Murray Mouth Research Articles

Visions of Water: Swimming in a drying Australian waterscape

Since the 1820s, the Murray Mouth (South Australia) has been subjected to such disfiguring abuse at the hands of colonists that it now faces an unprecedented health crisis. My research consists of implementing a liquid methodology to explore and illuminate this mouth’s d(r)ying waterscapes. To borrow Celan’s phrase, my words represent “attempts to swim on dry land”: they speak of the harsh dialectics of drought and desertification, and yet, water shapes them as they crisscross pages and landscapes. In this essay, I discuss some of those “attempts to swim on dry land”. I illustrate how I articulate and play with the vulnerable interface between (wet) theories and the (dry) realities of the Mouth’s acoustic textures – or, more precisely, how I recorporealise the conceptual in the sensory. We need this recorporealisation because we need to keep trying to swim on dry land. Only through those attempts can we learn how to listen to the wet ontologies hidden behind the colonial veil of blue-green algae blooms, salt and the staccato pounding of the dredgers working hard to keep the Mouth open.

Encounter Bay, South Australia, an important aggregation and nursery area for the southern right whale, Eubalaena australis (Balaenidae: Cetacea)

ABSTRACT Endangered Australian southern right whales, Eubalaena australis, are vulnerable to threats from human activities, particularly at calving aggregation areas. As the population increases, new calving areas are being established, which are important to monitor. In the Encounter Bay/Lacepede Bay region, South Australia, distribution, relative abundance, residency and site fidelity were studied using historical sightings (n = 1071, 1970–2013) and photo-identified individuals (n = 191, 2006–2019). Whales were observed throughout the study area and concentrated in Encounter Bay during April to November where an inshore core calving area was identified between Port Elliot and the River Murray Mouth. Annual maximum daily sightings increased from 2 to 8 ( = 2.9) whales during 1983–1997 to 1–25 ( = 8.6) after 2002. Numbers of identified female-calf pairs (CC) increased from 10 (2006–2012) to 31 (2013–2019). During 2013–2019, when survey effort increased, a mean of 4.4 (1–9 pairs/year) CC and 18.0 (7–40/year) unaccompanied animals (UA) visited Encounter Bay each season. Mean residency was greater for CC (51.3, 13–126 days) than UA (13.4, 2–40 days). Calving females that arrived pregnant had more than twice the residency time than those first sighted with a calf. A quarter of calving females returned in two or three subsequent seasons. Encounter Bay is an important calving area and requires re-classification by the Commonwealth from “emerging aggregation area” to “small, established aggregation area”. Ongoing research is needed to document southern right whale population dynamics at Encounter Bay in the context of the broader Australian population.

Impact of salinity and carbonate saturation on stable Sr isotopes (δ88/86Sr) in a lagoon-estuarine system

Local carbonate cycling in lagoon-estuarine systems, involving processes such as inorganic and biogenic carbonate precipitation/dissolution, represents an important but poorly constrained component of the coastal carbon budget. This study investigates the sensitivity of stable Sr isotope tracer (δ88/86Sr) with respect to carbonate saturation and salinity of local waters in the Coorong, Lower Lakes and Murray Mouth (CLLMM) estuary in South Australia. The CLLMM has an extensive range of salinity from fresh to hypersaline (from ∼0 to over 100 PSU), with corresponding variations in water chemistry and major ion composition that in turn controls mineral saturation states, and thus CaCO3 precipitation/dissolution in local waters. Here we use the novel δ88/86Sr tracer in tandem with the more established radiogenic Sr isotope ratio (87Sr/86Sr), where the latter is a robust proxy for Sr sources and thus water provenance. We also produced a geochemical (PHREEQC) model of calcium carbonate (CaCO3) saturation changes across this unique lagoon-estuarine system.The results indicate a systematically increasing trend of δ88/86Sr (from ∼0.25‰ to ∼0.45‰) with increasing salinity and CaCO3 (aragonite, calcite) saturation indices of the coastal waters, which in turn suggest an overall control of carbonate dissolution/precipitation processes on the stable Sr isotope composition in the CLLMM system. This was further corroborated by Ca isotope data (δ44/40Ca) published previously on the same samples from the Coorong, as well as a quantitative simulation of local carbonate removal in the lagoon based on Rayleigh modelling and Sr isotope data.Overall, our results confirm that a coupled Sr isotope approach (combining 87Sr/86Sr and δ88/86Sr) can be used to constrain not only the main water sources (continental versus marine Sr) but also local CaCO3 dissolution/precipitation processes, and thus inorganic carbon and coastal carbonate cycling in the CLLMM system. Finally, this coupled δ88/86Sr and 87Sr/86Sr approach can be potentially applied to fossil carbonate archives to reconstruct paleo-hydrology and salinity changes in the CLLMM and/or other carbonate-producing coastal systems.

