WHiting Et Al 1987 Nitrogen Exchange Between Wetland and Coastal Ocean

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Marine B iology 95, 173-182 (1987) Marine. . . . . . . . . . . . . . . Biology

| Springer -Verlag 1987

Nitrogen exchange between a southeastern USA salt marsh ecosystem

and the coastal oc ean*

G . J . W h i t i n g 1 . , , , H . N . M c K e l l a r , J r . 2, B . K j e r f v e 3 a n d J . D . S p u r r i e r 4

Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina; Columbia, South Carolina 29208, USA

1 Also Department of Biology

2 Also Department of Environmental Health Science and the Marine Science Program

3 Also Department of Geology and the Marine Science Program

4 Also Department of Statistics

Abstract

The sal t marsh ecosystem at North Inlet , South Carolina,

USA consistently expor ted dissolved inorganic ni trogen

via t idal exchange with the coastal Atlantic Ocean. Con-

cen t r a t ions o f NH4 a nd NO ~+ NO ;- d i sp layed d is t inc t

t idal patterns with r is ing values dur ing ebb f low. These

pat terns sugges t the im por tance o f b iogeochemical p ro -

cesses in the f lux of mate r ial f rom the sal t ma rsh. NH~-

expor t peaked dur ing the sum mer (15 to 20m gm -2

tide - I ) dur ing a net balanc e of tidal w ater ex change.

Reminera l iza t ion o f NH4 wi th in the sa lt mar sh sys tem

appear s to be con t r ibu t ing to the es t imated annual ne t

expor t o f abou t 4 .7 g N H4 +-N m- 2yr 1 . NO~-+NOi- ex-

por ts were higher in the fal l and winter of 1979 (2 to

4 mg N m -2 t ide-Z). T he winter expo r t c oincide d with a

considerable net exp or t of water with no dist inctive con-

centrat ion patterns, suggesting a s imple advective expor t .

H o w ev e r, t h e f a ll p eak o f N O ; - + N O ; ex p o r t occu r r ed

dur ing a per iod o f ne t water ba lance in t ida l exchange

and an insignif icant f reshwater input f rom the western,

fo res ted boundary . Dur ing the summer and f a l l , t ida l

concen t r a t ion pat terns were par t icu lar ly apparen t , sug-

gest ing that ni tr if icat ion within the sal t marsh system was

con t r ibu t ing to the es t imated annual ne t expor t o f ca

0 .6 g NO ~+ N O ~- N m -2 y r -1 .

Introduction

Much research has evaluated the nu t r ien t exchange be-

tween sal t marsh - estuar ine systems and their adjacent

coastal waters ( for review see Nixon, 1980) . Since nitrogen

is considered a major l imit ing nutr ient in many coastal

* Contribution No. 637 from the Belle W. Baruch Institute of Ma-rine Biology and Coastal Research

** P resent address: NASA , Langley Research Center; A ttn./Mailstop 483, Ham pton, Virginia 23665-5225, USA

marshes as well as in estuar ine and coastal waters (Rytherand Dunstan, 1971; Valiela and Teal, 1974; Patrick and

Delaune, 1976) considerable at tention has been focused

on the t idal exchange o f this nutr ient . Several s tudies have

genera l ly shown that mos t in ter t ida l mar shes expor t r e-

duced fo rms o f n i t rogen ( ammo nia and d isso lved o rgan ic)

and impor t ox id ized fo rms (n i t r a te+n i t r i te ) (Axel r ad ,

1974; Vafiela and Teal, 1979; Woodwell et al., 1979;

J o r d an et al., 1983) . Signif icant t idal expo r t of ni trate was

measured f rom a f ew marshes and was a t t r ibu ted to inpu ts

f rom groundwater (Heinle and Flemer , 1976; Valiela et al.,

1978).

Al though some cons is ten t t r ends have been ind ica ted ,

there is s t i l l considerable var iabil i ty among the var ious

marshes wi th r espect to the magn i tude o f the n i t rogen f lux

via t idal waters . Mu ch o f this var iabil i ty may be due to

factors related to geographic location, marsh morphology,

an d h y d r o lo g y ( O d u m et al., 1979; Odum, 1980). Most of

the direct measures of the t idal ni trogen e xchang e are

from relat ively small marsh drainage areas in the nor th-

eas tern USA and Chesapeake Bay (Hein le and Flemer ,

1976; Valiela et al., 1978; Woodwell et al., 1979; Jordan et

al., 1983) . Only a few mea surem ents of ni trogen c oncen-

trat ion distr ibutions and est imates of t idal t ranspor t have

been r epor ted fo r the expans ive sa lt mar shes which dom i-

nate the southeaste rn coast of the USA (Haines, 1979;I m b er g e r et al., 1983).

The Nor th In le t sa l t mar sh ecosys tem located on the

South Carolina coast has been the s i te of intensive s tudies

of mater ia l t ranspor t via t idal water (Kjerfve and Mc-

Kellar , 1980; Chrzanowski et al., 1982a, b, 1983; Dame,

1982) . We present a detai led seasonal s tudy o f net f luxes

and t ida l concen t r a t ion pat terns fo r to ta l n i t rogen , am-

monium, and nitrate + nitr i te.

Ma te r ia l s a n d me th o d s

The N orth Inlet sal t marsh is character is t ic of marshes

along the sou theas tern coas t o f the USA f rom Georgetown,



174 G.J. W hiting e t a l . : Salt marsh-ocean nitrogen exchange

CAROLINA

IRTH INLETAREA

LABORATORY

: ~ .))~TOWN CREEK

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S O UT H J O NE ~

CRE E K

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Z

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Fig. 1. M ap o f No rth Inlet salt marsh an d location of the study'sthree sampling transects. Inset shows the location of the marsh onthe South C arolina, USA coast

SC to J acks onv i l l e , FL , w i th a de ndr i t i c pa t t e rn o f t i da l

c r e e k s w i t h i n b r o a d e x p a n s e s o f t h e s a lt m a r s h c o r d g r a ss

S p a r t i n a a l t e r n i f l o r a (F ig . 1 ). T he 34 km 2 sa l t m a rs h

cons i s ts o f 70% vege ta t ed m ars h s u r face , 23% s ub t ida l

c reek bo t tom, 4% oys te r ba r s , and 3% mudf la t s . I t i s a we l l

]n ixed , h igh s a l in i ty e s tua ry (30 to 35%0 S) , c la s s i f i ed a s a

T y p e 1 A e s t u a r y ( K j e r f v e a n d P r o e h l , 1 9 7 9 ; K j e r f v e ,

1984) acco rd ing to the c l a s s i f i c a t ion s ys t em o f Ha ns e n a nd

Ra t t ray (1966). Ra in fa l l i s app r ox i ma te ly 1 .3 m y r -1 , wh ich

a c c o u n t s f o r o v e r 7 5% o f t h e f r e s h w a t e r i n p u t t o t h e s a l t

m a r s h s y s te m . T h e m a j o r i t y o f t h e r a i n f a ll o c c u r s d u r i n g

t h e f a l l a n d w i n t e r m o n t h s a n d t h e r e m a i n d e r d u r i n g

s u m m e r t h u n d e r s t o r m s ( T . M . W i l l i a m s , p e r s o n a l c o m -

m u n i c a t i o n ) . S u r f a c e f l o w f r o m u p l a n d f o r e s t o n t h e

m a r s h ' s w e s t e r n b o u n d a r y i s l i m i t e d t o t h e w i n t e r m o n t h s

When the w a te r t ab le reac hes the s u r face o f the s oi l. M ean

f re s hw a te r inp u t ( ra in fa l l + fo re s t s u r face runo f f ) t o the s a l t

m a r s h o v e r t h e y e a r m e a s u r e s a p p r o x i m a t e l y 7 . 0 X 104 m 3

t ide -1 (T . Wi l l i ams , pe r s o na l co mm unic a t ion ) .

