nitrogen pools and soil characteristics of a temperate estuarine wetland in eastern australia

Aquatic Botany, 23 (1985) 275--290 275 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

NITROGEN POOLS AND SOIL CHARACTERISTICS OF A TEMPERATE ESTUARINE WETLAND IN EASTERN AUSTRALIA

P.J. CLARKE*

School o f Life Sciences, New South Wales Institute o f Technology, Sydney, N.S. W. 2007 (Australia)

(Accepted for publ icat ion 4 September 1985)

ABSTRACT

Clarke, P.J., 1985. Nitrogen pools and soil characteristics of a tempera te estuarine wetland in eastern Australia. Aquat. Bot., 23: 275--290.

The nitrogen status of the soil and plant components of an estuarine wet land near Sydney were investigated over 6 months to de tec t seasonal and spatial changes in ni trogen content . Organic carbon, organic nitrogen and inorganic nitrogen concentra t ions were measured in the soil at various depths in six vegetat ion zones across the wetland. Carbon and nitrogen content of the plant biomass were also determined in each o f the zones. Soil redox potentials and pH were measured in situ and both were found to vary with depth and inundat ion frequency. Organic carbon, organic nitrogen and inorganic nitrogen in the soil decreased significantly from the fringe Casuarina forest (1391 g N m -2) through to the Avicennia mangrove zone (133 g N m-2). Exchangeable NH +, NO~ and NO~ concentrat ions form less than 1% of the soil nitrogen pool and vary seasonally. The distinctive feature of the mangrove zone is tha t the plant componen t o f the total nitrogen pool is large (55%). This contrasts with the saltmarsh and fringe communit ies , where the plant pools are small (15%) in comparison with the soil. These findings are consis tent with the hypothesis that mangroves expor t organic nutrients whereas the saltmarsh and fringe communit ies act as nutr ient sinks.

INTRODUCTION

The importance of nitrogen as a limiting nutrient in marine ecosystems has been recognized for some time and recent studies have extended the range of marine and estuarine autotrophs known to be limited by nitrogen. These include phytoplankton (Boynton et al., 1982), macroalgae (Mann, 1979) seagrasses (Orth, 1977; Bulthuis and Woelkering, 1981), saltmarsh plants (Buresh et al., 1980) and mangroves (Onuf et al., 1977; Boto and Wellington, 1983). The influence that nitrogen has on the productivity of saltmarsh communit ies has resulted in numerous studies of the nitrogen

*Present address: School of Biological Sciences, The University of Sydney, Sydney, N.S.W. 2006, Australia.

0304-3770/85/$03.30 © 1985 Elsevier Science Publishers B.V.

276

cycle along the east coast of North America, but only in a few instances are nitrogen budgets available (e.g., Valiela and Teal, 1979; Smith et al., 1982).

Comparative examples of the nitrogen status and cycles for southern hemisphere estuaries are lacking. In particular, the nitrogen status and soft characteristics of the emergent communities in eastern Australia are virtually unknown. This paper describes the nitrogen status of the soft and plant corn: ponents through a temperate estuarine wetland in south~eastern Australia.

MATERIALS AND METHODS

The study site

Towra Point is located within Botany Bay, 14 km south of Sydney in south~eastern Australia (Fig. la). The hydrology surrounding the point is dominated by marine influences with a tidal range of about 2 m. Mean salinity for Botany Bay is 33.8% with a range of 18.7--36.0% (State Pollu- tion Control Commission (SPCC), 1978). Additional descriptions of the physical and biological characteristics of the bay are given in the Environ- mental Control Study of Botany Bay {SPCC, 1978).

The estuarine wetlands of Botany Bay are comprised of 399 ha of mangrove and 161 ha of saltmarah. Seagrass communities once covered much of the bay, but are now restricted to areas adjacent to the mangroves (Larkum, 1976). The mangrove zone is characterized by a wide zone of Avicennia marina (Forsk.) Vierh. with sporadic occurrences of Aegiceras eorniculatum (L.) Blanco. Saltmarsh areas are dominated by Sarcocornia quinqueflora {Bunge ex Ungen-Sternberg) A.J. Scott on hypersaline soils, while Juncus kraussii Hochst. and Casuarina glauea Sieber ex Spreng. fringe the saltmarsh on higher ground (Clarke and Hannon, 1967). The study site reported here transects these intertidal communities at Pelican Point (lat. 34°01'S, long. 151°08'E) (Fig. lb) . Details of the vegetation distribution and sample locations along the transect are presented in Fig. 2.

