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Page 1: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Estuarine, Coastal and Shelf Science (1985) 20,205-227

Observations on the Ecological Importance of Salt Marshes in the Cumberland Basin, a Macrotidal Estuary in the Bay of Fundy

Donald C. Gordon Jr., Peter J. Cranford and Con Desplanque Department of Fisheries and Oceans, Marine Ecology Laboratory, Bedford Institute of Oceanography, Dartmouth, N.S. B2Y 4A2, and Maritime Resource Management Service, P.O. Box 310, Amherst, N.S. B4H 325, Canada

Received 23 October I983 and in revised form 25 April I984

Keywords: Bay of Fundy; salt marshes; primary production; exports

The Cumberland Basin, a 118 km’ estuary at the head of the Bay of Fundy which has an average tidal range of about 11 m, contains large tracts of salt marsh (15”,, of the area below highest high water). Low marsh (below about 0.9 m above mean high water) is composed almost exclusively of Spartina alterniflora while the vegetation on high marsh is more diverse but dominated by Spartina patens. Because of its higher elevation, high marsh is flooded infrequently for short periods by only extreme high tides. Low marsh is inundated much more frequently by water as much as 4 m deep for periods as long as 4 h per tide. Temporal variability in the occurrence of extreme tides influences the flooding frequency of high marsh for any given month and year. Using a modification of Smalley’s method, the mean annual net aerial primary production (NAPP) of low and high marsh is estimated to be 272 and 172 g C m ‘, respectively. Vegetation turnover times average 1 .O and 2.0 y for low and high marsh, respectively. Because of abundant tidal energy, much of the low marsh production appears to be exported and distributed widely about the estuary. Since high levels of turbidity suppress phytoplankton production, salt marshes produce approximately half of the carbon fixed photosynthetically in the Cumberland Basin. It is concluded that salt marshes play a major ecological role in the Cumberland Basin.

Introduction

In the late 1970s when we started ecological studies in the Cumberland Basin at the head of the Bay of Fundy, primary production studies focused upon benthic microalgae and phytoplankton (Hargrave et al., 1983). However, observations that Spartim detritus is very abundant in suspended matter and sediment throughout the region (Schwinghamer et al., 1983; Roberts, 1982) suggested that salt marsh primary production and subse- quent export is probably an important factor in the Cumberland Basin energy budget. Extensive salt marshes are found in the macrotidal (average tidal range greater than 4 m) upper reaches of the Bay of Fundy and are especially well-developed in the Cumberland Basin (Ganong, 1903) where the average tidal range is approximately 11 m.

205

0272-7714:85~020205+23 $03.0010 0 1985 Academic Press Inc. ilondon) Limited

Page 2: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

206 D. C. Gordon, P. 3. Cranford 0 C. Desplanque

Surprisingly, very little is known about the production and export of salt marshes in the upper reaches of the Bay of Fundy. The only quantitative study in the Cumberland Basin has been that of Morantz (1976) on the John Lusby marsh near Amherst, while Smith et al. (1980) have studied two marshes in the Minas Basin. Observations of waterfowl, effects of extreme tides and elevations pertinent to Fundy salt marshes have been made by Van Zoost (1968), Bleakney (1972) and Palmer (1979).

Since one of the overall objectives of our research is to gain an understanding of the entire Cumberland Basin ecosystem, we decided it was necessary to initiate research on salt marshes. In 1981 we measured the above-ground production and vegetation loss at eight salt marshes distributed around the Cumberland Basin. Emphasis was placed upon examining the influence of elevation, which affects the flooding regime, upon marsh above-ground production and export. As well as providing us with a preliminary assess- ment of the ecological importance of salt marshes in the Cumberland Basin, the results of our study are of wider interest because few quantitative studies have been made of salt marshes in macrotidal environments. Unique features of these special salt marshes are identified and the importance of tidal energy subsidy (Odum, 1980) under extreme conditions is evaluated. The results also shed some light on the present controversy over the extent and importance of salt marsh export (Nixon, 1979; Odum, 1980).

Description of Cumberland Basin

The principal environmental characteristics of the Cumberland Basin have been described by Gordon & Baretta (1982), Schwinghamer et al., (1983), and Gordon & Desplanque (1983). Tidal properties, freshwater discharge, sedimentation and ice are of particular importance to the salt marshes.

Mean tidal range is approximately 11 m and high spring tides can attain a range of 16 m in the upper parts of the Basin. Due to astronomical effects the elevation of high water can vary as much as 5 m at any given location. This variation is greater than the entire tidal range in salt marshes along the U.S. Atlantic Coast (Linthurst & Reimold, 1978). About two-thirds of the Basin volume drains into Chignecto Bay each ebb tide, resulting in strong tidal currents averaging about 0.7 m s- ‘. The volume of the spring tidal prism is about 1 km3.

Six small rivers draining an area of about 1900 km’ enter the Basin and contribute an average of about 57 m3 s-i of fresh water which is equivalent to just 0.25”,, of the spring tidal prism. The marshes come into contact with seawater having a salinity of about 22%0 or greater since they are flooded for just a few hours around high tide.

The Bay of Fundy has been macrotidal for about 6000 years (Amos, 1978). Being surrounded by erosive cliffs of Paleozoic sandstones, siltstones and shales, the Chignecto Bay region has an abundance of fine sediment. Suspended sediment concentrations in Cumberland Basin are generally in the range of 100-1000 mg 1~ ’ and even higher concentrations can occur in the upper reaches of the estuaries and tidal creeks. Thick, extensive deposits of fine inorganic sediment have accumulated around the perimeter of the Cumberland Basin forming an ideal substratum for salt marsh development (Ganong, 1903). Upward marsh growth is continuing today because rising mean sealevel and increasing tidal amplitude together increase the elevation of mean high water 30-45 cm century-’ (Amos, 1978; Dohler & Ku, 1970). The depositional history of Cumberland Basin marshes has been considered by Ganong (1903) and more recently has been studied in detail by Dekker & van Huissteden (1982).

Page 3: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Ecological importance of salt marshes 207

From December to March, the Cumberland Basin contains large amounts of ice (Gordon & Desplanque, 1983). Thick shorefast ice develops in the zone between neap and spring high water levels and covers the lower part of the salt marsh area for most of the winter. Other parts of the salt marshes can be periodically affected by moving or stranded drift ice.

Fundy salt marshes have been traditionally differentiated into low and high com- ponents which are relatively easy to distinguish. Low marsh is generally defined as those portions which are flooded frequently and composed primarily of Spartina alterni’oru. In contrast, high marsh occurs at higher elevations, is flooded infrequently and irregularly and is dominated by Spartina patens. Most of the original high marsh areas have been diked for agricultural use beginning with the Acadian settlers in the seven- teenth century (Ganong, 1903). Approximately 328 km2 of high marsh has been diked around the entire Bay of Fundy of which 150 km2 occurs in the Cumberland Basin.