T i d a l w a t e r s e n t e r a n d l e a v e t h e N o r t h I n l e t s a lt m a r s h

th rough th ree ma jo r c reeks (F ig . 1 ) . T he l a rge s t , T own

C r e e k , i s 3 2 0 - m - w i d e a n d e x c h a n g e s w i t h t h e A t l a n t i c

Ocea n . Wi th a m ean t ida l p r i s m o f 15 . 0 x 106 m 3 , t h i s

c reek accoun t s fo r 80 to 85% of the to t a l t i da l p r i s m fo r the

N o r t h I n l e t m a r s h s y s t e m . N o r t h J o n e s C r e e k i s 7 6 - m -

w i d e ; i t a l s o e x c h a n g e s w i t h t h e o c e a n a n d a c c o u n t s f o r

1 5% o f t h e t o t a l w a t e r e x c h a n g e . T h e s m a l l es t c r e e k , S o u t hJ o n e s ( 7 3 - m - w i d e ) , e x c h a n g e s w i t h a m e s o h a l i n e e m b a y -

m e n t ( M u d B a y ) a n d a c c o u n t s f o r a p p r o x i m a t e l y 1 to 2%

o f th e t o t a l w a t e r e x c h a n g e f o r t h e m a r s h s y s te m . B a t h y -

m e t r i c p r o f i l e s o f e a c h c r e e k a t t h e s a m p l i n g t r a n s e c t a r e

p r o v i d e d i n W h i t in g e t a l . (1985).

I n t e n s i v e s a m p l i n g o f w a t e r f l o w a n d n i t r o g e n c o n c e n -

t r a t i o n s w e r e c o n d u c t e d o v e r e i g h t c o m p l e t e t i d a l c y c l e s

d u r i n g t h e w i n t e r ( F e b r u a r y ) , s p r i n g ( M a y ) , su m m e r ( J u ly ) ,

a n d f a l l ( O c t o b e r - N o v e m b e r ) o f 1 9 7 9 . D u r i n g e a c h s e a -

s o n , w e s a m p l e d f o u r c o n s e c u t i v e t i d a l c y c l e s c e n t e r e d

a r o u n d a n e a p t i d e a n d f o u r a d d i t i o n a l c y cl e s a r o u n d a

s p r i n g t i d e . T h i s s a m p l i n g d e s i g n a l l o w e d a n e x a m i n a t i o n

o f s e as o n a l, d i u r n a l a n d t i d a l v a r i a b i li t y i n c o n c e n t r a t i o n s

and f luxes .

F o r e a c h s a m p l i n g p e r i o d , s a m p l i n g t r a n s e c t s w e r e

e s t ab l i s hed ac ros s each c reek (3 s t a t ions ac ros s T own

C r e e k a n d 2 s t a t i o n s e a c h i n N o r t h a n d S o u t h J o n e s

C r e e k s ) a n d w e r e s a m p l e d a t a p p r o x i m a t e l y 9 0 -r a i n in t e r -

v a l s f o r v e r t i c a l a n d l a t e r a l v a r i a b i l i t y i n w a t e r v e l o c i t y

a n d n u t r i e n t c o n c e n t r a t i o n s . A t e a c h s t a t i on , w a t e r v e l o c i t y

w a s m e a s u r e d a t m e t e r i n t e r v a l s f r o m t h e s u r f a c e t o t h e

b o t t o m , u s i n g b i p l a n e c u r r e n t c r o ss e s. W a t e r s a m p l e s w e r e

p u m p e d i n t o a c i d - w a s h e d g la ss b o t t l e s ( 5 00 m l ) f r o m t h e

n e a r - s u r f a c e , m i d - d e p t h , a n d n e a r - b o t t o m w a t e r , u s i n g

h a n d - o p e r a t e d p u m p s ( G u z z l e r , D a r t U n i o n C o . , P r o v i -d e n c e , R I , U S A ) w i t h a u t o c l a v e d t y g o n t u b i n g . T h e s a m -

p l e s w e r e p l a c e d o n i c e a n d t r a n s p o r t e d b a c k t o t h e

l a b o r a t o r y w i t h i n 2 h . P o r t i o n s o f e a c h w a t e r s a m p l e w e r e

f i lt e re d a n d a n a l y z e d im m e d i a t e ly f o r a m m o n i u m c o n c e n -

t r a t i o n s u s i n g t h e p h e n o i - h y p o c h l o r i t e m e t h o d ( S o l o r z a n o ,

1 9 6 9 ) o n a T e c h n i c o n a u t o a n a l y z e r ( G i l b e r t a n d L o d e r ,

1 97 7) . A d d i t i o n a l p o r t i o n s o f e a c h s a m p l e w e r e f r o z e n f o r

l a t e r a n a ly s i s o f n i t r a t e + n i t r i t e a n d t o t a l n i t r o g e n .

N i t r a t e + n i t r i t e w a s d e t e r m i n e d b y c a d m i u m r e d u c t i o n

a n d a u t o - a n a l y s is o f n i t r it e ( G i l b e r t a n d L o d e r , 1 97 7) .

T o t a l n i t r o g e n ( p a r t i c u l a te + d i ss o l v ed ) w a s d e t e r m i n e d b y

p e r s u l f a t e o x i d a t i o n o n a n u n f i l t e r e d s a m p l e ( D ' E l i a e t a l . ,

1977) fo l lowed b y n i t ra t e + n i t r i t e ana lys i s . Fu r the r d e ta i l s

o f t h e s a m p l i n g a n d a n a ly s i s m e t h o d s h a v e b e e n d i s cu s s e d

b y K j e r fv e e t a l . (1981) and Whi t ing e t a l . , (1985).

F o r e a c h 9 0 - m i n s a m p l i n g i n t e r v a l , t h e v e l o c i t y a n d

n u t r i e n t c o n c e n t r a t i o n s w e r e s p l i n e - f i t t e d ( a c u r v e f i t t i n g

t e c h n i q u e : C a r n a h a n e t a l . , 1969) to ob ta in in s t an taneous

ve r t i c a l p ro f i l e s fo r e ach s t a t ion in the s ampl ing t rans ec t .

T h e p r o f i le s o f c o n c e n t r a t i o n a n d v e l o c i t y w e r e m u l t i p l i ed

w i t h t h e c r o s s - s e c t i o n a l a r e a r e p r e s e n t e d b y e a c h s t a t i o n

a n d d e p t h i n t e r v a l a n d t h e n s u m m e d t o y i e l d t h e i n -

s t an taneous f lux ac ros s the t r ans ec t . T he in s t an taneous

f lux va lue s (F) , ob ta in ed o ve r the fou r t i da l cyc le s , we re

t h e n f i tt e d to p e r i o d i c f u n c t io n s o f ti m e ( G L M p r o c e d u r e ,



G. J. Whiting e t a L : Sal t marsh-o cean nitrogen exchange 175

SAS Ins t i tu t e Inc ., 1982) rep re s en t in g d iu rna l , s emi -d iu rna l ,

a n d s h a l l o w w a t e r t i d a l p e r i o d i c i t ie s ( T a b l e 1 ). T h i s m o d e l

c o m p u t e d t h e m e a n a n d c o n f i d e n c e l im i t s f o r e a c h n i t r o -

g e n f l u x o v e r t h e s a m p l i n g p e r i o d . T h e u t i l i t y a n d l i m i t a -

t i on s o f th i s c o m p u t a t i o n a l d e s i g n h a v e b e e n d i s c u ss e d i n

m o r e d e t a i l b y W h i t in g e t a l . (1985).

Re su l t s

C o n c e n t r a t i o n p a t t e rn s

Table 1. Regression model used for estimation of m ean in-stantaneous flux (~)

F = / ~ + a l+/31

+ ~22

+f12+ a3

+f13+ a4

sin (2 JT• (semi diurnal tide)cos (2 :r x T ime/12.42)sin (2 7cx Time/24.84) (diurnal tide)cos (2 ~X Time/24.84)sin (2 sz• (shallow water tide)cos (2 x • Time/6.21)

sin (2 ~• Time/24.00) (diel cycle)+fi4 cos (2 sz x Time/24.00)+ error

S e a s o n a l t re n d s o f c o n c e n t r a t i o n w e r e a p p a r e n t f o r t o t a l

n i t r o g e n a n d a m m o n i u m ( T a b l e 2 ) . T o t a l n i t r o g e n w a s l o w

dur ing the w in te r and inc rea s ed in the fa l l a c ros s a l l t h ree

t r a ns e c ts . A m m o n i u m w a s a l so l o w d u r i n g t h e w i n t e r a n d D a te

s p r i n g ( 1 . 4 / 2 M , N o r t h J o n e s ) , a n d i n c r e a s e d t o m a x i m u m

conc en t ra t ion s o f 4 .6 to 7 . 2 /2M in the fa l l , w i th the h ighe r

c o n c e n t r a t i o n s m e a s u r e d a t t h e S o u t h J o n e s t r a n s e c t e x - 2 1 -2 3 F eb

c h a n g i n g w i t h t h e m e s o h a l i n e b a y . N i t r a t e + n i t r i t e c o n - 2 5 -2 7 F e b

c e n t r a t i o n s d i d n o t s h o w a n a p p a r e n t s e a s o n a l t r e n d . 1 8 - 2 0 M a y