The role of coastal processes in the management of the mouth of the River Murray, Australia: Present and future challenges

AbstractThe Murray–Darling Basin is the largest river system in Australia to enter the sea. Prior to regulation of water flows, the Murray Mouth remained open to the sea even during droughts. An open mouth assists in sustaining the ecology of a Ramsar listed wetland and enables the flushing of salt, nutrients, and suspended sediments to the sea. Construction of barrages designed to prevent saltwater ingress has separated the estuary into two sections, a set of freshwater lakes and a saline tidal lagoon area, creating a unique set of management challenges. Under current overextraction of water resources upstream, river flows have been largely insufficient to counter wave and tide processes, which propel marine sands thereby constricting the Murray Mouth. Dredging has been required to maintain an open entrance. Managing this system is part of a 2012 agreement between state and federal governments, through the Murray–Darling Basin Plan. This plan recognizes a healthy end of system; however, the hydrological models failed to factor in the power of the sea in blocking the Murray Mouth. The plan requires that there will be sufficient river flows for the mouth to be open 95% of the time without dredging. Currently, sand ingress from the sea requires dredging most of the time. It is unlikely that there will be sufficient river flows to counteract continued sequestration of marine sand into the mouth. Sea level rise and decreased rainfall in the southern half of the Basin under climate change conditions will require a review of management options to prevent the long‐term degradation of the end of system.

Indigenous nation building for environmental futures: Murrundi flows through Ngarrindjeri country

ABSTRACTIn 2015, the Ngarrindjeri Nation in concert with the South Australian government won the Australian Riverprize for best practice in water management, after leading the development of a co-management approach to the Coorong, Lower Lakes and Murray Mouth (CLLMM) region during the Australian Millennium drought crisis. The purpose of this article is to explain why the prize-winning advances in water management in this region are an outcome of a strategic political process of Indigenous Nation (re)building, pursued by Ngarrindjeri leaders with the ongoing support of a formal research program focussed on Aboriginal governance. The primary insight revealed by the research is that Indigenous contributions to successful environmental management are not best conceived in terms of the protection of ‘cultural flows’ – as is suggested by much of the literature in the field – but instead should be understood primarily in political terms. Like other Indigenous Nations, Ngarrindjeri consider they have an inherent and sovereign right to enjoy, use and protect the flow of water through their Country. Ngarrindjeri have effectively articulated their sovereign Aboriginal environmental rights and have successfully negotiated these rights with the South Australian state by producing targeted legal and political innovations that enable shared authority in the co-development of natural resource management policy. The article argues that Indigenous Nation (re)building and self-governance has positive implications for the development of best practice models of land and water management, both in Australia and internationally.

