Fortescue Marsh Research Articles

Using Genetics to Evaluate the Success of a Feral Cat (Felis catus) Control Program in North-Western Australia.

Simple SummaryThe management of invasive species is a major challenge for the conservation of biodiversity globally. One technique that has been widely used to control feral cats (Felis catus) and red foxes (Vulpes vulpes) in Western Australia is the aerial broadcast of toxic baits, but assessing its efficacy can be difficult. Here, we report on a method of evaluating the effectiveness of this method for the abatement of feral cats using genetic analysis techniques. However, our results were unable to provide robust evidence that, over a five-year program, baiting had a detrimental impact on both genetics and demography in this population, and the results were not significant. Monitoring the impact of control programs in this way may provide valuable information to managers on the effectiveness of their management strategy, but further refinement of the methodology is recommended.The feral cat has been implicated in the decline and extinction of many species worldwide and a range of strategies have been devised for its control. A five-year control program using the aerial broadcast of toxic Eradicat® baits was undertaken at Fortescue Marsh in the Pilbara region of north-western Australia, for the protection of biodiversity in this important wetland area. This program has been shown to have had a significant detrimental effect on cats in this landscape, but the long-term impact is difficult to ascertain. We assessed population genetics across three cohorts of feral cats sampled as part of the control program. We also compared cat populations in natural habitats and around human infrastructure. A key challenge in any study of wild animal populations is small sample sizes and feral cats are particularly difficult to capture and sample. The results of this study superficially appear to suggest promising trends but were limited by sample size and many were not statistically significant. We find that the use of genetic techniques to monitor the impact of invasive species control programs is potentially useful, but ensuring adequate sample sizes over a long enough time-frame will be critical to the success of such studies.

Evaluating the efficacy of a landscape scale feral cat control program using camera traps and occupancy models

The impact of introduced predators is a major factor limiting survivorship and recruitment of many native Australian species. In particular, the feral cat and red fox have been implicated in range reductions and population declines of many conservation dependent species across Australia, including ground-nesting birds and small to medium-sized mammals. The impact of predation by feral cats since their introduction some 200 years ago has altered the structure of native fauna communities and led to the development of landscape-scale threat abatement via baiting programs with the feral cat bait, Eradicat. Demonstrating the effectiveness of broad-scale programs is essential for managers to fine tune delivery and timing of baiting. Efficacy of feral cat baiting at the Fortescue Marsh in the Pilbara, Western Australia was tested using camera traps and occupancy models. There was a significant decrease in probability of site occupancy in baited sites in each of the five years of this study, demonstrating both the effectiveness of aerial baiting for landscape-scale removal of feral cats, and the validity of camera trap monitoring techniques for detecting changes in feral cat occupancy during a five-year baiting program.

Paleoenvironmental and paleohydrochemical conditions of dolomite formation within a saline wetland in arid northwest Australia

Groundwater dolocrete occurring within the Fortescue Marsh, a large inland wetland in the Pilbara region of northwest Australia, has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the Quaternary Period. Two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete, based on differences in depth, δ18O values and mineral composition. Group 1 (G1) occurs at depth 20–65 m b.g.l. (below ground level) and contains stoichiometric dolomite with δ18O values of −4.02–0.71‰. Group 2 (G2) is shallower (0–23 m b.g.l.), occurring close to the current groundwater level, and contains Ca-rich dolomite ± secondary calcite with a comparatively lower range of δ18O values (−7.74 and −6.03‰). Modelled δ18O values of paleogroundwater from which older G1 dolomite precipitated indicated highly saline source water, which had similar stable oxygen isotope compositions to relatively old brine groundwater within the Marsh, developed under a different hydroclimatic regime. The higher δ18O values suggest highly evaporitic conditions occurred at the Marsh, which may have been a playa lake to saline mud flat environment. In contrast, G2 dolomite precipitated from comparatively fresher water, and modelled δ18O values suggested formation from mixing between inflowing fresher groundwater with saline-brine groundwater within the Marsh. The δ18O values of the calcite indicates formation from brackish to saline groundwater, which suggests this process may be associated with coeval gypsum dissolution. In contrast to the modern hydrology of the Marsh, which is surface water dependent and driven by a flood and drought regime, past conditions conducive to dolomite precipitation suggest a groundwater dependent system, where shallow groundwaters were influenced by intensive evaporation.

