Contemporary and sub-recent pollen record for the Leschenault Inlet estuary: towards a palynological baseline

14 Pages·2000·5.6 MB·

by  V Semeniuk

Journal of the Royal Society of Western Australia, 83: 335-348, 2000
Contemporary and sub-recent pollen record for the
Leschenault Inlet estuary:
towards a palynological baseline
V Semeniuk1, L A Milne2 & H Waterhouse3
1V & C Semeniuk Research Group,
21 Glenmere Road, Warwick WA, 6024
2Department of Geography
The University of Western Australia
Nedlands WA, 6907
3 Department of Geology and Geophysics
The University of Western Australia
Nedlands WA, 6907
Abstract
Palynological analysis of contemporary and sub-recent sediments from Leschenault Inlet, an estuarine lagoon
on the south-west coast of Western Australia, has determined if a contemporary palynological baseline can be
established to interpret the sub-recent pollen assemblages, and was used to determine the mangrove Avicennia
marina was a component of the vegetation in the recent past. Leschenault Inlet is a relatively simple estuarine
system with north-south trending sedimentary environments and parallel vegetation complexes, and with both
easterly and westerly winds and two fluviatile sources contributing to the pollen influx. Using predominantly
family groupings (<?.g. Chenopodiaceae, Myrtaceae, Casuarinaceae, Gramineae, Restionaceae) and several species
prominent in the vegetation (Frankenia pauciflora, Olearia axillaris, Lepidosperrna gladiatum), preliminary results indi¬
cate that the major sedimentary environments have characteristically different pollen assemblages. In transects
across the sedimentary environments, individual species show relative abundance gradients that can be explained
in terms of proximity to vegetation source and potential transport systems. Conversely, these serve to distinguish
specific environments and the nature of the immediate upland source vegetation. Avicennia marina pollen is a
minor component of the contemporary sediments near sites of mangrove habitation. It is absent from sub-recent
samples in comparative environments, implying that it is a recent arrival to Leschenault Inlet. A late Holocene
change in climate may be responsible for an intensification of the Leeuwin Current and subsequent delivery of
Avicennia propagules from tropical regions. Leschenault Inlet is an excellent site to study the effect on palynological
assemblages of proximity to vegetation source, wind directions, dispersal via estuarine currents, and taphonomy.
It also presents an ideal setting from which to develop pollen assemblage baselines for the different estuarine
sedimentary environments. From a geoheritage perspective, the Leschenault Inlet estuary probably ranks as sig¬
nificant at a national level.
Keywords: estuarine palynology, palynology, Leshenault Inlet, south-western Australia.
Introduction Avicennia marina, a species that is otherwise not known
south of Houtman Abrolhos. Avicennia marina is a poten¬
Leschenault Inlet is a north-south trending estuarine
tial indicator of past Holocene climates and environments,
lagoon situated on the southwest coast of Western Aus¬
and it has been suggested anecdotally that this isolated
tralia. It is barred by a long barrier dune system, the stand of a normally tropical species represents a relict popu¬
Leschenault Peninsula, and has a range of depositional (ac¬
lation. However, it is also possible that A. marina is a recent
cretionary) environments and pollen-source habitats (both
arrival, its propagules having been transported by an in¬
oriented north-south), an east-west to southwesterly aeolian
tensified Leeuwin Current.
delivery system, and two southerly located fluvial deliv¬
ery systems. The estuarine sedimentary fill is entirely To adequately interpret the sub-recent pollen record
Holocene in age, and in the context of a retrograding bar¬ in the estuarine sediments, a baseline of pollen assemblages
rier a complete estuarine sedimentary record from ca 8 000 in the various contemporary sedimentary suites or facies
yrs BP to the present is preserved (Semeniuk 1985), Con¬ is required. This paper provides a preliminary account of
sidering its depositional setting, Leschenault Inlet estuarine the pollen record preserved in contemporary (surface)
lagoon potentially contains a valuable palynological record sediments and the upper parts of the Holocene sedimen¬
of Holocene environments. tary sequence (= sub-recent viz from 150 yrs BP to 500-1500
yrs BP) in Leschenault Inlet (Fig 1).
