Figure 3-11: Conceptual isosurfaces of brine situated underneath the Fortescue Valley (looking
west, groundwater salinity is represented as follows: red 100,000 mg/L, orange 50,000 mg/L,
green 10,000 mg/l, pale blue 5,000 mg/L, blue 1,000 mg/L TDS)
Hydrochemical types
The spatial distribution of hydrochemical types based on major ion hydrochemistry is shown on Map 3 -
04. It shows that the majority of samples are of Na-Cl type being consistent with the original rainfall
signature that evolved through widespread evaporative processes in the study area, in particular in
transitional units of the study area in the Fortescue Valley, and, presumably within the Marsh.
Groundwater samples characterising the upland units are available from the Chichester Range and from
the Coondiner sub-catchment in the Hamersley Range. The Ca-Mg-HCO
3
type is dominant, consistent
with water entering the groundwater system from rainfall with low residence times in these areas,
constituting recharge to groundwater.
Some of the samples in the Chichester upland units show increased sulphate concentration that is not
present in samples from the Hamersley Range. This indicates the potential influence of Jeerinah Shale
Formation which has sulphidic mineral enrichment.
On entering the Fortescue Valley the groundwater rapidly becomes chloride -dominated, sometimes with
notable contents of sulphate. These anions are both indicative of strong evaporative processes and
potential role of sulphide oxidation.
Hydrochemical evolution of groundwater from upland recharge producing areas to discharge areas is
also evident from the Piper diagram of different hydrogeological units in the study area (Figure 3-12).
For example, samples from ‘Alluvium’ show evolution from
Ca-Mg-HCO
3
type on the left side of the
Piper diamond to Na-Cl on the right side of the diamond. Samples from all upland units plot within the
left side of the Piper diagram consistent with their position at the beginning of the groundwater cycle.
These include the Brockman Iron Formation, CID and alluvium in upland areas of the Hamersley Range
as well as basalt in the Chichester Range.
The samples from the Paraburdoo Member dolomite are affected by the brine underneath the Fortescue
Valley which is overriding the original dolomite water signature.
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Figure 3-12: Piper diagram of water samples from different hydrogeological units in the study
area
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3.2.9
Key water balance components based on hydrogeological
conceptualisation
The overall water balance for the aquifer system of the study area is focused on the Marsh being the
terminal discharge point of the relatively large catchment area that extends beyond the study area. The
key components of the water balance are related to the hydrological processes observed or assumed to
be working at the Marsh and include surface water groundwater interaction, groundwater recharge and
discharge and changes in groundwater storage.
The presented water balance is considered high-level as there is limited information available on surface
water flows and water level dynamics. The key features and processes, relevant to the Fortescue Marsh
aquifer system, are presented in Figure 3-13 and can be summarised as follows:
Regional aquifers include: the basement (fractured) aquifer(s) (mineralised Marra Mamba
Formation in the Chichester Range and mineralised Brockman Iron Formation in the Hamersley
Range; the Fortescue Valley aquifer (Tertiary Detritals and Wittenoom Formation); and the CID
aquifers associated with major drainage lines within and at the foot of the Hamersley Range.
The main components of groundwater recharge include infiltration of surface runoff and overland
flows from uphill areas in the break of slope zone at the valley margins (Figure 3-13); occasional
Marsh flood recharge, streambed infiltration along the main creeks within the Fortescue Valley and
a small component of diffuse recharge that may reach the watertable in parts of the study area.
The ultimate groundwater discharge point is the Marsh. The groundwater flow direction in the study
area is towards the Marsh, originating from topographically-driven flow in the ranges in the northern
and southern limits of the study area to the topographic low points in the Marsh floor.
The main regional aquifer
situated in the basin’s valley
transmits water towards the Marsh; the
shallow unconfined alluvial aquifer that is intermittently supported or sustained by surface water
infiltration and the deeper confined section, which is a hydraulically connected regionally occurring
calcrete/silcrete and weathered dolomite of the Wittenoom Formation.
The throughflow contribution from the shallow section to the Marsh is considered negligible due to
the low permeability of this generally clayey unit and the flat groundwater gradient. The confined
aquifer component that is subject to upward leakage in the Marsh area is estimated to equate to
about 28 GL/yr, with the majority of inflow incoming from the north of the Marsh. This value is
consistent with the typical estimate of recharge in Pilbara as it equates to slightly over 1% of the
area rainfall.