Groundwater seepage controls salinity in a hydrologically terminal basin of semi-arid northwest Australia

Very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments. However, this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds. In this study, we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the Fortescue Marsh (FM), one of the largest wetlands of semi-arid northwest Australia (∼1100km2). The groundwater outflow from aquifers underlying the FM to the Lower Fortescue catchment is constrained by an extremely low hydraulic gradient of <0.0001anda small ‘alluvial outlet’ of 0.35km2 because of relatively high bedrock elevation. However, FM groundwater salinity is far below saturation with respect to halite (TDS<160g/L), episodic flood water is fresh to brackish, and salt efflorescences are very sparse and evident only when the FM is dry. We show that if the FM was 100% “leakage free” i.e., a true terminal basin, groundwater would have achieved halite saturation (>300g/L) after ∼45ka. We calculated that only a very small seepage of ∼2GL/yr (∼0.03% of the FM water volume) is sufficient to maintain current salinity conditions. The minimum time required to develop the current hydrochemical groundwater composition under the FM ranges from ∼60 to ∼165ka. We conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins.

Interpreting vegetation change in tropical arid ecosystems from sediment molecular fossils and their stable isotope compositions: A baseline study from the Pilbara region of northwest Australia

Detection of source diagnostic molecular fossils (biomarkers) within sediments can provide valuable insights into the vegetation and climates of past environments. However, hot and arid regions offer particularly challenging interpretive frameworks for reconstructions because baseline data are scarce, organic matter is generally very low and in the inland tropics in particular, sediments are also often subject to flooding and drought. Here, we investigated whether biomarkers and compound-specific δ13C values could be extracted from a late Holocene sediment record from the Fortescue Marsh (Pilbara, northwest Australia) to allow interpretation of past catchment vegetation and hydroclimate. The low total carbon (TC) content (<1.4%) was a major challenge for the molecular analyses over the ~2000years old sequence. Nevertheless, they revealed that the dominant hydrocarbon features (e.g., long chain n-alkanes) indicative of terrestrial plants (e.g., C4 grasses; riparian and other C3 plants) encompassed the last ~1300yrs and that low abundance of products from aquatic sources (e.g., n-C17) were detected in the uppermost sediments only when permanently inundated conditions prevailed (recent decades). Similarly, the lower δ13C values (i.e., a difference of −2.3‰) of long chain n-alkanes in upper sediments reflected a vegetation response to the emergence of wetter conditions through the late Holocene in the region. Based on the diverging dominant source contributions obtained from the molecular distributions and arid based Bayesian mixing model (δ13C of n-C27–33 alkanes) results, less arid conditions may have favoured the input of 13C depleted n-alkanes from the Eucalyptus (C3) dominant riparian vegetation. The deepest sediments (<700CE) however, had a TC content of <0.4%, and no organic compounds were detected, consistent with local and regional records of hyperarid conditions. These results demonstrate that n-alkanes can provide a molecular and stable isotopic fingerprint of important - and perhaps underappreciated - ecological processes in modern tropical arid environments for future paleoclimate investigations.

Evidence for extreme floods in arid subtropical northwest Australia during the Little Ice Age chronozone (CE 1400–1850)

Here we report a ∼2000-year sediment sequence from the Fortescue Marsh (Martuyitha) in the eastern Pilbara region, which we have used to investigate changing hydroclimatic conditions in the arid subtropics of northwest Australia. The Pilbara is located at the intersection of the tropical Indian and Pacific Oceans and its modern rainfall regime is strongly influenced by tropical cyclones, the Intertropical Convergence Zone (ITCZ) and the Indo-Pacific Warm Pool. We identified four distinct periods within the record. The most recent period (P1: CE ∼1990–present) reveals hydroclimatic conditions over recent decades that are the most persistently wet of potentially the last ∼2000 years. During the previous centuries (P2: ∼CE 1600–1990), the Fortescue Marsh was overall drier but likely punctuated by a number of extreme floods, which are defined here as extraordinary, strongly episodic floods in drylands generated by rainfall events of high volume and intensity. The occurrence of extreme floods during this period, which encompasses the Little Ice Age (LIA; CE 1400–1850), is coherent with other southern tropical datasets along the ITCZ over the last 2000 years, suggesting synchronous hydroclimatic changes across the region. This extreme flood period was preceded by several hundred years (P3: ∼CE 700–1600) of less vigorous but more regular flows. The earliest period of the sediment record (P4: ∼CE 100–700) was the most arid, with sedimentary and preservation processes driven by prolonged drought. Our results highlight the importance of developing paleoclimate records from the tropical and sub-tropical arid zone, providing a long-term baseline of hydrological conditions in areas with limited historical observations.