Methods

Six sample sites were chosen across the wetland, each of which was located in homogeneous zones of vegetation varying in tidal inundation (Fig. 2). Nitrogen content was determined on soil and plant samples taken over a 6-month period in 1982. Soil organic carbon content, redox potentials and pH were also measured in the soil at various depths.

Soil samples were collected at low tide each month to minimize tidal differences and frozen. Exchangeable inorganic nitrogen ions were extracted from the samples within 5 h of their collection. Subsamples of soil at 0--10 cm, 20--30 cm and 40--50 cm depth were extracted with 1M potassium chloride (pH 3) for 1 h on an orbital shaker. The supernatant was filtered and analysed for ammonium and nitrite immediately, some being frozen and

277

,Towra Point

(b)

Urban areas

Natural vegetation

10 km

11510101

Pel

.34010 '

Fig. 1. (a) The location of Towra Point in Botany Bay on the east coast o f Australia. (b) The location o f the site transect and the distribution o f mangrove and saltmarsh communities .

278

MS.L ~ ~ ' ~ - - - - ~ - ~ ' - " ' ~ ' ~ A ~ ) B C1160)

E.LW L 150m 1100m

Zostera caprlcorni

Avicennia marina

Aegiceras cocnlculatum

Sporobolus vifljinicus

Caaua*ina glauca

Sua4Kla ~ t r a l i s

Sarcocorn~a qt~ctquefiofa

Samo~s ¢epens

Triglochin atriat a

Juncus k raussii

L150m

Fig. 2. The topography and distribution of vascular plant species along the site transect. Site locations are lettered and the estimated number o f tidal inundations per year are in parentheses.

later analysed for nitrate by the cadmium reduction method (American Public Health Association, 1975). Organic nitrogen was determined by the Kjeldahl method and organic carbon was measured by the Walkley--Black method (Black, 1965). All live root material was removed from the soils before analysis. Soil redox potential (Eh) and pH were measured in situ in the field with platinum--calomel and glass--calomel electrodes, respectively, and redox potentials given have been adjusted for the calomel standing potential but not for pH differences. Above-ground plant mass was sampled at those sites where harvesting was possible; 25 × 25-cm quadrats were clipped at monthly intervals for 8 months. Live and dead (litter) components were sep- arated and dried to a constant weight at 70°C in a forced<lraught oven. At sites A and F, tree mass was estimated from wood density and volume measures for Avicennia and Casuarina stands (Briggs, 1977). Samples of litter, leaves and stems were also harvested at monthly intervals and dried. All plant material was ground and desiccated before analysis for nitrogen by the Kjeldahl method. Subsamples of plant material were also analysed for carbon, nitrogen and hydrogen with a Heraeus CHN analyser.

Live root biomass has been measured for the same site by Lichacz et al. (1984). Nitrogen concentrations in the live root component of the plant are assumed to be the same as the shoots, an assumption which appears to be valid because of similar root and shoot nitrogen levels in the same saltmarsh plants analysed by Congdon and McComb (1980a).

Total plant nitrogen pools were calculated from average biomass estimates and average nitrogen concentrations for each vegetation type across the wetland. Soil nitrogen pools were calculated to a depth of 30 cm using bulk soil

279

density measures by Clarke and Hannon (1967) for the same location. Live root mass was subtracted from the soil mass so that the soil organic nitrogen content reflected the true detrital pool of nitrogen in the soft.

RESULTS AND DISCUSSION

Vegetation b iomass and nitrogen content

Mean biomass and nitrogen concentrations of samples for the dominant species in the vegetation zones examined are given in Table I. Both tree species have similar above-ground standing crops on an area basis (2--3 kg dry wt. m-2). Total tree mass for A. marina is less than that found by Attiwill and Clough (1974), Briggs (1977) and Goulter and Allaway (1979), who report values of 22--29 kg dry wt. m -2. The low density of trees (0.18 m -2) and height o f the stand (6 m) may account for the difference. Estimates of the total biomass for Casuarina glauca were not possible as the root mass consisted of roots of several species, which technically could not be sepa- rated.

