 ; « = 2 7 ) , al-
though there was some evidence o f biological a c t i v i t y i n the estuary ( h i g h
concentrations i n c h l o r o p h y l l a n d p h a e o p h y t i n o n M a r c h 11 a n d A p r i l 3, for
instance). E i t h e r the p h y t o p l a n k t o n i c species o f the spring b l o o m d i d n o t ex-
crete any carbohydrates, or the excreted carbohydrates were very quickly used
a n d d i d not b u i l d up any significant a m o u n t o f T D C H O .
Relationship between TDCHO and phaeophytin
Dwnngtbc period of biological a c t i v i t y ( J u n e - S e p t e m b e r ) , there was a sig-
• i C f j i jffatinmdiip (r=0.76. calculated w i t h o u t the a b n o r m a l l y high phaeo-
p k v t i B v a l a e (10.3 /Jig ~ ) of July 1 at station E , ) between T D C H O a n d
p h a c o p k v t i B (see Fig. 3). B u r n e y et al. ( 1 9 8 1 a ) also noted a correlation be-
tween TDCHO and phaeopigmem fluctuations i n a study o f diel variations
of TDCHO in a emulated estuarine ecosystem. Similarly, I t t e k k o t et al.
(1981) measured m a x i m u m dissolved c o m b i n e d carbohydrate concentra-
tions towards the end o f a b l o o m i n the N o r t h Sea. A c c o r d i n g t o these w o r k -
ers, n u t r i e n t h m i t a t i o n leads t o the release o f large a m o u n t s o f carbohydrates.

9. D I S S O L V E D C A R B O H Y D R A T E S I N E S T U A R I N E E N V I R O N M E N T S 27
9 0 0
8 0 0
7 0 0
(c)
6 0 0 -
5 0 0 - ( ]
4 0 0 -
3 0 0 -
2 0 0 -
1 0 0 -
0 - -
•an
~T 1 1 1 1 1 1 1 1 1 1 1 1 r
4 6 8 1 0 1 2 1 4 1 6 1 8
Chlorluitj (in %o)
Fig. 2. The inverse relationship of TDCHO to Cl%o. (a) For the overall measurements, the
regression line was [TDCHO] = -18 ( ± 3 ) [Cl%o]-l-560 ( ± 180) (/-=0.58; « = 83; P<0.001),
but that shown here was calculated without the June-July-September values ( + ):
[TDCHO] = - 2 2 ( ± 2 ) [Cl%o] + 560 ( ± 1 3 0 ) (r=0.77; « = 62;/'<0.001). (b) In spring, the
regression line was [TDCHO] = - 1 5 ( ± 2 . 5 ) [Cl%o]+420 ( ± 9 0 ) (r=0.77; « = 27; P<0.001).
(c) in autumn-winter, the regression line was [TDCHO] = -27 ( ± 2 . 5 ) [Cl%o]+680 ( ± 1 1 5 )
(r=0.87:/7 = 35;P<0.00I).
Usually, d u r i n g a p h y t o p l a n k t o n b l o o m , accumulation o f dissolved carbohy-
drates is a t a m a x i m u m i n the stationary phase ( M y k l e s t a d t , 1977; Brock-
mann et al., 1 9 7 9 ) . Indeed, i n Fig. 2a, i t is obvious that large excretions o f
carbohydrates occurred i n the bay i n s u m m e r w h e n nutrients were depleted.
For instance, nitrate fell f r o m 20 / z M 1 ~ ' i n A p r i l t o 4 1 " ' i n June and
0 ^ r ' i n July at station E7 (Senior, 1 9 8 6 ) . Consequently, during this pe-
riod, T E K T H O were not o n l y f o r m e d by refractory carbohydrates c o m i n g f r o m
I k e river, but also by n e w l y biosynthesised sugars released by senescent algal
o e f e o r produced by z o o p l a n k t o n excretion ( B u r n e y et al., 1981a).
ti§mmiM} dissolved carbohydrates (TDCHO or MCHO) and DOC
The TDCHO D O C relationship calculated for the overall points was
«cak md I k eregressionline aberrant (see Fig. 4 a ) . H o w e v e r , i f the J u n e -
JuK—ScplcBbervahies. together w i t h three additional a b n o r m a l l y high D O C
values (statkm Ej of Febriiar> 1 1 . stations E2 o f December 9; station E7 o f