New bird records from the Fortescue Marsh and nearby claypans, Pilbara bioregion, Western Australia

The Fortescue Marsh in the Pilbara bioregion, Western Australia, is an extensive ephemeral wetland that fills episodically. It is considered as a potential Ramsar site and is recognised as a nationally important wetland and an Important Bird Area. We surveyed birds at 21 sites on the Fortescue Marsh and a further 23 sites (44 sites in total), including nearby claypans Coondiner Pool and Mungthannannie Pool, in the Fortescue Valley over 12 days in March–April and July 2012. A total of 100 bird species (34 waterbird and 66 landbird species) was recorded during the survey. A further 86 bird species (including 28 waterbird species and 58 landbird species) were recorded for this area from searches of databases and the literature (total of 187 species; 62 waterbirds). New and significant observations during the survey included the first breeding record of Australian Shelduck Tadorna tadornoides for the Pilbara, the first breeding records on the Marsh of Black-tailed Native-hen Tribonyx ventralis and Caspian Tern Hydroprogne caspia, and the first record of Australian Painted Snipe Rostratula australis for the Fortescue Valley. Despite this area’s importance to breeding and visiting waterbirds, the birds of the Fortescue Marsh remain surprisingly under-studied. We highlight some significant but overlooked literature records of waterbirds on the Marsh. Further ground and aerial surveys, and ongoing monitoring of this region would be valuable.

Impacts of high inter-annual variability of rainfall on a century of extreme hydrologic regime of northwest Australia

Abstract. Long-term hydrologic records provide crucial reference baselines of natural variability that can be used to evaluate potential changes in hydrologic regimes and their impacts. However, there is a dearth of studies of the hydrologic regimes for tropical drylands where intraseasonal and interannual variability in magnitude and frequency of precipitation are extreme. Here, we sought to identify the main hydroclimatic determinants of the strongly episodic flood regime of a large catchment in the semi-arid, subtropical northwest of Australia and to establish the background of hydrologic variability for the region over the last century. We used a monthly sequence of satellite images to quantify surface water expression on the Fortescue Marsh, the largest water feature of inland northwest Australia, from 1988 to 2012. We used this sequence together with instrumental rainfall data to build a statistical model with multiple linear regression and reconstruct monthly history of floods and droughts since 1912. We found that severe and intense regional rainfall events, as well as the sequence of recharge events both within and between years, determine surface water expression on the floodplain (i.e. total rainfall, number of rain days and carried-over inundated area; R2adj = 0.79; p value &lt; 0.001, ERMSP = 56 km2). The most severe reconstructed inundation over the last century was in March 2000 (1000 km2), which is less than the 1300 km2 area required to overflow to the adjacent catchment. The Fortescue Marsh was completely dry for 32% of all years, for periods of up to four consecutive years. Extremely wet years (seven of the 100 years) caused the Marsh to remain inundated for up to 12 months; only 25% of years (9% of all months) had floods of greater than 300 km2. The prolonged, severe and consecutive yearly inundations between 1999 and 2006 were unprecedented compared to the last century. While there is high inter-annual variability in the system, if the frequency and intensity of extreme rainfall events for the region were to increase (or be similar to 1999–2006), surface water on the Marsh will become more persistent, in turn impacting its structure and functioning as a wetland.