The diverse range of habitats that border the estuarine
system supports a mosaic of vegetation complexes that The specific objectives of this paper are: to character¬
range from saltmarsh to freshwater terrestrial associations. ise the pollen record in the surface sediments of the five
Of particular interest is the presence of the mangrove main sedimentary suites (or facies) in the estuary, and from
these interpret the pre-modern Holocene stratigraphic
record; to determine the extent and mode of pollen trans-
© Royal Society of Western Australia, 2000
335
Journal of the Royal Society of Western Australia, 83 (4), December 2000
A
y
i
i
WESTERN
AUSTRALIA
Study i i
Area
seagrass covered
E ' * #1 EEaasstteerrnn oorr Western
platforms
Central basin
1 I I I I I I I I 1 I n " P 1 ¥ ,-ri - i ¥ ¥ 1 i ¥ i I T I I I
I I I I I I I 1 I 1 I 1 I 1 I f Pleistocene Limestone ] 1 | 1 | 1 | 1 | ' '| 1 r1 I 1 'I 1 I 1 I ,
1 I I I I 1 I I I I I I (Kooallup Limestone) I I I 1 I I I | | | | | | "| 1 |
Figure 1. Leschenault Inlet showing location of main sedimentary/ geomorphic units, sampling sites, locations of detailed study ;
and Holocene stratigraphic framework.
336
Semeniuk, Milne & Waterhouse : Pollen record for Leschenault Inlet
port from its source, and to determine if Avicennia pollen is level, formed earlier in the Holocene as a sub-aqueous es¬
present in the sub-recent stratigraphic record. The general tuarine sand platform. The depositional units of interest in
patterns in the contemporary and sub-recent pollen assem¬ this paper are the central basin, the eastern and western
blages will provide preliminary conclusions and point the platforms, the high-tidal platform, the supratidal flat, and
way for future more detailed studies of the pollen record the Preston River delta. The characteristics of these units
and factors that influence its composition. are described briefly in Table 1. The main estuarine
geomorphic and sedimentary units within Leschenault In¬
Setting let, and the Quaternary stratigraphy of the area (after
Semeniuk 1983,1997), are illustrated in Fig ID.
Estuarine sedimentary environments
Vegetation contributing pollen
Leschenault Inlet is an estuarine lagoon located along
There are nine main categories of vegetation that may
the Western Australian coast within the southern part of
act as pollen sources for the estuarine sediments: barrier
the Swan Coastal Plain (Fig 1; Semeniuk & Meagher 1981a).
dune vegetation; Mandurah-Eaton Ridge vegetation;
The lagoon is separated from the Indian Ocean by a bar¬
Yalgorup Plain vegetation; supratidal vegetation on emer¬
rier dune system, the Leschenault Peninsula (Semeniuk
gent deltaic shoals; freshwater vegetation on the east shore
1985). To the east, it onlaps the Mandurah-Eaton Ridge and
of the estuary; saltmarsh vegetation fringing the shore of
the Yalgorup Plain (Semeniuk 1997).
the estuary; mangrove vegetation along the shore of the
The Leschenault Peninsula is a linear, north-south ori¬ estuary; seagrass vegetation; and exotic vegetation. The lo¬
ented dune barrier 0.5 to 1.0 km wide, and is comprised of cations of these polen sources are shown in Fig 2.
east-west oriented mobile to vegetated parabolic dunes
The barrier dunes are comprised of a mosaic of habitat
(Semeniuk & Meagher 1981a; Semeniuk et al. 1989). The
types and vegetation (Semeniuk & Meagher 1981a,b;
Mandurah-Eaton Ridge is a high ridge of quartz sand and
Trudgeon 1984; Cresswell & Bridgewater 1985; Smith 1985;
limestone, oriented north-south and bordering the eastern
Semeniuk et al. 1989). Semeniuk & Meagher (1981b) cat¬
margin of the Holocene estuarine complex (Semeniuk 1997).