The groundwater throughflow associated with the two largest surface water inflow components, the
Fortescue River and the Weeli Wolli Creek is estimated at 2 and 8 to 10 GL/yr respectively. The
estimate of the Weeli Wolli Creek throughflow is provided at its outflow point from the Fortescue
Range.
The groundwater flow component in the Marsh area is generally lost to soil evaporation and
transpiration since the potential evapotranspiration rates greatly exceed the rate of upward flow.
This process locks the salt load underneath the Marsh creating a hypersaline brine that migrates
downward due to its higher density.
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Figure 3-13: Hydrogeological conceptualisation of the Fortescue Marsh
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4
Ecohydrological conceptualisation
4.1
Regional receptor assessment
4.1.1
Landscape EHUs
All nine EHUs are represented in the landscapes of the Fortescue Marsh study area as described in
Section 1.3.3 (See also Table 4-1 and Map 4-01).
Upland areas (EHUs 1 and 2) are principally associated with the peaks, ridges and slopes of the
Hamersley and Chichester Ranges. Within EHU 1, dendritic drainage networks emanating from the
ranges aggregate into more substantial drainage floors (EHU 3) and channels (EHU 4). EHU 2 includes
sloping land down-gradient from EHU 1, and also other low hills and rises across the Fortescue Valley.
These areas are often dissected by ephemeral creeks with small drainage floors (EHUs 3 and 4), which
may further coalesce before feeding into lowland areas. Lowland areas include the extensive alluvial
flats of the Fortescue Valley (EHU 6), sandplains adjacent to the foothills of the Hamersley Range and
western flank of the Upper Fortescue River (EHU 5), and calcrete plains abutting the margins of the
Fortescue Marsh (EHU 7).
Major channel systems (EHU 8) are associated with the Upper Fortescue River, the Weeli Wolli, Mindy
Mindy and Coondiner Creeks deriving from the Hamersley Range, and Kondy Creek d eriving from the
Chichester Range.
The Fortescue Marsh (EHU 9) is the vast terminus for surface inflows from the Upper Fortescue River
and other creek systems. A number of small claypans (EHU 9) provide localised drainage termini on the
extensive alluvial and calcrete flats south of the Fortescue Marsh. West of the Goodiadarrie Hills, a
series of freshwater claypans (EHU 9) occur within the Coolibah Land System (EHU 8) proximal to
Fortescue River.
In addition to the Marsh and Lake Bed Land System mapping units, additional EHU 9 areas were
defined based on Quaternary Lacustrine (Ql) 1:250,000 geology mapping; and claypans associated with
the Freshwater Claypans of the Fortescue Valley PEC. Within the study area, these alternative mapping
units provide greater resolution of drainage termini than the land system mapping undertaken by Van
Vreeswyk et al. (2004).
4.1.2
Identification of ecological receptors
Ecological assets in the study area which display a high level of connectivity are considered to be
ecological receptors. These include Fortescue Marsh and the Freshwater Claypans of the Fortescue
Valley PEC (Map 4-01 and Map 4-02). These are discussed in the following sections.
Ecological assets considered to have a low level of ecohydrological connectivity and therefore
considered not to be ecological receptors, are summarised as follows:
Flora of conservation significance such as Lepidium catapycnon (Declared Rare Flora) and
various priority flora taxa recognised by DPaW, which do not occur in EHUs 8 and 9. Such flora
are considered to be xerophytic (i.e. their water use requirements are met by direct and locally
redistributed rainfall).
Fauna species of conservation significance whose habitat requirements are not strongly
dependent on, or otherwise intimately associated with, the Fortescue Marsh and /or the
Freshwater Claypans of the Fortescue Valley PEC. These include the Australian Bustard, Bilby,
Bush Stone-curlew, Mulgara, Northern Quoll and Western Pebble-mound Mouse.
Fortescue Valley Sand Dunes PEC
–
principally associated with EHU 5, below the northern
flanks of the Hamersley Range. The PEC includes red, linear sand dunes dominated by open
shrubland vegetation communities that are atypical for the Pilbara. It does not receive significant
surface inflows from beyond its boundaries. Groundwater is deep a nd disconnected from the
surface ecosystem. Potential threatening processes include weed invasion (principally by Buffel
Grass) and erosion.
Mosquito Land System PEC - occurs in EHU 2 near the eastern boundary of the study area. It is
distant from any current or future proposed BHP Billiton Iron Ore mining developments and
therefore has not been considered further as a key receptor.