The riparian flora and plant communities of the Pilbara region of Western Australia

A survey of riparian fl ora and plant communities was undertaken at 98 wetlands and rivers in the Pilbara region of Western Australia. Sampling was quadrat-based, with fl oristics, surface soils and wetland attributes recorded. Selected sites captured the full range of Pilbara wetland types including springs, river pools, claypans, salt marshes and rock pools. A total of 455 taxa was recorded from the survey sites, representing ca. 25% of the known fl ora of the Pilbara bioregion. The fl ora is dominated by taxa with Eremaean and tropical affi nities, with only six taxa endemic in the region. Of recorded taxa known from four or fewer bioregions, most are shared with the adjacent Carnarvon and Gascoyne bioregions rather than the adjoining internally draining deserts. Sixteen taxa of conservation signifi cance were documented, with claypans, the Fortescue Marsh, and Millstream and Karijini National Park sites dominating occurrences of rare species. Eight major groups were defi ned by classifying wetlands in terms of species presence/absence data. Floristic patterning was strongly aligned with the major wetland types (geomorphic/hydrological) used in the primary sampling stratifi cation. A combination of wetland morphology/hydrological setting, site edaphic attributes and distance to the coast were dominant variables related to riparian fl oristic composition. Primary compositional separation was observed between riverine and non-riverine sites, with lowland turbid riverine sites with fi ne- textured soils compositionally related to claypans and clay fl ats. Limited biogeographic patterning was evident except where individual IBRA subregions and drainage basins were dominated by few wetland types.

Unravelling sources of solutes in groundwater of an ancient landscape in NW Australia using stable Sr, H and O isotopes

The Precambrian meta-sedimentary fractured rock aquifers of the Hamersley Basin in northwest Australia are some of the oldest water-bearing formations on the planet and host enormous iron ore deposits. Groundwater is the only permanent source of water in the basin, therefore understanding the hydrological processes that effect water quality and quantity is a pre-requisite for sustainable water management. We used a combination of major dissolved ion concentrations, including Sr and Ca, in combination with δ2H, δ18O and δ87Sr in flood water and groundwater as tracers to constrain the processes affecting groundwater chemistry. The δ87Sr composition of groundwater in three major aquifer types ranges from 11.8‰ to 40.6‰ and reflects the mineralogy of altered Precambrian dolomite (15.1‰ to 55.4‰) rather than the host iron ore formations (22.5‰ to 46.5‰ >95% iron oxides) or highly radiogenic shale bands and clay minerals (200‰ to 2322.5‰). Groundwater in the terminal Fortescue Marsh wetland of the basin has a rather constant δ87Sr signature of 36.6±1.4‰ irrespective of variations in TDS, δ18O and Sr concentration. This groundwater is considered to be mature in a geochemical sense, representing the final stage of water evolution on a basin scale. Mixing calculations utilising δ87Sr and Ca/Sr data demonstrate contributions of salts from three major sources: on average >92% from precipitation, ~7% from carbonate rocks and <1% from rocks with highly radiogenic signatures (shales and clays). These results demonstrate groundwater evolution from a recharge area to discharge area at the regional scale, but more importantly that water quality in the terminal wetland is primarily driven by rainfall chemistry in floodwaters rather than water–rock interactions in the catchment.

Drought tolerances of three stem-succulent halophyte species of an inland semiarid salt lake system.

Succulent halophytes of the genus Tecticornia are dominant in salt marshes of inland lakes of Australia. We assessed the drought responses of a C4 species, Tecticornia indica subsp. bidens (Nees) K.A.Sheph. & Paul G.Wilson, and two C3 species, Tecticornia auriculata Paul G.Wilson (K.A.Sheph. & Paul G.Wilson) and Tecticornia medusa (K.A.Sheph. & S.J.van Leeuwen) that occur in the Fortescue Marsh, north-west Australia. In a glasshouse experiment, the three species were grown individually and in different combinations, with varying number of plants per pot to achieve comparable dry-down rates among pots. Prior to the imposition of drought (by withholding water) the three species showed differences in dry mass and physiological variables. As the soil dried out, the three species showed similar reductions of transpiration, osmotic potential and photochemical efficiency. Shoot growth was depressed more than root growth. Tissue water loss from portions of the succulent shoots accounted for ~30% of transpiration during severe drought stress. There was no osmotic adjustment. Shoot tissue concentrations of Na+ and Cl- tended to increase during drought, and those of K+ decreased; however, these changes were not always statistically significant. Chlorophyll concentration decreased but betacyanin concentration increased. Despite occupying distinct positions in a water and salinity gradient, the three Tecticornia species had remarkably similar responses to soil water deficit.