H o w e v e r , t h e r e w a s a n o r d e r o f m a g n i t u d e g r e a t e r c o n c e n - 2 5 -2 7 M a y

t r a t i o n o f n i t r a t e + n i t r i t e i n t h e t i d a l w a t e r e x c h a n g i n g 1 7- 19 J u ly

w i t h t h e m e s o h a l i n e b a y ( S o u t h J o n e s ) c o m p a r e d t o 1 0 - 1 2 J u ly

o c e a n i c e x c h a n g e p o i n t s ( T a b l e 2 ). M e a n c o n c e n t r a t i o n s o f 2 6 -2 8 O c t

n i t r a t e + n i t r i t e d u r i n g s p r in g t i de s f o r S o u t h J o n e s a l so 2 - 4 N o v

a p p e a r e d t o b e c o n s i d e r a b l y h i g h e r t h a n t h e n e a p t i d e s

d u r i n g m o s t o f th e s e a s o n a l s a m p l i n g s .21-23 Feb

T i d a l p a t t e r n s o f d i s s o lv e d i n o r g a n i c n i t r o g e n c o n c e n - 2 5 -2 7 F e b

t r a t io n s d u r i n g t h e f o u r s e a s o n a l s a m p l i n g s f o r b o t h o f th e

o c e a n i c e x c h a n g e s it e s a r e r e p r e s e n t e d b y t h e l a r g e s t 1 8 - 2 0 M a y25-27 May

t r a n se c t , T o w n C r e e k ( F i g . 2 ). A n e x a m p l e o f c o n c e n t r a -

t i o n p a t t e r n s o f i n o r g a n i c n i t r o g e n i n t h e w a t e r e x c h a n g i n g 1 7- 19 J u ly10-12 Julyw i t h t h e m e s o h a l i n e b a y ( S o u t h J o n e s , N o v e m b e r - S p r i n g 2 6 -2 8 O c t

t ida l s e t ) i s p re s en te d in F ig . 3 . A t a l l t he s amp l ing si te s, 2 -4 Nov

t h e t o t a l n i t r o g e n c o n c e n t r a t i o n s w e r e h i g h l y v a r i a b l e o v e r

e a c h s a m p l i n g p e r i o d w i t h n o a p p a r e n t t i d a l o r d i e l

pa t t e rn s (da ta no t s hown) . 21 -23 Feb

T h e a m m o n i u m ( N H 4 ) c o n c e n t r a t i o n s f o r t h e w i n t e r 2 5 - 27 F e b

and s p r ing s am pl ing pe r iod s we re va r i ab le w i th l i t tl e o r no 18 -20 M ay

t ida l o r d i e l pa t t e rn s fo r the ocean ic (F ig . 2a , b ) o r ba y 25 -27 M ay

excha nge s it es . Ho wev e r , a s m ean concen t ra t ion s inc rea s ed 17 -19 J u ly

f r o m 1 . 7 / 2M N H ~ d u r in g t he s u m m e r t o 4 . 6 # M N H 4+ in 10 -12J u ly

the fa l l a t t he ocean ic excha nge t rans ec t s (T ab le 2 ) , NH4 26-28 Oc t

d i s p l a y e d d i s ti n c t t i d a l p a t t e r n s w i t h h i g h c o n c e n t r a t i o n s 2 - 4 N o v

o n t h e e b b t i d a l f l o w a n d l o w e r c o n c e n t r a t i o n s o n t h e

f lood in g t ide (F ig . 2 c , d ) . T hes e p a t t e rns we re a l s o cons i s -

t e n t w i t h r e s u l t s o b t a i n e d f r o m a d a i l y m o n i t o r i n g o f

n u t r i e n t c o n c e n t r a t i o n s o v e r t h e y e a r a t t h e T o w n C r e e k

s a m p l i n g t r a n s e c t ( W o l a v e r e t a l . , 1984).

T h e m o s t c o n s i s t en t t i d a l p a t t e r n o c c u r r e d f o r n i t r a t e +

n i t r i t e ( N O ~ + N O ~ - ) d u r i n g t h e s p r i n g , s u m m e r , a n d f a l l

s amp l ing p e r iods in T ow n C reek (F ig . 2 b , c , d ) . N i t ra t e +

n i t r i t e concen t ra t ions we re h igh (0 . 6 to 0 . 8 /234) on the ebb

f low and low (0 . 1 to 0 . 2 /234) on the f lood , wh ich was

s i m i l ar t o t h e p a t t e r n s e e n w i t h N H 4 . T h i s p a t t e r n w o u l d

s u gg e st a N O ~ - + N O y e n r i c h m e n t o f th e t i d a l w a t e r

d u r i n g i t s r e s i d e n c e w i t h i n t h e s a l t m a r s h . H o w e v e r ,

Table 2. Mean concentration of nitrogen in tidal water over eachsampling period. M ean ( + SE). TC: Town Creek, NJ: NorthJones, SJ: South Jones. n = 120 to 300 for each m ean

Tidal Total nitrogen ~ M )sets

TC NJ SJ

Mid a 23.6 (0 . 5) 23 .3 0 .7) 29.6 (0 .8)Spr 24 .4 (0 . 5 ) 26 . 1 0 . 8 ) 4 2 . 1 1 .3 )

Neap 39.0 (0 .7 ) 39 .0 0 .9) 51.6 (1 .4)Spr 33.0 (0.7) 33.5 (0 .9) 58 .0 2.3)

Neap ND b ND NDSpr ND ND ND

Neap 48 .0 (0 . 6 ) 46 . 3 0 . 9 ) 57 . 0 1 .0 )Spr 56.1 (0.8) 52.6 (1 .0) 66 .6 1.7)

Ammonium (#M)

Mid 1 .62 (0 .05) 1 .75 0 .06) 2 .90 0 .10)Spr 1.56 (0.06 ) 1.65 0.09) 2.91 (0.08)

Neap 1.52 (0.05 ) 1.52 0.07 ) 1.54 0.08)Spr 1.44 (0.05 ) 1.39 0.05 ) 1.76 0.09)

Neap 1 .73 (0 .05) 1 .90 0 .08) 3 .43 0 .10)Spr 2.34(0.06) 2.4 4(0 . ll) 3.67(0.13)

Ne ap 4.57(0.14) 4.55(0.18) 7.18(0.22)Spr 3.09(0.05) 2.98(0.06) 4.94(0.12)

Nitrate + nitrite (/~M )

Mid 0.36(0.01) 0.38(0.02) 5.51(0.22)Spr 0 .45 (0 .01) 0 .43 (0.02) 7 .30 0 .20)

Neap 0.29(0.01) 0.28(0.01) 1.88(0.18)Spr 0 .30 (0 .01) 0 .31 (0 .01) 5 .62 0 .31)

Neap 0.33 (0.01) 0.39 0.03 ) 1.81 (0.10)Spr 0 .26 (0 .01) 0 .28 0 .01) 3 .63 (0 .18)

Neap 0 .32 (0 .01) 0 .27 0 .01) 4 .84 0 .23)Spr 0 .68 (0 .01) 0 .63 (0 .01) 3 .64 0 .17)

Mid tide substituted fo r the neap set due to inclement w eatherND: samples suspected of reagent contamination

d u r i n g t h e w i n t e r s a m p l i n g ( a p e r i o d o f h i g h r a i n fa l l ), t h is

p a t t e r n w a s n o t a p p a r e n t ( F i g . 2 a ) . T h e c o n c e n t r a t i o n

p a t te r n s o f N O ~ + N O i - m e a s u r e d d u r i n g t he s e f o u r s e a-

s o n a l s a m p l i n g s a r e c o n s i s t e n t w i t h t h e p a t t e r n s d o c u -

m e n t e d b y d a i l y w a t e r s a m p l e s o v e r t h e e n t i r e y e a r

( W o l a v e r e t a l . , 1984).