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Wona Land System PEC - occurs in EHU 2, on upland basaltic plains along the northern
western fringe of the study area. It does not receive significant inflows from beyond its
boundaries, and is up-gradient from BHP Billiton Iron Ore
’s Roy Hill mining tenements.
Groundwater is deep and disconnected from the surface ecosystem. Potential threatening
processes include weed invasion, grazing and changes in fire regime.
Brockman Iron cracking clay communities of the Hamersley Range PEC - occurs in EHU 6; in the
upper part of a small catchment area west of the Goodiadarrie Hills. Groundwater is deep and
disconnected from the surface ecosystem. Although run-on from surrounding areas may be
important for sustaining the Tussock grassland vegetation community in this PEC, the catchment
source areas are localised and disconnected from any current or future proposed mining
developments.
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Table 4-1: Summary of EHUs within the study area
EHU
Percent
study area
Distribution in study area
Component land systems
1
27%
The Hamersley Range along the southern margin of the study area (predominantly the
Newman Land System).
The Chichester Range along the northern margin of the study area (predominantly the McKay
Land System).
Capricorn; Granitic; McKay; Newman; Rocklea; Kumina; Robe;
Laterite; Table
2
8%
Northern foot slopes of the Hamersley Range (predominantly the Boolgeeda Land System).
Eastern periphery of the Chichester Range (predominantly the Elimunna Land System).
Adrian; Billygoat; Bonney; Boolgeeda; Egerton; Elimunna; Mosquito;
Platform; Wona
3
1%
Drainage floors within EHUs 1 and 2
Within EHU 1: Capricorn; Granitic; McKay; Newman; Rocklea;
Kumina; Robe; Laterite; Table
Within EHU 2: Adrian; Billygoat; Bonney; Boolgeeda; Egerton;
Elimunna; Mosquito; Platform; Wona
Channel beds and banks accept and store water during flow events.
Large flows are transmitted down-gradient.
Channels may support intermittent or persistent pools replenished
by flood flows.
4
1%
Major channels within EHUs 1 and 2
5
9%
Disjunct areas on the flats north of the Hamersley Range. Widespread occurrence in the east
of the study area, south of the Fortescue River.
Divide
6
37%
Widespread on the alluvial flats of the Fortescue Valley, north (predominantly Cowra,
Jamindie and Turee Land Systems) and south (predominantly Fan, Marillana and Turee Land
Systems) of the Fortescue Marsh.
Brockman; Christmas; Cowra; Fan; Jamindie; Jurrawarrina;
Marillana;
Narbung;
Pindering;
Spearhole;
Turee;
Urandy;
Wannamunna; Washplain
7
4%
Widespread along the southern margin of the Fortescue Marsh (predominantly the Calcrete
Land System).
Calcrete; Warri
8
4%
Associated with major drainage lines existing the Hamersley Range (Weeli Wolli, Mindy
Mindy, Coondiner creeks) and the Chichester Range (Kondy Creek in the north east). Also
associated with the extensive floodplain of the Fortescue River upstream from the Fortescue
Marsh.
Coolibah; Fortescue; River
9
8%
The Fortescue Marsh is the dominant feature.
Small claypans and ephemeral lakes classified as EHU 9 occur on the calcrete and alluvial
flats south of the Fortescue Marsh, and west of the Goodiadarrie Hills.
Marsh; Lake Bed
Also includes Quaternary Lucustrine (Ql) 1:250,000 geology
mapping units; and claypans associated with the Freshwater
Claypans of the Fortescue Valley PEC.
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4.2
Ecological receptor
–
Fortescue Marsh
While earlier sections have described aspects of the regional setting hydrology and ecology of the
Fortescue Marsh, it is useful here to focus on, and restate, the specific attributes of the Marsh itself. The
ecological values of the Marsh are presented in Sections 4.2.1 to 4.2.3. Hydrological and
ecohydrological aspects are then discussed in later sections.
4.2.1
Overview
The Marsh is a brackish to saline, endorheic wetland formed in the drainage terminus of the Upper
Fortescue River. It is a unique regional-scale landscape feature, extending for approximately 100 km
along the Fortescue Valley with a width of typically 3 to 10 km.
