ORIGINAL PAPER

Diatom and foraminifera relationships to water qualityin The Coorong, South Australia, and the developmentof a diatom-based salinity transfer function

D. Haynes • R. Skinner • J. Tibby • J. Cann •

J. Fluin

Received: 3 December 2009 / Accepted: 8 February 2011 / Published online: 27 February 2011

� Springer Science+Business Media B.V. 2011

Abstract The Ramsar-listed Coorong lagoon lies at

the terminus of the Murray-Darling River system in

South Australia. Diatom and foraminifera relation-

ships with water quality were characterised in order

to develop diatom- and foraminifera-based models

with the potential to infer water column salinity.

Seventy-four samples were collected during 2007, a

year of continuing drought in the catchment, and of

no discharges at the Murray Mouth. The sample sites

had a salinity gradient of 1.8–190 g l-1 total dis-

solved solids. The diatom data set comprised 215

taxa, while there were only eight taxa in the

foraminiferal data set. Canonical correspondence

analysis of diatom species-environment relationships

showed that salinity explained the largest proportion

of diatom variance. Hence, a diatom-based salinity

transfer function with reasonable predictive power

(measured vs. diatom-inferred salinity rjack2 = 0.82;

Root Mean Squared Error of Prediction = 16 g l-1)

was developed. Application of the transfer function to

fossil diatom assemblages from The Coorong sug-

gested that pre-European salinity values were gener-

ally [50 g l-1 and that salinity declined following

settlement. These results, however, contradict the

recent history of The Coorong where there have been

substantial lagoon-wide salinity increases. The pre-

impact diatom flora has no analogue in the modern

data set, highlighting the degree of departure from

past conditions. CCA of the foraminiferal data set

identified salinity and total nitrogen as the variables

with the greatest explanatory power. However, accu-

rate predictive models could not be developed using

either variable due to low foraminiferal abundance

and species richness. These factors may have been a

consequence of diminished foraminiferal recruitment

rates over successive years, an artefact of reduced

marine water input to The Coorong. Future attempts

to generate predictive models from this region would

benefit from the inclusion of data from distant

locations, since suitable analogue sites do not exist

in close proximity. The study has generated useful

insights to the apparently broad salinity tolerances for

Electronic supplementary material The online version ofthis article (doi:10.1007/s10933-011-9508-y) containssupplementary material, which is available to authorized users.

D. Haynes (&) � R. Skinner � J. Fluin

School of Earth and Environmental Sciences, University

of Adelaide, Adelaide, SA 5005, Australia

e-mail: deborah.haynes@adelaide.edu.au

R. Skinner

e-mail: rachael.skinner@adelaide.edu.au

J. Fluin

e-mail: jennie.fluin@adelaide.edu.au

J. Tibby

Geography, Environment and Population, University

of Adelaide, Adelaide, SA 5005, Australia

e-mail: john.tibby@adelaide.edu.au

J. Cann

School of Natural and Built Environments, University

of South Australia, Adelaide, SA 5095, Australia

e-mail: John.Cann@unisa.edu.au

123

J Paleolimnol (2011) 46:543–560

DOI 10.1007/s10933-011-9508-y

several cosmopolitan diatom and foraminifera spe-

cies, and has identified a number of diatom and

foraminifera taxa that may prove useful in the

qualitative interpretation of down-core trends in The

Coorong and the lower Murray River region.

Keywords Estuary � Diatoms � Foraminifera �Staurosirella pinnata � Transfer function � Salinity

Introduction

The ecological health of coastal wetlands worldwide

is increasingly under pressure from accelerating

settlement of the coastal zone and catchment devel-

opment (de Jonge et al. 2002; NLWRA 2002).

Catchment-wide pressures are manifest in a broad

range of end-of-system impacts. These include

reductions in discharge volumes and increased salin-

ity, nutrient, pollution and sediment loads in lakes,

lagoons and river mouths (Roy and Crawford 1984;

Larsson et al. 1985; Bourman and Barnett 1995;

Cooper et al. 2004; Kauppila et al. 2005). Such

degradation is a challenge to managers responsible

for the formulation and implementation of manage-

ment strategies, particularly those aimed at remedi-

ation (McLusky and Elliott 2004).

Successful management of coastal systems

requires a comprehensive understanding of the range

of variability prior to modifications, so that the full

extent of any human-induced impacts can be docu-

mented (Cooper 1999). In Australia, the historical

record is useful in gauging the effect of anthropo-

genic modifications to catchments and coastal sys-

tems, though continuous records are uncommon

(Tibby 2003). In order to assess temporal variation

over longer time periods, a sediment-based approach

is required.

Quantitative reconstructions of past environments

are possible utilising proxies (for example diatoms

and foraminifera), and an understanding of the

ecological tolerances of extant species (Murray

1991; Battarbee et al. 2001). In coastal regions,

diatom-based models have provided useful insights

into past sea-level, nutrient and salinity fluctuations

(for example Plater et al. 2000; Ryves et al. 2004;

Hassan et al. 2009), whereas foraminifera have been

used to infer salinity, benthic and sea-surface tem-

peratures, and primary productivity in off-shore

settings (for example Pflaumann et al. 2003; Ivanova

et al. 2003; Sejrup et al. 2004).

In Australia, coastal proxy-based models are

sparse, and the majority of diatom-based models have

been developed in non-coastal lacustrine systems, to

infer nutrient status, salinity and pH (for example Gell

1997; Tibby et al. 2003; Taukulis and John 2009).

Coastal palaeoecology in Australia has generally used

qualitative data (Taffs et al. 2008; OzCoasts 2010),

and few coastal or estuarine transfer functions have

been developed using diatoms (Saunders et al. 2007:

diatom-inferred salinity; Saunders et al. 2008: diatom-

inferred phosphate and salinity). No foraminferal

salinity transfer functions have been developed in

coastal regions of Australia. In New Zealand estuar-

ies, Hayward et al. (2004a) produced a foraminferal

transfer function to estimate past sea level that reflects

the salinity preferences of the foraminifera.

This paper aims to characterise diatom and fora-

miniferal relationships to water quality, and develop

diatom- and foraminifera-based models to infer past

conditions (particularly salinity) in The Coorong and

Lake Alexandrina. Prior to the current study, there

was no systematic investigation of the distribution of

foraminifera in The Coorong, despite observations of

foraminiferal tests in sediments of the south lagoon

(Thomlinson 1996). Similarly, the composition of

diatom assemblages in The Coorong was unknown,

although diatoms are likely to be major contributors to

biological productivity in The Coorong (Ford 2007;

Krull et al. 2009; McKirdy et al. 2010).

Study area

At the terminus of the Murray-Darling river system,

the back-barrier Coorong lagoon is an elongate

wetland extending 140 km from the Murray Mouth.