Calcium and strontium isotope systematics in the lagoon-estuarine environments of South Australia: Implications for water source mixing, carbonate fluxes and fish migration

This study uses Ca and Sr isotopes (δ44/40Ca and 87Sr/86Sr), coupled with elemental ratios, to better understand the water source apportionment and carbonate output in the Coorong, Lower Lakes and Murray Mouth Estuary, which represents the terminus of Australia’s longest river system. The geochemistry of waters in the Coorong (i.e., North and South Lagoon) can be explained by mixing of three major components, including: (i) the Southern Ocean seawater, (ii) local freshwaters, and (iii) hypersaline lagoon waters, the latter significantly modified by ongoing evaporation and carbonate formation. The Sr and Ca isotope composition of the North Lagoon is indistinguishable from that of the Southern Ocean (i.e., normal salinity of ∼35 PSU), with the exception of transient freshwater input events that can temporarily lower the salinity to brackish levels. Interestingly, our results from the hypersaline South Lagoon (salinity up to ∼120 PSU) confirmed that the latter is highly evaporated brackish water (with ≥40% contribution from continent-derived waters), which has been additionally modified by in-situ carbonate precipitation. Importantly, our Ca isotope and elemental constraints showed that about 15–17% of the dissolved Ca2+ in the South Lagoon has been removed as CaCO3 (primarily as aragonite). This in turn has implications for the local carbonate cycle and blue carbon studies, suggesting that the South Lagoon acts as a net sink for the dissolved inorganic carbon (DIC).Ca isotope data from the otoliths of smallmouth hardyhead fish species (Atherinosoma microstoma) collected in the Coorong indicate that δ44/40Ca is primarily controlled by biological processes (i.e., kinetic isotope fractionation effects related to growth rate), rather than by the Ca isotope composition of local lagoon waters. As to 87Sr/86Sr in otoliths, the latter confirmed the importance of continent-derived water sources in the Coorong, recorded over the life span of the fish.Overall, with suitable fossil carbonate archives (e.g., bivalve shells, foraminifera), our calibration of 87Sr/86Sr and δ44/40Ca in the modern hydrological system, with respect to a large salinity gradient (ranging from fresh to hypersaline, i.e., 0 to ∼120 PSU), implies potential future applications of these isotope tracers in carbonate-producing coastal systems, which include (i) tracing and apportioning different water sources, (ii) quantifying local carbonate outputs, and (iii) reconstructing paleo-salinity changes.

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

River discharges are decreasing in many regions of the world; however, the consequences of this on water quality and primary productivity of receiving coastal oceans are largely unclear. We analysed satellite remote-sensing data (MODIS) of the coastal ocean zone that receives outflows from the Murray River, from 2002 to 2016. This system has experienced historical flow reductions and a recent extreme hydrological ‘Millennium’ drought. Remotely sensed chlorophyll-a and particulate organic carbon in the coastal ocean were strongly correlated with river outflows (R2>0.6) in an 8-km radial buffer zone from the Murray Mouth, and the river influence extended up to ~60km from the Murray Mouth during high-flow periods. This distance was approximately three times greater than the freshwater plume extent during maximum flows in 2011, suggesting that new primary productivity was created. In contrast, there was no additional coastal ocean productivity above background levels from 2007 to 2010 when river outflows ceased. Hindcast calculations based on historical flows from 1962 to 2002 suggest that declining Murray River flows have greatly reduced primary productivity in adjacent coastal waters. This has potential consequences for higher trophic levels and should be considered in future management planning.

A century of intervention in a Ramsar wetland – the case of the Coorong, Lower Lakes and Murray Mouth

ABSTRACTCoastal wetlands are among the more valuable ecosystems on the planet. Managing wetlands to maintain ecosystem function is physically and politically challenging, especially during drought. Management of the Coorong, Lower Lakes and Murray Mouth has been characterised by a sequence of active and reactive infrastructure interventions, first as active interventions to supply consumptive water demands and more recently as reactive emergency drought responses. However, infrastructure solutions are not necessarily synonymous with achieving sustainability. Infrastructure interventions have occurred at significant public expenditure and high opportunity cost. Greater attention to demand-based management strategies including time-limited environmental water acquisitions and state-based environmental water holdings provides an alternative to future infrastructure reliance. There is also considerable scope for greater provision of cultural flows and engagement with traditional owners to improve ecological condition.