Standing crop values for saltmarsh plants are mean values for harvests taken each month for 8 months. Sarcocornia quinqueflora was the most widespread species observed with a total biomass of 1--2 kg dry wt. m -2. The largest standing crops measured were for Juncus hraussii which are similar to those obtained in Western Australia by Congdon and McComb (1980b). No seasonal growth trends were observed for the saltmarsh plants and it appears that the standing crop does not represent annual productivity (Congdon and McComb, 1980b).

Concentrations of nitrogen in the leaves of A. marina vary from 0.9 to 1.5% N dry wt., which falls within the range previously reported (Bunt, 1982). Nitrogen levels for saltmarsh plants are higher than those recorded by Congdon and McComb (1980a) and Van der Valk and AttiwiU (1983a). These concentrations were later checked by CHN analysis on random samples for each species and found to be similar to the preceding analysis. Sub- samples were also taken from a month's harvest o f J . hraussii to check variation within samples. The coefficient o f variation for the subsamples was small (6%) compared with month-to-month variation (31%). The large coeffi- cients of variation should, therefore, reflect the seasonal variation in the nitrogen status of the saltmarsh plants. Large variations in the nitrogen concen- tration of J. hraussii have been measured elsewhere, although no clear seasonal trends in nutrient content were observed (Congdon and McComb, 1980a).

Carbon--nitrogen ratios were obtained by CHN analysis on single samples of each species. These ratios indicate nitrogen depletion in the dead standing crop of saltmarsh plants. However, the average nitrogen concentrations for dead stems of J. hraussii and S. quinqueflora were similar to those of the live stems; this may indicate an increase in microbial biomass on dead stems

b~

CO

TA

BL

E I

Pla

nt

biom

ass,

pla

nt

nit

rog

en c

on

cen

trat

ion

s an

d c

arb

on

--n

itro

gen

rat

ios.

Fro

m C

lark

e (1

98

3)

Spe

cies

S

ite

Co

mp

on

ent

Bio

mas

s N

itro

gen

(k

g m

-' +

1 S

.E.M

.)

con

cen

trat

ion

(K

jeld

ahl

Met

ho

d)

((%

N)

± 1

S.E

.M.)

(n

=5)

Nit

rog

en

con

cen

trat

ion

(H

erae

us

CH

N

anal

yse

r)

(% N

)

Car

bo

n--

N

itro

gen

n

itro

gen

co

nte

nt

rati

o

(g N

m -

s)

Avi

cenn

ia m

arin

a

Cas

uari

na g

lauc

a

Spom

bolu

s vi

rgin

icus

Mix

ed r

oo

ts

Sarc

ocor

nia

quin

quef

lora

C

A

Ste

ms

2.2

--

1.5

0

(0.0

6)

Lea

ves

0.2

--

0

.91

(0

.25

) B

elo

w g

rou

nd

li

ve t

o 3

0 cm

10

.2

--

1.2

0

--

B

Ste

ms

3.4

--

0.9

0

(0.2

2)

Bra

nch

lets

0.

3 --

1

.01

(0

.24

) B

L

ive

culm

s 0

.43

(0

.05

) 1

.57

(0

.38

) D

ead

cu

lms

0.5

5

(0.0

6)

1.4

2

(0.2

0)

B

To

tal

bel

ow

gro

un

d

live

to

30

cm

3.4

0

--

1.2

2

--

Liv

e st

ems

0.6

8

(0.0

6)

1.90

(0

.53

) D

ead

ste

ms

0.3

0

(0.0

5)

1.67

(0

.39

) B

elo

w g

rou

nd

liv

e to

30

cm

1

.30

--

1.

78

--

1.4

2

1.86

1.5

8

0.8

5

1.17

1.

33

1.71

1.

44

35.1

33.0

21.5

1.8

--

122.4

157.2

--

30.6

--

3.0

36.2

6.7

36.0

7.8

--

41.5

89.6

20.5

32

.1

12.9

5.