Constrained to the west by the Younghusband

Peninsula, a Holocene coastal dune barrier, and to

the east by last interglacial beach deposits, The

Coorong is constricted to a narrow (approximately

50 m) channel at Parnka Point (Fig. 1). This effec-

tively separates The Coorong into two portions that

are informally referred to as the north and south

lagoons (Fig. 1). At the northern end of The Coorong,

the Murray River debouches into the Indian Ocean,

maintaining an opening at the Murray Mouth, and

facilitating the ingress of sea water to the north

544 J Paleolimnol (2011) 46:543–560

123

lagoon. Surface water enters the southern extremity

of the south lagoon through Salt Creek. A shallow,

unconfined aquifer contributes to the water budget,

particularly of the south lagoon (Haese et al. 2008,

2009). The Coorong and Lakes Alexandrina and

Albert were accorded Ramsar status in 1985 (DE-

HAA 1999), in particular recognition of their impor-

tance to local and migratory bird populations.

Since European settlement, modifications of the

catchments at both ends of The Coorong have impacted

water quality in the lagoon. Water abstraction for

irrigation in the Murray-Darling Basin (Fig. 1) has

reduced discharges of freshwater by more than 75%

(Bourman et al. 2000). The construction of barrages at

the Murray Mouth reduced the Murray estuary to less

than 10% of its former extent. The decrease in river

discharges has caused flood-tide sedimentation at the

Murray Mouth, which closed completely in 1981 for

the first time since European settlement, and which

required continual dredging from 2001 to 2010 to

maintain an opening (Everingham 2007; Caica 2010).

Surface and ground water that once entered the south

lagoon is now diverted out to sea by an extensive

drainage network constructed throughout southeastern

South Australia (Everingham 2007). The extensive

hydrological modifications have resulted in reduced

water exchange and increases in salinity, particularly

in the south lagoon, where submerged macrophytes

have all but disappeared (CSIRO 2009), and the

Australian brine shrimp, Parartemia zietziana now

dominates the hypersaline water (CSIRO 2009). These

factors are thought to be the main causes underpinning

large scale reductions in fish biomass and aquatic

plants that once supported a rich and diverse avifauna

in The Coorong (Phillips and Muller 2006; CSIRO

2009).

Materials and methods

The length of The Coorong, in combination with low

regional rainfall, causes substantial evaporative

0 5 10 20 30km

Barrages

Murray Darling Basin

Sites

•

••

•

•

•••

•

•

•

••

12

3

4

5

6

7

8

9

10

11

12

12a,b

north lagoon

south lagoon

Parnka Point

Lake AlexandrinaGoolwa Channel

Murray Mouth Lake Albert

Indian Ocean

The Coorong

Younghusband Peninsula

Meningie

GM

B E

T

G GoolwaM MundooB Boundary CreekE Ewe IslandT Tauwitcherie

*C3 core site

MorellaBasin

SA

South Australia

Tauwitcherie Channel

MDB

MDBSouth AustraliaSA

Salt Creek

Australia

Study Area

N

139°E

36°S

Fig. 1 Study area with location of sample sites. Site numbers

and names as follows: site 1—Goolwa Channel; site 2—

Beacon 19; site 3—Ewe Island; site 4—Pelican Point; site 5—

Lake Alexandrina; site 6—Mark Point; site 7—Long Point; site

8—Noonameena; site 9—Parnka Point; site 10—Stoney Well;

site 11—Jack Point; site 12—South Salt Creek; site 12a—Salt

Creek channel; site 12b—Salt Creek estuary

J Paleolimnol (2011) 46:543–560 545

123

concentration of salts (Phillips and Muller 2006).

The distinctiveness of this environment and the

absence of similar sites elsewhere, necessitated the

development of an ‘‘internal’’ transfer function (sensu

Mackay et al. 2003) using sites in The Coorong and

Murray Mouth. The latter was sampled to provide

relatively low salinity environments that were possi-

bly analogous to pre impact conditions. The efficacy

of internal transfer functions has been demonstrated

by Mackay et al. (2003) for Lake Baikal in Russia

and by Reavie et al. (2006) for the Great Lakes in the

United States.

Field techniques

After a pilot project conducted in November 2006, 12

sampling sites were selected between Goolwa and a

location south of Salt Creek (Fig. 1). At near shore

and off-shore locations at each site, sediment samples

for diatom and foraminifera analyses were collected

synchronously with water samples on four occasions

during 2007; in mid-summer and mid-autumn (Jan-

uary and April), late-winter and late-spring (August

and November). In early summer (December) addi-

tional diatom and water samples were collected from

Salt Creek channel and estuary following releases

from the Morella Basin (Fig. 1).

Water samples were collected in 2 9 1 l polyeth-

ylene terephthalate (PET) containers for chlorophyll

a and b analyses and 2 9 600 ml PET containers for

nitrogen, phosphorus, conductivity, pH and turbidity

analyses. The samples were refrigerated, and trans-

ported to the Australian Water Quality Centre within

24 h of collection. Water temperature was measured

in the field with an YSI 556 Multiprobe, while water

depth was measured using graduated range poles.

Surface sediments for diatom and foraminiferal

analyses were obtained using a purpose-built, 80 mm

diameter, vacuum corer. The corer was pushed at

least 30 cm into the sediment to ensure the sediment

was retained. Sediments were vertically extruded

within 2 cm of the top of the barrel and a sterile

syringe was used to collect 10 ml of the sediment–

water interface for diatom analysis. These samples

were transferred to sterile centrifuge tubes, and

preserved in 100% ethanol. The sediment was then

extruded to 1 cm above the top of the barrel and a

slicer used to remove approximately 48 cm3 of

sediment for foraminiferal analysis. These samples

were placed in screw-top pots, stained with Rose

Bengal and fixed with 100% ethanol. Selected stained

foraminiferal samples were examined in the field to

assess the presence of live specimens. All samples

were kept cold in the field, and later placed in

refrigerated storage at the University of Adelaide.

Water quality analyses

The water samples were analysed at the Australian

Water Quality Centre for the following parameters:

chlorophyll a (Chl a), chlorophyll b (Chl b), ammonia

(NH3), nitrate and nitrite (NOX), total Kjeldahl

nitrogen (TKN), filterable reactive phosphorus

(FRP), total phosphorus (TP), turbidity, pH and

electrical conductivity (EC). Total dissolved solids

(TDS) were calculated from EC, using a unique

empirical formula developed by the Australian Water

Quality Centre for Coorong samples, as described in

Thomas and Lang (2003). Chlorophyll concentrations

were extracted following the Australian Standard

3753 (1990) for ethanol analyses, and following the

equations derived by Wintermans and de Mots

(1965). APHA (1998) standard methods were

employed for all other analyses.

Biological sample preparation and counting

Diatom sample preparations followed the methods

recommended by Battarbee et al. (2001) with stan-

dard hydrochloric acid and hydrogen peroxide diges-

tion. Digested samples were deposited on coverslips

and mounted on slides with Naphrax mountant. All

samples were enumerated to a minimum of 300

valves, using a Nikon Eclipse 80i light microscope

with differential interference contrast at 1,500 times

magnification. Identification was undertaken with

reference to Desikachary (1986, 1987, 1988a, b,

1989); Krammer and Lange-Bertalot (1986, 1988,

1991a, b); Sournia (1987); Witkowski et al. (2001).