egorised the vegetation on the barrier in relation to the main
Leschenault Inlet is an elongate, narrow, north-south ori¬
landforms (or habitats), recognising four broad assem¬
ented estuarine lagoon approximately 1.5 to 2.5 km wide,
blages: 1. Olearia scrub assemblage, with Olearia axilaris,
and 13 km long (Wurm & Semeniuk 2000). Bordering its
Rhagodia bacatta, Spyridium sp. Acacia rostellifera, and A. Cy¬
eastern shore is a stranded sand platform 1-2 m above sea
clops inhabiting recently fixed dunes; 2. Acacia scrub
assemblage, with Acacia rostellifera, A. cyclops, and Agonis
Table 1. Description of geomorphic/sedimentary units in flexuosa inhabiting older fixed dunes; 3. the peppermint low
Leschenault Inlet selected for study in this paper_ forest assemblage, with Agonis flexuosa, inhabiting
geomorphically degraded dunes; and 4. the tuart wood¬
Geomorphic/ Description
land assemblage with Eucalyptus gomphocephala, Agonis
sedimentary
flexuosa, Hakca prostrata, Acacia rostellifera, and A. cyclops
unit
inhabiting swales in the dunes. Other species generally
central basin long, shore-parallel relatively deep occurring in the dunes include Hibbertia cuneiformis,
water mud-floored depression, generally Jacksonia furcellata, Trachyandra divaricata, Acacia saligna,
1.5-2.0 m deep Isolepis nodosa, Apium prostratum, and Lepidosperma
gladiatum.
eastern shore-parallel narrow, shallow water
platform sand platform (low tidal to 1.0 m deep), On the quartz sand high ground of the Mandurah-
vegetated by the seagrass Halophila ovalis Eaton Ridge the vegetation comprises a mosaic of
assemblage types (Heddle et al. 1980). Key species in this
western shallow water muddy sand platform or system include Eucalyptus calophylla and E. marginata,
platform ramp (low tidal to 1.5 m deep), also Allocasuarina fraseriana, Proteaceae (various species of
vegetated by Halophila ovalis Banksia and Isopogon, Stirlingia latifolia, Xylomelum
occidentale), Kunzea ericifolia, Macrozamia reidlei, and Hibbertia
high-tidal high-tidal platforms located on the east
hypericoides. On the low limestone and quartz sand plain
platform and west shores of the estuarine lagoon;
of the Yalgorup Plain, key species include Eucalyptus
width varies from narrow (5-10 m) to
gomphocephala, E. calophylla, Allocasuarina fraseriana, Banksia
wide (>500 m); mainly saltmarsh-
attenuata, Macrozamia reidlei, and Hibbertia hypericoides. Veg¬
vegetated
etation on the emergent supratidal deltaic shoals in the
supratidal broad flat, nearly horizontal, to very Preston River delta complex (Semeniuk 2000), equivalent
flat gently inclined towards the estuary, to the sandy rise complex of Pen et al. (2000), may be com¬
emergent by progradation, underlain by prised of Jacksonia furcellata, Casuarina obesa, Hakea prostrata,
mud, and colonised by samphire; Acacia saligna, A. cyclops, A. cochlearis, Viminaria juncea,
Hibbertia cuneiformis, Sporobolus Virginians, and Isolepis
borders the northern estuary
nodosa.
Preston River complex of linear, tidal-current-aligned
Freshwater vegetation inhabits the broad wetland com¬
delta shoals and emergent islands, with
plex on the eastern shore of the estuary. This zone is a low
intervening shallow channels
level platform, formed as a stranded mid-Holocene subtidal
337
Journal of the Royal Society of Western Australia, 83 (4), December 2000
bidens, Halosarcia halocnemoides, Salicornia quinqueflora,
Suaeda australis, Polypogon monspelliensis, Sporobolus
virginicus, Samolus repens, Sarcocornia quinqueflora,
Northern barrier: Bulboschoenus cal dwell ii, and Frankenia panciflora (Pen et ai
wide barrier, least
parabolic encoach- 2000). The white mangrove Avicennia marina forms scrub
ment into estuary;
wide tidal flats; and heathland (following Specht 1970) in local areas around
diverse assemblage
of mobile and fixed the shores of the estuary (Fig 3). Seagrass vegetation (i.e.
dunes, and plains
aquatic estuarine/marine vegetation) forms shallow wa¬
ter meadows in Leschenault Inlet, and includes Halophila
ovalis, Heterozostera megacarpa, and Ruppia tasnuinica.