0

23.1

41

.0

Sarc

ocor

nia

quin

quef

lora

D

Junc

us k

raus

sii

E

Junc

us k

raus

sii

F

Cas

auri

na g

lauc

a F

Mix

ed r

oo

ts

F

Liv

e st

ems

0.5

0

(0.0

5)

1.1

9

(0.4

1)

Dea

d s

tem

s 0

.21

(0

.05

) 1

.23

(0

.37

) B

elo

w g

rou

nd

liv

e to

30

cm

1

.30

--

1

.21

--

Liv

e eu

lms

0.7

3

(0.1

7)

1.2

5

(0.6

4)

Dea

d c

ulm

s 1

.06

(0

.13

) 1

.42

(0

.43

) B

elo

w g

rou

nd

liv

e to

30

cm

1

.60

--

1

.82

--

Liv

e cu

lms

0.2

7

(0.0

5)

1.3

2

(0.4

1)

Dea

d c

ulm

s 0

.77

(0

.21

) S

tem

s 2.

4 --

B

ran

chle

ts

0.2

--

T

ota

l b

elo

w g

rou

nd

li

ve t

o 3

0 c

m

7.8

--

1.3

4

(0.2

8)

o.9

0

(0.2

1)

--

(0.2

4)

1.1

4

--

1.43

0.9

7

1.1

4

0.8

3

1.3

5

(0.0

8)

n =

5 1

.55

1

.58

0

.85

23

.3

43

.1

38

.9

41

.5

35

.1

44

.5

42

.5

5.9

2.6

21

.8

30

.3

9.1

15

.0

21

.1

45

.2

3.5

10

.3

21

.6

2.0

88

.9

12

6.3

['0

O3

282

(Rice and Tenore, 1981). The apparent conflict between high C : N ratios and increased litter nitrogen levels requires further study.

Soil characteristics

pH and redox potential Soil pH decreases significantly at those sites which fringe the saltmarsh

(see Fig. 3a). This may be a result o f the accumulation o f organic matter in the zones of Juncus and Casuarina which release organic acids. The coeffi- cients o f variation are large for these sites as irregular tidal inundations can cause a rapid increase in pH. An apparent decrease in pH with depth at all

(a) T ~ | ~ ! . . T T

1-" "--l-I "-",, \!!

' ! ! ! !

o.~th(c,.) ~ 2'5 ;5 is ~ 2'5,~ ~ 2's,'s 5 2s,'s s 2's s is S i t e A B C D E F

(b)

5 0 0

4 0 0

A > E 3 0 0

2 0 0

100

i% %,

!

% .l.%

x-o f s ~ 's , ; ' 65

A

T

T

1

I J.

Depth{cm) 5 215 415 5 215 415 5 25 45 5 25 5 25 S i t e B C D E F

Fig. 3. (a) Soil pH and (b) soil redox potential at various depths for each site. ±1 S.E.M., n = 6 .

283

locations may indicate the product ion of organic acids and carbon d ioxide by actively metabolizing roots. In general, the surface softs remain neutral to slightly acid due to the influence of alkaline estuary water.

Redox potentials (Eh) were measured in situ and found to decrease with depth and f requency o f tidal inundation {Fig. 3b). Mangrove softs are strongly reducing, especially at depth, while the lower saltmarsh soils remain anaerobic bu t less reduced. Higher saltmarsh and fringe zone softs are aerobic (Eh > 350 mV), although the Eh decreases below the water table. Soil Eh and pH both strongly influence the concentrat ions o f dissolved nutrients in the sediments (Patrick and DeLaune, 1977). The effects o f Eh and pH on the nitrogen status o f the soft are discussed below.

Inorganic nitrogen A summary of soft inorganic nitrogen concentrat ions is presented for com-

parison with other sediments in Table II. Exchangeable NH4 + concentrat ions are lower than those previously recorded for anaerobic sediments in mangroves and saltmarshes, although nitrate levels are similar to those of Haines et al. (1977). Both spatial (Fig. 4) and seasonal (Fig. 5) variations in inorganic nitrogen concentrat ions are evident for this site, although the large coeffi- cients o f variation limit detailed interpretation.