Micrographs and voucher specimens are retained at

the University of Adelaide.

Sediment samples for foraminiferal analysis were

wet sieved on 63 lm mesh, dried and stored in

airtight containers, using the method recommended

by Murray (1991). From each of the dried residues,

100 tests (when present) were counted and identified

under a Zeiss stereo zoom microscope, following the

recommendations of Buzas (1990), who found that

546 J Paleolimnol (2011) 46:543–560

123

samples with few (for example \10) foraminiferal

species required counts of only 100 rather than the

usual 300 tests, to enable statistically accurate

representations of community composition. The tax-

onomy used follows that of Albani (1979) and Albani

et al. (2001), with reference to Hayward et al.

(2004b).

Statistical analyses and water quality

reconstruction

To assess the water quality data for normality, the

one-sample Kolmogorov–Smirnov test (Levesque

2007) was used. Normal distribution was indicated

by p values [ 0.05. Variables without normal distri-

butions were transformed where this improved the

frequency distribution. Following this procedure, a

Pearson correlation matrix in SPSS 16.0 (Levesque

2007) was used to identify highly correlated (i.e.

redundant) variables which were subsequently

deleted.

Diatom species with maximum relative abun-

dances of \1% were removed from the data set,

leaving a total of 215 taxa. All foraminifera counts

were included as total abundances were low at sites 4,

6, 7, 8, 11, and 12 (see Fig. 7). The diatom and

foraminiferal data sets were subjected to detrended

correspondence analysis (DCA) (Hill and Gauch

1980) with detrending by segments, using CANOCO

version 4.53 (ter Braak and Smilauer 2004), to

determine whether analyses that assume linear or

unimodal species responses were most appropriate.

Canonical correspondence analysis (CCA) (ter

Braak 1986) was performed on the diatom and

foraminiferal data sets, incorporating manual selec-

tion with 999 Monte Carlo randomised permutations,

to determine which environmental variables signifi-

cantly explain (a = 0.05) species variation. The

CCAs were illustrated using CANODRAW 4.13

(Leps and Smilauer 2003). The relative abundances

of diatoms and foraminifera were illustrated in C2

(Juggins 2003).

C2 (Juggins 2003) was used to derive transfer

functions for diatoms and foraminifera. All weighted

averaging (WA), weighted averaging-partial least

squares (WA-PLS) and PLS calibration methods

were assessed using the lowest root mean squared

error of prediction (RMSEP) as a criterion. Following

Birks’ (1998) criterion for determining the ‘minimal

adequate model’, models of increasing complexity

were only considered if they improved the RMSEP

by C5%. This criterion was also applied to the

deletion of outliers, themselves defined as having a

residual difference between the predicted and actual

water quality variable of[1 standard deviation of the

gradient (sensu Gasse et al. 1995), to achieve

progressive improvement in the RMSEP.

The diatom-salinity transfer function was applied

to a previously analysed core (C3) retrieved in 2005

from a site located between modern sample sites 4

and 6 in the north lagoon (Fig. 1) (Fluin et al. 2007).

Results

During 2007, the water level in Lake Alexandrina

was lower than that in The Coorong and, conse-

quently, there were no freshwater releases to The

Coorong at its northern end (MDBC 2008). The

major inflow to The Coorong in 2007 was seawater

via the Murray Mouth, along with small discharges

(approximately 0.04 km3) from the Morella Basin

through Salt Creek into the south lagoon in December

(Fig. 1). Annual rainfall at Meningie for 2007 was

453 mm, of which 42.4 and 30.8 mm fell in the

2 days immediately before the respective January and

November samplings. Precipitation between the Jan-

uary and April sampling was \10 mm, and 250 mm

of rain fell during the 4 months prior to the August

sampling (BoM 2009).

During the pilot study, diatoms were abundant at all

sites, however foraminifera were not recovered from

Lake Alexandrina sediments or in those sampled

upstream of the Goolwa Barrage. Consequently, those

sites were eliminated from the foraminiferal sampling

programme. Very fine-grained sands and silts occurred

at most north lagoon sites, and site 8 had dense

concentrations of submerged macrophytes. At site 9

the channel was narrow and shallow, the sediment fine,

organic silt, and the ostracod Osticythere baragwana-

thi was particularly abundant. The sediments at all

south lagoon sites were fine, salt-encrusted sands.

Water quality

Figure 2 illustrates selected water quality results

sorted by site, starting at the ‘fresh’ northern sites

(1 and 5), followed by The Coorong sites 2–12

J Paleolimnol (2011) 46:543–560 547

123

(all results in electronic appendix S1). Generally,

salinity, turbidity, Chl a, TP and TN were lower in the

north lagoon, and average salinity in the south lagoon

was three to five times greater than that of seawater.

Water temperatures declined over successive sam-

pling occasions, increasing again in November. The

greatest fluctuation in water depth occurred at site 8.

For all Coorong sites pH varied between 7.3 and 8.4,

and was 8.2 and 8.6 at sites 5 and 1 respectively, while

the highest value (9.4) was recorded at site 12a in

December. The highest Chl a (79.4 lg l-1) was

recorded in the south lagoon during August at site 9,

while the highest concentrations of TP (1.68 mg l-1)

and TN (10.2 mg l-1) were at, respectively, sites 11

and 12 in January. The highest turbidity (140 NTU)

was at site 5 in November (Fig. 2).

Analysis of water quality data

Two water-quality data sets were assessed for

normality, one comprising all samples (n = 74) for

analysis with the diatom data, and a smaller data set

(n = 45) including only sites at which foraminifera

were present. In the full data set, FRP, TDS, and

temperature have normal distributions (p val-

ues [ 0.05) in a Kolmogorov–Smirnov test. NH3,

NOX, TP and pH were not transformed as there was

no improvement using natural log, square root or

log10 transformations. Chl a and Chl b, TKN, TN,

turbidity and depth data were all natural log trans-

formed. In the smaller data set, Chl a, FRP, pH and

temperature have normal distributions (p [ 0.05) in a

Kolmogorov–Smirnov test. TP, NH3 and NOX were

0 5 0 1 0 0 1 5 0 2 0 0 0 5 0 1 0 0 0 4 8 1 2 0 1 2 0 60 1 20 7 8 9 1 0 0 1 2 3 8 1 2 1 6 2 0 2 4 2 8

Site n

umbe

r

Lake Alexandrina 5

1

2

3

4

6

7

8

9

10

11

12

12b,a

Goolwa Channel

n

o

o

g

a

l h

t r

o

N

n

o

o

g

a

l h

t u

o

S

g l µg l mg l mg l NTU pH units m ºC - 1 - 1 - 1 - 1

near shore samples off-shore samples

Beacon 19

Ewe Island

Pelican Point

Mark Point

Long Point

Noonameena

Stoney Well

Parnka Point

Jack Point

Sth Salt Creek

Salt Creek estuary (b) channel (a)

lower salinity months

TDSChl

aTN TP Tu

rbidi

ty

pH Depth

Tem

pera

ture

Site n

ames

Fig. 2 Selected water quality data at site 5 (Lake Alexandri-

na), site 1 (Goolwa Channel), sites 2–8 (Coorong—north

lagoon), and sites 9–12a (Coorong—south lagoon) in 2007 (see

electronic supplementary S1 for all water quality results).