Exotic vegetation (i.e. alien species) in the region that
may contribute pollen to the Leschenault Inlet estuary in¬
clude. pine plantations (Pinus radiata and P. pinaster), blue
gum plantations (Eucalyptus globulus), crop, horticultural,
and garden plants (e.g. Lupinus), and weeds such as couch
grass (Cynodon dactylon), kikuyu (Pennisetum clandestinum),
Paspalum grass (Paspalum vaginatum), and pigface
Middle barrier; (Carpobrotus edulis). Generali v, the pines, blue gums, and
narrower barrier,
parabolic encoachment crop, horticultural, and garden plants are located to the
into estuary; inter-dunal
corridors with tidal flats; east of Leschenault Inlet, so that the occurrence of their
mixed mobile/fixed dunes, pollen in estuarine sediments signals transport from east¬
some bar-and-lagoons
ern sources. Weeds also are mainly located to the east of
Leschenault Inlet in residential areas, pasture land, and on
the Collie River delta.
Given this range of contributing vegetation there are a
Southern barrier:
narrow barrier, number of mechanisms that result in anemophilous (rather
abundant parabolic
encoachment into than entomophilous) pollen being emplaced in the estua¬
estuary; mainly mobile
dunes and recently rine environment. These are: transport by wind, (by
fixed dunes; spits, and
bar-and-lagoons seabreezes transporting pollen from the western barrier
dune vegetation, saltmarsh, and mangrove formations, and
Fluvial source by landbreezes transporting pollen from the eastern
Mandurah-Eaton Ridge, saltmarsh vegetation, and from
peripheral freshwater vegetation; and locally from the
Collie River
delta emergent deltaic shoals); transport within the estuary by
currents, including later re-working of previously depos¬
ited pollen; transport by wind and/or rivers from the east
from a variety of hinterland vegetation formations, and
delivered to the estuary by fluvial current within and proxi¬
KEY TO POLLEN SOURCES
mal to the deltas; transport by avifauna (this may be a minor
Mandurah-Eaton Leschenault
Ridge /• Yalgorup Plain Peninsula transport mechanism); and in situ accumulations.
barrier
Freshwater wetlands Peripheral Fluvial The range of source species, transporting media, and
on stranded mid- saltmarsh influx transportation directions would appear to complicate the
Holocene platform
palynological records. However, the large-scale
geomorphic units in the area have diagnostic vegetation
Figure 2. Aerial photograph of the Leschenault Inlet area show¬ assemblages, and thus a single species or group of spe¬
ing main vegetation systems and the pollen sources.
cies can signal derivation from a particular habitat. For
instance, Banksia does not occur on the dune barrier, nor
on the saltmarshes; Olearia does not occur on the
estuarine platform (Pen et al. 2000; Semeniuk 2000). The
Mandurah-Eaton Ridge or on the saltmarshes; and
most widespread and dominant species is Melaleuca
Halosarcia spp specifically inhabit only the saltmarshes.
rhaphiopln/lla. Also occurring in this habitat are Eucalyptus
In this context, there are key species that are diagnostic of
rudis, Baumea juncea, A gouts flexuosar Acacia saligna,
source environment (Table 2).
Hemarthria uncinata, Baumea articulata, Lepidosperma
longitudinalej L. gladiatum and funcus pallidus. Towards its
contact with the present estuarine shore, the wetland com¬ Pollen vectors: wind, currents and runoff
plex surface is inhabited by Melaleuca cuticularis, M. viminea,
The three main vectors for transporting pollen in the
and Casuarina obcsa. Local areas emergent above the
Leschenault Inlet system are wind, estuarine currents, and
watertable support Eucalpytus gomplwcephala.
fluvial run-off. Estuarine currents in the Leschenault Inlet
Saltmarsh vegetation occurs as low herbland forma¬ estuary are driven by wind and tides. Wind waves rework
tions around the periphery of Leschenault Inlet. The species the muddy sediment of the platforms, and under the effect
that comprise these formations include. Halosarcia indica of a northward net current, deposit mud in the deep water
338
Semeniuk, Milne & Waterhouse : Pollen record for Leschenault Inlet
of the central basin or in the northern parts of the estuary Table 2. Diagnostic key species of the source environment for
(Semeniuk 2000). Any pollen delivered to the platforms Leschenault Inlet
potentially can be reworked under these conditions, and Large scale habitat Key species diagnostic to the
redeposited along with mud particles in the sites of mud setting setting
accumulation.