T A B L E II

Inorganic n i t rogen c o n c e n t r a t i o n s for es tuarine s e d i m e n t s . Ranges given wi th m e a n values in parentheses

Sediment type NH4 + (~M) NO~ (uM) NO~ (uM)

Mangrove 7--39 (18) 0--3 (2) 3--20 (12) (330) - - - -

2 2 2 - - 1 3 8 8 - - - -

Saltmarsh 4--67 (20) 0--5 (2) 3--42 (17) 36--95 (58) 2--3 2--18 (10) 105--1630 -- 30--1200

Fringe 8--111 (33) 0--5 (2> 5--37 (21) 1170--42430 --

Benthic 80--1313 (110) -- 0--20 (10) 200--1700 -- --

This s t u d y Boto and Wellington (1983) Van der Valk and Attiwill (1983a)

This study Haines et al. (1977) Beeftink (1977)

This study B e e f t i n k (1977) H o p k i n s o n and Wetze l (1982) Bulthuis and Woelkering (1981)

Nitrate and to a lesser extent ammonium concentrat ions decrease from the fringe forest to the mangroves while nitrite levels remain constant . A possible explanation for the rapid decrease in nitrate is the low redox potentials in the mangrove zone. Alternatively, regular tidal incursions m a y re- move nitrate which is more soluble than ammonium from the soft. Amino-

2 8 4

nium may also be lost from these soils as it is more soluble under low redox potentials (DeLaune et al., 1981).

The presence o f nitrate and nitrite in anaerobic soils can be accounted for by nitrification in the aerobic rhizospheres near the roots o f wetland plants (Haines et al., 1977). Nitrite and ammonium concentrations increase with depth in the anaerobic soil, indicating denitrification beyond the rhizospheres. In general, however, the surface layers of the sediments have the highest levels of inorganic nitrogen. This is related to the faster rates of decomposition found on the surface of the sediments than at depth (Van der Valk and Attiwill, 1984).

2.0

1.5

"o

v

1.0 Z

._o

0.5

0.4

0.3

0.2

0.1

Depth (cm)

Site

T ! L ]" !,'i /I \r * I I ~/,. ~! I.

# ...'~ ~, ~.-4" ~---l'"

A B C D

!

1

] .... i---I

E F

Fig . 4 . S o i l i n o r g a n i c n i t r o g e n c o n c e n t r a t i o n s at v a r i o u s d e p t h s for e a c h s i t e . -+ 1 S , E . M . , n ffi 6 , N H + ffi =, NO~" = * , NO~- = e .

285

1.4 . 0.,

~ 1 . 0 ~ . ~ 0 . 3

-~ o.a. -~o.2

0.4 - 0.1

O - 0

T T A ===,====-=-,==- A

2o°c

15

10

5

0

Fig. 5. Seasonal concentrations for ammonium • and nitrate • for the saltmarsh. ± I S.E.M.,

n = 6. Mean annual temperature denoted by e.

Organic carbon and organic nitrogen Organic carbon concentrat ions increase from the mangrove zone (2% dry

wt.) through to the fringe forest where they attain the highest levels (23% dry wt.) (Fig. 6a). Organic carbon levels in the saltmarsh and fringe zones are higher at the surface than at depth while the mangrove soils show no stratification in organic carbon.

Soil organic nitrogen concentrat ions range from 0.4 mg N g- 1 dry wt. in the mangrove zone through to 3.7 mg N g-1 dry wt. in the fringe forest (Fig. 6b). High levels of nitrogen in the fringe forest can be at tr ibuted to the fixa- t ion of nitrogen in the roots o f Casuarina glauca and the large accumulat ion of litter for the site. High nitrogen levels were also expected for the levee bank site (B) which has a similar stand density to that of the fringe forest. The root zone at the levee did have increased nitrogen concentrat ion compared to the surface, however, the overall level of nitrogen in the soil was much lower than the fringe forest. Saltmarsh soil had a higher surface con- centration of nitrogen than at depth, while the mangrove sediments have uniformly low levels o f nitrogen. A similar increase in soil nitrogen concen- tration from open-water to fringe forest has been described by Congdon and McComb (1980a) for a wetland where mangroves are absent.

Removal of both organic C and N in the mangrove zone and lower saltmarsh zones by tidal action would explain the low levels o f nutrients observed in these sites. Nitrogen appears to be retained relative to carbon as the C : N ratio for the soil is lower than litter fall. Low C : N ratios may also be maintained by nitrogen fixation, which has been observed in A. marina (Van der Valk and Attiwill, 1983b). In contrast , the fringe zones have high C : N ratios indicating an accumulat ion o f carbon relative to nitrogen; this carbon probably originates from debris washed on to strand lines.