Within each site, samples are in month order (January, April,

August and November). Where applicable, near shore samples

are shown as outlines, off-shore samples as solid bars. Site 7

has additional mid transect samples (solid bars). Site 8 near

shore has data for January only, and sites 2, 3, 4, 7 and 11 are

without near shore data for November. Site numbers and

corresponding sample numbers are as follows: site 1—8, 28,

47, 62; site 5—1, 21, 40, 59; site 2—near shore 2, 22, 41 off-

shore 3, 23, 42, 60; site 3—near shore 4, 24, 43 off-shore 5, 25,

44, 61; site 4—near shore 6, 26, 45 off-shore 7, 27, 46, 62; site

6—near shore 9, 29, 48, 64 off-shore 10, 30, 49, 65; site 7—

near shore 11, 31, 50 mid-transect 12, 32, 51, 66 off-shore 13,

33, 52, 67; site 8—near shore 14 off-shore 15, 34, 54, 68; site

9—16, 35, 54, 69; site 10—17, 36, 55, 70; site 11—near shore

18, 37, 56 off-shore 19, 38, 57, 71; site 12—20, 39, 58, 72; site

12a—73; site 12b—74

548 J Paleolimnol (2011) 46:543–560

123

not transformed as square root, natural log and log10

transformations did not improve their normality.

TDS, TKN, TN, Chl b, turbidity and depth data were

natural log transformed. In both data sets Chl b, TKN

and FRP were very highly correlated (p \ 0.005)

with six or more variables, and so were removed from

further analyses. Following removal of these vari-

ables, TP and TDS had weak correlation with other

variables, and were retained for further analyses (see

correlation matrices in electronic appendix S2).

Diatom assemblages and water quality

The diatom flora north of site 7 in the north lagoon

consists almost exclusively of Staurosirella pinnata,

Staurosira spp. (S. construens agg. and S. elliptica),

Amphora cymbamphora, Catenula adhaerans, Nitzs-

chia valdestriata, Fragilaria sp. and Cocconeis spp.

(C. neothumensis var. marina, C. neodiminuta and

C. scutellum var. parva). Planothidium delicatulum,

P. deperditum, P. lanceolatum, P. sp. 6, P. aff.

lilljeborgei and P. aff. haukianum (illustrated as

Planothidium spp. group) do not occur south of site 8,

the only location with a notable occurrence of

Paralia sulcata. Opephora pacifica, O. mutabilis

and O. naveana occur at sites north of site 8, while

site 9 is dominated by O. schwartzii (all grouped in

Opephora. spp.). Except for low relative abundances

at site 3, the distribution of C. placentula is confined

to sites south of site 8. Diatom assemblages in the

south lagoon are dominated by varying abundances of

Amphora delicatissima, A. coffeaeformis, A. acutius-

cula and A. subacutiuscula in association with

Navicula sp. 13 and Nitzschia communis. Site 12a is

dominated by Navicula sp. 13, with C. placentula and

A. acutiuscula (Fig. 3a).

Diatom species-environment relationships

DCA indicated that the axis 1 gradient length in the

diatom data set was 5.584; hence unimodal ordination

(CCA) was used to explore species-environment

relationships. Seventy-four samples, with 215 diatom

taxa, and nine environmental variables were included

in the CCA. Seven of the environmental variables

explain a significant proportion of the species vari-

ation (at a = 0.05): TDS, TN, TP, Chl a, pH and

depth all have p = 0.001; and turbidity has

p = 0.008 (electronic appendix S3a). The first CCA

axis explains 8.9% of the variance in the diatom data,

and a total of 45.1% of the species-environmental

relationship. The total species variance explained by

the significant variables is 35.9%, with TDS explain-

ing the greatest variance (8.3%).

There are distinct groupings in the diatom CCA

(Fig. 4). Samples from The Goolwa Channel and Lake

Alexandrina (sites 1 and 5) cluster together and have

low axis 1 and high axis 2 scores, and a positive

association with pH and depth. All north lagoon

samples (except sample 68) together with the south

lagoon sample 73 (site 12a) are grouped together in the

centre and bottom-left quadrant of the CCA and are

mostly associated with low Chl a, Turbidity, TDS, TN

and TP. All south lagoon samples (except site 12a)

together with the north lagoon sample 68 plot together.

These samples, most closely associated with high TDS,

TN and TP, are from the south lagoon, together with

sample 68 from the north lagoon.

Weighted averaging partial least squares (WA-PLS)

regression

CCA indicated that salinity is the most appropriate

variable for development of a diatom transfer func-

tion. A one component WA-PLS model performed

better than WA regression with inverse and classical

de-shrinking and with tolerance downweighting,

while more complex models only performed moder-

ately better (\5% improvement in RMSEP, Table

S4). The full model performed moderately well

(rjack2 = 0.65, RMSEP = 25.07 g l-1 TDS). How-

ever, several samples had residual differences

between the actual and predicted salinity exceeding

45 g l-1 TDS. After iteratively deleting 5 outliers

with residuals greater than the standard deviation of

TDS (42.5 g l-1) model performance improved. The

final model (rjack2 = 0.82, RMSEP = 16 g l-1 TDS)

showed an ultimate improvement in the RMSEP of

36% (electronic appendices; S4: model statistics; and

Fig. 5: diatom inferred vs. measured-salinity plots).

Diatom-based salinity reconstruction

The diatom transfer function was applied to a north

lagoon core (C3) of early Holocene age (7,200 ±

60 years cal BP: Fluin et al. 2007). The majority of

pre-European samples have reconstructed salinity

that exceeds 45 g l-1 (Fig. 6a). Seventy per cent of

J Paleolimnol (2011) 46:543–560 549

123

species in the fossil assemblages are present in the

modern diatom data set, but with the exception of

small Fragilariaceae taxa (Staurosirella pinnata and

Staurosira spp.), most have low relative abundances

(Fig. 6a, b).

Foraminiferal assemblages and water quality

Field examination of the foraminiferal samples

showed that few specimens adsorbed the Rose Bengal

stain. Given this situation, all tests that were in good

condition, showing no signs of wear or breakage were

counted, as this was taken to indicate in situ

deposition (Cann et al. 2000).

Marine taxa Trochulina dimidiata, Elphidium

crispum, Cibicides sp., together with some unilocular

and miliolid species are relatively abundant at the

northern end of the north lagoon, and the seaward

side of the Goolwa Barrage (Fig. 7). Euryhaline taxa

Ammonia aff. aoteana (Hayward et al. 2004b) and

E. excavatum forma excavatum dominate the assem-

blages at most sites in both lagoons, with the

exception of site 2, the only site at which T. dimidiata

was abundant. Sites 3 and 4 have similar assem-

blages, with A. aff. aoteana dominant over

E. excavatum forma excavatum and a few individuals

of E. crispum. A total of \10 individuals in four

sampling sessions were observed at near shore and

off-shore locations at site 6. At site 7, only off-shore

sediments yielded specimens of E. excavatum forma

excavatum over the four sampling periods. Site 8 had

only E. crispum and A. aff. aoteana in three of the

0 20 40 60

Staur

osire

lla p

innata

0 20 40

Staur

osira

spp.