Zooplankton in the Murray estuary and Coorong during flow and no-flow periods

ABSTRACTFrom 2001 to 2010, River Murray flows were extremely low because of drought and over allocation. Barrage releases to the Murray Mouth were small and intermittent, with an extended period of closure and no flow from December 2001 to September 2003 and from February 2006 to November 2010. We studied the zooplankton communities in the Murray estuary and Coorong North Lagoon from 2003 to 2008 to identify the distribution and abundance of zooplankters in flow and no-flow periods, to compare zooplankton communities to those in other Australian estuaries and to consider the role of zooplankton in trophodynamics. Most of our samples were taken with a 59 µm net. In September/October, 2003 a barrage release brought freshwater zooplankters into the Murray estuary. By November and December, salinities had risen and only estuarine and hypermarine species were collected. In the spring/summer of 2004/05, salinities ranged from 16 to 88 parts per thousand (ppt) and a limited estuarine/hypermarine community was present. By 2007/08, salinities had risen to be 35–130 ppt and the distribution of the estuarine/hypermarine community was restricted and the Australian brine shrimp Parartemia zeitziana was collected. Overall, the zooplankton community was of low diversity compared to other estuaries in south-east Australia and lacked several of the common copepods. Rotifers, especially Synchaeta spp., were well represented especially in the hypermarine regions. The diversity and abundance of zooplankters was the highest during the period of River Murray outflow. The low abundance of adult calanoid copepods during the no-flow period might suggest that large bodied individuals were removed by high fish predation. The abundance of copepodites and nauplii shows that small mesh nets are required to see the complete zooplankton community and also that copepodites and nauplii can be surprisingly abundant when adults are rare.

Drought and flood effects on macrobenthic communities in the estuary of Australia's largest river system

Estuaries are prone to drought and flood events, which can vary in frequency and intensity depending on water management and climate change. We investigated effects of two different drought and flow situations, including a four year long drought (referred to as Millennium drought) and a major flood event, on the macrobenthic community in the estuary and coastal lagoon of the Murray Mouth and Coorong, where freshwater inflows are strictly regulated. The analysis is based on ten years of annual monitoring of benthic communities and environmental conditions in sediment and water. The objectives were to identify changes in diversity, abundance, biomass and distribution, as well as community shifts and environmental drivers for the respective responses. The Millennium drought led to decreased taxonomic richness, abundance and biomass of macrobenthos as hypersaline conditions developed and water levels dropped. More taxa were found under very high salinities than predicted from the Remane diagram. When a flood event broke the Millennium drought, recovery took longer than from a shorter drought followed by small flows. A flow index was developed to assess the biological response subject to the duration of the preceding drought and flow volumes. The index showed higher taxonomic richness, abundance and biomass at intermediate and more continuous flow conditions. Abundance increased quickly after flows were restored, but the benthic community was initially composed of small bodied organisms and biomass increased only after several years once larger organisms became more abundant. Individual densities and constancy of distribution dropped during the drought for almost all macrobenthic taxa, but recoveries after the flood were taxon specific. Distinct benthic communities were detected over time before and after the drought and flood events, and spatially, as the benthic community in the hypersaline Coorong was split off with a salinity threshold of 64 identified by LINKTREE analysis. Salinity, low dissolved oxygen saturation and sediment properties accounted for further community splits in the estuarine Murray Mouth. This long term monitoring revealed ecological benefits of intermediate and continuous flow and that resilience of estuarine macrobenthos to drought and flood events was affected by flow history. The index can be applied to other flow regulated estuaries and inform environmental watering targets.