I n S o u t h J o n e s C r e e k w h e r e w a t e r e x c h a n g e s w i t h t h e

m e s o h a l i n e b a y , ti d a l p a tt e r n s f o r N H + a n d N O ~ + N O ;

w e r e t h e o p p o s i t e f r o m t h e o c e a n e x c h a n g e s i t e s w i t h



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F i g . 2 . R e p r e s e n t a t i v e c o n c e n t r a t i o n p a t t e r n s o f a m m o n i u m a n d n i t r a t e + n i t r i t e f o r T o w n C r e e k ( T C ) d u r i n g ( a ) w i n t e r , ( b ) s p r in g ,( c) s u m m e r , a n d ( d ) f a l l s a m p l i n g p e r i o d s . P o i n t s r e p r e s e n t t h e m e a n ( _+ S E ) o f a l l s a m p l e s ( n = 9 ) t a k e n a c r o s s t h e t r a n s e c t. E a n d F

s y m b o l i z e t h e p e r i o d o f t i m e o f e b b a n d f l o o d t i d a l f lo w s , re s p e c t iv e l y . T w e l v e o n t h e t i m e a x i s i n d i c a t e s n o o n o n t h e f i r s t d ay - o fs a m p l i n g



G. J. Wh iting et al.." Salt mar sh-o cean nitrogen exchange 177

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Time (h)

Fig. 3. Representative concentration pattern s of amm oni um , andnitrate + nitrite fo r South Jones Creek (S J) during the Nov em berspring tidal regime. Points represe nt the me an o f all samples(n = 4) taken across the transect. E and F symbolize the period of

time of ebb and flood tidal flows, respectively. Twelve on the timeaxis indicates noo n on the first day of sampling

higher concentrat ions on f lood t ide (Fig. 3) . This pat tern

was especial ly enhanced for spring t ides during the sum-

mer and fa l l . E leva ted NO#+NOi- concent ra t ions on

flood t ides were correlated to lower sal ini ty bay water

e n r i c h e d w i t h N O ~ + N O s b e i n g b r o u g h t i n t o t h e m a r s h

during the f lood t ide.

Tidal f lux

Net mo vem ent s o f water w ere s ignif icant (p <__ 0.05) in the

ebb direct ion during f ive of the eight samplin g periods for

the larges t creek, Town Creek (Fig. 4) . These net water

expor t s a re poss ib ly ba lanced by per iods o f imp or t over a

t ime period longer than the four t idal cycles sampled.

Sa l in i ty measurements a t the Town Creek t ransec t d id not

indica te tha t an inpu t o f low sa l in i ty wa te r f rom the fores t

or the mesoha l ine bay had cont r ibuted to these expor t s .

These ne t expor t s of wa te r had an inf luence on the f lux of

mate r i a l through the t ransec t . Dur ing the s ampl ing pe-

riods that showed a s ignif icant net export of total ni t rogen,

water f lux was also measured as an export [Table 3, see

Town Creek , February-spr ing t ida l s e t ( spr ) ; Nor th Jones ,

October-neap; South Jones , October-spr] . Since t idal pat-

t e rns of to ta l n i t rogen concent ra t ions were not a ppare nt

dur ing these pe r iods of export , i t appea rs to have been the

ne t expor t o f wa te r in the f lux equa t ion tha t de te rmined

the ne t f lux of to ta l n i trogen f rom the m arsh .

Ammonium expor t was s igni f i cant dur ing a l l s easons ,

wi th the l a rges t expor t dur ing the summer (Table 3 , Town

Creek). The seasona l exchanges o fN H + based on a pe r m 2of s a lt marsh es tua ry indica ted tha t a pea k of 17 mg

N H + -N m -2 t ide -1 was expor ted dur ing the Ju ly spr ing

t ide s ampl ing for the Town Creek dra inage bas in

(23.8 km 2, Fig. 4) . The winter and spring NH + exports

measured a t the Town Creek t ransec t cor responded to

periods of s ignif icant water export . How ever, even durin g

periods of net water balan ce (Fig. 4, Town C reek: July -spr,

Oc tober -spr ; T able 3 , Nor th Jones: Ju ly-neap) , NH +

export from the marsh was also s ignif icant . I t was during

these pe r iods of ne t wa te r ba lance tha t t ida l pa t t e rns in

N H + concen trat ion were pa rt icularly a pp aren t (Fig. 2 c , d) .

The occur rence of t ida l concent ra t ion pa t t e rns and a

measur able expor t of NH4 dur ing a ba lanced w ate r pe r iod

suggests that processes within the marsh produced the

expor t ofNH4 dur ing the summer and fa l l .

A s w i t h a m m o n i u m , N O ~ + N O y w a s s i g n i f i c a n t l y

exported from the marsh during al l seasons (Table 3) . For

the Town C reek dra inag e bas in , peak e xpor t was 3 .3 mg

N O ~ + N O ~ - N m - 2 t i d e -1, m e as u r e d d u r in g t h e w i nt er

whe n wat er was also exported (Fig. 4) . During this

sampl ing , t ida l pa t t e rns in concent ra t ion were not ev ident

(Fig. 2a) , suggest ing that the net advect ion of wate r was

t h e m a j o r c o n t ro l li n g f a ct o r o f N O ~ + N O s e x p o r t d u ri n g

th is time . However , s ignif i cant expor t of N O ~+ N O ; was

measured dur ing those pe r iods in which the ne t f lux ofwater was not s ignif icant ly different from zero (Fig. 4,

spring, summe r, and fal l ) and t idal pat terns of conce ntra-

t ion were a ppa ren t (Fig. 2) . Signif icant export o f ni t rate +

ni t ri t e dur ing the s ampl ing per iods o f ne t wa te r ba lance

indica tes tha t processes wi th in the m arsh de te rmined the

net flux.

Discus s ion

The accura te m easur emen t of wa te r exchange i s c r i ti ca l to

the mea surem ent of mate r i a l f lux ac ros s a t ransect . M any

s tudies have shown a shor t - t e rm imba lance in the wa te r

budget (Kjerfve and Proehl , 1979) which may be at t r i -

buted to far-f ie ld wind forcing, a tmospheric pressure

changes , or she l f -propaga t ing long waves (Kje r fve e t al . ,

1978). Another factor contribut ing to the imbalances

measured dur ing the present s tudy may be shee t f low over

the marsh during high t ides that f loods outs ide the

meas urem ent t ransec t but i s subsequently expor ted through

the main channel (Mil ler and Gardner, 1981).

Eb b directed f luxes can have a great effect on m aterial

f luxes tha t in te rdepend on the d i rec t ion and magni tude of

wate r movem ent . Dur in g per iods of ne t wa te r loss f rom

the sal t marsh sys tem, nutr ients are also exported (e .g.



178 G . J . W hi t i ng e t a L . " Sa l t m a r s h - oc e a n n i t r oge n e xc ha nge

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Fi g . 4 . Se a s ona l fl ux m e a s u r e m e n t s o f w a te r , t o t a l n i t r oge n , a m m on i um , a nd n i t r a t e + n i t r it e f o r t he T ow n C r e e k d r a i na ge ba s i n . N u t r i e n tf luxes a re ba se d on a pe r m 2 of s a l t mar sh + e s tua ry (23.8 k in2) . The l ab e l s (M, N, S) wi th in the b a r s r epre s ent mid, neap , or sp r ing t ida l

sam pl ing se ts . Er ror b a r s a r e 1 SE w i th * indica t ing a f lux wh ich i s s igni f i cant ly d i f f e rent f rom ze ro a tp < 0 .05. Pos i t ive va lues indic a te an

e xpor t f r om t he N o r t h I n l e t s y s t em

T o w n C r e e k , F e b r u a r y - s p r ) . T h is e x p o r t a p p e a r s t o b e a

s i m p l e a d v e c t i v e m o v e m e n t o f m a t e r i a l i n t h e w a t e r a n d

d o e s n o t c o i n c i d e w i t h b i o g e o c h e m i c a l p r o c e s s e s in t h e

m a r s h . T h e r e f o re , e c o l o g i c a l i n t e r p r e t a t i o n o f f lu x v a l u e s

r e q u i r e s a c o n s i d e r a t i o n o f c o n c e n t r a t i o n p a t t e r n s a s w e l l

a s n e t w a t e r m o v e m e n t s t o d e t e r m i n e t h e b i o g e o c h e m i c a l

s i g n if i c an c e o f t h e c o m p u t e d f lu x .