Barrier dunes Acacia cyclops, A. rostellifera,
The Collie River and the Preston River discharge fresh¬ Eucalyptus gomphocephala, Olearia
water into the estuary, and their drainage basins potentially axillaris, Rhagodia bacatta
draw on pollen material delivered by in situ fall from ripar¬
Mandurah-Eaton Banksia spp, Eucalpytus calophylla,
ian vegetation, eroded from soils in the hinterland that
Ridge Eucalyptus marginata, Isopogon spp,
support a variety of vegetation types, and reworked wind-
Kunzea ericifolia, Stirlingia latifolia
delivered material (e.g. pine pollen raining down on the
drainage basin and floodplains of the rivers). All such pol¬ Yalgorup Plain Eucalyptus gomphocephala,
len, through fluvial reworking and transport, can find its Eucalyptus calophylla
way into the Leschenault Inlet estuary.
emergent deltaic Casuarina obesa, Hakea prostrata,
Wind patterns, and their strength and direction in re¬
shoals Viminaria juncea
lation to anemophilous plant flowering times, are critical
factors in determining the types of pollen and the amount freshwater to Baumea articulata, Baumea juncea,
of pollen that is delivered to the depositional environment. saltwater wetlands, Melaleuca cuticularis, M.
The Leschenault Inlet area is characterised by three wind east shore rhaphiophylla, M. viminea
patterns (Semeniuk & Meagher 1981a). a summer pattern
saltmarsh Frankenia pauciflora, Halosarcia
of landbreezes and seabreezes, a prevailing winter pattern,
indica bidens, H. halocnemoides,
and a winter-storm pattern. The pattern in spring is transi¬
Juncus kraussii, Salicomia
tional between winter and summer patterns, with easterlies
quinqueflora, Suaeda australis
and the landbreeze/seabreeze system progressively inten¬
sifying. The wind patterns of interest are those that occur mangrove Avicennia marina
during the flowering season, from August to November,
and for some species progressing to February. seagrass Halophila ovalis, Heterozoster a,
Ruppia megacarpa, Zostera muelleri
It is important to note that other factors may contrib¬
ute to the composition of a pollen assemblage. For example, exotic plants Finns radiata, P. pinaster, Eucalyptus
prolific anemophilous plants on the Mandurah-Eaton globulus, Lupinus spp, Cynodon
Ridge, flowering at a time of calm or weak easterly winds dach/lon, Pennisetum clandestinum,
in say, August, may not deliver as much pollen to the sedi¬ Paspalum vagin at urn, Carpobrotus
mentary repository as a less prolific pollen-producing plant edulis
flowering at a time of strong easterly winds in summer.
Also, there may be prolific entomophilous pollen produc¬
tion, which may be preserved in situ, but this would have
sub-aquatic estuary platform (B9, 13, and C16, 18), estua¬
a negligible contribution via winds. A full analysis of the
rine basin (Bll, C17), and saltmarsh zone. Pen et al (2000),
flowering times of anemophilous and entomophilous
Wurm & Semeniuk (2000), and Semeniuk (2000) provide
plants, their location, their abundance, the wind speeds and
general descriptions of the settings of these sites.
direction at times of plant flowering, and the abundance of
their pollen within Leschenault Inlet, however, is beyond The stratigraphic samples, collected to investigate the
the scope of this study. sub-recent (very late Holocene) occurrence of Avicennia ma¬
rina, were obtained from (Fig 3): 1. the Preston River delta,
The saltmarsh plants Frankenia pauciflora, Halosarcia
where mangroves are currently extant; 2. the sub-surface
indica bidens, H. halocnemoides, Sarcocornia quinqueflora, and
muds in the vicinity of mangroves at Site LIMB; 3. the sub¬
Suaeda australis flower at various times of the year
surface muds in the vicinity of mangroves at Site LI-6; and
(Marchant et al 1987). In addition to wind dispersal in situ
4. along a north-south oriented transect across supratidal
accumulations of pollen on the tidal flat are dispersed by
flats in northern Leschenault Inlet. The sampling strategy
estuarine currents to sub-aquatic platforms and the central
for these sub-recent stratigraphic settings was designed to
basin. For Avicennia marina, which commences flowering
target the zone of most likely occurrence of mangrove pol¬
in March-May (Semeniuk et al 1978), in situ accumulation
len , if indeed mangroves were present at that time.