10. 28 W . S E N I O R A N D L. C H E V O L O T
1.6
0 2 4 6 8 1 0
P h a e o p h y t i n ( I n / i j / 1 )
Fig. 3. The direct relationship between TDCHO and phaeophytin in June-July-September. The
value for July 1 at site E , ( • ) is not included in the calculation of the regression line:
[TDCHO] = 140 ( ± 3 0 ) [Phaeo]+90 ( ± 170) (/•=0.76; « = 20;/'<0.001).
A p r i l 3 ) , are discarded, a m u c h better relationship is obtained (see F i g . 4 a ) .
V e r y s i m i l a r results have been f o u n d for M C H O . A m o d e r a t e l y good correla-
t i o n between M C H O a n d D O C m a y be calculated for the overall measure-
m e n t s ( r = 0 . 3 5 ; « = 84; P < 0 . 0 1 ) . T h e c o r r e l a t i o n coefficient is better i f the
same values as before are discarded ( a - = 0 . 6 1 ; « = 60; P < 0 . 0 0 1 ) . T h e corre-
lation becomes excellent i n a u t u m n - w i n t e r , w i t h the exclusion o f the corre-
sponding a b n o r m a l l y h i g h D O C values ( r = 0 . 8 9 ; « = 33; / ' < 0 . 0 0 1 , see F i g .
4 b ) . Consequently, i n the p e r i o d o f l o w biological activity, dissolved carbo-
hydrates ( T D C H O o r M C H O ) a n d D O C were correlated, a n d consequently
h ad s i m i l a r origins a n d e v o l u t i o n s . A s the b u l k o f the D O M is k n o w n t o be
Fig. 4. The direct relationship between dissolved carbohydrates and DOC. (a) TDCHO vs.
DOC relationship: the broken regression line ([TDCHO] = 38.5 ( ± 12) [DOC] +230 ( ±210);
/•=0.33; « = 83; P<0.01) was calculated from overall points. The solid regression line
([TDCHO] = 126 ( ± 1 3 ) [ D O C ] - 1 0 ( ± 120); r=0.79; « = 59; i'< 0.001) was calculated
without the June values ( + ) the July-September values ( O ) and three additional high DOC
values ( A ) , (b) MCHO vs. DOC relationship: the regression line ([MCHO]=61 ( ± 6 )
[DOC] - 5 5 ( ±50); r=0.89; « = 33; P<0.00 was calculated from only the autumn-winter
measurements ( • ) . • : Winter measurements not included in calculation of the regression; +:
early spring measurements; A: June measurements; O- July-September measurements.

11. D I S S O L V E D C A R B O H Y D R A T E S I N E S T U A R I N E E N V I R O N M E N T S
DOC ( i n m g C / 1 )
a — = - ^ ^ 1 1 r " 1 i 1 1
1 3 5 7 9 1
DOC (in mgCA)