T o t a l n i t r o g e n c o n c e n t r a t i o n s d i d n o t s h o w c l e ar t id a l

p a t t e r n s t h a t w o u l d i m p l y a n e t f l u x i n t o o r o u t o f t h e s a lt

m a r s h s y s te m . T h e m e a s u r e d n e t e x p o r t o f to t a l n i tr o g e n

d u r i n g t h e w i n t e r ( T a b l e 3 ) c o i n c i d e d w i t h t h e n e t f l u x o f

w a t e r f r o m t h e m a r s h ( F ig . 4 ), w h i c h i s p o s s ib l y b a l a n c e d

d u r i n g p e r i o d s o f w a t e r i m p o r t t o t h e m a r s h a s su g g e s t e d

a b o v e . M e a n c o n c e n t r a t io n s d i d s h o w s o m e s e a s o n a l tr e n d



G. J. Whiting e t a l . : Sal t marsh -ocean ni t rogen exchange 179

Ta ble 3 . Me an net t idal exchange of water, to ta l n i t rogen (TN), amm onium (NH+), and ni t ra te + ni tr i te (N + N) for each sampl ing per iod.Mean ( + SE) . TC: Tow n Creek, NJ: N or th Jones , SJ : South Jones . ( - ) indicates impor t , (+ ) indicates expor t

D a t e T ida l W a te rset (106 m 3 tide -1)

Ni t rogen f lux (kg N/ t id e)

T N N H 4 + N + N

21 -23 Feb Mid TC 4.37 (1.74)* 883 (532) 106 (45)* 16.3 (11.2)NJ -0 .18 (0.34 ) 28 (148) - 11 (12) -0 .7 (2 .7)

SJ 0.14 (0.14) 22 (63) 7 (7) 9.0 (12.0)25 -27 Feb Spr TC 8.95 (2.21)* 4 063 (1 108)* 252 (73)* 77.4 (14.2)*

N J" -1 . 88 (0 . 96 ) -74 5 (407) -4 6 (36 ) -8 . 7 (4 .0 )*SJ 0.31 (0.21) 92 (146) 7 (10) 27.4 (23.5)

18-2 0 May Ne ap TC 0.39 (1.76) 1 471 (1 121) - 53 (53) 14.4 (6.9)*N J -0 . 76 (0 . 41 ) -2 7 (299) -1 7 (12 ) 1 .7 (1 .8 )SJ 0.64 (0.19)* 449 (135)* 6 (5) 1.6 (7.5)

25 -27 Ma y Spr TC 3.49 (1.68)* 1 452 (952 ) 217 (59)* 28.5 (10.0)*NJ -0 .25 (0 .38) -2 44 (227) 11 (9) 2 .6 (1 .7)SJ 0.08 (0.18) 30 (150) -0 .3 (3) -5 .7 (14.5)

17-1 9 Jul Ne ap TC 4.13 (1.89)* ND b 197 (56)* 27.2 (8.0)*NJ -0 .3 3(0 .34) NO 37 (13)* 3 .4 (2 .0)SJ 0.26 (0.17) N D 10 (6) -2 .0 (5.2)

10-1 2 Jul sp r TC 2.10 (2.97) N D 415 (142)* 19.0 (12.5)NJ a - 1.40 (0.57) N O 72 (51) 3.0 (3.0)SJ 0.53 (0.26)* ND 8 (17) - 19.2 (27.2)

26- 28 Oct Ne ap TC 2.96 (1.44)* 1 346 (1 190) 173 (139) 26.6 (7.6)*N J -0 . 7 5 (0 .36 )* -88 3 (260)* -4 5 (38 ) -0 . 4 (1. 28 )SJ 0.13 (0.17) 36 (15) 1 (15) - 32.9 (14.4)*

2- 4 No v Spr TC 1.82 (1.29) 1 384 (1 409) 219 (8l)* 46.9 (21.4)*N J - 1 . 6 4 ( 0 . 3 8 ) * - 8 8 9 ( 4 6 6 ) - 2 5 ( 2 0 ) -11.0 (5 .1)*SJ 1.05 (0.23)* 939 (264)* 42 (23) 6.6 (25.6)

* Significantly differe nt from zero a tp _-<0.05~ On ly 0 .5 of the t ransect sampledb N D : samples suspected o f reagent co ntamina t ion

w i t h h i g h e r v a l u e s i n t h e f a l l ( T a b l e 2 ) , s i m i l a r t o t h o s e

o b s e rv e d b y W o l a v e r e t a l . ( 1 9 8 4 ) f o r t h e N o r t h I n l e t

s y s t e m a n d i n o t h e r m a r s h s t u d i e s ( V a l i e l a e t a l . , 1978 ;

W o o d w e l l e l a l . , 1 9 7 9 ) . T h e s e e l e v a t e d v a l u e s m a y b e

r e l a t e d t o th e f a ll s e n e s ce n c e a n d d e c o m p o s i t i o n o f t h e

m a r s h p l a n t s a s s u g g e s t e d b y V a l i e la e t a l . (1978) .

T h e c o m b i n a t i o n o f se v e ra l p r o c e ss e s m a y c o n t r ib u t e

t o t h e N H 4 t i d a l c o n c e n t r a t i o n p a t t e r n s a n d e x p o r t o b -

s e r v e d i n t h e p r e s e n t s t u d y . D u r i n g l o w - t i d e e x p o s u r e o f

t h e m a r s h s u r fa c e , G a r d n e r ( 1 9 7 5 ) f o u n d a n e n r i c h m e n t o f

s i l i c a , p h o s p h a t e , a n d b i c a r b o n a t e a n d i n d i c a t e d a s i m i l a r

i n c r e a s e f o r N H 4 i n t h e r u n o f f w a t e r f r o m t h e m a r s h

s u r f a ce i n s m a l l t id a l c r e e k b a s i n s a d j a c e n t t o T o w n C r e e k .

A n i n c r e a s e i n t h e c o n c e n t r a t i o n o f N H 4 i n t h e t i d a l

w a t e r l e a v i n g t h e m a r s h s u r f a c e w a s a l s o m e a s u r e d b y

H a i n e s ( 1 9 7 9) i n a G e o r g i a s a l t m a r s h . T h e d i s t r ib u t i o n s o f

N H 4 a l o n g a lo n g i t u d i n a l t r a n s e c t o f t h e D u p l i n R i v e r ,

G e o r g i a a l s o i n d i c a t e d t h a t t h e m a r s h w a s o n e m a j o r

s o u r c e o f N H 2 t o th e e s t u a r i n e t i d a l w a t e r ( I m b e r g e r e t a l . ,

1 9 83 ). A d v e c t i o n o f in t e r st i ti a l w a t e r ( e n r i c h e d w i t h a m -

m o n i u m ) f r o m c r e e k b o t t o m s i n t o t h e o v e r l y i n g t i d a l c r e e k

w a t e r ( 3 .0 t o 5 .0 m g N H ; - N m - 2 t i d e - I ) m a y a l s o p l a y a n

i m p o r t a n t r o l e in t h e e x p o r t o f t h is n u t r i e n t f r o m t h e

m a r s h ( W h i t i n g a n d C h i l d e r s , u n p u b l i s h e d d a t a ) . P o s s i b l y

a c o m b i n a t i o n o f p r o c e s s e s p r o v i d e s N H 4 t o t h e e b b i n g

t i d a l w a t e r , t h u s c o n t r i b u t i n g t o t h e o b s e r v e d t i d a l p a t t e r n s

o f c o n c e n t r a t io n a n d e x p o r t d o c u m e n t e d h e r e f or N o r t h

In l e t .

T h e a p p e a r a n c e o f N H 4 t id a l c o n c e n t r a t io n p a t t er n s

a n d e x p o r t d u r i n g t h e s u m m e r a n d f a l l i s m o s t l i k e l y

r e la t e d t o h i g h e r r a te s o f a m m o n i u m r e m i n e r a li z a t io n

t h a n u p t a k e b y p r i m a r y p r o d u c e r s . V a l ie l a e t a l . ( 1 9 7 8 )

o b s e r v e d s i m i l a r s e a so n a l p a t t e r n s o f a m m o n i u m f l ux in a

N e w E n g l a n d s a l t m a r s h a n d s p e c u l a t e d t h a t th i s p a t t e r n

w a s c a u s e d b y a n i n c r e a s e in n i t r o g e n u p t a k e b y S p a r t i n a

a l t e r n i J T o r a d u r i n g t h e s p r i n g a n d s u m m e r . I n c r e a s i n g

r e g e n e r a ti o n o f a m m o n i u m f r o m th e s e d im e n t s d u r i n g t h e

h i g h t e m p e r a t u r e s o f l a te s u m m e r c o i n c i d i n g w i t h a fa ll

s e n e sc e n c e o f t h e p r i m a r y p r o d u c e r s m a y h a v e p r o d u c e d

a n e x c e s s o f r e d u c e d i n o r g a n i c n i t r o g e n w h i c h w a s e x -

p o r t e d f r o m t h e m a r s h i n th e c u r r e n t s t u d y .