0 20 40

Cocco

neis

spp.

0 20

Amph

ora

cymba

mphora

0 20

Caten

ula a

dhae

rans

0 20 40 60

Nitzsc

hia va

ldestr

iata

0 20

Frag

ilaria

sp.

0 20

Nitzsc

hia o

valis

0 20 40 60 80 100

Planot

hium

spp.

Parali

a su

lcata

0 20 40 60

Opepho

ra sp

p.

0 20 40

Cocco

neis

place

ntula

0 20 40

Amph

ora

coffe

aefo

rmis

0 20

Amph

ora

delic

atiss

ima

0 20 40

Amph

ora

suba

cutis

cuila

0 20 40

Nitzsc

hia co

mmun

is

0 20 40

Amph

ora

acuti

scula

0 20 40 60

Navicu

la sp. 1

3

TDS

* S

tau

rosi

rella

pin

na

ta

* S

tauro

sira

elli

ptic

a

* S

tauro

sira

const

ruens

agg.

* S

tauro

sira

punct

iform

is

Fra

gila

ria s

apote

nsi

s

Am

phora

cym

bam

phora

Cate

nula

adhaera

ns

Nitz

schia

vald

est

riata

* P

lan

oth

idiu

m s

p. 6

* P

lanoth

idiu

m d

elic

atu

lum

* P

lanoth

idiu

m la

nce

ola

tum

Pla

noth

idiu

m d

eperd

itum

Pla

noth

idiu

m a

ff h

auki

anu

m

Pla

noth

idiu

m a

ff li

lljeborg

ei

Pla

noth

idiu

m a

ff e

ngelb

rech

tii

Pla

no

thid

ium

sp.

5

Pla

no

thid

ium

sp.

7

* C

occ

on

eis

ne

oth

um

en

sis

va

r. m

ari

na

* C

occ

oneis

neodim

inuta

* C

occ

on

eis

scu

tellu

m

va

r. parv

a

Nitz

schia

ova

lis

Fra

gila

ria s

p.

* P

ara

lia s

ulc

ata

Opephora

kru

mbenei

Opephora

sp.

4

* O

pephora

paci

fica

Opephora

sp.

* O

pephora

muta

bili

s

* O

pephora

nav

eana

Opephora

hors

tiana

Opephora

obl

ongella

Opephora

sch

wart

zii

* C

occ

oneis

pla

centu

la

Am

phora

deilc

atis

sim

a

* A

mphora

coffe

aefo

rmis

Am

phora

acu

tiscu

ila

Am

phora

subacu

tiscu

ila

* N

avic

ula

sp.

13

* N

itzsc

hia

com

munis

2040

0

6080

120100

1

2

5

3

4

7

6

9

10

8

11

12

12b,a

No

rth la

go

on

South

lag

oo

n

Goolwa Channel

Lake Alexandrina

0 20

Site

near shoresamples

off-shore samples

0 50 100 150 200

T

DS

g l

-1

Sea water salinity 35 g l -1

b

a

Fig. 3 a Diatom assemblages at site 5 (Lake Alexandrina),

site 1 (Goolwa Channel), sites 2–8 (Coorong—north lagoon),

and sites 9–12a (Coorong—south lagoon) in 2007. Within each

site, samples are in month order (January, April, August and

November) and where applicable, with near shore samples

shown as outlines, off-shore samples shown as solid bars. Site

7 has additional mid transect samples (solid bars). Site 8 near

shore has data for January only, and sites 2, 3, 4, 7 and 11 are

without near shore data for November. Only taxa which occur

in abundances C10% in at least two samples are displayed (see

Fig. 2 for sample numbers that correspond to the sites).

b Diatom species weighted averaging salinity optima and

tolerance. Note: taxa which are grouped in 3a under the epithet

‘‘spp.’’ are displayed individually in 3b, and those species that

occur in the fossil assemblage for core C3 are indicated with

asterisks. The dashed line indicates average sea water salinity

(35 g l-1)

550 J Paleolimnol (2011) 46:543–560

123

four sampling periods. Site 9 assemblages are co-

dominated by E. crispum and A. aff. aoteana.

Ammonia aff. aoteana dominates the south lagoon

assemblages, along with E. excavatum forma excav-

atum at site 11 and Cibicides sp. at site 10, although

total counts of foraminifera were low at sites 11 and

12 (Fig. 7).

Foraminifera species-environment relationships

Normal distribution of the foraminiferal data could

only be achieved following natural log transforma-

tion, an artefact of low species richness and low

abundances. DCA of the transformed data had an axis

1 gradient length of 3.515. Eight taxa and nine

environmental variables from 45 sites were subjected

to CCA. Sample 58 was downweighted as it had very

high NH3 (electronic appendix S1). Five environ-

mental variables explain significant variation in the

foraminiferal data; TDS, TN and pH (p values =

0.002); Chl a (p = 0.006) and TP (p = 0.01).

The first CCA axis explains 12.8% of the variance

in the foraminiferal data, and a total of 62.8% of the

species-environmental relationship. The amount of

variance in species data explained by the significant

variables is 43.8%, and TDS and TN had equivalent

explanatory power (both 10.8%) (electronic appendix

S3b).

With the exception of samples from sites 4, 7 and

8 (sample numbers 11, 14, 15, 23, 31, 32, 66, 68), the

majority of north lagoon samples cluster reasonably

closely, with most associated with high pH and low

Chl a, TN, TP, TDS, depth and turbidity (Fig. 8). By

contrast, all south lagoon samples are positively

associated with these variables, but have a high axis 2

dispersion, highlighting the between sample differ-

ences from the south lagoon (Fig. 8).

Partial least squares regression

The low foraminiferal species richness inhibited the

application of WA-based techniques. Hence partial

least squares (PLS) regression was used in an attempt

to develop a predictive model for both total nitrogen

and salinity. The relationships between measured and

foraminifera-inferred salinity and TN are not strong

(rjack2 = 0.32; RMSEP = 0.447 LN g l-1 TDS and

rjack2 = 0.32; RMSEP = 0.566 LN mg l-1 TN) for

five-component models. Since salinity was the var-

iable of interest, the two largest outliers were

removed, but model performance was only improved

by 11.2% (rjack2 = 0.36; RMSEP = 0.397 LN g l-1

-4 6

-33

TDS

Chl a

TN

Turbidity

Depth

TP

pH

Lake Alexandrina& Goolwa Channel

North lagoon South lagoon

near shoreoff-shore

near shoreoff-shore

Axis 1 (8.9% variance explained)

Axi

s 2

(3.7

% v

aria

nce

expl

aine

d)

Fig. 4 Canonical

correspondence analysis

biplot of modern diatom

sample scores and vectors

of significant environmental

variables (see Fig. 2 for the

sites that correspond to the

sample numbers)

J Paleolimnol (2011) 46:543–560 551

123

TDS). Accordingly, a robust foraminifera-salinity

model could not be determined.