and subsequent estuarine current dispersion are signifi¬
cant factors. Pollen and spore assemblages were recovered from the
sediments following the extraction techniques of Phipps &
Methods Playford (1984). Residue strew mounts from thirty two sam¬
ples in total were microscopically examined. All samples
Samples were collected from the undisturbed sedimen¬ were scanned for the presence of Avicennia marina pollen,
tary surface of estuarine and saltmarsh environments, and 12 samples were counted to characterise the pollen assem¬
from stratigraphic profiles (Fig 3). Sampling sites were se¬ blages from different contemporary depositional
lected from the 22 sites of Wurm & Semeniuk (2000), across environments, and nine of the sub-recent samples were
the estuary to illustrate across-estuary trends. Contempo¬ counted for comparison with the contemporary assem¬
rary environments sampled include the mangrove zone, blages. Table 3 lists all samples, their stratigraphic location/
339
Journal of the Royal Society of Western Australia, 83 (4), December 2000
Figure 3. Location of transects and study sites in study areas, and stratigraphic setting and location of pollen samples.
environment, rationale for sampling, type of palynological Eucalyptus globulus and grasses such as Cynodon dactylon,
analysis, and the presence or absence of Avicennia marina Pennisetum clandestinum. and Paspalum vaginatum were not
pollen. differentiated from native species. The total percent occur¬
rence of taxa counted in each sample is listed in Table 4. To
Modern pollen reference slides were prepared from
characterise and compare the pollen assemblages from each
acetolysed pollen samples collected from fourteen critical
site, Pinus pollen was removed and minor taxa further
species in the local flora, and Avicennia marina pollen was
grouped. Note that in these analyses the data are presented
obtained from specimens mounted on herbarium sheets
as relative percentages, and not as absolute numbers for a
held at the Western Australia Herbarium. A range of pol¬
given volume of sediment.
len which are thin-walled did not survive the acetolysis
process i.e. ]uncus kraussii (Juncaceae) and the seagrasses
Scans for Avicennia ntarina pollen
Halophylla ovalis, Heterozostera sp, Ruppia megacarpa, and
Zoster a muelleri, and consequently are not recorded in the For each sample, one to two strew slides were scanned
pollen assemblages. for the presence of Avicennia marina pollen. For samples
rich in palynomorphs, up to 15 000 pollen grains were in¬
Pollen counts cluded in the scan. For the rare samples depauperate in
palynomorphs, only several hundred grains were scanned.
In the pollen counts, species identification was carried
out where possible and critical, but the majority of speci¬ Avicennia marina pollen grains are tricolporate and ob¬
mens were identified only to the generic or family level. late spheroidal with distinct colpi and circular pores
Pollen from the five species of Chenopodiaceae sampled averaging 10 mm in diameter. Colpi terminate sharply and
from the local vegetation were grouped together because have a distinctive psilate colpal membrane. Grains are
their differing preservation in the samples made it diffi¬ sculpturally reticulate with prominent but short columel-
cult to reliably differentiate between species. Similarly, lae, the expanded heads of which are fused to form the
pollen of Myrtaceae are grouped together in the analysis, lFm wide muri; lumina are irregular and as thick as, or
but the dominance of Eucalyptus over the Melaleuca/Agonis thinner than, the muri. Pollen of A. marina has an average
group in particular samples is referred to where appropri¬ polar diameter of 26 Fm and an average equatorial diam¬
ate. Pinus was the main exotic palynomorph readily eter of 29 Fm.
identified in the samples. Other potential exotic pollen, from
The tricolporate/colpate pollen group listed in the rela-
340
Semeniuk, Milne & Waterhouse : Pollen record for Leschenault Inlet
tive percent occurrence of species (Table 4) includes sev- terminate identification: Dicotyledons, Tricolporate/
eral types that, without close examination, could be colpate gen indet, Dicotyledon Gen. et sp indet. Crypto-
mistaken for A. marina pollen. The large pores, prominent gam spores, Hepaticae (IPhaeoceros), Selaginellaceae, and
colpal membranes, and distinctive reticulum of A. marina Gen et sp indet. The results of the pollen counts are pre¬
pollen serve to differentiate it from the other tricolporate sented in Table 3 to 5.
types in the Leschenault Inlet samples.