Methods

Eight salt marsh transects were established along the Cumberland Basin (Figure 1). They were selected to represent the complete range of salt marsh types (high and low) and environmental settings (exposed and sheltered) found in the basin. Ease of access was also a factor. In late April 1981, one to six sampling stations were established at more or less even spacing along each transect. Nine 0.04 m3 contiguous quadrates were outlined at each station using plastic survey tape held in place by galvanized nails. All 29 stations were sampled monthly from May to November (except in October). On each visit the height of ten random plants was recorded. All above-ground plant material (live and dead) was removed from a pre-selected quadrate and placed in a plastic bag. Also, general observations were recorded and photographs taken.

Additional above-ground vegetation samples were collected at intermediate sites along the transects in August. On the same date, belowground vegetation (0.04 m2) was collected to a depth of 12 cm at each station. In September, five replicate above- ground vegetation samples were collected to estimate sampling error (C.V. = 17”,,:1. Unpublished data from another marsh site shows little seasonal variation in sampling error.

Leaf loss from frequent tidal immersion was measured at the Pecks Cove and Minudie transects by tagging ten Spartina alterni’ora plants and counting the numbers of leaves (live and dead) on each visit. Our estimates of leaf loss, expressed as a percent of annual net aerial primary production (NAPP), were 16.7 no at Pecks Cove (1.54 m below MHW) and 15.9”,, at Minudie (1.01 m below MHW). Morantz (1976) observed a leaf loss of 6,8”,, from S. alterni’ora growing in the sheltered high marsh region of the John Lusby marsh (Figure 1) which has an elevation of about 1 m above MHW (Figure 2). These limited data suggest that leaf loss increases with decreasing elevation which is reasonable since the frequency, depth and duration of tidal flooding also increases. We therefore fitted these three points with a straight line and used it to estimate leaf loss at other low marsh sites. We assume that there is no significant tidally promoted leaf loss from high marsh during the growing season because of its different vegetation and much less frequent flooding.

In the laboratory, samples were washed to remove silt. Aboveground vegetation was sorted into three categories: (1) live (L)-green shoots and leaves from the current grow- ing season, (2) new dead (ND)-dead vegetation from the current year’s growth which is

Page 4: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

208 D. C. Gordon, P. J. Cranjh-d & C. Desplanque

.64"20 6475'

BRUNSWICK

W30’ 64025' 64"20' 64'15'

Figure 1. Map of Cumberland Basin showing the distribution of salt marshes and intertidal sediment flats. LLW indicates the location of lowest low water (approxi- mately chart datum). The study sites are (1) Pecks Cove, (2) Allen Creek, : 31 Tantramar, (4) John Lusby, (5) Maccan, (6) Elysian East, (7) Elysian West and 181 Minudie. The lines represent the orientation of sampling transects.

brown in colour and (3) old dead (OD)-dead material produced during previous year(s) which is usually quite dark in colour and more markedly weathered. New and old dead material were easy to distinguish but at times there were problems separating live and new dead material. It was not possible to separate belowground vegetation into live and dead components. Vegetation weights were recorded after drying at 65 C to constant weight. Plant species were identified by means of live samples and from Roland & Smith (1963). Carbon and nitrogen contents of live and old dead Spartirta alterrtifZora tissue collected on 29 May 1981 at Allen Creek (Figure 1) were determined with a Perkin- Elmer 240B elemental analyser (using cyclohexanone-2 : 4-dinitrophenylhydrazone as a standard) after samples had been rinsed with distilled water and dried at 65 C.

Net aerial primary production (NAPP), expressed as dry weight, was measured using a variation of Smalley’s (1959) method (Table 1). This method, which computes changes with time in the biomass of live and dead material, has been widely used for salt marsh studies (e.g. Shew et al., 1981). In comparing it to other methods, Linthurst & Reimold

Page 5: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Ecological importance of salt marshes 209

MHW

\

TQNTRAMAR 131

\

Figure 2. Profiles of salt marsh transects plotted relative to mean high water (MHW). MHW in Cumberland Basin increases from approximately 5.3m (above geodetic datum) at Pecks Cove to 6.0 m at Maccan. See Figure 1 for transect locations. Triangles mark the sampling stations. Note the scale break for the Tantramar transect. The broken parts of profile lines represent exposed sediment without marsh vegetation.

TABLE 1. Procedures used to calculate salt marsh production and the loss of new dead material per sampling interval using the Smalley method (1959)

AL AND Production Loss

+ t AL + AND 0 - 0 AL + AND

+ AL AND + ALfAND if >O AL+AND if tO

AL = change in live biomass, AND = change in new dead biomass.

Page 6: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

210 D. C. Gordon, P. J. Cranjord & C. Desplanque

(1978) drew attention to several of its faults, namely not including new shoot growth during periods of high mortality and underestimating the loss of dead material due to tidal flushing between sampling intervals. Nevertheless, they concluded that it was a suitable method for salt marsh production studies and that its accuracy could be improved by using shorter sampling intervals and measuring more accurately the removal of dead material by tidal activity. Another fault of the method, not previously recognized, is that increases in new dead material, which may contribute to production (Table l), can be masked by simultaneous decreases in old dead material if the two dead forms are not distinguished.

Taking these factors into consideration, we used a sampling interval of approximately 30 days [compared with the 56-day interval used by Linthurst & Reimold (1978)] and distinguished between new and old material. The sampling interval was determined by logistics. All dates except August coincided with or were just after neap tides. We also determined the elevation of sampling stations and estimated leaf loss during the growing season to help correct for mortality and tidal export of vegetation between sampling intervals.

Marsh type and areas for all of Cumberland Basin were determined by the Canadian Wildlife Service (Sackville, N.B.) using I : 10000 colour aerial photographs for the Nova Scotian area and 1 : 20000 black and white photographs for the New Brunswick area according to techniques detailed in Hudgins et al. (1983). During June, the transects were surveyed from the upland border to just beyond the seaward limit of marsh vege- tation by the Maritime Resource Management Service (Amherst, N.S.). Elevations of all stations and major marsh features were determined relative to geodetic datum which is about 20 cm below mean sea level (MSL) (Gordon & Desplanque, 1983) in Cumberland Basin. The elevation of mean higher high water and higher high water of very infrequent large tides at Pecks Point was obtained from Canadian Tide & Current Tables (1981) and calculated relative to geodetic datum. Elevations of mean high water (MHW) and highest high water (HHW) (relative to geodetic datum) at all transects were estimated by use of the observed relationship that tidal amplitude increases 0.35”, each kilometre up Cumberland Basin. Flooding frequency and depth were estimated using the frequency distribution of predicted high water elevations at Saint John, N.B. (Canadian Tide & Current Tables, 1981). Flooding duration was estimated by use of a sine curve model after it was shown that tidal curves in Cumberland Basin approximate sine curves above MHW (J. Matthews, unpublished data). Since very few extreme tides occurred during 1981 because of astronomical conditions, comparisons of flooding conditions are made with 1976 which had a relatively large number of extreme tides (Gordon & Desplanque, 1983).