The Marsh landform consists of sparsely vegetated, clay flats fringed by samphire vegetation
communities (Figures 4-1 to 4-6). The Marsh boundary is approximately defined by the Marsh Land
System described by van Vreeswyk et al. (2004). Bed levels in the Marsh lie between 400 m and
405 m AHD, and the samphire vegetation typically extends to about 407 to 408 m AHD.
The Marsh becomes inundated episodically in association with cyclonic rains, surface runoff and
flooding. Following the largest events floodwaters may persist for several months, providing breeding
and foraging habitat for waterbirds and other biota. Surface waterbodies in the Marsh rapidly evaporate,
providing a mechanism for salt accumulation that has probably been occurring for hundreds of millennia
(Skrzypek et al. 2013). Beneath the Marsh, the groundwater is hypersaline.
The Marsh bed comprises saline and sodic clays. Shallow calcrete and silcrete hardpans (within the
upper 150 cm of the soil profile) are common in the vegetated Marsh periphery. The upper sediments
support a shallow groundwater system, with the depth to watertable during inter-floods probably set by
an evaporation extinction depth of a few metres. Deep Tertiary sediments beneath the Marsh host a
series of variably connected aquifer systems, with heavier clay sequences functioning as aquitards.
The spatial scale of the Marsh is a key factor defining its ecohydrological attributes and potential
susceptibility to hydrological change. The Marsh has a wide range of ecological values summarised as
follows:
classified as a wetland of national importance within the Directory of I mportant Wetlands in
Australia;
recognised as a nationally important Bird Area (Dutson et al. 2009); supporting multiple species
subject to international treaties (e.g. JAMBA, CAMBA, ROKAMBA);
the Marsh Land System is recognised as a Priority Ecological Community (Priority 1) by the
Department of Parks and Wildlife (DPaW 2013);
provides habitat for rare flora (endemic Eremophila, Tecticornia and other Priority species);
provides habitat for rare vertebrate fauna (possibly including the critically endangered Night
Parrot (Pezoporus occidentalis); and
provides habitat for rare invertebrate fauna (locally restricted aquatic invertebrates ).
These values collectively contribute to the Marsh’s high conservation status. In 2013
, the Environmental
Protection Authority (EPA) published information and management guidance for protecting the water
regime and ecological values of the Marsh (EPA Report 1484; EPA 2013). Further details on specific
ecological values of the Marsh are provided in the EPA guidance document.
The Marsh has a history of pastoral land use since the late 19
th
century and remains accessible to cattle
at present. However, large portions of the Marsh have been identified for transition into conservation
tenure and management in relation to the expiry of Western Australian pastoral leases in 2015.
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Figure 4-2: A University of Western Australia research plot in samphire vegetation near the
northern fringe of the Marsh
–
photograph: D. Huxtable
Figure 4-1: Saline clay flats in the Marsh interior (recently established samphire on the
dry lake bed during a dry phase probably won’t survive the next major inundation
event)
–
photograph: D. Huxtable
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Figure 4-3: Samphire vegetation in the outer Marsh with a patch of Melaleuca glomerata
woodland in the background
–
photograph: D. Huxtable
Figure 4-4: The boun
dary of samphire vegetation (in this case ≈407.5 m
AHD) is typically abrupt
and probably aligns with zones of seed dispersal by floods
–
photograph: D. Huxtable
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Figure 4-5: Lignum (Muehlenbeckia florulenta) shrubland in the outer Fortescue Marsh
–
photograph: D. Huxtable
Figure 4-6: A drainage line fringed by Salt Water Couch entering the Fortescue Marsh
–
photograph: D. Huxtable
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4.2.2
Previous work
Geology and groundwater investigations
Information on the stratigraphy beneath the Marsh is limited. The current hydrogeological
conceptualisation is principally based on extrapolation of drilling information from the greater Fortescue
Valley. Skrzypek et al. (2013) presented a conceptual geological model of the broader Fortescue Valley,
as part of their recent study examining hydrological processes controlling groundwater salinity in the
Marsh.
Fortescue Metals Group (FMG) is a key custodian of geological and hydrogeological information
relevant to the Marsh. FMG has established a large bore network nested piezometers in areas north of
the Marsh associated with the Cloudbreak and Christmas Creek mining operations. FMG has also
undertaken investigations associated with the Nyidinghu project, south of the Marsh. Some of the
information compiled by FMG is in the public domain as part of environmental impact assessment
documentation (e.g. ENVIRON, 2005; FMG, 2011a; FMG, 2011b). This includes a Marsh
hydrogeological conceptualisation that was included in EPA Report 1484 (EPA 2013).