12. refractory. this resuh imphes that dissolved carbohydrates should be refrac-
tor. However, we have t o recognize that some usable dissolved carbo-
hydrate m a y be lost, especially for the period preceding fixation (see M e t h o d s
and M a t e r i a l section). F o r T D C H O , the probable losses ( 1 5 - 3 0 /ig C 1 " ' )
were l o w relative t o T D C H O concentrations ( o n l y t w o values under 100 //g
C I " ' ) , and consequently d i d n o t invalidate o u r result. F o r M C H O , concen-
trations were lower a n d monosaccharides were used m o r e rapidly ( O c h i a i
a n d N a k a j i m a ( 1 9 8 5 ) measured a glucose degradation rate o f 14 //g C 1 " '
h ~ ' ) ) ; consequently, the M C H O vs. D O C correlation is better t h a n i t should
be. I t is still true that, i n a u t u m n - w i n t e r , a significant part o f the M C H O
fraction (measured b y t h e M B T H m e t h o d ) w a s n o t m a d e u p o f usable
monosaccharides.
W h e n the biological a c t i v i t y is high, this correlation is n o longer observed.
F o r instance, i n July a n d September, m o s t points are under the regression
lines (see F i g . 4a,b), because at this t i m e , concentrations o f D O C were very
high, but those o f M C H O o r T D C H O were not. O n the contrary, i n June,
there was a large excess o f T D C H O (see Fig. 4 a ) , m a i n l y composed o f P C H O .
It is n o t e w o r t h y that s i m i l a r correlations between T D C H O and D O C have
been previously observed i n various e n v i r o n m e n t s . B u r n e y et al. ( 1 9 7 9 ) re-
ported that M C H O , P C H O a n d T D C H O showed significant correlations
( P < 0 . 0 1 ) w i t h D O C i n a study p e r f o r m e d i n a large area o n the continental
shelf o f N o r t h A m e r i c a a n d across the N o r t h A t l a n t i c Ocean, w i t h sampling
at the surface or at depth. F o r instance, the T D C H O vs. D O C regression line
calculated f r o m their data ( r = 0 . 7 1 ; « = 84; / ' < 0 . 0 0 1 ; [ T D C H O ] = 170
(±20) [ D O C ] - 2 5 (±30)) is reasonably s i m i l a r t o that obtained i n o u r
study. T h e same group had previously pubUshed ( B u r n e y and Sieburth, 1977)
data collected i n Narragansett B a y f r o m F e b r u a r y t o July 1975. F r o m these
data, a good linear correlation between T D C H O and D O C (/•=0.83; « = 20;
P < 0 . 0 0 1 ; [ T D C H O ] = 115 (±20) [ D O C ] - 7 0 (±120)) o r between
M C H O a n d D O C ( r = 0 . 8 7 ; n = 20; P < 0 . 0 0 1 ; [ M C H O ] = 4 8 ( ± 6 )
[ D O C ] — 6 2 (±45)) c a n be deduced. I n t h e Sargasso Sea, these authors
( B u r n e y et al, 198 l b ) , observed similarities between T D C H O a n d D O C pat-
terns, but u n f o r t u n a t e l y they d i d n o t give any detail o r explanation. O n the
other hand, they d i d n o t find any correlation between T D C H O a n d D O C i n
the Caribbean Sea ( B u r n e y et al., 1 9 8 2 ) . I n freshwater. Sweet a n d Perdue
( 1 9 8 3 ) also noticed " a moderately good correlation b e t w e e n " T D C H O and
D O C i n the W i l l i a m s o n R i v e r . Satoh et al. ( 1 9 8 6 ) f o u n d a s i m i l a r result i n
L a k e Suwa.
Such correlations between D O C a n d dissolved carbohydrates cannot be
fortuitous. I t w o u l d be very surprising for D O C a n d biogenic and even refrac-
t o r y T D C H O t o follow s i m i l a r evolutions i n such a variety o f e n v i r o n m e n t s .
A better explanation could be that a significant part o f T D C H O (especially
i n periods o f l o w biological a c t i v i t y ) is i n a refractory f o r m associated w i t h

13. D I S S O L V E D C A R B O H Y D R . J 1 T E S I N E S T U A R I N E E N V I R O N M E N T S
4 0 0
3 5 0 - i
3 0 0
1
4 0 0
T D C H O ( i n f J g C A )
5 0 0
450
400
9S0
300
250
(b)
I n
CD
•
•
•h
0 . 2 0.4 0 . 6
( T h o u s a n d s )
T D C H O ( I n MgC/1)
0.8
Fig. 5. The direct relationship of MCHO to TDCHO. (a) in autumn-winter: [MCHO] =0.44
(*0.02) [ T D C H O ] - 3 5 ( ± 3 0 ) (r=0.96: « = 35: P<0.001). (b) For overall points except
those for June ( + ): [MCHO]=0.44 ( ± 0 . 0 3 ) [ T D C H 0 ] - 5 ( ± 5 0 ) (r=0.87; « = 77;
;'<0.001).