~°

o

9 ~ 0

I+ E. ~

. "

0

It

O

~.~

"

.~.~

Q

U)

0 o

= =T

A t'1

>;]

:;]

o;]

o 2]

1,414

I 14

14

Org

anic

N

itro

gen

( °/

o dr

y w

t)

P P

9

w

! u

I

,j'~

"\

I •

!

A O"

Org

anic

C

arbo

n (

%

dry

wt)

i i

1o

/ •

-] ~.

.,-

,. 0

M

/ (~

n I-i

, •

/

I

A

~] I I

I I

I I

I I

o!;e

a w

o;v

N:3

2 8 7

Nitrogen pools

Soil nitrogen pools decrease substantially from the fringe Casuarina forest (1391 g N m -2) through to the mangrove Avicennia zone (133 g N m -2) (Fig. 7) (Table III). This gradient is consistent with decreasing levels o f organic matter found in each zone. Most of the soil nitrogen is in the organic form and is not readily available for plant uptake unless mineralized. Inor- ganic forms of nitrogen contribute less than 0.2% of the total pool of nitro-

[ ~r

~i te A B

[ l l / l l l l l l l t

- --.::.-:.:: !-/.'.':

; . . - . . . . . y....::.-'. (g N / m 2) 2 4 6 261 217 .t 2 4 2 502 911

°°2" 2 o g # e c

C D E F

I I I I N I H I I I I

.:::o(: : °° ~" °°

02°0: : o ° . ~ o o

"::...':: : ° ° 0 ° o

0 ) ' : : :o°oOoo ":) ' : : ; o ° . ~ o o ;:J;i'.::

7 3 3

/ oo #:-

/ ,

]ttt l t ~ , ~ 1 0 0 %

[ ] Shoot pool i .~2o ; ,2 =

~= : °0 - ~80 p_o ° ° ! ~ E ° - : 2 ° L - - J Root p o o l e o : ~ o :

"°o : °°°° , __ 6 0 L i t t e r pool . oo . ==

. . . . [ ] S

o o ° , : ~ o : 2 o . . . . - - 4 0 oi l pool

_0 o_o . o ° . ° o

.0 ° . o , : ° o : ° o

-o= 0=- o"

'=- - ° " - - , , ~ 0 501

_ _ 2 0

Fig. 7. The proportion of nitrogen in differing components of the total pool through the wetland. Total content of nitrogen is given for each site for a 30-cm depth o f soil.

TABLE IH

Nitrogen pools in the various zones of the estuarine wetland (g N m-2)

Components Sites

A B C D E F

Plant live above ground 34.8 40.3 23.1 21.8 21.1 2.1 Plant live below ground 122.4 41.5 12.9 5.9 9.1 88.9 Litter - - 7.8 5.0 2.6 15.0 10.3 Soft organic-N (30 cm) 132.6 194.4 213.2 263.7 621.6 1391.4 Soil inorganic-N ( 30 cm) 0.1 0.4 0.2 0.3 0.6 0.5

Total 289.9 284.4 254.4 294.3 667.4 1581.2

288

gen in the wetland, which is similar to that found along the east coast o f North America (Haines et al., 1977).

The total pool o f nitrogen is greatest in the fringe marsh and forest communities where the plant pools are small (15--20%) in comparison with the soil (Fig. 7). These areas accumulate decay-resistant organic mat te r which acts as a nutr ient sink unless recycled by detritivores. Similar accumulations of soil nutrients have been found in a Western Australian marsh (Congdon and McComb, 1980a) and in North America (Haines et al., 1977).

The distinctive feature o f the mangrove zone is that the plant componen t of the nitrogen pool comprises 55% of the total pool. This contrasts with most terrestrial forests where the major i ty of the nitrogen pool is in the soil (Baker and Attiwill, 1981). The cont inuous removal o f li t ter f rom the mangrove zone by the t ide would prevent the accumulat ion of organic mat ter and account for the depleted pool o f nitrogen in the mangrove sediments. Most o f the lit ter appears to be expor ted to the estuary, as mangrove litter does not accumulate on strand lines or in the mangrove zone. Quantitative estimates of detrital expor t from wetlands are difficult to obtain as there is considerable spatial and seasonal variation. Estimates for tidal expor t o f litter in Australian mangroves range from 40 to 100% of all l i t ter fall (Boto and Bunt, 1981; Van der Valk and Attiwill, 1984). Lit ter fall for mangroves in the Sydney region has been measured at 520 g m -2 year -~ (Goulter and Allaway, 1979) which if total ly expor ted would represent a loss of 4 g N m -~ year -~. If product ivi ty is to be maintained, inputs of nitrogen via nitrogen fixation, rainfall and the water column are needed (Boto, 1982). A possible source of nutrients for mangroves, no t previously considered, is the saltmarsh and fringe zone soils which have large stocks of nitrogen. These may be mobil ized in the dissolved form and moved into the mangrove zone via the water table.