Fish productivity in the lower lakes and Coorong, Australia, during severe drought

Anthropogenic modification of catchments and river flow can significantly alter estuarine habitats, hydrology and nutrient delivery with implications for fisheries productivity. The Coorong estuary at the terminus of Australia’s River Murray supports an economically important fishery as well as being recognised internationally as a critical site for migratory birds. Salinity near the Murray Mouth varies between fresh and marine depending upon river flow, but the Coorong becomes increasingly saline along its 120 km length. Freshwater flow to the Coorong is naturally variable but has significantly reduced by extraction for irrigated agriculture and domestic use upstream. Extreme drought from 2000 to 2010 and over-allocation of water resources resulted in the cessation of freshwater flow to the Coorong, significantly increasing salinity. During this period the diversity and abundance of organisms in the Coorong declined which reduced food web complexity. During lower flows the system generally becomes less productive as evidenced by: lower nutrient concentrations and loads, lower chlorophyll and primary productivity, a decrease in the abundance of fish-prey items (zooplankton, macroinvertebrates and small fish), a decrease in fish abundance, although this is not well reflected in fishery catch data because of the concentration of fishing in available habitat. The maintenance of flow is the only management strategy that stimulates recruitment, delivers nutrient resources to the estuary and ensures maintenance of habitable area by maintaining appropriate salinity.

Rapid Evolution of a Flood Tidal Deltaic Island in the River Murray Estuary, South Australia: A Canary in the Cage of River Management

James, K.F.; Bourman, R.P., and Harvey, N., 2015. Rapid evolution of a flood tidal deltaic island in the River Murray estuary, South Australia: A canary in the cage of river management.Bird Island, at the oceanic outlet of Australia's largest exoreic river system, the Murray-Darling, did not exist before 1940. Originally, flood tidal sediments were moulded by tides, waves, wind, and river flows in the back-barrier lagoon, landward of the migrating River Murray Mouth. The estuary was fluvially dominated, and the terminal lakes were mainly fresh. Following more than a century of European settlement and freshwater abstraction, salinity levels increased, prompting the construction of barrages (completed in 1940) near the Murray Mouth to restore the former predominantly freshwater character of the estuary. Further reduced river flows, a restricted tidal prism, and management strategies produced irreversible changes in the dynamics of the River Murray Mouth. These are archived in the landforms and vegetation of Bird Island. By the mid-1950s, sand shoals were enlarging and a small patch of vegetation was established, forming the core of an incipient island. Progressively, dunes and salt marshes were established, reflecting intimate associations between landform evolution, vegetation colonisation, and island stability. As the mouth migrated to the NW, so did the flood tidal shoals, the sources for newer generations of dunes, thereby developing a clockwise establishment of dunes on the expanding island. Approximately 1 km in diameter and carrying more than 80 plant species, Bird Island assisted mouth closure in 1981. During the 2002–10 drought, dredging maintained the mouth and improved lagoonal water quality. Subsequent healthy river flows cleared the mouth, highlighting the important role of river flows in maintaining oceanic access, and sediment removal, while flushing the river system. The evolution of Bird Island as documented in this study demonstrates how anthropogenic activities can cause rapid and irrevocable changes to coastal–estuarine environments.

Hunter‐gatherer variability: Dental wear in South Australia

Often it is assumed that hunter-gatherer dentitions are dominated by heavy attrition. Recent analyses, however, have shown unexpected variability in the pattern of wear between groups. It had been previously noted that wear differed between neighboring groups on the Murray River, Australia. This analysis extends that geographic scope as well as focusing on wear across the dentition, including the premolars. The samples came from coastal and riverine regions of southern Australia. The analysis used records from the Yorke Peninsula, Adelaide Plains (Gillman site), and Euston regions. These were compared with previously published work from the Adelaide Plains and four locations on the Murray River. The results confirm the overall severity of wear but reveal systematic differences between the samples in terms of the pattern of wear. Heavy wear on the incisors and canines is observed among males from the Euston, Kaurna, Middle A, Murray Mouth, and Yorke Peninsula samples but with marked intra-individual variability. Extensive premolar wear is noted among females from Kaurna and Middle B samples as well as among males and females from Euston. It is argued that these patterns relate to gendered non-masticatory use of teeth and reliance upon bulrush (Typha spp.) and related species for both food and fiber among some groups. We argue that analyzing the degree of variability within samples and across all teeth provides a more nuanced understanding of dental wear among hunter-gatherers.