A c o n s e rv a t iv e e x t r a p o l a t i o n o f ar e a b a s e d a m m o n i u m

f l u x e s ( F i g . 4 ) o v e r t h e y e a r f r o m t h e T o w n C r e e k m a r s h

d r a i n a g e b a s i n y i e l d s 4 . 7 g N m - 2 y r - I . C a l c u l a t i o n s w e r e

m a d e u s i n g o n l y t h o s e s a m p l i n g p e r i o d s i n w h i c h t i d a l

p a t t e r n s o f c o n c e n t r a t i o n w e r e p r e s e n t a n d w a t e r f l u x w a s

n o t s i g n i f i c a n t ( J u l y a n d O c t o b e r , s p r ) . A n u p p e r b o u n d

e s t i m a te o f 5 .6 g N m - 2 y r - I i s o b t a i n e d b y t h e m e a n o f al l



180 G.J.Whiting e t a l . : Salt ma rsh-ocean nitrogen exchange

Table 4. Com parison of nitrogen exchange measurements. (+ ) denotes exp ort from the estuary

Location g N m -2 yr 1 Reference

Am monium Ni t rate + n i trate

G. Sippewissett, MA 4.2 3.9Flax Pond, NY 2.1 - 1.2Rh ode River, M D 1.3 to - 0.09 0.34 to 0.07

Go tt 's Marsh, MD 0.4 0.93Wa re Creek, VA 2.9 - 2.2Ems-D ollard, Ne therla nds 1.2 - 3.95Crom me t Creek, NH - 2.1 - 0.32No rth Inlet, SC 4.7 0.58

Valiela e t a l . (1978)Woodwell e t a l . (1979)Jordan e t a l . (1983)

Heinle and Flem er (1976)Axelrad (1974)Dankers e t a l . (1984)Da ly and M athieson (1981)This study

f l u x e s m e a s u r e d , i n c l u d i n g t h o s e w i t h n e t w a t e r m o v e -

m e n t . B o t h o f t h e s e e s t i m a t e s a r e a t t h e u p p e r e n d o f t h e

r a n g e r e p o r t e d f o r o t h e r m a r s h e s ( T a b l e 4 ). S o m e d i f fe r -

e n c e s m a y b e d u e t o th e v a r i e t y o f s a m p l i n g d e s i g n s u s e d

a n d , i n t h e c u r r e n t s t u d y , t h e e x t r a p o l a t i o n o f s e a s o n a l

f l ux v a l u e s t o a n n u a l e s t i m a t e s . M o s t v a l u e s f a ll w i t h i n t h e

r a n g e o f 2 t o 4 g N m - 2 r - 1, su g g es t i n g so me s imi l a r i t y

a m o n g s a l t m a r s h e s i n t h e p r o c e s s e s d e t e r m i n i n g t h e

ex ch an g e o f NH4 +-n i t rog en wi th t h e co as t a l o cean .

T h e n i t r a te + n i t r i t e f l ux m e a s u r e m e n t s i n d i c a t e d t h a t

t h e m a r s h e x p o r t s t h i s i n o r g a n i c n u t r i e n t t o t h e c o a s t a l

o c e a n d u r i n g t h e s p r in g , s u m m e r , a n d f a ll m o n t h s . B e -

c a u s e p e r i o d s o f w a t e r e x p o r t c o m p l i c a t e t h e i n t e r p r e t a -

t i o n o f f l ux m e a s u r e m e n t s , o n l y t h o s e e s t i m a t e s , i n w h i c h

t h e r e w e r e t i d a l c o n c e n t r a t i o n p a t t e r n s a n d n e t w a t e r

b a l a n c e , w e r e u s e d i n c a l c u l a t i n g a n a n n u a l e x c h a n g e o f

n i t r a t e + n i t r i t e b e t w e e n t h e m a r s h a n d t h e o c e a n . T h is

p r o d u c e d a c o n s e r v a t i v e a n n u a l e x p o r t o f 0 .5 8 g N m -2

y r - 1 f r o m t h e T o w n C r e e k d r a i n a g e b a s i n . I f al l s a m p l i n gr e s u l t s a r e i n c l u d e d i n a n a n n u a l e s t i m a t e , t h e e x p o r t i s

a lm o s t d o u b l ed t o 0 .9 4 g N m -2 y r -~. Th i s ex p o r t o f n i -

t r a t e + n i t r i t e i s i n co n t r as t t o m o s t o th e r s t u d i es r ep o r t i n g

a n u p t a k e b y t h e e s t u a r y a n d m a r s h i n t h e r a n g e o f 0 .3 4 to

3 .95 g N m -2 yr -~ (Table 4 ) .

T h e c o n c e n t r a t i o n o f n i t r a t e + n i t r i t e i n t h e f l o o d in g

t i d a l w a t e r a p p e a r s t o a f f e c t t he d i r e c t i o n o f t he f l ux i n t h e

N o r t h I n l e t m a r s h . A t th e i n t e rf a c e b e t w e e n t h e m a r s h

a n d t h e r i v e r - i n fl u e n c e d m e s o h a l i n e b a y (S o u t h J o n e s

C r e e k ) , c o n c e n t r a t i o n s h a d p e a k v a l u e s n e a r 1 0. 0 g M . T h e

S o u t h J o n e s t r a n s e c t a l s o h a d t h e l a r g e s t s i g n if i c a n t i m p o r t

o f n i t r a t e + n i t r i t e d u r i n g a p e r i o d o f z e r o n e t w a t e r

e x c h a n g e ( T a b l e 3 : O c t o b e r , n e a p ) . T h i s a r e a o f t h e m a r s h

m a y b e m o r e s i m i l a r t o t h o s e m a r s h e s t h a t r e c e i v e h i g h

c o n c e n t r a t i o n s o f n i t r a t e + n i t r i t e g e n e r a t e d o u ts i d e th e

s y s t e m a n d b r o u g h t i n t o t h e m a r s h b y t h e t i d a l w a t e r

( D a n k e r s e t a l , 1 9 8 4 ) . Ex cep t i o n s t o t h i s t r en d a r e mar sh es

t h a t r e c e i v e s i g ni f ic a n t in p u t s o f g r o u n d w a t e r o r u p l a n d

r u n o f f ( H e i n l e a n d F l e m e r , 1 97 6; V a l i e l a e t a l . , 1978) and

h a v e m e a s u r a b l e e x p o r ts o f n it r a te f r o m t h e m a r s h s y s te m .

F r e s h w a t e r i n p u t v i a s u r f a c e a n d g r o u n d w a t e r f r o m

t h e u p l a n d s s u r r o u n d i n g N o r t h I n l e t d o e s n o t a p p e a r t o

c o n t r i b u t e t o t h e e x p o r t o f n i t r a t e + n i t r i t e i n th i s st u d y .

F o r t h e N o r t h I n l e t m a r s h , p e a k r a i n f a l l o c c u r s d u r i n g t h e

w i n t e r a n d e a r l y s p r in g m o n t h s , p r o d u c i n g m a x i m u m

f r e s h w a t e r r u n o f f f r o m t h e f o r e s t o n t h e w e s t e r n b o u n d a r y

i n t o t h e m a r s h ( T . W i l l i a m s , p e r s o n a l c o m m u n i c a t i o n )

t h a t d i d n o t c o r r e s p o n d t o a n y m e a s u r a b l e i n c r e a s e s o f

N O ; - + N O ; d u r i ng t h e w i n t e r s a m p l in g . T h e h i g h c o n c en -

t r a t i o n s o f n i t r a t e + n i t r i te a t l o w t i d e (F ig . 2 c , d ) a p p ea r t o

i n d i c a te a n a c t iv e n i tr i fi c a ti o n o f a m m o n i u m i n r u n o f f fr o m

th e ma r sh su r f ace. Co n cen t r a t i o n s o f n i tr a t e + n it r i te i n l o w

t id e ru n o f f f ro m th e m ar sh su r f ace (Wh i t i n g an d Ch i ld e rs ,

u n p u b l i s h e d d a t a ) a r e h i g h e r t h a n t i d a l c r e e k w a t e r ,

s u g g e s ti n g t h a t n i t r i f ic a t i o n o f N H 4 r i ch r u n o f f w a t e r m a y

b e i m p o r t a n t .

S u m m i n g t h e i n o r g a n i c n i t r o g e n f l u x e s fo r t he y e a r , t h e

To w n Creek d ra in ag e b as in ex p o r t s 5 .3 t o 6 .5 g N m -2 y r -1.