Discussion

Coorong salinity during 2007

The highest salinity was recorded at site 12 during

April (190 g l-1 TDS). In August at sites 9, 10, 11

and 12 in the south lagoon, salinity was lower than in

all other months, while in November at sites 10, 11

and 12 salinity was less than for January and April

(Fig. 2; electronic appendix S1). This may be attrib-

uted to rainfall (280 mm up to November sampling)

(BoM 2009), although if precipitation alone was

responsible, a concomitant lowering of north lagoon

salinity in August and November might also be

expected. The results, however, indicate that salinity

increased over successive sampling occasions at all

sites north of site 9 (Parnka Point) during 2007

(Fig. 2; electronic appendix S1). This may be a

consequence of the absence of discharges from Lake

Alexandrina for the year (MDBC 2008) in combina-

tion with evaporation. But lower salinity in the south

lagoon during August and November may be the

product of the mitigating effects of groundwater

discharge (Haese et al. 2008, 2009), in combination

with winter rainfall.

Diatom distributions

A marked north–south diatom species gradient is

evident in all months, and species richness is greater

in the north lagoon (mean: 105) than in the south

lagoon (mean: 52). There are considerable differ-

ences in assemblage composition at the northern and

southern extremities of The Coorong (Fig. 3a).

Salinity explained the greatest amount of variance

in the diatom data, highlighting the suitability of this

data set for developing a salinity transfer function.

All sites are dominated by a small number of taxa,

although more diverse assemblages and greater

proportions of marine varieties at the northernmost

north lagoon sites are in accord with a stronger

connection with the ocean. A gradual assemblage

change southward in the north lagoon may reflect

increasing salinity (Fig. 3a).

While the two freshest sites (1 and 5) are

dominated by small Fragilariaceae, the diatom flora

at site 8 consists almost exclusively of unidentified

Planothidium species (sp. 5 and sp. 7), and is

compositionally different from assemblages of all

other sites in both lagoons. Opephora schwartzii

dominates the diatom assemblage at site 9. Many

epipelic or episammic Opephora species are able to

tolerate low-oxygen conditions (Moss 1977), and

suboxic conditions at the site are indicated by high

densities of the ostracod Osticythere baragwanathi

(Yassini and Jones 1987 as O. reticulata). Salt-

encrusted fine sands and silts provided the growth

Measured salinity (g l-1 TDS)

Dia

tom

in

ferr

ed s

alin

ity (

gl-1

TD

S)

Measured salinity (g l-1 TDS)

Mea

sure

d-d

iato

min

ferr

ed s

alin

ity

(gl-1

TD

S)

0

-50

-40

-30

-20

-10

0

10

20

30

40

0 50 100 150 200

50

150

200

0 50 100 150 200

a

b

100

Fig. 5 a Measured versus diatom-inferred salinity from the 69

sample Coorong model. b Measured versus the diatom-

inferred-measured residuals in the model

552 J Paleolimnol (2011) 46:543–560

123

substrate for all south lagoon sites, where Navicula

sp. 13 co-dominates, with several Amphora varieties

and Nitzschia communis, in varying relative abun-

dances that appear to be site specific (Fig. 3a).

Diatom ecology

There are significant discrepancies between salinity

optima for some diatom species in this data set and

those published elsewhere, the most notable example

being for Staurosirella pinnata (Fig. 3b). Davies

et al. (2002) noted the similarity in salinity optima for

S. pinnata from different regions (optimum in

Mexico: 205 lS cm-1; in Africa: 145 lS cm-1),

while Gell’s (1997) optimum for this species is

slightly higher (in Australia: 3.9 g l-1), but all the

values are well within the ‘fresh’ ecological range

suggested by Krammer and Lange-Bertalot (1991a).

In The Coorong data set, S. pinnata has a salinity

optimum in excess of 29 g l-1 ([46,250 lS cm-1)

(Fig. 3b). As well as dominating assemblages at a

number of north lagoon sites in the current study, the

species dominates assemblages in recent sediments

from the north lagoon core (C3) (see Fig. 6a), a

situation that occurs in another core from the north

lagoon (C7) (Fluin et al. 2007). Taken together these

findings may indicate that S. pinnata has a wider

salinity tolerance than previously recognised,

-1 SCD

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Litho

strat

igrap

hy

0 20 40

Campylod

iscus

daemeli

anus

*

0 20 40

Coccon

eis sp

p.

0 20 40

Gram

mato

phor

a spp

.

0 20

Opeph

ora

spp.

0 20 40

Parali

a su

lcata

0 20

Staur

osira

pun

ctifo

rmis

0 20

Aulaco

seira

spp.

0 20

Campylod

iscus

eche

neis

*

0 20

Coccon

eissp

p.

0 20

Fragil

aria

cf su

bsali

na

0 20

Rhopalo

diasp

p.

0 20 40 60

Staur

osire

llapin

nata

0 20 40

Staur

osira

spp.

Estim

ated

TDSby

WA

(inve

rse de

shrin

king)

Marine Non-Marine

Depth

(cm

)

# 7255 ± 60

# 390 ± 140

1962

20

perc

entile

th

10

perc

entile

th

Pinus

g l

(data courtesy of DEH)

% % % % % % % % % % % % %

20

40

60

80

0

Sta

uros

irella

pin

nata

Sta

uros

ira e

llipt

ica

Sta

uros

ira c

onst

ruen

s ag

g.

Sta

uros

ira p

unct

iform

is

Fra

gila

ria c

f sub

salin

a

Aul

acos

eira

gra

nula

ta

Coc

cone

is h

offm

anii

Coc

cone

is p

elto

ides

Ope

phor

a pa

cific

a

Coc

cone

is s

taur

onei

form

is

Ope

phor

a m

utab

ilis

Ope

phor

a na

vean

a

Coc

cone

is d

iscu

loid

es

Par

alia

sul

cata

Gra

mm

atop

hora

oce

anic

a

Coc

cone

is n

eoth

umen

sis

var

. mar

ina

Coc

cone

is n

eodi

min

uta

Coc

cone

is s

cute

llum

Rho

palo

dia

mus

culu

s

Coc

cone

is k

ram

mer

i

Coc

cone

is p

lace

ntul

a

2005

March 2005 salinity rangesite 4 (33.7 g l )site 6 (36.3 g l )

-1

-1

2005 =

a

b

0 20 40 60 80 100 15 45 75 105 135 165

100

Distan

ce to

nea

rest

mod

ern

sam

ple

Sal

inity

g l

-1

Sea watersalinity 35 g l -1

→

→

→

Black silt

Grey silt/mud

Shell band

Dark grey silt/mud

Grey sand/silt

Key

Lithology

Date

# years before 2005

1966

1955

Fig. 6 a Diatom stratigraphy from north lagoon core C3. The

diatom inferred salinity data and results of analogue matching,

including the 10th and 20th percentiles of similarities in the

modern data set are shown. Only species or groups that

occurred in abundances C10% in at least one sample are

displayed. The dashed horizontal line represents the first

detectable appearance of exotic Pinus pollen in the record.