Pollen assemblages
Results ^ ^ _ . .
Gramineae and Casuarmaceae pollen are relatively
Pollen groups and species identified in this study are consistent and show no trends in relative abundance in
as follows: 1) identification to Family level: Casuarinaceae, the main sedimentary environments (viz the saltmarsh, the
Chenopodiaceae, Compositae, Gramineae, Liliaceae, western platform, the central basin, and the eastern plat-
Myrtaceae, Proteaceae (excluding Isopogon and Stirlingia), form).
and Restionaceae; 2) identification to genus level: ,
~ T ' r±‘ ¥ n\ Pollen assemblages in the saltmarsh environment on
Gonocarpus, Isopogon, Lignlana?, Pinus, and Stirlingia; 3) ,, . , • . ., .• T1
. , ! . , , ? the western shore are dominated by Chenopodiaceae. 1 he
identification to species level: Acacia cyclops, Aprum „ , . r ,/ t r
, . . r , . :n native pollen assemblages from the sub-aquatic western
prostratum, Avicenma marina, trankema pauciflora, . , r . , • , , , ,,
T •, , , ... , platform, central basm, and sub-aquatic eastern platform
Lepiaosperma glaaiatum, and Oleana axillaris; and 4) mde- r ...... , 1 ., . /
environments are similar in being dominated by Myrtaceae,
Table 3. Samples studied, rationale for study, pollen counts (NB. all samples were scanned), and presence of mangrove (Avicennia marina)
pollen.
Sampling rationale Samples (environment) Pollen Mangrove
count pollen
present
Contemporary samples
Presence of mangrove pollen; typify pollen LIMB 10 cm (mangrove zone) Yes Yes
assemblage 98-dune surface (mangrove zone) Yes
98 PRD surface (mangrove zone) Yes Yes
Typify pollen assemblages across estuary; A4 (subaquatic estuary platform) No
presence of mangrove pollen C9 (subaquatic estuary platform) Yes No
Cll (estuarine basin) Yes No
C13 (subaquatic estuary platform) Yes No
B16 (subaquatic estuary platform) Yes No
B17 (estuarine basin) Yes Yes
B18 (subaquatic estuary platform) No
C-Sa (saltmarsh) Yes No
Typify saltmarsh pollen assemblages; Br-Sa (saltmarsh) Yes No
presence of mangrove pollen T3x-5C (saltmarsh) No
T3x-Hb (H. indica bidens zone) No
T3x-Jk (Juncus kraussii zone) Yes
T4-3 (saltmarsh) Yes
T4-4 (saltmarsh) No
LI-5B 10 cm (saltmarsh) No
T5-Sa (saltmarsh) No
T5-Hb (H. indica bidens zone) Yes No
T5-Jk (Juncus kraussii zone) No
Stratigraphic samples
Determine if mangrove pollen present in AI/1 30-40 cm (Preston River delta) No
subrecent sediments under extant mangrove AI/3 20-30 cm (Preston River delta) Yes No
sites, or nearby BW/1 20-30 cm (Preston River delta) Yes No
BW/3 10-20 cm (Preston River delta) Yes No
BW/3 40-50 cm (Preston River delta) Yes No
determine if mangrove pollen present in LI-6 10-20 cm (saltmarsh, NE inlet) No
subrecent sediments under extant mangrove LI-6 40-50 cm (saltmarsh NE inlet) Yes
sites or nearby BR/N-1 40-50 cm (northern supra tidal flat) Yes No
BR/N-1 90-100 cm (northern supratidal flat) Yes No
BR/N-3 40-50 (northern supratidal flat) Yes No
BR/N-5 40-50 cm (northern supratidal flat) Yes No
341
Journal of the Royal Society of Western Australia, 83 (4), December 2000
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Semeniuk, Milne & Waterhouse : Pollen record for Leschenault Inlet
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Table 5. Percentage occ <<HX3 : Uasuarinaceae s4Q0au0->33Jj uQaqgsassjJ SCaK/5 <vicennia marina Uhenopodiaceae rpidosperma gladiatu cestionaceae d *u-CQd0b5Q0oa6oM/33)OJ5j Oiearia axillaris Igularia ? Urankenia pauciflora h pium prostratum oac1eo/5“ 1—sbosoVjo1. roteaceae gen. inde •CVVCuCV23JJjj^ Uien et sp indet JHX4Q0OuQ0uOaouX-3»3JJ* T‘5aC55hsb .1Q0Qu523JJ 0C&s<00OH>u/H3n5 XXrXQ~UOQ0Q00QC333-,JJJJL C^laginellaceae /5 Uen et sp indet
343
Journal of the Royal Society of Western Australia, 83 (4), December 2000
Chenopodiaceae, Gramineae, and Casuarinaceae (Fig 4).