Additional information relating to the eastern end of the Marsh has been gathered by Hancock
Prospecting Pty Ltd (HPPL) for the Roy Hill project. Some data is available through environmental
impact assessments such as MWH (2007); MWH (2009); ENVIRON (2009). A recommendation
document by the EPA (2011) commented on Roy Hill project impacts on vegetation in the area. RHIO is
currently developing groundwater resources in the eastern part of the study area; however, relevant
information is not in the public domain.
Finally, Rio Tinto has recently undertaken a drilling program including areas of the Marsh in association
with Australian Research Council (ARC) Linkage Project LP120100310 (refer to Section 4.2.2.3. below).
The evaluation of results is on-going and not publically available.
Surface hydrology
An understanding of flood levels in the Marsh is limited to data from the Roy Hill streamflow gauging
station (Ref. S708008), which operated during the period September 1973 to September 1986 and was
located at the eastern edge of the Marsh (Map 3-01). This data has been augmented by anecdotal
observations made by land managers. The main flow channel bed level at the gauging station was
around 405.5 m AHD and during the 13 years of record, the maximum recorded water level was 408.75
m AHD, observed in February 1980 (Aquaterra, 2005). The gauged water level corresponded with a
peak storage level of 406.5 m AHD in the Marsh (downstream) and occurred after two consecutive
cyclones. Based on observations made by mining company personnel, large floods in the early 1970s
caused Marsh inundation levels up to the level of the existing BHP Billiton Iron Ore railway track
(Aquaterra 2005).
The impact of the Ophthalmia Dam on the flow regime of the Upper Fortescue Catchment was
investigated by Payne and Mitchell (1999). The dam captures water from three of the 15 major
tributaries of the Fortescue River, intercepting long term median inflows of about 30 GL. The dam do es
not prevent large flows from reaching downstream areas (Florentine, 1999), but has reduced flow
volumes, peak flows, flooded width and frequency of flooding on the downstream floodplain (Payne and
Mitchell, 1999). In particular it appears to have prevented or reduced medium-sized flows (recurrence
interval of one to three years) from reaching the downstream floodplain. The effect of this flow
attenuation diminishes with distance towards Roy Hill, but was detectable at the eastern edge of the
Marsh near Roy Hill.
As a component of the Roy Hill Stage 1 Public Environmental Review (PER), Gilbert and Associates
(2009) derived an indicative water balance for the Marsh, summarised as follows:
estimated total basin capacity of the Marsh is 10,000 GL;
estimated surface inflows to the Marsh in a median rainfall year is 300 GL;
the storage capacity of the Marsh greatly exceeds inflows, even under extremely high rainfall
scenarios;
evaporation equals or exceeds runoff inflows in most months, such that in typical yea rs inflows
mostly evaporate within weeks to months (i.e. are not carried over the following dry season); and
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groundwater inflows were considered to be a small, insignificant component of the water
balance (estimated to be 6 GL/yr based on analysis of data from gauged catchments in the
eastern Pilbara).
ARC Linkage Projects relating to the Fortescue Marsh
In the period 2008 to 2011, an Australian Research Council (ARC) research project entitled
“Ecophysiology of stem succulent halophytes subject to changes i
n salinity and water availability:
distinguishing natural dynamics from potential mine related impacts” was undertaken by the UWA
School of Plant Biology, in collaboration with the WA Herbarium and with industry funding support from
Fortescue Metals Group (ARC Linkage Project LP0882350). The project was managed by Prof. Tim
Colmer (UWA) and Prof. Erik Veneklaas (UWA), with the experimental work largely implemented by PhD
student Louis Moir-Barnetson.
The project had the following objectives:
identify the dominant samphire species that are present in the Marsh and environmental factors
that explain their distribution pattern;
relate samphire population dynamics with the dynamics of water availability (flooding and water
deficit) and salinity, as related to weather conditions (rainfall, air temperature, and evaporative
demand);
relate key plant health indicators, including transpiration, water status, ionic relations, organic
osmolytes, pigment composition (chlorophyll and photoprotective carotenoids) and chlor ophyll
fluorescence, with varying levels and combinations of stress factors (salinity, drought, flooding)
under field conditions; and
rigorously test, in controlled environments with defined treatments, hypotheses developed during
the field work regarding physiological processes contributing to resistance of salinity, drought,
and flooding, and also to ascertain reliable early-warning stress indicators.