Geochemical and hydrological processes controlling groundwater salinity of a large inland wetland of northwest Australia

Understanding mechanisms of hydrochemical evolution of groundwater under saline and brine wetlands in arid and semiarid regions is necessary to assess how groundwater extraction or injection in large-scale basins may affect the natural interface between saline–fresh aquifers in those systems. We investigated the evolution of groundwater of the Fortescue Marsh, a large inland wetland of northwest Australia that is mainly supplied by floodwater from the upper Fortescue River catchment. The marsh is located in the Pilbara region, one of the world's major iron ore provinces, where mining activities often occur below water tables. Here, we quantified the stable isotope and chemical composition of groundwater, surface water and rainfall in and around the marsh to better understand how saline marshes and playa lakes function geochemically, hydrologically and ecologically. The deep groundwater (>50m depth) of the Fortescue Marsh is highly saline (>100gL−1), whilst shallow groundwater (~0–20m depth) and surface water are mainly fresh or brackish. Currently, the marsh is mainly recharged by occasional floodwater. Consequently, salt in the marsh is concentrated by evaporation of rainfall. We expected that the hydrochemical composition of surface and groundwater would therefore reflect the chemical composition of rainwater. We analysed 206 water samples for stable isotope composition (δ2H, δ18O) and water chemistry, including: pH, dissolved oxygen, electrical conductivity (EC), and total dissolved solids (TDS), as well as Na, Ca, Mg, K, Si, Fe, HCO3, SO4, Cl, Sr and Br. We then developed geochemical models and a salt inventory to estimate the geological time of salt accumulation and to decouple geochemical characteristics of salt from modern groundwater. We found that groundwater associated with the marsh can be divided into two distinct groups that are characterised by their stable isotope compositions; i) fresh and brackish groundwater (TDS <10gL−1; δ18O −8.0±0.9‰) and ii) saline and brine groundwater (TDS >10gL−1, δ18O varies from +2.5 to −7.2‰). Fresh groundwater was evaporated by <20% compared to rainwater. Brackish water mainly reflects modern recharge whilst saline and brine groundwater reflects mixing between modern rainfall, brackish water and relatively old groundwater. The Cl load in the groundwater originates from rainfall and accumulates over time as it is recycled due to precipitation of evaporates and re-dissolution on the marsh during subsequent flooding events. The stable isotope composition of the deeper brine groundwater also suggests a complex evolution, which cannot be explained by evaporation under current conditions from modern rainfall. We thus conclude that the deeper brine groundwater under the Fortescue Marsh developed under a different climatic regime and that the current salt in the marsh has accumulated over at least 40,000years, but could have been as long as 700,000years.

Stable isotope and hydrochemical evolution of groundwater in the semi-arid Hamersley Basin of subtropical northwest Australia

Summary The Hamersley Basin, in the semi-arid Pilbara region of northwest Australia, is currently subject to increasing pressure from altered hydrology associated with mining activities as well as water abstraction for regional development. Sustainable water management across the region must be underpinned by an understanding of the factors that constrain water supply in arid zones. We measured the amount and isotopic signature of individual rainfall events over three consecutive years (2009–2011) to determine the likely processes that control surface water pools in streams and groundwater recharge across the Hamersley Basin. We also measured concentrations of ions (in particular bromide and chloride) to define and quantify sources of major recharge. Stable isotope composition of precipitation across the basin forms a Local Meteoric Water Line (LMWL) defined by the equation: δ2H = 7.03 ± 0.17 × δ18O + 4.78 ± 1.45. Thus, the slope of the LMWL was similar to the Global Meteoric Water Line (GMWL). However, the intercept of the LMWL was significantly different to the GMWL, which is attributable to the amount or “rainout” effect. The stable isotope composition of rainfall events was highly variable and dependent on event size. However, the δ2H and δ18O values of fresh groundwater from the alluvium and fractured aquifers were similar and characterised by a very narrow range (alluvium aquifer δ18O −8.02 ± 0.83‰, δ2H −55.6 ± 6.0‰, n = 65; fractured aquifer δ18O −8.22 ± 0.70‰, δ2H −56.9 ± 5.0‰, n = 207). Our findings suggest that intense rainfall events of >20 mm with limited evaporation prior to infiltration contribute most to recharge. In contrast, the δ2H and δ18O values and chemical composition of the relatively saline groundwater in the terminal Fortescue Marsh suggest a combination of evaporation and cyclic drying and wetting of the marsh surface prior to recharge. Saline groundwater samples were more 18O enriched than fresh groundwater; δ2H and δ18O values shifted to the right of the LMWL, forming a straight line with a slope of 3.58 ± 0.20 and an intercept of −25.55 ± 0.71 (R2 = 0.95, p

