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In their recent paper, Williams et al. (2022) evaluated salinity management in the Murray-Darling Basin (MDB) as 'unsustainable', and a risk to water availability and quality in the Basin. However, this evaluation was weakened first by a failure to analyse the Basin salinity strategies of the last thirty-five years, noting that these have led to Basin salinity target being met since 2010; and second to not providing Basin-specific data to support their evaluation. Contrary to Williams et al. comments, existing evidence indicates that infrastructure intended to improve water use efficiency (e.g. salt leaching, salt disposal basins) will generally reduce stream salinity. The requirement for a leaching efficiency means that there is a lower limit to water use efficiency improvements, but this is unlikely itself to be a major risk. We agree that the changes that have occurred over the last twenty years would warrant a review of salt storage options in the MDB that better matches future needs. [ABSTRACT FROM AUTHOR]

Solute dynamics depend strongly on hydrologic flow paths and transit times within catchments. In this paper, we use a travel time tracking method to simulate stream salinity (as measured by electrical conductivity) in the Duck River catchment, NW Tasmania, Australia. The study couples storage selection function transit time modelling with two alternate approaches to model electrical conductivity (EC). The first approach assumes the catchment has a cyclic salt balance (i.e., rainfall source, stream flow sink) that is in dynamic equilibrium and evapoconcentration of salt is the only process changing concentration. The second approach assumes that the salinity of water in catchment storages is a function of water age in those stores, without explicitly simulating salt mass balance processes. The paper compares these alternate approaches in terms of EC simulation performance, simulated stream water age distributions, and simulated storage age distributions. A split sample calibration‐validation analysis was conducted using the 2008 and 2009 water years. Both EC simulation approaches reproduced stream EC variations very well under both calibration and validation. The simulations using the age‐related EC simulation approach produced less biased results and, consequently, higher model coefficient of efficiency for validation periods. This approach also produced more consistent model parameter estimates between periods. There were systematic differences in the resultant age distributions between models, particularly for the solute balance‐based simulations where parameters (catchment storage size) changed more between the two calibration periods. The effect of time varying versus static storage selection functions were compared, with clear evidence that time varying storage selection functions with parameters linked to catchment conditions (flow) are essential for adequate simulation of EC dynamics during flow events. [ABSTRACT FROM AUTHOR]

In deeply weathered laterite catchments of the Darling Range in south‐western Australia, the direct contribution (i.e., discharge) of permanent groundwater to streamflow has long been considered as minor. Instead, downslope shallow throughflow was thought to dominate, generating more than 90% of streamflow. We used a chemical hydrograph separation approach to estimate annual groundwater discharge for three catchments over periods of up to 39 years, and found that direct groundwater contributions to streamflow were far more variable across catchments and through time than has previously been acknowledged. The estimated proportion of annual streamflow sourced directly from groundwater ranged from 0 to 93% and was related linearly to the size of the groundwater discharge area in the catchment valley floor. In contrast, contributions from shallow sources including shallow throughflow varied primarily and linearly with annual rainfall. However, the response to rainfall was "amplified" in a predictable way by the size of the groundwater discharge area, consistent with the variable source area concept. We derived a functional relationship between catchment annual rainfall‐runoff ratio and groundwater discharge area and successfully applied this to a further four catchments, inferring that the results were broadly applicable across the Darling Range. The implications for an improved understanding of streamflow generating processes in the study region, and for laterite catchments generally, are discussed. [ABSTRACT FROM AUTHOR]

Plastic pollution is ubiquitous within the marine environment, including surface waters, water column and benthic sediments. Marine plastic contamination is expected to increase if future projections of increased plastic production eventuate. Conversely, national and international efforts are aiming to reduce marine plastic contamination. In this context, scientists, managers and the general public are increasingly interested in understanding the status and temporal trends of plastic contamination in the marine environment. Presented here is the first temporal assessment of plastic contamination in surface waters of the Great Barrier Reef (GBR), Australia. Specifically, duplicate surface seawater samples (n = 66) were collected at the SS Yongala shipwreck (Central GBR) monthly from September 2016 to September 2019 and analysed for plastic presence and abundance. The processing workflow involved density separation, followed by filtration, visual identification and sizing of putative plastics using stereomicroscopy, and chemical characterisation using Fourier transform infrared spectroscopy. A total of 533 plastic items were identified across all tows, consisting of macro-, meso- and microplastic fragments and fibres, with polypropylene and polyethylene being the most common polymers. Plastic contamination was detected in every replicate tow, bar one. Plastic concentrations fluctuated and spiked every three months, although contamination did not significantly alter across the three-year period. Wind speed, salinity and river discharge volume, but not surface current speed nor sea surface temperature, had a significant influence on the levels of plastic contamination. This study reveals, for the first time, the chronic presence of plastic debris in the surface waters of the GBR highlighting the need for long-term and on-going monitoring of the marine environment for plastic contamination. [Display omitted] • PE and PP fragments and PEST fibres were most abundant microplastics (MPs). • GBR surface plastic contamination varied, albeit did not increase, over three years. • Wind speed, salinity and river discharge volume influenced plastic contamination. • Long-term monitoring of marine plastics and physicochemical parameters is essential. [ABSTRACT FROM AUTHOR]