Project work included the following components (pers. comm. Dan Huxtable, Equinox Environmental Pty
Ltd 2014):
Field observations of climatic, soil and samphire ecology/ecophysiology parameters conducted
at two locations near the northern margin of the Marsh over a three year period (commencing in
October 2008). At each location, a transect of replicated 20 x 20 m plots was established that
spanned an ecological gradient with respect to soil water and salinity dynamics, depth to
watertable and frequency of flooding within the Marsh ecosystem. Manual installation of shallow
piezometers was attempted in the each of the plots; however impenetrable silcrete hardpans
were invariably encountered within 120 cm of the surface.
Controlled glasshouse experiments were undertaken to test the responses of major marsh
samphire species to the individual and combined effects of salinity, water deficit, flooding.
Several journal papers related to the project have been published including:
a major review of halophyte physiology and salinity tolerance (Flowers and Colmer, 2008);
a review of halophyte flooding tolerance (Colmer and Flowers, 2008);
a review of flooding tolerance in plants (Colmer and Voesenek, 2009); and
taxonomic work with the formal description of two new samphire species from the Marsh
(Tecticornia globulifera and Tecticornia medusa) (Shepherd and van Leeuwen, 2011).
Additional journal papers are at an advanced stage of preparation (pers. comm. E. Veneklass, UWA
2014). The proposed paper titles include:
‘Submergence tolerance in stem
-succulent halophytes is associated with resistance to the
osmotic swelling and rup
turing of shoot tissues’;
‘The distribution and population dynamics of stem
-succulent halophytic shrubs (Tecticornia
species) at an ephemeral inland salt lake in arid-
zone northwest Australia’;
‘Ecophysiological responses of
Tecticornia species to seasonal
changes at Fortescue Marshes’;
and
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Drought tolerance of three Tecticornia stem succulent halophytes of an inland arid-zone salt lake
system’.
In 2012, an Australian Research Council (ARC) research project entitled “Climate
-related regime shifts
in inland semi-
arid ecosystems through ecohydrological proxies” was commenced by the UWA School of
Plant Biology with industry funding support from Rio Tinto under ARC Linkage Project LP120100310.
The project aims to investigate the dynamics of climate, especially r ainfall, of the northwest of Australia
over the last few thousand years through analysis of stable isotopes in surface water and groundwater,
sediment cores (in the Marsh) and tree rings. The project has a 3 -year duration.
As part of the project Rio Tinto has established a series of nested piezometers in and adjacent to the
Marsh, which in combination with existing FMG bores provide pseudo-grid coverage along the east-west
and north-south axes of the Marsh. The drilling methods have enabled the recovery of sediment cores
from the upper profile of the Marsh for geochemical analysis .
To date a journal paper has been released discussing hydrological processes controlling the salinity of
the Marsh (Skrzypek et al., 2013). Several additional journal papers are pe nding publication in 2014,
including a paper addressing the flooding regime of the Marsh ( pers. comm. Pauline Grierson, UWA
2014). This information is anticipated to greatly improve understanding of the Marsh flooding dynamics.
DPaW Marsh assessments
In April 2008, the then Department of Environment and Conservation (now DPaW) completed a resource
condition assessment of selected wetlands of the Fortescue River system, including the Marsh, as part
of the Department’s Inland Aquatic Integrity Resource Condit
ion Monitoring project (DEC, 2009).
Field investigations were carried out at three locations within the Marsh boundary (Fortescue Marsh
West, Moorimoordinina Pool and Fortescue Marsh East). The assessment included:
vegetation species and percentage cover;
water quality of Moorimoordinina Pool (note that the other locations had no standing water at the
time of sampling); and
aquatic invertebrates in Moorimoordinina Pool.
In addition, DPaW has recently commenced a floristics survey of the Marsh, with fund ing support from a
Fortescue Metals Group environmental offset. The survey is scheduled for completion in mid -2015
(pers. comm. Dr Stephen van Leeuwen, DPaW 2014) and no survey findings are available at the
present time.
Vegetation, flora and fauna surveys by other parties
FMG is the only mining company to have commissioned vegetation and flora surveys over portions of
the Marsh. This work has focused on the northern margins of the Marsh near the Cloudbreak and
Christmas Creek project areas. The key survey reports in the public domain include:
ENV Australia (2010) - Christmas Creek Flora and Vegetation Assessment, Prepared for Fortescue
Metals Group Ltd, ENV Australia Pty Ltd, Perth.