Results Elevation and vegetation

The profiles of the eight salt marsh transects are plotted relative to MHW in Figure 2. The Pecks Cove and Minudie transects near the mouth of the Cumberland Basin (Figure 1) are relatively short (less than 200 m) and steep (about 2”,,); both occur at the landward edge of broad (about 1 km wide) mudflats. Transects at Allen Creek and Elysian East are intermediate in length and more gradual in slope (about 0.7O,,). In contrast, the transects at Tantramar, John Lusby and Elysian West are long (greater than 500 m) and very flat; they are dissected by natural drainage channels and man-made ditches and in

Page 7: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Ecological importance of salt marshes 211

JOHN LUSBY (4) ELYSIAN EAST 6)‘~,

TANTRAMAR (3),

ALLEN CREEK (2) ELYSIAN WEST 17)

I rib

- PECKS COVE III

i RANGE OF HIGH TiDE

Figure 3. The elevation of high water levels and salt marsh vegetation at the eight transects. The solid bars denote high marsh vegetation and the open bars low marsh vegetation; some overlap occurred at the Elysian West and Minudie transects. LHW indicates lowest low water, MHW mean high water and HHW highest high water. The 1976 tidal data are included to illustrate how marsh flooding frequency increases during years with a large number of extreme tides. Predicted tides were obtained from Canadian Tide & Current Tables for the appropriate year.

places shallow ponds dot the surface. An abandoned dike, now breached, is found near the seaward edge of the John Lusby transect. The Maccan transect is quite different from the rest. It is located far up the Basin (Figure l), is very short, and is situated between a dike and a tidal river. Transects in the middle and upper regions of the Cumberland Basin terminate seaward in erosional banks about 1 m high.

The absolute elevations (above geodetic datum) of salt marsh vegetation boundaries generally increase up the Basin because of increasing high tide elevations (Figure 3). For example, MHW and HHW elevations increase approximately 0.7 and 1.2m, respectively, over the distance of 42 km between Pecks Cove and Maccan (Figure 1). Palmer (1979) reported similar increases in high tide elevations moving up Cumberland Basin.

The elevations and dominant vegetation of individual sampling stations are listed in Table 2. The lower elevations of marsh (below about 0.9 m above MHW), commonly referred to as low marsh, are composed almost exclusively of Spar&a aZternij?ora. Other plants occasionally encountered in this zone include Puccinellia maritima, Salicornia europaea and Suaeda maritima. Vegetation at higher elevations (above about 0.9 m above

Page 8: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

212 D. C. Gordon, P. J. Cranford Q C. Desplanque

TABLE 2. Selected features of the 29 sampling stations (see Figures 1 and 2 for locations)

Station Elevation relative

to MHW (m) Vegetation Marsh type

l-l -1.54 2-l -0.61 2-2 -0.10 2-3 0.81 3-1 0.88 3-2 I.04 3-3 0.85 34 1.22 3-5 1.16 4-l 1.24 4-2 1.03 4r3 1.18 4-4 1.09 5-l 1.58 5-2 1.45 6-I 0.59 6-2 0.65 6-3 0.78 6-4 1.41 6-5 1.47 7-l -1.16 7-2 0.84 7-3 0.93 74 0.93 7-5 0.48 7-6 1.02 8-1 - 1.01 8-2 0.63 8-3 1.05

Sa Sa Sa

Sa

Sa

Sa

Sa Sa Sa

Sa Sa Sa

Sa

Sa Sa

SP SP SP

SP SP SP

SP

SP

SP

SP

SP

SP SP

Pa

Spec Ar

Spec

Pm

Pm

pi V,Jg

LE LE LE

H H H

LS H H H

LS H

LS H H

LE LE LE

H H

LE H

LS H

LS H

LE H H

Vegetation is: Sa, Spar&a alternij?ora; Sp, Spartina patens; Pa, Puccznellla amerisutki; Spec, Sparrina pectinata; Pm, Puccinella martima; Pj, Plantago juncoides; Ar, Agrop-vron repens; and Jg, Juncus gerardi. Marsh types are: LE, low exposed; LS, low sheltered; and H, high.

MHW), commonly referred to as high marsh, is much more diverse. Spurt&a putens dominates but Puccinellia americana, S. pectinata, P. maritima, Plantago juncoides, Juncus gerardi, Agropyron repens and S. alterni’ora also occurred at the stations. Other plants found at higher marsh elevations in Cumberland Basin include Limonium nashii, Carex paleacea, Atriplex patula, Hordeum jubatum and Solidago sempervirens. Although their ranges overlap, S. alterniflora and S. patens were found in the same quadrate at only two stations. At higher elevations S. altermj7ora is found in moist areas along drainage channels and around ponds while S. patens is restricted to drier areas.

On the basis of vegetation and elevation the 29 sampling stations were divided into three different marsh types: exposed low marsh (LE), sheltered low marsh (LS) and high marsh (H) (Table 2). This division is consistent with the coastal wetland classification of the Canadian Wildlife Service (Hudgins et al., 1983) with the exception that we subdivided low marsh into exposed and sheltered components. Both are composed predominantly of Spartina alterniflora but they differ in elevation and exposure. Exposed low marsh generally occurs at lower elevations along sloping transects of short

Page 9: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Ecological importance of salt marshes 213

to intermediate length and is exposed to tidal currents and waves at high tide. In contrast sheltered low marsh is found at higher elevations within the extensive high marsh areas of the longer transects, especially along creek banks, and receives considerable protection from waves and currents during flooding. The average elevations of each marsh type at the stations sampled are given in Table 3.

The vertical range of vegetation varied from about 0.2 m at Maccan to 3 m at Minudie (Figures 2 and 3) and averaged about 2 m for the entire Basin. Salt marshes in the Cumberland Basin therefore occupy less than 20°, of the mean tidal range.