Temporal variation of larval fish assemblages of the Murray Mouth in prolonged drought conditions

Estuaries are transition zones that link freshwater and marine ecosystems and are often used as nursery areas by fish. The Murray–Darling Basin, which is heavily affected by flow regulation and water extraction, is the largest river system in Australia and terminates at the Murray Mouth estuary. Protracted drought conditions resulted in extremely low flows to the Murray Mouth that affected water condition, fish abundance, community structure and fish use of the estuary (e.g. nursery areas). The aims of the present study were to examine temporal changes in larval fish assemblages in this estuary. The assemblages were dominated by two gobiid species, Arenigobius bifrenatus and Tasmanogobius lasti. There was a noticeable absence or low abundance of freshwater, diadramous and large-bodied marine species that use this estuary for reproductive functions. Monthly differences in larval fish assemblages, between August–September and October–November, were attributed to increases in the abundances of A. bifrenatus in October and November and oscillation in T. lasti during the entire sampling period. The outcomes of the present study suggested that larval fish assemblages in drought conditions are limited to small-bodied species tolerant of high salinities and that freshwater flows are needed for the estuary to function as a nursery for other species.

Ecology, Ontology, and Pedagogy at Camp Coorong

Ecology, Ontology, and Pedagogy at Camp Coorong

Tidal asymmetry in a coastal lagoon subject to a mixed tidal regime

Tidal asymmetry is a key factor in the geomorphology of many coastal lagoons. Whilst tidal asymmetry in semi-diurnal tidal regimes has been extensively studied, its occurrence in mixed tidal regimes is less well understood, and has a number of unique causes and characteristics. Tidal phase duration analysis and least squares harmonic analysis have been used to study the temporal and spatial nature of asymmetry in both offshore and coastal lagoon tides at the Murray Mouth in south-eastern Australia. GIS analysis of bathymetric survey data has been used to study the roles of lagoon bathymetry on tidal distortion. Tidal asymmetry in the Murray Mouth coastal lagoon results from frequency relationships between major astronomical driving tides as well as bathymetry-induced tidal transformations. The frequency difference between the K 1 and S 2 tides produces an important 6-monthly ebb/flood-dominant asymmetry cycle in the incoming oceanic tides, whilst phase relationships between the K 1 and K 2 tides contribute to persistent asymmetry. The use of standard relationships between the M 2 and M 4 tides as asymmetry indicators is shown to be invalid for this mixed tidal regime. In this shallow, microtidal system, the impacts of bathymetry on tidal asymmetry within the lagoon are profound, with inlet and channel configurations identified as the most important controlling factors. The results of this study may inform the strategic management of tidal inlets in mixed tidal regimes, such as the Murray Mouth, that are subject to intermittent or long-term constriction.

A history of aquatic plants in the Coorong, a Ramsar-listed coastal wetland, South Australia