ACKNOWLEDGEMENTS

I would like to thank Rod Buckney for his supervision and assistance through the study. Bill Allaway, Mark Curran, Audrey Graham, Sean Hardiman, Wieslav Lichacz and Peter Myerscough are also thanked for their comments , discussion and technical help.

REFERENCES

American Public Health Association, 1975. Standard Methods for the Examinat ion o f Water and Wastewater, 13th edn., 874 pp.

Attiwill , P.M. and Clough, B.F., 1974. The role of the mangrove and seagrass communit ies in nutrient cycling in Westernport Bay. Repor t to Westernport Bay Environmental Study, Ministry for Conservation, Victoria, 120 pp.

Baker, T.G. and Attiwill , P.M., 1981. Nitrogen in Australian eucalypt forests. In: Pro- ductivi ty in Perpetui ty . Proc. Australian Forest Nutr i t ion Workshop, CSIRO Division of Fores t Research, Canberra, pp. 159--170.

289

Beeftink, W.G., 1977. The coastal salt marshes of Western and Northern Europe. An ecological and phytosociological approach. In: V.J. Chapman (Editor) , Wet Coastal Ecosystems. Elsevier, Amsterdam, pp. 109--155.

Black, C.A., 1965. Methods of Soil Analysis, Vol. 2. American Society of Agronomy, pp. 772--1571.

Boto, K.G., 1982. Nutr ient and organic fluxes in mangroves. In: B.F. Clough (Editor) , Structure, Func t ion and Management of Mangrove Ecosystems in Australia. ANU Press, Canberra, pp. 239--258.

Boto, K.G. and Bunt, J.S., 1981. Tidal expor t of part iculate organic mat ter from a northern Australian mangrove system. Estuarine Coastal Mar. Sci., 13: 247--255.

Boto, K.G. and Wellington, J.T., 1983. Phosphorus and nitrogen nutr i t ional status of a northern Australian mangrove forest. Mar. Ecol. Prog. Ser., 11: 63--69.

Boynton, W.R., Kemp, W.M. and Keefe, C.W., 1982. A comparative analysis o f nutrients and other factors influencing estuarine pby top lank ton product ion. In: V.S. Kennedy (Editor) , Estuarine Comparisons. Academic Press, New York, pp. 69--90.

Briggs, S.V., 1977. Estimates o f biomass in a tempera te mangrove communi ty . Aust. J. Ecol., 2: 369--373.

Bulthuis, D.A. and Woelkering, Wm.J., 1981. Effects o f in situ nitrogen and phosphorus enrichment of the sediment on the seagrass Heterozostera tasmanica (Martens ex Aschers) den Hartog in Westernport, Victoria, Australia. J. Exp. Mar. Biol. Ecol., 53 : 193--207.

Bunt, J.S., 1982. Studies of mangrove litterfall in tropical Australia. In: B.F. Clough (Editor), Structure, Func t ion and Management of Mangrove Ecosystems in Australia. ANU Press, Canberra, pp. 223--238.

Buresh, R.J., DeLaune, R.D. and Patrick, W.H., Jr. , 1980. Nitrogen and phosphorus util- ization by Spartina alterniflora in a Louisiana Gulf coast marsh. Estuaries, 3: 111-- 121.

Clarke, P.J., 1983. Nitrogen pools in a mangrove--saltmarsh system. Wetlands (Australia), 3: 85--93.

Clarke, L.D. and Hannon, N.J., 1967. The mangrove swamp and saltmarsh communit ies of the Sydney District. I. Vegetation, soils and climate. J. Ecol., 55: 753--771.

Congdon, R.A. and McComb, A.J., 1980a. Nutr ient pools of an estuarine ecosystem - - the Blackwood River Estuary in south-western Australia. J. Ecol., 68: 287--313.