Flooding regimes The flooding regimes of salt marsh stations are affected by their elevations and the height of high water. The diagonal lines in Figure 3 represent the elevations of all theoretical high tides ranging from LHW to HHW at the eight transects (Figure 1). Superimposed upon these tidal lines are the elevation ranges of high and low marsh observed along the transects. The upper axes of Figure 3 indicate the predicted fre- quency distributions of high tide elevation for 1981 (the year of observation) and 1976 (a year with a large number of extreme tides). This figure can be used to estimate the frequency and depth of flooding for the stations. For example, in 1981 the Maccan transect was theoretically flooded only about 15 times and water depth never exceeded 0.5 m. In contrast, the lowest vegetation at Pecks Cove was flooded on every high tide and water depth at high tide approached 4 m.

During 1981, the year of our sampling, the low exposed marsh stations were flooded an average of 375 times (53”,, of the high tides). Theoretical maximum water depth and duration average 1.9 m and 3.0 h, respectively (Table 3). In contrast, high marsh stations were expected to be flooded just 41 times (only 6”, of the high tides) and the average maximum water depth and duration were only 0.5 m and 1.5 h, respectively. Low sheltered marsh had intermediate values. The frequency, depth and duration of flooding are all considerably greater in years with a larger number of extreme tides such as 1976 (Table 3).

Area The total salt marsh area in Cumberland Basin is 1714 ha or 15O, of the area below highest water. Low marsh (both exposed and sheltered) and high marsh comprise 45 and 55”,, of the marsh area, respectively. Since there is no information available on the relative areas of exposed and sheltered low marsh, low marsh is usually treated as a single entity in the rest of this paper. Also, because of its very small area, location and different vegetation the Maccan transect data are not included in the following production and loss calculations.

Production Growth of above-ground biomass in Cumberland Basin salt marshes is restricted to the five month period between May and September (Figure 4). In the early spring after ice and snow disappear, only old dead material is present. The lowest low marsh sites, such as Pecks Cove, are almost completely barren. New shoots appear in April and growth is rapid thereafter. Maximum aerial biomass, maximum plant height and flowering occur in July or August. Thereafter vegetation begins to die and by the end of autumn only dead material is present.

The annual NAPP of individual exposed low marsh stations varied by more than an order of magnitude (Figure 4). Much of the variability can be attributed to elevation. For

Page 10: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

TABL

E 3.

A

sum

mar

y of

th

e flo

odin

g re

gim

e (fr

eque

ncy

out

of

705

annu

al

tides

, de

pth

and

dura

tion)

fo

r th

e th

ree

mar

sh

types

at

the

29

st

atio

ns

sam

pled

fo

r th

e ye

ar

durin

g wh

ich

prod

uctio

n m

easu

rem

ents

we

re

mad

e (1

981)

an

d an

othe

r ye

ar

(197

6)

havin

g a

larg

e nu

mbe

r of

ex

trem

e tid

es

(num

bers

in

dica

te

mea

ns

and

rang

es

due

to m

axim

um

and

min

imum

el

evat

ions

)

Mar

sh

type

Elev

atio

n re

lativ

e to

M

HW

(m)

Floo

ding

fre

quen

cy

Max

imum

wa

ter

dept

h (m

)

1976

19

81

1976

19

81

Max

imum

du

ratio

n (h

)

1976

19

81

Tim

e flo

oded

(‘,

/

Low

expo

sed

Low

shel

tere

d

High

-0.3

0 40

4(

125-

680)

37

5(65

-685

) 25

(1+3

.6)

1.9(

0.8-

3.0)

3.

3(2.

5-4~

1)

3.0(

1.

9-4.

0)

12.8

-15.

2

0.88

12

1(95

-180

) 68

(50-

130)

1.

3(1.

2-1.

6)

0.8(

0+1.

1)

2.4(

2.2-

2.7)

1,

8(16

-2.3

) 1 G

3.3

1.12

91

(50-

160)

41

(10-

95)

l.l(O

.S-1

.5)

0.5(

0.1-

0.9)

2,

1(1.

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6)

15(0

.8-2

.1)

0.7-

2.2

Page 11: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Ecological importance of salt marshes 215

W 2

5

o---------‘--------------------------~----------------------~~~-----

d -0.5 - [L 0

2 -1.0 - 0 LOW MARSH (EXPOSED) Q o 0

5 -1.5 0 0 how MARSH (SHELTERED)

W . HIGH MARSH

d -2.0 -

0 5KJ 1000 ANNUAL NAPP (g rTTe)

Figure 4. Annual net aerial primary production (NAPE’) at all stations plotted against elevation (relative to MHW).

example, the smallest values occur at the lowest elevations, about 0.5 to 2.0m below MHW, where inundation is most frequent (Figure 3). The largest values occur between 0.5 and I.0 m above MHW where inundation is much less frequent, shallower and of shorter duration (Figure 3 and Table 3). The correlation between the NAPP of exposed low marsh and the elevation is statistically significant (r’ =0.69, P=O.O2). It therefore appears that the most favourable growth conditions for Spartina alternij?ora occur above the MHW level in Cumberland Basin. Physical stress is probably responsible for suppressing production at lower elevations. The annual NAPP of sheltered low marsh varied only by a factor of two with no clear relationship to elevation (the vertical range is much less). The average NAPP of all low marsh stations was 637 g mm2 (Table 4).

High marsh stations showed the least variability in annual NAPP (Figure 4) which averaged 403 g mm2 (Table 4). Within the same elevation range the annual NAPP of Spartina alterni’ora is considerably greater (Figure 4). Even averaging all low marsh stations, the annual NAPP is significantly greater than that of high marsh (Table 4).

The maximum height of low marsh vegetation tended to be greater than that of high marsh but the difference comparing mean values for all stations was not significant (Table 4). The below-ground biomass was 1.7 and 5.7 times the annual NAPP for low and high marsh respectively and was significntly greater on high marsh (Table 4). There was no correlation between below-ground biomass and annual NAPP but both maximum aerial biomass and maximum plant height were significantly correlated with annual NAPP (r’ = 0.94, P= 0.001 and r2 = 0.64, P= 0.001, respectively).