Species with asterisks did not occur in the modern dataset.

Note: Marine Cocconeis spp. = C. heteroidea, C. krammeri,C. neothumensis var. marina, C. peltoides, C. scutellum; Non-

marine Cocconeis spp. = C. neodiminuta, C. scutellum var.

parva, C. placentula. b Diatom species weighted averaging

optima and tolerance. Note: taxa which are grouped in 5a under

the epithet ‘‘spp.’’ are displayed individually in 5b. The dashedline indicates average sea water salinity (35 g l-1)

J Paleolimnol (2011) 46:543–560 553

123

particularly as average salinity in the north lagoon

during 1997 and 2002 was 35 (practical salinity

units), increasing to 52 between 2003 and 2007

(Webster 2010, p. 270).

The two diatom species that periodically dominate

the fossil records from the north and south lagoons of

The Coorong are respectively, Paralia sulcata and

Cocconeis placentula (Fluin et al. 2007; McKirdy

et al. 2010). P. sulcata is generally characterised as

marine-euryhaline or marine-polyhalobous (McQuoid

and Nordberg 2003; Horton et al. 2006), while

C. placentula is fresh-brackish or oligohalobous-

indifferent (Vos and de Wolf 1993; Hassan et al.

2006). Sullivan (1999) attributes the dominance of

euryhaline taxa to fluctuating salinity regimes, as this

dominance results from an ability to tolerate variable

salinity, rather than reflecting the absolute concen-

tration of salts. The dominance of P. sulcata in

the north lagoon core (C3) record (Fig. 6a) and

C. placentula in cores from the south lagoon

(McKirdy et al. 2010) therefore inhibits precise

hind-casting of salinity.

The derived salinity optimum of Paralia sulcata in

The Coorong is 65 g l-1 (Figs. 3b, 6b). However,

Zong (1997) suggests the species favours salinities as

low as 10, while McQuoid and Nordberg (2003)

found the species only in brackish or marine envi-

ronments. Given the dominance of P. sulcata in

Coorong fossil assemblages, its low representation in

the lower salinity north lagoon environment during

2007 is puzzling. To some extent, this could arise

because of high absolute abundances of Fragilaria-

ceae suppressing the relative abundances of P. sulcata.

This point has been previously noted in regard to

small Fragilariaceae by Bennion et al. (2001) and

Sayer (2001), both of whom suggest that increased

counts of non- Fragilariaceae taxa may result in better

water quality reconstructions.

While low absolute abundances of C. placentula in

The Coorong may reduce the reliability of the data,

by comparison with other studies, the optimum of

82.1 g l-1 (108,000 lS cm-1) (Figs. 3b, 6b) appears

to demonstrate the extent of the species’ indifference

to salinity. In Spanish salt lakes, Reed (1998) noted

0 25 50 0 25 50 0 5 10 0 25 50 75 100 0 25 50 75 0 25 50 75 100 0 25 50 75 100 0 25 50 75 100

Marine Euryhaline

2

3

4

6

7

8

9

10

11

12

North lagoon

South

lagoon

Troc

hulin

a dim

idiat

a

Milio

lidsp

.

Uniloc

ular sp

.

Elphidi

um cr

ispum

Cibicid

essp

.

Unkno

wn sp

.

Elphidi

um ex

cava

tum

form

a ex

cava

tum

Amm

onia

aff.

aote

ana

TDSSite

near shore samples off-shore samples

0 50 100 150 200

Numbe

r of t

ests

325

508

117

21

139

26

395

292 10

16

386

100

15

14

10

60

Fig. 7 Foraminifera taxon relative abundances at sites 2–8

(Coorong—north lagoon) and sites 9–12 (Coorong—south

lagoon) in 2007 (see Fig. 2 for sample numbers that correspond

to the sites). Within each site, samples are in month order

(January, April, August and November). Where applicable,

near shore samples are shown as outlines, and off-shore

samples as solid bars. Site 7 has additional mid transect

samples (solid bars). Site 8 near shore has data for January

only, and sites 2, 3, 4, 7 and 11 are without near shore data for

November

554 J Paleolimnol (2011) 46:543–560

123

the conductivity optimum of Cocconeis placentula is

20,700 lS cm-1 (approximately 12.9 g l-1 TDS),

while in North American lakes its optimum is

16,800 lS cm-1 (approximately 10.5 g l-1 TDS)

(Fritz et al. 1993). A study of African salt lakes

(Gasse et al. 1995) showed the species to have an

optimum of 469 lS cm-1 (approximately 0.2 g l-1

TDS), which agreed well with the optimum of

433 lS cm-1 in fresh, slightly alkaline Mexican

lakes (Davies et al. 2002).

Salinity-based diatom transfer function

Although the diatom data set is relatively small

(n = 69, following outlier deletion), it has reasonable

predictive power (rjack2 = 0.82) (electronic appendix

S4), albeit not as high as models from continental

settings in Africa (measured vs. diatom-inferred (DI)

conductivity rjack2 = 0.87: Gasse et al. 1995), Australia

(measured vs. DI salinity rjack2 = 0.87: Gell 1997) and

Spain (measured vs. DI conductivity rjack2 = 0.91:

Reed 1998). Smaller diatom data sets from coastal

environments have been used to derive models; 40

samples were used by Hassan et al. (2009) to derived

a model for salinity in Argentinian estuaries with less

predictive power (measured vs. DI salinity

rjack2 = 0.75), while Ryves et al. (2004) used a 36

sample data set from brackish lakes and fjords in

Denmark with better predictive power (measured vs.

DI salinity model rjack2 = 0.88).

Application of the diatom-salinity model to fossil

assemblages in The Coorong, however, underlines a

drawback in the development of statistically signif-

icant models, viz. that good model performance does

not necessarily result in accurate reconstructions.

Inferences derived from down-core application of the

model suggest that salinities in excess of 45 g l-1

prevailed in the pre-European Coorong, and that

salinity declined in recent times (Fig. 6a). These

findings are at odds with the known recent history of

The Coorong, where salinity has increased over

successive decades since the 1985 Ramsar listing

(Thomlinson 1996; Thomas and Lang 2003; Phillips

and Muller 2006; Webster 2010). Several key diatom

species found in fossil material are either not

represented in the modern flora, or are present in

much lower proportions (Fig. 6a). For example

Campylodiscus daemelianus has a Hill’s (1973) N2

(a measure of the effective number of occurrences) of

nine and a maximum relative abundance of 31% in

the north lagoon core (C3) (Fig. 6a), but does not

occur in the modern data set. Although Paralia

sulcata occurs in the modern data set (N2 = 5.4,

maximum = 28%), it is much less abundant

(N2 = 14.6, maximum = 48%) than in the fossil

record of core C3 (Fig. 6a).