The Coorong in South Australia is an internationally recognised ecologically significant coastal lagoon that extends 140 km south-east from the mouth of the River Murray. The Coorong has increasingly been impacted by a variety of human activities. Declining migratory bird abundance has been linked to the loss of Ruppia tuberosa, an aquatic plant that is the main feedstock for a wide variety of water birds. Analysis of Ruppia remains from a radiometrically dated core in the southern lagoon of The Coorong shows that the salt-tolerant annual Ruppia tuberosa has only been present at this site in recent times. By contrast, the perennial Ruppia megacarpa, which has limited tolerance to elevated salinity, appears to have been present at the site for several millennia, although it had never been observed in ecological surveys of this part of The Coorong. Diatom analysis from the same core reveals a shift from estuarine/marine assemblages to an assemblage reflective of elevated salinity levels. Charophyte, ostracod and foraminifera remains also indicate that the change in the aquatic plant community is associated with increased salinity at the study site since European settlement. Elevated salinity is the result of catchment modifications which have reduced freshwater inflows at the northern and southern extremities of The Coorong, and marine input via the Murray Mouth. This study demonstrates the utility of multiproxy palaeoecological data in addressing complex management questions. In the absence of such information, managers must ultimately rely on data sourced only from the historical record which, more often than not, is already skewed by the impact of European settlement.

Diatom and foraminifera relationships to water quality in The Coorong, South Australia, and the development of a diatom-based salinity transfer function

The Ramsar-listed Coorong lagoon lies at the terminus of the Murray-Darling River system in South Australia. Diatom and foraminifera relationships 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 dissolved 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 r jack 2 = 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 suggested that pre-European salinity values were generally >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, accurate 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 several cosmopolitan diatom and foraminifera species, 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.

A Ramsar wetland in crisis - the Coorong, Lower Lakes and Murray Mouth, Australia

The state of global freshwater ecosystems is increasingly parlous with water resource development degrading high-conservation wetlands. Rehabilitation is challenging because necessary increases in environmental flows have concomitant social impacts, complicated because many rivers flow between jurisdictions or countries. Australia’s Murray–Darling Basin is a large river basin with such problems encapsulated in the crisis of its Ramsar-listed terminal wetland, the Coorong, Lower Lakes and Murray Mouth. Prolonged drought and upstream diversion of water dropped water levels in the Lakes below sea level (2009–2010), exposing hazardous acid sulfate soils. Salinities increased dramatically (e.g. South Lagoon of Coorong >200 g L–1, cf. modelled natural 80 g L–1), reducing populations of waterbirds, fish, macroinvertebrates and littoral plants. Calcareous masses of estuarine tubeworms (Ficopomatus enigmaticus) killed freshwater turtles (Chelidae) and other fauna. Management primarily focussed on treating symptoms (e.g. acidification), rather than reduced flows, at considerable expense (>AU$2 billion). We modelled a scenario that increased annual flows during low-flow periods from current levels up to one-third of what the natural flow would have been, potentially delivering substantial environmental benefits and avoiding future crises. Realisation of this outcome depends on increasing environmental flows and implementing sophisticated river management during dry periods, both highly contentious options.

An Investigation into the Effect of Dredging on Tidal Asymmetry at the River Murray Mouth

The coastal lagoon adjacent to the River Murray mouth has been filling with sediment brought in from the ocean by tidal currents for at least the last 170 years. Recently, reduced river flows have led to an increase in the rate of infilling, and in 2002 a program of dredging commenced in the lagoon to remove the millions of cubic metres of sediment that had accumulated there. Elsewhere, researchers have argued that it should be possible to manipulate the natural tidal asymmetry and, in doing so, alter the balance between ebb and flood dominance in a coastal lagoon. If this is possible in practice, it should be feasible to move a lagoon towards a self-flushing mode through a program of strategic dredging. Geographic Information Systems (GISs) were used to interpret bathymetric survey data in the lagoon so that channel characterisation, changes to sediment volume, and basin hypsometry could be analysed. Analysis of water-level data in the lagoon showed that flood durations were usually shorter than ebb durations, which demonstrated the occurrence of flood dominance. It was also found that the degree of flood dominance has reduced since dredging. The dredging has led to fewer, deeper channels and hence a reduction in the degree of flood dominance. The main conclusion is that it has been possible to manipulate the tidal asymmetry through the use of dredging and move the lagoon system towards ebb dominance and, therefore, natural flushing.