Loss The monthly losses of new and old dead material from both high and low marsh during the period of measurement are plotted in Figure 5. During the growing season prior to September the loss of new dead vegetation was relatively minor and due primarily to loss from more frequently flooded low marsh stations. In September, when marsh vegetation started to die, there was a maximum in the loss of new dead material at the low marsh sites while the loss from high marsh sites remained consistently low. The loss of old dead

Page 12: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

216 D. C. Gordon, P. 3. Cranjord & C. Desplanque

TABLE 4. Comparison of selected variables (means and standard deviations) for low and high marsh. Low marsh includes both exposed and sheltered types. High marsh excludes the Maccan stations which had quite different vegetation. The r statistic tests the means of two independent random samples. Units are g mm2 except for turnover time (years) and height (cm). New dead loss includes leaf loss. All comparisons have 25 degrees of freedom

Variable Low marsh High marsh r I’

Annual NAPP

Maximum aerial live biomass, 1981

Maximum plant height

Below-ground biomass

(Aw)

New dead loss (Apr-Nov)

Old dead loss (Apr-Nov)

Overwinter loss (Nov-Apr)

Annual loss

Minimum aerial total biomass (MATB)

Turnover time (MATBiannual NAPE’)

637 (353)

563 (338)

48 (24)

1072 (545)

290 (171)

199 (233)

145 (168)

634-351)

647 (394)

1.0 (0.2)

403 (90) 2-40

371 (64) 2.09

38(11) 1.52

2310 (1222) 3.35

96 (99) 3.64

316 (135) 1.62

-30 (145) 2-92

382 (89) 2.60

789 (269) 1.03

20 (0.6) 5.85

OXl25-0 02

0.05 -0.025

0.20 -0.10

0~0055040 1

o~oo5-u~oOl

0.20 -0~10

0.01 -0 005

0.02 -0.01

0.40 -0,30

<U~OOl

HIGH MARSH

100 .-.

NAPP

Y E

. ,

0%.

/

\ ‘*...?DL

.A*

m . “* . . . . . . . . . . ..-1’ ..*..

/

. . . .

\..

..*..........- . . . . . . .

ND+*--:.---- -*

0 0’

LOW MARSH 200-

s 0 N

Figure 5. Monthly values of net aerial primary production (NAPP), new dead loss including leaf loss estimates (NDL) and old dead loss (ODL) between April and November 1981. Data represent average values from all high and low marsh stations except the Maccan transect.

Page 13: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

Ecological importance of salt marshes 217

.

9 U.

0 LOW MARSH

d . HIGH MARSH . l

.

OO Nxcl i%AL NAPP ( gm-2)

Figure 6. Annual net aerial primary production (NAPE’) plotted against estimates of annual vegetation loss (five overlapping points near 350 g m- ’ are omitted because of lack of space).

0 LOW MARSH

y -1.0 0 . HIGH MARSH Cl

0 TLkNOVER TIME ;YEARSl

3

Figure 7. Turnover time (years) of marsh vegetation at all stations plotted against elevation. Turnover time is defined as the maximum aerial total biomass (both live and dead components) (MATB) divided by annual net aerial primary production (NAPE’). Data from the Maccan transect are omitted.

material on both low and high marsh was greatest in the spring and decreased during the summer and autumn. On high marsh the loss of old dead material was always greater than that of new dead material.

All categories of vegetation loss, except old dead loss, were significantly greater on low marsh than on high marsh (Table 4). There is a very close balance between annual NAPP and loss, both for individual stations (Figure 6) (r2 = 0.98, P=O.OOl) and average values for low and high marsh (Table 4).

Vegetation turnover times, defined as maximum aerial total biomass (MATB) divided by annual NAPE’, are plotted in Figure 7. Average turnover times were 1.0 and 2.0

Page 14: Observations on the ecological importance of salt marshes in the Cumberland Basin, a macrotidal estuary in the Bay of Fundy

218 D. C. Gordon, P. J. Cranford Q C. Desplanque

TABLE 5. Carbon and nitrogen contents of live and old dead Sparrina ulrerniflora collected on 29 May 1981 at Allen Creek. The old dead vegetation had over-wintered and was still attached when collected. Mean (and standard deviation) of three replicate analyses

Property Live Old dead

“,,C 42.7 (0.7) 29.9 (3.7) “,,N 3.9 (0.2) 0.6 (0.2)

CN ratio (by weight) 11.0 49.8

years for low and high marsh respectively (Table 4). The turnover time of low marsh vegetation was significantly correlated with elevation (Y’ = 0.55, P= 0.01).

Carbon and nitrogen contem The carbon and nitrogen contents of live and old dead Spartina alterniflora are given in Table 5. During weathering vegetation looses nitrogen at a faster rate than carbon and the CN ratio increases accordingly more than four fold.

Discussion Flooding regime

Unfortunately direct measurements of salt marsh inundation are unavailable and there are several reasons why the actual flooding frequency of the high marsh stations is pro- bably somewhat less than indicated in Table 3. Because of their flat nature (Figure 2) it takes longer for flooding water to penetrate into the more remote portions, especially where creekside levees are present. Vegetation also impedes the flow of water across the high marsh surface. During the winter shorefast ice builds up around the edge of high marsh and can retard flooding (Gordon & Desplanque, 1983). Sea ice never reached the high marsh areas during the winter of 1981 but it can in years with extreme winter tides such as 1975 (Morantz, 1976).

As noted by Blum (1968) the occurrences of the highest spring tides capable of flooding high marsh are irregular and they tend to occur in groups with considerable temporal variability. In the Cumberland Basin the highest tides generally fall into two periods each year about 206 days apart (Gordon & Desplanque, 1983). Several months can pass between flooding events and the timing of these gaps shifts slightly from year to year. During periods of prolonged emersion, high marsh vegetation is subjected to considerable dessication. There also is pronounced annual variability in the number of extreme tides (Bleakney, 1972; Gordon & Desplanque, 1983) so that flooding characteristics between given calendar years can differ markedly (Table 3).

It is well established that vertical zonation of salt marsh vegetation is controlled primarily by flooding regime (e.g. Adams, 1963) and the pattern observed in the Cumberland Basin is consistent with that observed further south along the U.S. coast. Flat high marsh, dominated by Spartina patens, is flooded infrequently for short periods by only extreme high tides (Table 3). This translates into just 0.7 to 2.2”,, of the time which compares favourably with the value of l-3”,, calculated by Redfield (1972) for high marsh in Barnstable Harbor on Cape Cod at the southern end of the Gulf of Maine.

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Ecological importance of salt marshes 219

The maximum depth of water flooding high marsh, about 1.5 m (Figure 3 and Table 3), is, however, considerably greater than that at Barnstable Harbor (Redfield, 1972). The average flooding depth at Cumberland Basin is probably less than half a meter or about the same as the average height of high marsh vegetation at maximum biomass near the end of the summer (Table 5). Relatively few tides appear to have the capability of com- pletely covering high marsh vegetation. Redfield (1972) concluded that infrequent sub- mergence for not more than l”,, of the time for periods not greater than about 2 h is probably sufficient to prevent less salt-tolerant upland vegetation from invading the upper salt marsh at Barnstable. The same general rule appears to apply to the Cumberland Basin (Table 3). Gleason & Zieman (1981) suggest that S. patens is restricted to high marsh because of its lesser ability to supply oxygen to below-ground components during flooding.