T o c o m p a r e t h is t o t h e c y c l i n g o f i n o r g a n i c n i t r o g e n i n t h e

v e g e t a t e d m a r s h , a n e s t i m a t e o f n i t r o g e n u t i l i z a ti o n w a s

m a d e f o r t h e p r i m a r y p r o d u c e r s ( S p a r t i n a a l t e r n i f l o r a )

o v e r t h e ye a r . A r e a - w e i g h t e d e s t i m a t e s o f n e t p r o d u c t i o n

( R . D a m e a n d P . K e n n y , p e r s o n a l c o m m u n i c a t i o n ) f or th e

T o w n C r e e k b a s i n a r e a p p r o x i m a t e l y 1 3 0 0 a n d 4 0 0 0 gd r y w t m - 2 y r -1 f o r a b o v e - a n d b e l o w g r o u n d t is s u es , r e -

s p e c t iv e l y . F r o m m e a s u r e m e n t s o f t h e n i tr o g e n c o n t e n t o f

t h is p l a n t m a t e r i a l [ a n n u a l m e a n % N ( d r y w t ) = 1 .7 , H .

O r n e s , p e r s o n a l c o m m u n i c a t i o n ] , e s t i m a t e s o f n i t r o g e n

u p t a k e a r e 1 6.0 a n d 2 3 .0 g N m - 2 y r -1 f o r a b o v e - a n d

b e l o w g r o u n d , r e s p e c t iv e l y . T h e s u m o f t h e s e a b o v e - a n d

b e l o w g r o u n d u p t a k e e s t i m a t e s a r e i n t h e s a m e r a n g e

e s t i m a t e d f o r t h e i n o r g a n i c N u p t a k e o f S . a l t e r n i f l o r a in

G e o r g i a m a r s h e s ( H o p k i n s o n a n d S c h u b a u e r , 1 98 4) . U s i n g

t h e a b o v e g r o u n d e s t i m a t e a s t h e m i n i m u m n i t r o g e n u t i -

l iz e d ( a s s u m i n g n o t u r n o v e r o f r oo t s ) a n d t h e s u m o f

a b o v e a n d b e l o w a s t h e m a x i m u m ( c o m p l e t e t u r n o v e r o f

r o o ts ) , t h e e x p o r t o f in o r g a n i c n i t r o g e n f r o m t h e s y s t e m i s

1 4 t o 4 07 o o f t h e n i t ro g en u t i l ized an n u a l l y b y t h e p l an t s .

W i t h r e s p e c t t o t h e p r i m a r y p r o d u c e r s , t h is e x p o r t o f a

k n o w n l i m i t i n g n u t r i e n t a p p e a r s t o r e p r e s e n t a s i g n i f i c a n t

l os s o f n i t r o g e n f r o m t h e s a l t m a r s h s y s t e m . F r o m a r e c e n t

m e a s u r e m e n t o f t id a l e x c h a n g e w i t h t he v e g e t a t e d m a r s h

s u r f a c e i n N o r t h I n l e t , t h e m a r s h s u r f a c e w a s e s t i m a t e d t o

b e e x p o r t i n g a p p r o x i m a t e l y 8 .0 g N m ' 2 y r -~ ( W h i t in g ,

1 9 8 5 ) t o t h e ad j acen t t i d a l c r eek . Th e s t u d y s i t e i s i n c l o se

p r o x i m i t y t o a f o r e s te d u p l a n d i n p u t t h a t d i d n o t a p p e a r

t o c o n t r i b u t e a s i g n i fi c a n t a m o u n t o f n i t r o g e n t o t h e

m a r s h . H o w e v e r , t h e n i t r o g e n l o s s f r o m N o r t h I n l e t s a l t

m a r s h c o u l d b e b a l a n c e d b y a n i n p u t o f n i t r o g e n t h r o u g h



G. J. Whiting et al. : Salt marsh -ocean nitrogen exchange 181

n i t r o g e n f i x a t i o n , m e a s u r e d i n t h is m a r s h ( W h i t i n g , 1 9 8 5 )

a t a r a t e o f app rox i m at e l y 38 .0 g N m -2 y r - 1.

D i f f e r e n c e s b e t w e e n m a r s h e s i n t h e d i r e c t i o n a n d

q u a n t i t y o f n i t ro g e n f lu x e s m a y b e p a r t i a l l y e x p l a i n e d b y

t h e c h a r a c t er i st i cs o f t h e g e o m o r p h o l o g y a n d h y d r o l o g y o f

t h e p a r t i c u l a r s i t e ( O d u m et al., 1979; Odum, 1980) . T he

d e p t h a n d w i d t h o f t h e i n l e t, t h e b i f u r c a t i o n o f t i d a l

c r e e k s, a n d t h e r a t i o o f w a t e r t o m a r s h a r e a a p p e a r s t oi n f l u e n c e t h e e x c h a n g e o f n u t r i e n t s . I f r u n o f f f ro m t h e

m a r s h s u r f a ce d u r i n g l o w t i d e is o n e o f th e m a j o r

p r o c e s s e s d e t e r m i n i n g n i t r o g e n e x p o r t , t h e r a t i o o f v e g e -

t a t ed m a r s h t o ti d a l cr e e k a r e a c o u l d b e a n i m p o r t a n t

f ac t o r . S i nce t he Nor t h In l e t sys t em has a 3 : 1 r a t i o o f

v e g e t a t e d m a r s h s u r f a c e t o c r e e k a r e a , l o w - t i d e d r a i n a g e

m a y c o n t r i b u t e s i g n i f i c a n t l y t o i n o r g a n i c n i t r o g e n e x p o r t .

A s th e e l e v a t i o n a n d a r e a o f t h e m a r s h s u r f a c e i n c r e a s e s,

t h e r e s h o u l d a l s o b e a g r e a t e r p o t e n t i a l f o r a n i n c r e a s e d

f l o w o f i n t e r s t i t i a l w a t e r f r o m c r e e k b o t t o m s . O n c e t h e s e

p r o c e s s e s h a v e b e e n i d e n t i f i e d a n d q u a n t i f i e d , a b e t t e r

c o m p a r i s o n o f m a r s h e s w i t h a p p a r e n t d i ff e r en c e s c an b e

m a d e . T h e u n d e r s t a n d i n g o f t h e s e d i f fe r e n c e s a n d t h e

p r o c es s e s th a t p r o d u c e t h e m s h o u l d g e n e r a te a d d i t i o n a l

i n s i g h t o n t h e r o l e t h a t s a l t m a r s h e s h a v e i n t h e o v e r a l l

n u t r i e n t c y c l i n g o f t h e c o a s t a l e c o s y s t e m s .

A c k n o w l e d g e m e n t s . T h is w o r k w a s s u p p o r t e d b y N a t i o n a l

S c ie n c e F o u n d a t i o n G r a n t s D E B 8 00 42 75 a n d D E B

8 1 19 7 52 . W e g r a t e f u l l y a c k n o w l e d g e t i le e x c e l l e n t t e c h n i -

c a l a s s i s t a n c e f r o m W . J o h n s o n , M . M a r o z a s a n d n u m e r -

o u s s t u d e n t v o l u n t e e r s d u r i n g f i e l d s a m p l i n g , l a b o r a t o r y

a n a ly s e s, a n d d a t a m a n a g e m e n t . W e a p p r e c i a t e t h e h e l p f u l

c o m m e n t s o f D r . C . H o p k i n s o n d u r i n g t h e f in a l r e v i s i o n s

o f th e m a n u s c r i p t .