Mattiske Consulting Pty Ltd (2007) - Flora and Vegetation near Fortescue Marshes, Prepared for
Fortescue Metals Group Ltd, Mattiske Consulting Pty Ltd, Perth.
These surveys found that the Marsh includes multiple samphire vegetation types, with zonal distribution
patterns evident for the major samphire taxa. Small patches of Melaleuca glomerata woodland have also
been noted south of Christmas Creek and along southern margins of the Marsh ( Figure 4-3).
4.2.3
Ecological description
Wetland type
As detailed in Section 4.2.1 the Marsh is recognised as being a unique and extensive inland fl oodplain
system within the Pilbara Region (McKenzie et al., 2009). The samphire shrubland is the largest
ephemeral wetland in the Pilbara Bioregion.
In terms of a modified version of the international Ramsar Classification System for Wetland Type
(Environment Australia, 2001), the Marsh includes two wetland types:
Ecohydrological Conceptualisation of the Fortescue Marsh Region
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Type B4: Riverine floodplains; includes river flats, flooded river basins, seasonally flooded grassland,
savanna and palm savanna; and
Type B6: Seasonal/intermittent freshwater lakes (>8 ha), floo dplain lakes.
Vegetation and flora
Much of the interior of the Marsh consists of sparsely vegetated clay flats, within a series of low
elevation flood basins. Vegetation recruitment may occur in these areas during dry phases; however, the
frequency and depth of inundation events is a constraint to long term vegetation persistence.
In slightly more elevated areas fringing the bare flats, samphire ( Tecticornia spp.) vegetation
communities are prevalent. Tecticornia medusa (Priority 1) is prominent in down-gradient areas deep
within the Marsh (about 1 to 1.5 km from the Marsh boundary). Further up -gradient T. auriculata, T. sp.
Christmas Creek (K.A. Shepherd and T. Colmer et al. KS 1063) (Priority 1) and/or T. sp. Dennys
Crossing (K.A. Shepherd and J. English KS 552) tend to be dominant taxa. Tecticornia indica subsp.
bidens is the pre-eminent species in up-gradient areas near the Marsh ecophysiographic boundary,
where it may grow in association with Eremophila spongiocarpa (Priority 1).
Patchy shrublands of Lignum (Muehlenbeckia florulenta) and False Lignum (Muellerolimon
salicorniaceum) often grow in association with the samphire communities and Atriplex flabelliformis
(Priority 3). These shrublands provide additional structural complexity. Small patches of Melaleuca
glomerata woodland also occur, and may provide an important structural element for waterbird roosting
and nesting (Figure 4-3).
Following large rain events and floods a variety of annual and ephemeral species emerge with some of
elevated conservation status (e.g. Nicotiana heterantha - Priority 1; Peplidium sp. Fortescue Marsh (S.
van Leeuwen 4865)
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Priority 1). Salt Water Couch (Sporobolus virginicus) and Buffel Grass
(*Cenchrus ciliaris) also occur in places near the Marsh periphery, associated with drainages entering
the Marsh.
The Marsh provides difficult growing conditions for vegetation owing to the combined stresses of
seasonal drought, soil salinity, waterlogging and inundation. In some areas shallow hardpans also
restrict samphire root depth. Flooding events dissolve and redistribute evaporitic salts that have
concentrated during dry phases, creating dynamic conditions for vegetation with respect to salinity
exposure.
Little information is available on the population dynamics of the samp hire vegetation communities;
however, the following observations by UWA scientists involved in ARC Linkage Project LP0882350 are
notable (pers. comm. Dan Huxtable, Equinox Environmental Pty Ltd 2014):
The major samphire taxa appear to be slow growing and long lived.
Samphire transpiration flux rates are low (i.e. relatively low water use), suggesting a
conservative water use strategy limited by the difficult growing conditions.
Seed dispersal and recruitment is likely to be controlled by the flood regime. Floodwaters are
likely to contribute to samphire recruitment by providing favourable conditions for germination
and seedling establishment. Inundation is also possibly a significant mortality factor for small
plants.
Fauna
The Marsh provides important breeding and foraging habitat for waterbirds (McKenzie et al., 2009).
Notable species that utilise the Marsh include the Australian Pelican ( Pelecanus conspicillatus) and
Black Swan (Cygnus atratus). According to DPaW, there were between 260,000 and 276,000 in dividuals
from 47 species of wetland birds observed when the Marsh was inundated in 1999 and 2003 (pers.
comm. Dr Stephen van Leeuwen DPaW).