Salt accessions are the major water quality issue of the rivers and streams of the Murray-Darling Basin. The saline Murray Group Aquifer, the salinity of which exceeds 20,000 μS/cm, discharges an estimated 200 t/d of salt into the River Murray in South Australia between Lock 3 and Holder, 40 km downstream. Salinity mitigation works were needed to sustain irrigated agriculture and to maintain the quality of domestic, industrial and urban water supplies. Forty nine wells were drilled to the aquifer between Lock 3 and Holder from late 1989 to August 1990. Pumping of saline groundwater commenced in 1990 to lower the groundwater gradient to the river to zero thus preventing saline water discharging into the river. Telfer and Way estimated that pumping from the aquifer lowered salinity in the river stream by 46.3 μS/cm. Regression analysis of data that restricted it to three years prior tofull pumping commenced and to 3 years after zero gradient was achieved, with sites as categorical variables, estimated a reduction of 58.4±9.4 μS/ cm for flows ≤ 10,000 ML/d resulting in a reduction in salt load of 277 t/d. Regression modelling methodology can be extended to assessments of similar saline groundwater interception schemes. [ABSTRACT FROM AUTHOR]

Summary: In south-western Australia, significant declines in annual rainfall in recent decades have been accompanied by even greater declines in annual streamflow. The disproportionate decline in annual streamflow is perplexing and while there has been speculation about the causes, the mechanisms responsible for the disproportionate decline have not been demonstrated. This study seeks to clarify the role of groundwater in the disproportionate decline in annual streamflow in a small catchment in the jarrah forest by examining records of annual streamflow, stream salinity and groundwater which progressively declined from 1976 to 2011. The records span the transition from connected groundwater–surface water systems to disconnected. This provided a unique opportunity to differentiate the groundwater contribution to streamflow for two reasons. Firstly, because the change in streamflow following disconnection can be largely attributed to streamflow that was previously generated because groundwater was connected. Secondly, because groundwater was the main source of stream salinity and hence stream salinity was a natural tracer which indicated the presence and relative proportion of groundwater in streamflow. Disconnection occurred around 2001 and was signalled by a change in the annual stream salinity signature from moderately high and variable, to low and constant, and by the transition in piezometric levels at the catchment outlet from mostly above ground, to mostly below ground. Following disconnection, the average runoff coefficient which had been slowly declining, abruptly fell by more than half and subsequently remained relatively low and constant. This indicated that whilst groundwater was connected it played a key role in streamflow generation. The contribution by groundwater to streamflow generation was non-linear and was dominant at higher rainfalls. The annual stream salinity signature indicated that direct groundwater discharge to the stream was a relatively minor component, especially at higher rainfalls. Hence connected groundwater contributed to streamflow generation mostly indirectly, thus amplifying other streamflow-generating processes, by facilitating additional surface runoff and/or throughflow which were relatively fresh. As groundwater levels, and hence connectivity, declined, the amplifying effect of groundwater-facilitated streamflow generation also declined. We suggest that the large disparity between the rates of decline in annual rainfall and inflow into reservoirs elsewhere in the forests in south-western Australia mostly reflects the aggregate loss of connectivity in the catchments of streams contributing inflow into the reservoirs. [Copyright &y& Elsevier]

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Abstract: The majority of the definitions of estuaries have been based on the characteristics of estuaries in temperate regions of the northern hemisphere. As previously pointed out (), such definitions do not take into account such features as periodic closure of their mouths and hypersaline conditions during dry periods, which characterise many estuaries in southern Africa and south-western Australia. There is also ambiguity as to whether an estuary sensu stricto must be fed by a river. The following definition was developed to encompass the main characteristics of all estuaries: An estuary is a partially enclosed coastal body of water that is either permanently or periodically open to the sea and which receives at least periodic discharge from a river(s), and thus, while its salinity is typically less than that of natural sea water and varies temporally and along its length, it can become hypersaline in regions when evaporative water loss is high and freshwater and tidal inputs are negligible. Estuaries are thus regarded as unique ecosystems, which, in the case of fishes, for example, are occupied by species that collectively represent a particular suite of guilds. [Copyright &y& Elsevier]

Acute (24 h) toxicity tests were conducted to determine the toxicity of the fungicide chlorothalonil towards the freshwater bdelloid rotifer (Philodina acuticornis odiosa). Since rotifers are the dominant zooplankton species in many inland freshwater lakes in Australia, the influence of salinity on chlorothalonil toxicty was also assessed. The rotifers used in this study appeared to be reasonably tolerant to changes in salinity, with little mortality observed at 3760 µS cm-1, increasing thereafter at higher salinity. The bdelloid rotifers were, however, found to be highly sensitive to chlorothalonil (24 h LC50, 3.2 µg L-1) with results also suggesting that as salinity increases, so does toxicity (e.g., 24 h LC50 at 5000 µS cm-1, 0.5 µg L-1). [ABSTRACT FROM AUTHOR]