Cloudbreak mine water conveyance infrastructure

Cloudbreak is an iron ore mine located in the Pilbara region of Western Australia. The mine extends 40 km east-west, 5 km north-south and has excavations up to 70 m depth. It is home to one of Australia's largest and most complex Managed Aquifer Recharge (MAR) operations. It also adjoins the new Christmas Creek mine, currently under development to the east, of similar scale and characteristics. The two mines form a single water managed entity. Ninety percent of the ore body is below the water table, the ore body itself containing the main aquifer of brackish water. The mine is bounded to the south by the Fortescue Marsh – an internally draining, periodically flooded wetland of national significance. The marsh and the ore body are underlain by hyper saline conditions in an irregular pattern trending more saline towards the marsh and with depth. MAR is the chosen method of dewatering operation to preserve the fresh and brackish water source, manage the quality of the remaining unexcavated ore body, safeguard groundwater levels at the marsh, and maintain balance to local ecology by zero surface discharge. Through an evolution of review and optimisation, a mix of infrastructure components have been installed and commissioned alongside ongoing mine expansion, within a very dynamic operational environment. The scheme currently includes 200 abstraction bores (60 operational at any time), ten in-pit sumps, 200 km of pipeline, six major transfer or settlement ponds, 100 brackish injection bores (50 operational, others for standby or future use) and 20 saline injection bores (currently operating five at a time on a trial basis). These numbers are due to be significantly augmented as dewatering license limits increase and the mine progressively develops. Hydraulic network modelling software is applied for system design and optimisation. The system is operated using a mix of manual and automatic controls, with regular monitoring for compliance and optimising system performance. This paper focuses on how the self contained MAR system has been designed, developed and operated successfully, though many challenges remain.

English

Salt lakes are common across inland Australia but within the Pilbara region, in the north west of Western Australia, saline habitats are infrequent. Fortescue Marsh is the predominant saline system in this region and two new species of conservation interest have been found to occur only on the Marsh and Weelarrana Lake south of Newman. Tecticornia globulifera K.A.Sheph. sp. nov. and T. medusa K.A.Sheph. & S.J.van Leeuwen sp. nov. are formally named and described herein. Images of these new species and a distribution map are included.

An arid zone awash with diversity: patterns in the distribution of aquatic invertebrates in the Pilbara region of Western Australia

The Pilbara region of Western Australia is an arid zone with an abundance of wetlands, ranging from springs and river pools to salt marshes, claypans, rockpools and gnammas. The Pilbara is also rich in mineral resources, which are being heavily exploited, and most of the region is under pastoral lease, with both land uses potentially having an impact upon aquatic systems. In order to provide information for improved conservation planning, including environmental impact assessment and reserve system design, a survey of wetland fauna was undertaken as part of a broader biodiversity survey of the region. This paper describes patterns in the distribution of the region's aquatic invertebrate diversity and identifies environmental correlates of those patterns. Invertebrates and environmental variables were surveyed at 100 wetlands in spring and autumn between 2003 and 2006. The Pilbara appears to have a particularly diverse fauna for an arid zone, with just over 1000 species collected, an average of 94 species per sample and a maximum sample richness of 226 species. About a fifth of the fauna is known to date only from the Pilbara. The remaining species are western endemics, occur elsewhere in northern and/or inland Australia, or have continental or wider distributions. Most species seem to be widespread in the Pilbara region but rare and/or restricted elements are present, especially in some permanently flowing springs, including those in Millstream and Karijini National Parks, and in ephemeral wetlands such as Fortescue Marsh and freshwater claypans. Faunal composition was not strongly correlated with season, drainage divides, stream order or previously recognised bioregional boundaries. A number of assemblages of species with common patterns of occurrence were identified, each showing unique associations with measured environmental variables. Flow, turbidity, salinity, sediments, macrophytes and hydrological persistence are among the environmental gradients most strongly correlated with occurrence patterns in the fauna.