Between 2005 and 2009, Birds Australia undertook an assessment of Australian locations with global
significance for bird conservation (Dutson et al.
2009). These locations are referred to as “important bird
areas” (IBAs). The Marsh was one of 314 Australian sites classified as an IBA. The findings of the
assessment included the statement “
The Fortescue Marsh IBA in Western Australia floods about once
every ten years and have supported more than one per cent of the world population of 14 waterbird
species
”. Twenty
-three globally-important bird species were reported to use the Marsh (Table 4-2)
(Dutson et al. 2009).
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The functionality of the Marsh as an important waterbird habitat needs to be considered in a regional
and national context. From an ecological perspective, the Marsh is one component of a network of
wetlands across Australia. As a collective of geographically dispersed wetlands, the network enables
bird populations to be sustained from year to year, despite much longer scale flooding and drought
cycles in individual wetlands. This concept is well described by Olsen and Weston (2004), restated as
follows:
“
Improved knowledge of waterbird distributions in Australia is showing that the arid zone is an important
nursery for waterbirds, something that was poorly recognised as recently as 25 years ago. The use of
arid zone wetlands in Western Australia is in the early stages of documentation, but Lake Gregory,
Fortescue Marsh and Mandora Marsh in the north, together support over a million waterbirds during the
late dry season in some years and are important breeding sites. However, it must be emphasised that
Fortescue and Mandora Marsh flood only occasionally, so that waterbird populations are maintained
only if other suitable wetlands in the arid zone, or elsewhere, are flooded when these lakes are dry.
Thus, it is important to ensure that a network of big wetlands wit h high waterbird carrying capacity,
throughout the arid zone and elsewhere, is conserved
”
Contemporary records have been made of the Critically Endangered
16
Night Parrot ( Pezoporus
occidentalis) near the Marsh (David and Metcalf, 2008). The low halophytic s amphire shrubland habitat
provided by the Marsh, in combination with surrounding hummock grasslands, may provide favourable
habitat for this species (McDougall et al. 2009). The Australian Bustard ( Ardeotis australis) is also found
at the margins of the Marsh (Davis et al. 2005).
A number of conservationally significant fauna species have been recorded in areas fringing the Marsh
including the Bilby ( Macrotis lagotis), Northern Quoll ( Dasyurus hallucatus) and Mulgara ( Dasycercus
cristicauda) (Davis et al. 2005). The significance of the Marsh habitat for these species is unclear;
however, it may contribute to their foraging range.
The Marsh hosts aquatic invertebrate assemblages of conservation interest, and several endemic taxa
of macro-invertebrates are known only from the Marsh. As part of the Pilbara Biological Survey
17
, two
areas near the western and eastern ends of the Marsh respectively were sampled for aquatic invertebrates
in the period 2003 to 2006 (Pinder et al., 2010). Several potentially endemic sp ecies were collected
including a variant of the rotifer Brachionus angularis, a new Alona cladoceran and a new Ainudrilus
oligochaete. Additional taxa recorded at the Marsh were only collected from one other location at
Weelarrana Salt Marsh including a new Mytilocypris ostracod and Coxiella snails. No information is
available on the ecological requirement of these taxa.
The Marsh has not been sampled for stygofauna owing to a lack of bores. However, areas north of the
Marsh associated with FMG Chichester Projects have been sampled (Bennelongia 2007), and also
areas east of the Marsh associated with Roy Hill Project ( HPPL, 2009). Several stygofauna and
troglobiotic taxa were collected in these studies. In each case, the subterranean fauna communities
were found to be relatively poorly developed in comparison with other locations in the Pilbara. None of
the taxa collected and identified at these locations were regarded as having conservation significance.
The Marsh includes a number of persistent pools associated with drainage scours along the Fortescue
River channel and other major channel inflows. These are probably sustained by storage in the
surriounding Marsh sediments after flood events. The pools could potentially function as refugia for
some aquatic fauna species during interfloods.
16
Under both the Wildlife Conservation Act 1950 and the Environment Protection and Biodiversity
Conservation Act 1999.
17
Further detail on the Pilbara Biological Survey is provided in MWH, 2014.
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Table 4-2: Globally-important bird populations in the Fortescue Marsh Important Bird Area
Source: Atlas of Australian Birds
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