14. 32 W . S E N I O R A N D L. C H E V O L O T
the b u l k o f the D O M . I t is n o t e w o r t h y that regression lines f o u n d i n various
e n v i r o n m e n t s are relatively similar, suggesting that the nature o f the ' D O C -
T D C H O complex' is relatively u n v a r i a n t . T o this refractory fraction, freshly
excreted polysaccharides m a y be added; they are responsible for the non-con-
servative b e h a v i o u r observed i n June i n o u r study, and for the diel T D C H O
variations often observed a n d reported (see I n t r o d u c t i o n ) . L a c k o f correla-
t i o n m a y also result f r o m p r o d u c t i o n o f large quantities o f dissolved organic
substances w h i c h disrupt the relationship between T D C H O and D O C (as i n
s u m m e r i n the present s t u d y ) .
Relationship between MCHO and TDCHO
T h e r e was a n excellent linear relationship between M C H O and T D C H O
(see Fig. 5a) i n a u t u m n a n d w i n t e r . Surprisingly, m o s t o f the other points are
relatively close t o this regression line except those for June. I f the June points
are ignored, a s i m i l a r regression line is obtained (see Fig. 5 b ) . I t is inconceiv-
able that truly free monosaccharides and polymeric carbohydrates follow such
similar patterns o f release a n d uptake. I t also seems unbelievable that M C H O
as well as P C H O are n o t significantly used d u r i n g their transport t h r o u g h the
estuary ( 2 - 4 days) at relatively h i g h concentrations such as 1 0 0 - 2 0 0 /zg C
1 " ' ) . Indeed, this result c o n f i r m s t h e previously advanced hypothesis, be-
cause, i f m o s t carbohydrates are l i n k e d t o t h e b u l k o f the organic matter,
T D C H O values and M C H O values are s i m p l y the results o f using t w o differ-
ent methods ( w i t h a n d w i t h o u t h y d r o l y s i s ) t o measure the same parameter:
the concentration o f carbohydrates ( a n d carbohydrate-like substances) pres-
ent i n the t r a n s f o r m e d organic matter.
It is n o t e w o r t h y that a s i m i l a r correlation could have been obtained f r o m
the data collected b y B u r n e y a n d Sieburth ( 1 9 7 7 ) i n w i n t e r a n d spring i n
Narragansett B a y ( r = 0 . 9 6 ; « = 20; P < 0 . 0 0 1 ; [ M C H O ] = 0 . 3 9 (±0.03)
[ T D C H O ] - 20 ( ± 2 5 ) ) . H o w e v e r , there was n o correlation between M C H O
a n d T D C H O either i n the study o f H a r v e y ( 1 9 8 3 ) o r i n that o f B u r n e y et al.
( 1 9 7 9 ) , b o t h p e r f o r m e d i n s u m m e r . Probably, i n this season, large quantities
o f n e w l y biosynthesized carbohydrates disturb t h e M C H O v s . T D C H O
relationship.
GENERAL DISCUSSION
A s noted i n the I n t r o d u c t i o n , o u r knowledge o n dissolved carbohydrates is
l i m i t e d . F o r instance, M C H O concentrations are often reported w i t h i n t h e
5 0 - 1 0 0 /zg C 1 " ' range, w h i c h is relatively h i g h for easily usable compounds.
Glucose, the m o s t d o m i n a n t monosaccharide constituent o f the M C H O frac-
t i o n ( M o p p e r et al., 1 9 8 0 ) , is measured by chemical m e t h o d s at m u c h higher
concentrations t h a n those expected f r o m the K^ + S^ values d e t e r m i n e d by m i -

15. D I S S O L V E D C A R B O H Y D R . T E S I N E S T U A R I N E E N V I R O N M E N T S 33
crobiological methods ( G o c k e et al., 1 9 8 1 ) . These last w o r k e r s supposed that
glucose m a y exist either i n a " t r u l y free f o r m " usable by heterotrophic m i c r o -
organisms o r i n a "reversibly b o u n d f o r m " that is unusable. T h i s last f o r m
could be associated, for instance, w i t h organic compounds. Indeed, i t is w e l l
k n o w n that carbohydrates are a constituent o f h u m i c substances ( H S ) ( W e r -
shaw et al., 1 9 8 1 ; W i l s o n et al., 1 9 8 3 ) . T h e m e l a n o i d i n theory even suggests
that H S are m a i n l y f o r m e d f r o m carbohydrates. T h i s theory has recently re-
ceived further support (Benzing-Purdie a n d Ripmeester, 1983; I k a n et al.,
1 9 8 6 ) , b u t httle is k n o w n about the nature a n d the strength o f bonds w h i c h
l i n k carbohydrates t o H S . I n fulvic acid ( F A ) , D e H a a n a n d D e Boer ( 1 9 7 8 )
f o u n d that m o r e t h a n 5 0 % o f carbohydrates were n o t associated, o r were
loosely associated by w e a k acid-labile bonds t o F A . Sweet and Perdue ( 1 9 8 2 )
identified o n l y 2.8% o f the aquatic h u m u s carbon as sugar carbon. Probably,
there is a c o n t i n u u m between sugars loosely associated t o H S a n d carbohy-
drate-like entities completely included i n H S .
O u r results support t h e v i e w that a significant part o f dissolved carbohy-
drates is associated w i t h the refractory organic matter. T o this T D C H O b o u n d
fraction, n e w l y biosynthesized carbohydrates m a y be added, but the t u r n o v e r
o f the n e w fraction is m u c h quicker.
ACKNOWLEDGEMENTS
W e t h a n k D r . P . le C o r r e for fruitful discussion a n d Professor P . C o u r t o t
for his interest i n this w o r k . T h e authors are particularly indebted t o R . S i -
korski for help w i t h the original text. W e are grateful t o A . A b i v e n for t y p i n g
Ac manuscript. T h e assistance o f the crew o f 'Saint A n n e d u P o r t z i c ' is also
ackaowledged.
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