In each of these environments Chenopodiaceae pollen show
Cryptogram spores Restionaceae a south to north increase in abundance, reflecting the in¬
crease in abundance of parent plants towards the northern
tidal saltmarsh flats. Olearia axillaris pollen is most com¬
Other angiosperms Myrtaceae
mon in the southern and central sites on the western
sub-aquatic platform and in the central basin, but is rare in
Frankenia pauciflora Gramineae the eastern sub-aquatic platform environment. This distri¬
bution reflects the proximity of the mobile and recently
fixed dune habitats in the southern and middle Leschenault
Olearia axillaris Chenopodiaceae
Peninsula barrier, a habitat that Olearia axillaris prefers. The
relative prominence of this species in the central basin pol¬
Lepidosperma gladiatum Casuarinaceae len assemblage suggests it is widely dispersed or re-worked
by wind and water.
Patterns across transects
Western Saltmarsh Zor
Trends in the relative abundance of pollen across the
South
different estuarine environments are best illustrated by
Transect C, incorporating Sites T5-Hb, C18, C17, C16, and
0) 0) C-Sa (Fig 5). These sites respectively occur in the western
pg saltmarsh, sub-aquatic western platform, central basin, sub-
aquatic eastern platform, and eastern saltmarsh
environments. Chenopodiaceae pollen dominate the west¬
Q.<
ern saltmarsh environment, decrease in abundance towards
the central basin, increase again on the eastern platform,
and become dominant again on the eastern saltmarsh.
Sampling Sites
B Gramineae pollen, away from the saltmarsh environments
Western Platform
where they are overshadowed by the over-representation
South
of Chenopodiaceae pollen, show a fairly consistent rela¬
tive abundance across the estuary. Casuarinaceae,
o a) Restionaceae, Olearia axillaris and Lepidosperma pollen are
ww
»rCe Tc«3 most abundant in the central basin and decrease in abun¬
« c dance towards the eastern and western shores. This pattern
may signal transport and deposition by currents as well as
a.<
wind. Pollen of the Myrtaceae are relatively consistent
across the basin, being similarly prominent on the eastern
and western platforms; their lower relative abundance in
the saltmarsh is likely related to the over-representation of
Central Basin Chenopodiaceae pollen.
South North
In Transect B, which incorporates Sites B13, Bll and
B9 (Fig 5), some species/groups have a similar pattern of
U 0
aoo su distribution as in Transect C (Fig 5), whereas others are
si quite different. From west to east, Chenopodiaceae pollen
are slightly more abundant on the platforms than in the
CL< central basin, reflecting proximity of the platforms to ad¬
joining saltmarsh environments. Gramineae pollen is
relatively consistent across the estuary, and Casuarinaceae
Sampling Sites
pollen is slightly more abundant in the central basin com¬
D Eastern Platforr pared to the sub-aquatic platforms, suggesting transport
South and deposition by currents as well as wind. Olearia axillaris
and Lepidosperma gladiatum pollen show comparable trends
0) 01
- they are more abundant in the western platform sites close
0re0 Uc 60
w re so to their source, and decrease in abundance from west to
40
o;"c east. The pollen of Myrtaceae show a trend of decreasing
K2 30
abundance from east to west across the estuary.
Q.< 20
¥ i
Patterns of distribution
B9 C I 6
Sampling Sites
From the transects, consistent patterns of pollen dis¬
Figure 4. Occurrence of pollen of selected/species groups from tribution can be seen for the major plant groups discussed
the contemporary surfaces of the western saltmarsh zone, west¬ above. Chenopodiaceae pollen decreases in abundance
ern platform, central basin, and eastern platform. away from its source; Gramineae is fairly consistent across
344