Literature cited

Axelrad, D. M.: Nutrient flux through the salt marsh ecosystem,

134 pp. Ph.D. thesis, College of Will iam and Mary, Will iams-burg, VA 1974

Carnaha n, B., H. A. Luther and J. O. Wilkes: App lied numericalmethods, 604 pp. New York: Joh n W iley and Sons 1969

Chrzanowski, T. H., L. H. Stevenson and J. D. Spurrier: Trans-

por t of par t iculate organic carbon through the Nor th Inletecosystem. Mar. Ecol. Prog. Ser. 7, 231-2 45 (1982 a)

Chrzanowski, T. H., L. H. Stevenson and J. D. Spu rrier: Transportof microbial biomass through the N or th Inlet ecosystem.Micro b. Ecol. 8, 139 -156 (1982 b)

Chrzanowski, T. H., L. H. Stevenson and J. D. Spu rrier: Transport

of dissolved organic carbon through a major creek of the

North Inlet ecosystem. Mar. Ecol. Prog. Ser. I3 , 167-174

(1983)Daly, M. A. and A. C. Mathieson: Nutrient fluxes within a small

north tem perate salt marsh. Mar. Biol. 61, 337-344 (1981)

Dame, R. F.: The flux of floating macrodetri tus in the North Inletestuarine ecosystem. Estuar. cstl ShelfSci. 15, 337 344 (1982)

Dankers , N. , M. Binsbergen, K. Zegers, R. Laane and M. R. vander Loeff: Transportation of water, particulate and dissolvedorganic and inorganic mat ter between a sal t marsh and theEms-Dollard estuary, the Netherlands. Estuar. cstl Shelf Sci.19, 143-165 (1984)

D'Elia, C. F., P. A. Steudler and N. Corwin: Determination of

total nitrogen in aqueous samples using persulfate digestion.

Limnol. Oceanogr. 22, 760-764 (1977)

Gardner, L. R.: Runoff from an intert idal marsh during t idal

exposure-recession curves and chemical characterist ics.

Limnol. Oceanogr. 20, 81-89 (1975)Gilbert , P. and T. Loder: Autom ated an alysis of nutrients in

seawater. Technical report WHOI-11-41, 46 pp. Woods Hole,

MA: Woods Hole Oceangr. Inst . 1977

Haines, E. B.: Nitrogen p ools in Ge orgia coastal waters. Estuaries

2, 34-39 (1979)Hansen, D. V. and M. Rattray, Jr .: New dimensions in estuary

classification. Limnol. Oceanogr. 11, 319-326 (1966)

Heinle, D. L. and D, A. Fleme r: Flows of materials between

poorly flooded t idal marshes and an estuary. Mar. Biol. 35,359-373 (1976)

Hopkinson, C. S. and J. P. Schubau er: Static and dyna mic aspects

of ni t rogen cycl ing in the sal t marsh graminoid Spartina

alterniflora. Ecology 65, 961-969 (1984)Imberger, J., T. Berman, R. R. Christian, E. B. Sherr, D. E.

Whitney, L. R. Pomeroy, R. G. Wiegert and W. J. Wiebe: The

inf luence of water mot ion on the dis t r ibution and t ranspor t of

materials in a salt marsh estuary. Limnol. Oceanogr. 28,201-214 (1983)

Jordan, T. E., D. L. Correll and D. F. Whigham: Nutrient flux inthe Rhod e River: t idal exchange of nutrients by brackish

marshe s. Estuar. cstl Shelf Sci. 17, 651-667 (1983)

Kjerfve, B.: Hydrographic considerations in estuarine outwelling

studies: an example and definit ions. In: Productivity of the

mangrove ecosystem: management impl icat ions , pp 37-47.Ed. by Ong J in Eong and Gong Wooi Khoon. Penang,

Malaysia: Universit i Sains Malaysia 1984

Kjerfve, B., J. E. Greer an d R. L. Crout: Low frequency response

of estuarine sea level to no n-local forcing. In: Estuarine inter-

actions, pp 497-513. Ed. by M. U Wilsy. Londo n: Ac adem ic

Press 1978

Kjerfve, B. and H. N. McKellar: Time series measurements ofestnarine mate rial f luxes. In: Estuarine perspectives, pp 3 41-357. Ed. by V. S. Kenned y. New Y ork: A cadem ic Press 1980

Kjerfve, B. and J. A. Proehl: Velocity variabil i ty in a cross-sectionof a well-mixed estuary. J. mar. Res. 37, 409-418 (1979)

Kjerfve, B., L. H. Stevenson, J. A. Proehl, T. H. Chrzanowski and

W. M. Kitchens: Estimation o f mate rial f luxes in an estuarine

cross section. A crit ical analysis of spatial measurement den-

sity and errors. Limnol. Oceanogr. 26, 325-335 (1981)

Miller, J. L. and L. R. Gardner: Sheet flow in a salt-marsh basin,North Inlet , South Carolina. Estuaries 4, 234-237 (1981)

Nixon, S. W.: Between coastal marshes an d coa stal waters - a

review of twenty years of speculation and research on the role

of salt marshes in estuarine productiv ity and water chemistry.In: Estuarine and wetland processes, pp 437-525. Ed. by P.

Hamilton and K. B. MacDonald. New York: Plenum Press

1980

Odum, E. P.: The status o f three ecosystem-level hypotheses

regarding salt marsh estuaries: t idal subsidy, outwelling, anddetri tus-based food chains. In : Estuarine perspectives, pp

485-495. Ed. by V. S. Kennedy. New York: Academic Pressi980

Odum, W. E., J. S. Fisher and J. C. Pickral: Factors controll ing

the flux of particulate organic carbo n from estuarine wetlands.In : Ecological processes in coastal and marin e systems, pp69-80. Ed. by R. J. Livingston, New Y ork: Plen um Press 1979

Patrick, W. H. Jr. and R. D. Delaune: Nitrogen and phosphorusuti l ization by Spartina alterniflora in a salt marsh in BaratariaBay, Louisian a. Estuar. cstl mar. Sci. 4, 59-6 4 (1976)

Ryther, J. H, and W. M. Dunstan: Nitrogen, phosphorus andeutrophication in the coastal marine environment. Science,Wash. D.C. 171, 1008-1013 (1971)

SAS Insti tute Inc.: SAS user 's guide: statist ics, 1982 ed.,584 pp.Cary, NC: SAS Institute Inc. 1982



182 G.J . W hi t ing e t aL : Sa l t m a r s h - oc e a n n i t r oge n e xc ha nge

So l o r z a no , L . : D e t e r m i na t i on o f a m m o n i a i n n a t u r a l w a t e r s by

t he phe no l hypoc h l o r i t e m e t hod . L i m no l . O c e a nogr . 14 ,

79%801 (1969)V a l i e l a , I . a nd J . M . T e a l : N u t r i e n t l i m i t a t i on i n s a l t m a r s h

vege ta t ion. I n : E c o l ogy o f ha l ophy t e s , pp 547 - 563 . E d . by R .

J . R e i m o l d a nd W . H . G r e e n . N e w Y o r k : A c a de m i c P r e s s

1974Va l i e l a , I . and J . M. Tea l : The ni t roge n bud ge t o f a s a l t ma r sh

e c os yst e m . N a t u r e , L ond . 2 8 0 , 652-656 (1979)

Va l i e l a , I . , J . M. Tea l , S . Volkman, D. Sha re r and E. J . Ca rpente r :N u t r i e n t a n d pa r t i c u l a t e fl uxe s i n a s a l t m a r s h e c os ys te m :

t i da l e xc ha nge s a nd i npu t s by p r e c i p i t a t i on a nd g r oundw a t e r .

L i m no l . O c e a nogr . 23 , 798-812 (1978)

Wh i t ing, G. J. : Ni t roge n cyc l ing in s a l t mar sh es : t i da l and

gaseous exchanges , 211 pp. P h.D. the s i s, Un ive r s i ty of Sou th

C a r o l i na , C o l um bi a , SC 1985

Wh i t ing, G. J . , H. N. M cKe l l a r J r . , B . Kje r fve and J . D. Sp ur r i e r :

Sa m pl i ng a nd c om pu t a t i ona l de s i gn o f nu t r i e n t f l ux fr om a

southea s t e rn U.S. s a l tm ar sh. Es tua r . c s t l She l f Sc i. 21, 273- 286

(1985)

W ol a ve r , T . G . , W . J ohns on a nd M . M a r oz a s : N i t r oge n a ndphos pho r us c onc e n t r a t ions w i t h i n N o r t h I n l e t, Sou t h C a r o l i na -

specu la t ion a s to sources an d s inks . Es tua r . c s t l She l f Sci . 19 ,

243-255 (1984)Woodwe l l , G. M. , C. A. S . Ha l l , D. E. Whi tney and R. A.

H ou gh t on : T he F l a x Pon d e c os ys t e m s t udy : e xc ha nge s o fi no r ga n i c n i t r oge n be t w e e n a n e s t ua r i ne m a r s h a nd L ong

I s l a nd Sound . E c o l ogy 60 , 695-702 (1979)

D a t e o f fi na l m a nu s c r i p t a c c e p t a nc e : M a r c h 6 , 1987 .

C om m un i c a t e d by J. M . L a w r e nc e, T a m pa

WHiting Et Al 1987 Nitrogen Exchange Between Wetland and Coastal Ocean

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