The elevation of Spartina patens distribution in Cumberland Basin is more than a meter above MHW (Figure 3 and Table 3), much higher than reported for other regions (e.g. Blum, 1968). This is presumably due to the extreme variability in the elevations of high water. As reported for marshes further south, the upper range of S. alterni’ora

overlaps slightly with S. patens while the lower range extends considerably below MHW (Figure 3 and Table 2). The lowest elevation of S. alterni’ora, at Pecks Cove, is about 2 m below MHW (Figure 3) which is the same as that observed at Barnstable Harbor (Redfield, 1972). However, because the tide range is much less at Barnstable (average about 3 m), S. alterni’ora there occupies about two-thirds of the tidal range. In contrast, in the Cumberland Basin it occupies less than 20”,, of the tidal range.

It therefore appears that factors other than flooding frequency and duration must limit the seaward or lowest limit of Spurt&a alterniflora in Cumberland Basin and prevent it from colonizing the extensive intertidal mudflats which make up about two-thirds of the total area. One factor may be the maximum depth of water that S. alterniflora can tolerate. At its lowest elevation it is flooded with 2 m of water on an average tide and over 4 m on extreme tides (Figure 3). Oxygen concentrations in stems and roots are influenced by tidal inundation (Gleason & Zieman, 1981) and the pressure exerted by more than 4 m of water during flooding may be more than S. alternijora can tolerate even for brief periods. Another factor may be ice scouring which churns up the surface of mudflats to a depth of several centimetres each winter (Gordon & Desplanque, 1983) and must place considerable stress upon the lowest elevations of S. ultern$ora which are not usually protected by shorefast ice or frozen crust.

As discused by Marinucci (1982), Spartina alternij¶ora commonly occurs in two forms along the east coast of the US; a tall form in frequently flooded areas such as along creek banks and a short form at higher elevations. Our observations indicate that a somewhat different pattern occurs in Cumberland Basin. The tallest plants do tend to occur along creek banks but these are quite high in elevation, usually well above MHW (Figure 2). S. alterni’ora may have difficulty colonizing the flat high marsh areas because of their even higher elevation. The shortest plants occur near the lower limit of the S. alterniflora range a meter or more below MHW (Figure 2). The stunted growth at these elevations is probably due to the rigorous flooding regime.

Production As recently reviewed by Marinucci (1982), the annual NAPP of Spartina alterniflora along the Atlantic coast of North America falls into the range of 550-2000 g m-‘. Our results lie at the lower end of this range and support the hypothesis that production

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220 D. C. Gordon, P.J. Cranford & C. Desplanque

generally decreases northward paralleling the latitudinal decrease in solar energy input (Turner, 1976). The average NAPP of S. alterni’ora in the Cumberland Basin (637 g mm2 years-‘, Table 4) is slightly less than the 7 10 g m- ’ years- ’ observed by Hatcher & Mann (1975) in Petpeswick Inlet about one degree south on the Atlantic coast of Nova Scotia. The average NAPP of high marsh, dominated by S. patens, is significantly lower (403g mm2 year- ‘, Table 4). These two values for Cumberland Basin bracket the weighted mean production of 483 g m-’ year- ’ derived for both low and high marsh areas on the John Lusby marsh (Figure 1) by Morantz (1976) using the maximum biomass method corrected for leaf loss (6.8”,,). Smith et al. (1980), also using the maximum biomass method corrected for leaf loss, estimated the aerial production of two salt marshes in the Minas Basin to be about 500 g m- * year-‘. Therefore, it is clear from the three studies that the average annual NAPP of Fundy salt marshes is quite low compared with salt marshes further south, ranging between about 400 and 600 g m- ’ year-‘. It is much higher however than the very low mean value of 227 g m-’ year -- ’ reported for a salt marsh much further north on James Bay (Glooschenko & Harper, 1982).

The production of salt marsh vegetation is influenced by a wide variety of environmental factors (e.g. Turner, 1976; Marinucci, 1982). Those that appear to be primarily responsible for the relatively low production of the Cumberland Basin marshes are the shortness of the growing season, nutrient limitation, tidal stress, inun- dation characteristics and sediment aeration. Because of the combined effects of relatively high latitude (45’-46”N) and severe winters, the major part of the growing season is limited to the five month period between May and September (Figure 5). Only dead vegetation is found on the marshes during the rest of the year. In contrast, live vegetation is found throughout the year on the more productive southern marshes such as occur along the Gulf coast of Louisiana (e.g. Kirby & Gosselink, 1976).

Smith et al. (1980) have demonstrated that the addition of ammonium nitrate to the soil increased the production of two Minas Basin salt marshes by an average of 88”, , These results suggest that Fundy salt marshes are nitrogen-limited even though they have the ability to fix nitrogen (Smith et al., 1979) and combined nitrogen (more than 2 pg atom l- ‘) is present in tidal waters the year round (Gordon & Baretta, 1982). Nutrient limitation is probably more important in high marsh which is flooded much less frequently (Table 3).

Odum (1974) proposed that the relatively high production of salt marshes is caused in part by a tidal energy subsidy which promotes mineral recycling, food transport and waste removal. This hypothesis was supported by Steever et al., (1976) who demonstrated a strong positive linear correlation between Spartina alterni’ora produc- tion and tidal range along the Connecticut shore. Both Odum (1974) and Steever er al:, (1976) recognized that the beneficial effects of tidal energy have an upper limit and would probably disappear in macrotidal environments due to increasing physical stress. Salt marsh production data from the Bay of Fundy (Morantz, 1976; Smith et al., 1980; this paper) support this prediction since values are quite low compared with other salt marshes. The stress of increased tidal range is probably greatest on low marsh which is exposed to the most extreme inundation (Table 3) because of its lower elevation. Because of infrequent and brief flooding, tidal stress probably exerts little adverse influence on high marsh.

Although wave action may be important, the tidal stress imposed on low marsh in macrotidal environments such as the Cumberland Basin appears to be related to the

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Ecological importance of salt marshes 221 --

depth and duration of inundation. As reviewed by Gleason & Zieman (1981) the underground organs of Spartina alterniflora require oxygen which is obtained from the above-ground shoots by diffusion through gas spaces (aerenchyma). The shoots obtain their oxygen by diffusion from the atmosphere and photosynthesis. Gleason & Zieman (1981) have demonstrated that inundation by water less than 1 m deep sharply reduces oxygen concentrations in shoot bases and roots. During darkness, when oxygen production by photosynthesis is prevented, inundation can even produce temporary anoxic conditions. They concluded that oxygen deprivation during submergence may limit the seaward limit of S. aZternijZora. It seems reasonable, therefore, to conclude that tidal inundation limits not only the distribution of S. alterniflora in Cumberland Basin but also its production. On average, exposed low marsh S. alterniflora is flooded for about 3 h to a maximum depth of about 2 m on more than half the tides each year (Table 3). Because of the excessive turbidity of Cumberland Basin water, photosynthesis of S. alterni’ora at its lower elevations must drop markedly during daytime inundation for Hargrave et al., (1983) report that no photosynthetically available radiation (PAR) penetrates the water deeper than an average of 1.5 m.