Congdon, R.A. and McComb, A.J., 1980b. Productivi ty and nutrient content of Juncus kraussii in an estuarine marsh in south-western Australia. Aust. J. Ecol., 5: 221--234.

DeLaune, R.D., Reddy, C.N. and Patrick, W.H., Jr., 1981. Effect of pH and redox potentials on concentrat ion of dissolved nutrients in an estuarine sediment. J. Environ. Qual., 10: 276--279.

Goulter, P.F.E. and Allaway, W.G., 1979. Lit ter fall and decomposi t ion in a mangrove stand (Avicennia marina Forsk. [Vierh. ] ) in Middle Harbour, Sydney. Aust. J. Mar. Freshwater Res., 30: 542--546.

Haines, E., Chalmers, A., Hanson, R. and Sherr, B., 1977. Nitrogen pools and fluxes in a Georgia saltmarsh. In: M. Wiley (Editor) , Estuarine Processes. Vol. H. Circulation, Sediments and Transfer of Materials in the Estuary. Academic Press, New York, pp. 241--254.

Hopkinson, C.S. and Wetzel, R.L., 1982. In situ measurements of nutrient and oxygen fluxes in a coastal marine benthic communi ty . Mar. Ecol. Prog. Ser., 10: 29--35.

Larkum, A.W.D., 1976. Ecology of Botany Bay. I. Growth o f Posidonia australis (Brown) Hook. f. in Botany Bay and other bays o f the Sydney Basin. Aust. J. Mar. Freshwater Res., 27: 117--127.

Lichacz, W., Hardiman, S. and Buckney, R.T., 1984. Below-ground biomass in some in- tert idal wetlands in New South Wales. Wetlands (Australia), 4: 56--62.

Mann, K.H., 1979. Nitrogen l imitat ions on the product iv i ty o f Spartina marshes, Lami- naria kelp beds and higher t rophic levels. In: R.L. Jeffries and A.J. Davey (Editors),

290

Ecological Processes in Coastal Environments. Blackwell, Oxford, pp. 363--372. Onuf, C.P., Teal, J.M. and Valiela, I., 1977. Interaction of nutrients, plant growth and

herbivory in a mangrove ecosystem. Ecology, 58: 514--526. Orth, R.J., 1977. Effect of nutrient enrichment on growth of the eelgrass Zostera marina

in the Chesapeake Bay, Virginia, U.S.A. Mar. Biol., 44: 187--194. Patrick, W.H., Jr. and DeLaune, R.D., 1977. Chemical and biological redox systems

affecting nutrient availability in the coastal wetlands. Geosci. Man, 28: 131--137. Rice, D.L. and Tenore, K.R., 1981. Dynamics of carbon and nitrogen during the decom-

position of detritus derived from estuarine macrophytes. Estuarine Coastal Mar. Sci., 13: 681--690.

Smith, C.J., DeLaune, R.D. and Patrick, W.H., Jr., 1982. Carbon and nitrogen cycling in a Spartina alterniflora saltmarsh. In: J.E. Calbally and I.E.J.R. Freney (Editors), The Cycling of Carbon, Nitrogen and Phosphorus in Terrestrial and Aquatic Ecosystems. Australian Academy of Science, Canberra, pp. 97--104.

State Pollution Control Commission of New South Wales, 1978. Environmental Control Study of Botany Bay. The Study and the Region. S.P.C.C. Report B.B.S.I., Sydney, 44 pp.

Valiela, I. and Teal, J.M., 1979. The nitrogen budget of a saltmarsh ecosystem. Nature (London), 280: 652--656.

Van der Valk, A.G. and Attiwill, P.M., 1983a. Above- and below-ground litter decomposition in an Australian saltmarsh. Aust. J. Ecol., 18: 441--447.

Van der Valk, A.G. and Attiwill, P.M., 1983b. Acetylene reduction in an Avicennia marina community in southern Australia. Aust. J. Bot., 18: 157--164.

Van der Valk, A.G. and Attiwill, P.M., 1984. Decomposition of leaf and root litter of Avicennia marina at Westernport Bay, Victoria, Australia. Aquat. Bot., 18: 205--221.

nitrogen pools and soil characteristics of a temperate estuarine wetland in eastern australia

Documents