Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
Our ref: FM-EcoConcept_v8.docx
quality from deeper zones is equally important. The collection of samples portrayed on maps 3 -04 and 3-
05 is sourced from the shallowest horizon where feasible so that these are mo re suitable for
ecohydrological purposes.
Data quality for most of the bores (as determined from ionic balance) is deemed to be acceptable
(considering major cations and anions) as the majority of samples have ionic balances in the range of 5%
to 10% or less.
From hydrogeochemical perspective the available samples typically do not report silica concentrations
which could be an important parameter for hydrogeochemical modelling of groundwater chemistry
evolution that involves important rock-forming silicate minerals.
Analyses of metals (where available) have been typically done after acid preservation but were not
focused on determination of redox species (such as Fe
III
/Fe
II
, Mn
IV
/Mn
II
).
An additional hydrochemical dataset that also includes stable isotopes of
18
O and D has been recently
published by Dogramaci and others (2012) and Skrzypek and others (2013).
Ecology
Land systems
The study area and surrounds was jointly surveyed by the Western Australian Departments of Agriculture,
Land Administration and La
nd Information in the mid 1990’s, as part of a wider rangeland resource survey
for the Pilbara region (Van Vreeswyk et al. 2004). This included the delineation and description of land
systems, broadly defined as “areas with a recurring pattern of topograph y, soils and vegetation”. Over 100
land systems are recognised in the Pilbara region. Land system information is useful for broad scale
assessment of surficial regolith characteristics (e.g. soil depth and composition), vegetation types and
fauna habitat types. The land systems that occur across the study area are shown in Map 2-07.
The Pilbara land system mapping was principally based on interpretation of 1:50,000 aerial photographs,
supplemented with other published data (
e.g. geology, vegetation and previous land and soil surveys) and
relatively limited field observations (Van Vreeswyk et al. 2004). This allowed the
spatial extent of each land
system to be defined. Descriptive information for each land system addresses:
geology;
geomorphology/landform;
soils; and
vegetation.
Within each land system a series of land units are described, including estimates of their proportional
contribution to the land system spatial extent. Each unit is associated with ecological site types described
according to their particular combination of topographic position, land surface, dominant plant species and
vegetation formation.
Van Vreeswyk et al. 2004 also grouped the land systems into 18 land surface types according to a
combination of more generic landforms, soils, vegetation and drainage patterns. This provides information
more suitable for regional scale assessments.
Vegetation and flora
Considerable descriptive information for vegetation types and flora assemblages from sites within the
study area is available. This has mainly been collected in association with mining and infrastructure
projects. Over the past decade most surveys have been undertaken in accordance with EPA Guidance
Statement 51, which provides minimum standards for different survey types (principall y Level 1 and Level
2). The standards under which older surveys were conducted may be more variable.
At a broader scale vegetation was mapped at a scale of 1:1,000,000 in the 1970’s (Beard 1975). The
Beard (1975) mapping is available digitally, but in som e cases may be offset from its true position. The
land system mapping of Van Vreeswyk et al. (2004) is generally considered to better depict broad
vegetation type boundaries.
Most survey reports include distribution maps for vegetation units and location d ata for species and
vegetation communities of interest. Information relating to vegetation functional ecology (e.g., vegetation
water use dynamics) is generally limited.