Linthurst (1980) and Howes et al., (1981) have demonstrated that Spartina alternifEora grows better in well-oxygenated sediments. In general, sediments comprising the Fundy salt marshes have a high silt content and low porosity (MacKinnon & Walker, 1979). As a result the surface aerobic layer in marshes appears to be quite shallow, 1 cm or less (Anderson & Hargrave, 1983), and this may reduce the production of both high and low marsh.

Vegetation loss The loss of salt marsh vegetation, calculated from observed changes in the biomass of new and old dead material, is due principally to tidal export and microbial decompo- sition. Tidal export can occur anytime of the year, removing both dissolved and particulate materials which then can be subjected to microbial decomposition in other parts of the Cumberland Basin ecosystem such as along the shoreline, in the water column or on mudflat sediments. Tidal export can also move vegetation from one part of a marsh to another, especially on low marsh, but this process does not seem to be very important in the Cumberland Basin. Once dislodged, vegetation appears to leave the marsh. The dead vegetation sampled was almost always attached to underground rhizomes. Microbial decomposition within the marshes can remove organic matter by converting it to an exportable form or degrading it to fine material which may be incorporated into the marsh sediment. It is temperature dependent and therefore most important during the summer months. The various decomposition pathways which marsh vegetation can follow are reviewed by Marinucci (1982).

Vegetation loss is much more rapid from low marsh than from high marsh (Table 4). The turnover time of low marsh averages 1.0 years but can vary at individual stations from 0.7 to 1.4 years depending upon elevation (Figure 7). In contrast, the turnover time of high marsh averages 2.0 years and individual stations range from about 1.0 to 3.0 years. Short turnover times for low marsh have also been reported in other studies (e.g. Marinucci, 1982).

Using the data collected during the seven month sampling program (Table 4 and Figure 5) and assuming that winter conditions are similar in successive years, an approximate picture of annual vegetation loss dynamics can be obtained (Table 6). An average of 46”,, of the low marsh annual NAPP is lost as new dead material during the

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222 D. C. Gordon, P. 3. Cranford & C. Desplanque

TABLE 6. A summary of vegetation loss at different stages expressed in terms of annual NAPP. Data represent average values from all high and low marsh stations except the Maccan transect (Table 5)

I’,, of annual NAPP

Loss Low marsh High marsh

New dead (Apr-Nov) 46 24 Overwinter (Nov-Apr) 23 0 Old dead (Apr-Nov) 31 78

growing season and following fall compared to only 24O (, of the high marsh annual NAPP. Over the winter it is estimated that a further 23c’,, of annual NAPP is lost from the low marsh compared with none from the high marsh [the high marsh was not flooded during the winters of 1981 and 1982 because of relatively low spring tides (Gordon & Desplanque, 1983)]. Therefore by early spring low marsh has lost almost three quarters of the previous year’s NAPP while high marsh has lost only about one quarter. In the spring the over-wintering vegetation, according to our definition, becomes old dead material. On low marsh, this disappears rather quickly during the summer and none remains by November (Figure 5). Hence the short turnover time for low marsh. Although the loss of old dead material from high marsh during the growing season is high because of the large biomass (Table 4 and Figure 5), some can persist into a third and maybe even a fourth year before it is exported or decomposed. As a result the average turnover time is double that of low mrsh (Table 4).

Rapid vegetation loss has also been reported in the two previous quantitative studies of upper Fundy salt marshes. Morantz (1976) observed that 71”,, of salt marsh production disappeared between August and May and concluded that little dead material accumulated on the marsh surface (low and high marsh vegetation combined). Smith ef al., (1980) observed that most low marsh above-ground production was swept away by early December and that dead material from several growing seasons accumulated on high marsh.

The differences in vegetation loss rates between low and high marsh are controlled primarily by frequency and extent of inundation (Table 3). Low marsh sites are flooded more frequently, longer and by deeper water than high marsh sites and therefore tidal export of material is more probable. Microbial decomposition is probably also greater at low marsh sites which are kept relatively moist by frequent flooding. As demonstrated by Blum (1968), the prolonged exposure to which high marsh is subjected can dry Spartim patens litter and retard decay.

The very close balance between annual NAPP and loss of dead material on both low and high marsh (Table 4 and Figure 6) was unexpected because not all production enters the dead vegetation pool. A small amount of salt marsh production is grazed directly, about 5’>,, on a Georgia salt marsh (Teal, 1962), but no quantitative data are available for Fundy salt marshes. It could be appreciable in Cumberland Basin where insects are very abundant on the salt marshes during the summer and where numerous water fowl feed on the leaves and seeds of salt marsh vegetation (Van Zoost, 1969). Measurable amounts of dissolved organic matter are released by live Spartina alternij?ora leaves during inun- dation (Gallagher et al., 1976) and, although it has not been adequately documented,

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Ecological importance of salt marshes 223

very large amounts of dissolved organic matter are probably leached from marsh vegetation immediately after death. Some of the production included in annual NAPP measurements may also end up as under-ground biomass which is considerable (Table 4).

Although the present study focused upon above-ground vegetation, below-ground production of marshes is high (e.g. Gallagher & Plumley, 1979) and the export of energy from below-ground production as reduced inorganic sulfur compounds may exceed above-ground production by a factor of two (Howarth & Teal, 1980).

Therefore, consistent with the recent findings of Shew et uZ., (1981) and Reidenbaugh (1983), it appears that we have underestimated NAPP despite the improvements we made to Smalley’s method (Smalley, 1959). If so, underestimates are probably more serious for low marsh which is subjected to a more rigorous flooding regime and has a shorter turnover time. Production estimates based on maximum biomass are only slightly less than the NAPP values calculated with Smalley’s method (Table 4). Work is in progress to determine more accurate estimates of NAPP in Fundy low marshes.

The timing and quantity of loss of dead vegetation from Cumberland Basin marshes, especially from high marshes, will not be constant because of variations with periods greater than several years in the occurrence of extreme high tides (Gordon & Desplanque, 1983). Greater loss can be expected in those years with a higher frequency of extreme tides because salt marshes will be flooded more frequently, with deeper water and for longer intervals (Table 3). These conditions will promote both increased tidal export and microbial breakdown, thereby reducing turnover time. Greater loss rates can also be expected in those years when extreme high tides occur in the fall when vegetation is dying. Winter export from high marsh was quantitatively unimportant during this study (Table 5), but can be appreciable in years with numerous winter-time extreme tides as observed by Bleakney (1972) in the Minas Basin. These variations are dependent upon tidal properties and are predictable. Variations in vegetation loss can be also caused by unpredictable storm events (Bleakney, 1972).