The high degree of anthropogenic disturbance in

The Coorong (Fluin et al. 2007) has resulted in a lack

of modern analogues, and highlights the problems

associated with attempting to reconstruct pre-distur-

bance environmental conditions in highly modified

ecosystems. Future attempts to generate a suitable

model would benefit from an expansion of the data

set to include more coastal sites from around

Australia, given that suitable analogue sites do not

exist in close proximity to The Coorong.

Foraminiferal distributions

Less than ten foraminiferal taxa were found in

sediments from the Coorong in 2007. Site 2 (Fig. 1)

-2 3

-33

Chl a

pH

TDS

TN

TurbidityDepth

TP

North lagoon South lagoonnear shore off-shore off-shore

Axis 1 (12.8% variance explained)

Axi

s 2

(3.7

% v

aria

nce

expl

aine

d)

Fig. 8 Canonical correspondence analysis biplot of modern

Coorong foraminifera sample scores and the vectors of

significant environmental variables (see Fig. 2 for the sites

that correspond to the sample numbers)

J Paleolimnol (2011) 46:543–560 555

123

was the only site to have abundances of all species

and taxon groups identified in the data set (Fig. 7).

High relative abundances of marine Trochulina sp. at

this site can be explained by the depth of the Goolwa

Channel ([2 m) and a good connection with the

ocean through the Murray Mouth. By contrast, site 4

south of the Murray Mouth (Fig. 1) had fewer

species, and few marine varieties (Fig. 7), despite

being a similar distance from the opening. Although

the Murray Mouth was maintained by dredging from

2001, movement of water southwards to the north

lagoon has been hindered by partial or complete

blockage of the connecting Tauwitcherie Channel

since complete closure in 1981 (Walker 2002)

(Fig. 1). The amount of marine water and organisms

entering The Coorong is therefore likely to have

decreased over the last 10–20 years, which may have

adversely affected foraminiferal recruitment within

the lagoons.

The dominance of euryhaline, halo-tolerant fora-

miniferal taxa (Murray 1991) reflects the present-day

enhanced salinities of The Coorong. Assemblages

south of site 4 include either E. excavatum forma

excavatum or A. aff. aoteana, or both. Except for site

7, all sites south of site 3 in the north lagoon are

dominated by A. aff. aoteana. Moreover, as signified

by the distribution of diatoms, site 8 appears to be the

transition zone wherein only E. excavatum forma

excavatum and A. aff. aoteana are present. Except at

site 10, where Cibicides sp. is abundant, these two

species co-dominate the south lagoon, and species

richness is considerably lower than in the north

lagoon (Fig. 7).

Foraminiferal ecology

In the absence of a reliable transfer function from

which to reconstruct water quality, we utilise the

foraminifera-water quality ordinations (Fig. 8) to

identify associations between species assemblages

and water quality which may be useful for future

qualitative inference of past environments.

In sites close to the Murray Mouth, the percentage of

marine species and species richness is higher. Most

assemblages at sites distant from the mouth are

dominated by two euryhaline species, A. aff. aoteana

and E. excavatum forma excavatum (Figs. 7 and 8).

Sites in the top-left quadrant of the CCA are charac-

terised by an assemblage comprising approximately

30% A. aff. aoteana, 20–40% T. dimidiata in combi-

nation with other marine species, associated with high

pH and lower salinities. The lower-left quadrant of

the ordination contains sites in the north lagoon

exclusively, and the assemblages are dominated by

A. aff. aoteana and E. crispum, exhibiting a positive

relationship with pH and, to a lesser extent, water

depth. The top-right quadrant contains exclusively

sites in the south lagoon where the assemblages are

dominated by A. aff. aoteana and E. excavatum forma

excavatum, with no marine taxa (Fig. 7 and 8). These

assemblages exhibit a strong positive relationship

with salinity, turbidity, Chl a and nutrients (Fig. 8).

Sites in the lower right-quadrant have similar species

assemblages, but slightly higher species richness. The

difference between the two groupings appears to be

related to differences in depth, turbidity, nitrogen and

salinity.

Conclusion

In 2007, the absence of discharges from Lake

Alexandrina may have caused salinity to increase

throughout the year in the north lagoon. In the south

lagoon, however, reductions in salinity during August

and November may have been the product of

groundwater discharge, in combination with rainfall.

Despite the seasonal subtleties, the evaporative

concentration of salts resulted in the characteristic

salinity gradient with increasing distance from the

Murray Mouth in The Coorong. Distinct changes in

the relative abundance of diatoms and, to a lesser

extent, foraminifera were evident along a water-

quality gradient. Canonical correspondence analysis

indicates that both diatom and foraminifera assem-

blages are strongly related to salinity. The type of

sediment differs from site to site in The Coorong, and

future studies may benefit from quantitative analysis

of sediment characteristics and its relationship to

benthic organisms. The derived salinity optima and

tolerances for several diatom species provide new

information on their ecological ranges.

A relatively robust salinity transfer function was

developed from the diatom assemblages, but not from

the suite of foraminifera. However, the down-core

application of the diatom-salinity transfer function

was not in agreement with the history of The

Coorong, a consequence of anthropogenic activities

556 J Paleolimnol (2011) 46:543–560

123

impacting The Coorong environment (see Dick et al.

this volume). Significantly heightened salinity, the

direct result of upstream regulation and excessive

water abstraction in catchments at both ends of The

Coorong, has altered the composition of its modern

biota. These impacts may have decreased foraminif-

eral abundances and contributed to a reduction in

species richness. It appears, therefore, that quantita-

tive reconstruction of salinity in The Coorong and in

Lake Alexandrina cannot be achieved through appli-

cation of the salinity-based models developed in this

study. Future models may function better with the

inclusion of species-environment data from other

coastal regions, though the paucity of research in

estuaries generally, and in Australia in particular,

may prove an impediment. Despite these limitations,

this study has provided ecological information about

diatom and foraminiferal taxa that will be useful in

the qualitative interpretation of down-core trends in

The Coorong and Lower Murray River region.

Acknowledgments This paper is a synthesis of the work

undertaken by the two lead authors for their respective PhD

projects. The project was supported by financial and in kind

contributions from the Department of Water, Land and

Biodiversity Conservation and the Department for

Environment and Heritage (South Australia), and an

Australian Research Council Linkage Grant LP0667819 to

Peter Gell, David McKirdy and John Tibby. We thank

traditional owners, the Ngarrindjeri, for permission to

undertake the work. The assistance of SA Water in accessing

some sites is appreciated. Peter Christie from the Environment

Protection Authority generously loaned the YSI 556

Multiprobe water meter for field use. Field assistance was

provided by Susan and Kathleen Haynes, Fiona Little, Patrick

Maiden, Ashley Natt, Eric Nicholson, Hossain Siddiqui, Jake

and Anne Skinner. Thanks to Ted Thurley, Geoff and Jake

Skinner for manufacturing the vacuum corer used in this

project (the Snikker), and to Eric Nicholson for assistance in its

design. Special thanks are also due to the reviewers whose

extensive suggestions resulted in substantial improvement to

the final manuscript.

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