Potential importance of salt marsh production in the Cumberland Basin ecosystem

Sufficient data are available to estimate the relative importance of salt marsh production in the entire Cumberland Basin ecosystem. The average annual phytoplankton pro- duction over the Pecks Cove mudflat, (Figure l), which includes resuspended benthic diatoms, has been determined by in situ radiocarbon experiments to average 7 g C m-’ (Hargrave et al., 1983). Phytoplankton production is very low because of the excessive turbidity which limits PAR to depths of less than 1.5 m. The estimate of 7 g C me7 year- ’ only includes phytoplankton production while the mudflat is flooded, which is about half the time. A value of 15 g C m- ’ year - ’ is probably a more reasonable estimate for the entire Basin. Possible lower concentrations of resuspended diatoms near the centre of the Basin, where suspended matter concentrations are lower, are probably balanced by greater PAR availability. Assuming that 15 g C m-’ year-’ is a reasonable estimate, using the water area at mean sea level it is estimated that phytoplankton contribute 1170 tonnes C year-’ to the Basin (Table 7).

Hargrave et al., (1983), using an in situ oxygen method, estimated that the annual production of benthic microalgae at Pecks Cove averaged 73 g C me2. Both Hargrave et al., (1983) and Cadee & Hegeman (1977) have observed a correlation between annual benthic microalgae production and annual surface sediment chlorophyll concentrations.

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224 D. C. Gordon, I’. 3. Cratzjord & C. Desplanque

TABLE 7. A summary of primary production dara for the Cumberland Basin

Average production

Source

Phytoplankton

Benthic microalgae

Low marsh

High marsh

Area (ha) g C m ’ year ’ tonnes C year I ‘I,, total tonnes

7800 15 1170 16

6200 38 2356 33

766 272 2084 29

948 172 1631 23

Total 7241

Using the average annual production/chlorophyll ratio calculated from the data of Hargrave et al., (1983) and our own unpublished surface sediment chlorophyll concen- trations from four mudflats in the Cumberland Basin, we estimate that the average annual production by benthic microalgae, weighted for the entire Basin mudflat area, is 38gCm-2yearY1 or approximately 2356 tonnes C year-’ (Table 7).

The carbon contribution of low and high salt marsh above-ground production to the Cumberland Basin system can be estimated by multiplying the annual NAPP values (Table 4), converted to carbon using the composition of live Sparrina alternij¶ora (Table 5), by their respective areas. The results are 2084 and 1631 tonnes C year-‘, respectively (Table 7).

As can be seen from the estimates in Table 7, the benthic microalgae appear to be the most important carbon source in the Cumberland Basin (33”,,). However, the carbon contribution of low salt marsh is only slightly less (29”,,). The contribution of high salt marsh production is 23”,, and that of phytoplankton is only 16”,, of the total. Macroscopic algal production is assumed minor because of the very small area of stable substrate (unpublished field observations) and is omitted from this calculation. These rough estimates will be refined as more data become available, but it is evident that salt marshes, both low and high combined, produce approximately half of the carbon fixed photosynthetically each year in the Cumberland Basin, even though they cover only 15”,, of the area.

A key question is how much of the salt marsh production is exported from the marshes and utilized elsewhere in the Cumberland Basin ecosystem? The extent and importance of tidal export from salt marshes has recently been the focus of considerable controversy (e.g. Nixon, 1979; Marinucci, 1982). As discussed by Odum or al., (1979) some confusion has been caused by differences in the definition of export. For example, some workers define it as transport to nearby tidal creeks (just metres away) while others define it as transport to coastal water (kilometres away).

Although microbial decomposition is undoubtedly important during the warmer months of the year, we propose that most of dead vegetation lost from our stations is due to tidal export and that much of this organic material is utilized elsewhere in the Cumberland Basin ecosystem or exported to Chignecto Bay. Considerable evidence exists to support this hypothesis. First is the very high level of tidal energy. Not only are marshes exposed to a stressful flooding regime (Table 3) but exported material can be carried considerable distances in a short period by the strong tidal currents (averaging

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Ecological importance of salt marshes 225

about 0.7 m s-l). F or example, water flooding the marsh at Tantramar (Figure 1) can reach the mouth of the Cumberland Basin at low tide. As discussed by Odum et al., (1979) estuarine geomorphology plays a major role in controlling the flux of particulate matter between wetlands and neighbouring waters. They postulate that the greatest net export would occur from exposed marshes located in basins that gradually deepen and widen toward their mouths. The numerous salt marsh/mudflat environments around the Cumberland Basin fit this description well (Figure 1). The most convincing evidence however, is the direct observations showing the widespread distribution of Spartina

detritus. Schwinghamer et al., (1983) found that salt marsh detritus made up the major portion of the non-living organic matter in both sediments and suspended matter in Cumberland Basin; Roberts (1982) made similar observations in sediments at Pecks Cove. Zooplankton tows in Cumberland Basin and the upper part of Chignecto Bay usually contain large amounts of coarse salt marsh detritus (Hildebrand, 1981; Prouse, unpublished data). These observations are in sharp contrast with those in Georgia estuaries where salt marsh detritus is hard to find (e.g. Haines, 1977). The combined influence of excessive tidal energy and geomorphology create very favourable export conditions in Cumberland Basin marshes. The relatively low production of phytoplank- ton, brought about by the excessive turbidity, makes the exported production relatively easy to detect and perhaps more valuable to the energy budget of the entire Basin.

We conclude that salt marshes play a major ecological role in the Cumberland Basin. Their importance might become even more apparent once we know more about the fate of dissolved organic matter and below-ground production. Although our results are only preliminary, we hope that they will stimulate further research into the energetics of these interesting and rather special salt marshes. Current questions of general interest to marsh ecology may be answered by further study of Fundy salt marshes.

Acknowledgements

We wish to thank the many people and agencies who made valuable contributions to this project. The Canadian Coast Guard provided the helicopter time used to select study transects and take aerial photographs. Al Smith of the Canadian Wildlife Service provided advice on locating the transects and arranged to have the salt marsh area data tabulated. Rob Dorion of the Maritime Resource Management Service supervized the surveying contract. Wallace Ross provided technical assistance during most of the project. Paul Keizer, Sifford Pearre and Jon Grant helped with the field work. Jim Matthews provided unpublished tidal data and Hinrich Harries assisted with vegetation identification. Al Smith, Barry Hargrave and Peter Schwinghamer kindly reviewed an earlier draft of this manuscript.

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