Abstract: It has been widely suggested that changing land use from annual to perennial crops reduces land and stream degradation due to salinisation. However, annual crops are financially attractive and increases in perennials can reduce stream flows with adverse effects on stream values. As such, salinity control is likely to involve tradeoffs between public and private costs and benefits. This study quantifies the expected on-farm economic and catchment-level water yield and salinity effects of altering land use among trees, perennial pastures and cereals. The structure of a two stage linear-programming (LP) process is described. The first stage is the MIDAS farm-level model of mixed cropping and sheep enterprises which provides inputs to a second stage catchment-level LP. It was concluded that perennial pastures can be used in conjunction with trees as a stream salinity-management tool in low to intermediate rainfall areas in New South Wales. The results indicate that land-use decisions should be informed by site-specific information if adverse effects on streams are to be avoided. [Copyright &y& Elsevier]

Cenozoic fluvial sediments present west of the Meckering Line occur at similar elevation ranges (mostly 200-260 m AHD) in the largely rejuvenated forested landscapes of the Darling Plateau between the Helena River catchment and the south coast of Western Australia. These widespread paleovalley sediments are more continuous than previously recognised, and possess common hydrogeological characteristics. The upper parts of catchments in southwest Western Australia are flat and poorly drained with widespread salt lakes and wetland systems developed on the sediments. The lower rejuvenated landscapes below the base of remnant sediments, which are locally marked by saline springs and right angle changes in river courses, have undulating topography with well-defined drainage lines cut into competent basement rocks. This paper identifies groundwater flow systems associated with the paleovalley sediments in three varied catchments and describes the role of the Cenozoic sand aquifer in the development and potential management of dryland salinity. Groundwater flow in the Cenozoic paleovalley sand aquifer has more significance for land and water salinisation than that in the local weathered basement. The sand aquifer is a conduit for salt mobilised from weathered basement following land clearing. Erosion of the sedimentary profile by rejuvenation has exposed this sand aquifer within specific elevation ranges in modern drainages facilitating saline groundwater discharge, and land and water salinisation. In the Helena River catchment 63% of the salt load to the Mundaring Reservoir is discharged through this sand aquifer in only 30% of the streamflow. Such mismatched salt load and flow means southwest landscapes respond differently to key dryland and stream salinity management actions. Revegetation to reduce the salt load should target areas of weathered basement locally discharging saline groundwater to the sand aquifer. Reforestation elsewhere in the rejuvenated bedrock landscape can, by contrast, reduce the streamflow (that is diluting large salt loads from the remnant sedimentary landscapes) and hence raise the overall stream salinity. [ABSTRACT FROM AUTHOR]

A major management decision in an ecological restoration or rehabilitation project is whether supplementary planting or natural vegetation regeneration is the better alternative or if a combination can be applied. Management decisions are further complicated when the project involves saltmarsh as tidal cycles, the effects of salinity and sea level rise add to the complexity of decisions. The ecological values of the saltmarsh community in Australia were only recognized relatively recently but the endangered ecological community listing in 1994 (under the New South Wales Threatened Species Conservation Act 1995) highlighted the need to protect, rehabilitate and restore saltmarsh. This project measured vegetation change after soil profile reconstruction in saltmarsh surrounding Sponsors Lagoon, Fingal Peninsula in north coastal New South Wales, Australia. Restored sites (planted and non-planted) were compared with nearby disturbed (control) and reference sites. The dominant species in the community to be restored were Saltwater Couch ( Sporobolus virginicus), Suaeda ( Suaeda australis), Sarcocornia ( Sarcocornia quinqueflora ssp. quinqueflora and Sea Rush ( Juncus kraussii ssp. australiensis). Changes in percentage cover of the species in the first three years after soil reconstruction work showed that the dominant Saltwater Couch established only from vegetative growth arising from remnant vegetation but there was strong seedling regeneration of several other species. It was concluded that planting is important for species that are less vagile, in larger, denuded parts of this site where their resilience is lower and natural regeneration potential is limited. An understanding of the biology of the individual species is therefore likely to be essential in saltmarsh restoration projects. A combination of techniques, incorporating planting of slower establishing species and encouragement of seed-germinated colonizers is useful for initial site stabilization and progressive ecological recovery at this site. The inclusion of migration zones in the planning phase will allow for the long-term viability of this restoration project. [ABSTRACT FROM AUTHOR]

Many important water issues such as over-allocation, stream salinity and environmental flows are influenced by the interaction between rivers and underlying aquifers. There are many indirect ways of estimating this flux (such as using hydrographs, tracers or geophysics) but the most common direct method is the use of seepage meters. Over recent decades, various modifications have been made to the basic seepage meter to address potential sources of measurement error and to handle operational issues. These aim to reduce the impact of factors such as upward advection of interstitial water (the Bernoulli effect), venturi effects of stream flow on the collection bag, anomalous short-term influx due to bag properties, gas accumulation in the chamber, frictional resistance causing head losses, ineffective seals and capture of shallow throughflow (rather than groundwater). We have attempted to incorporate these improvements in our seepage meter design and development of simple field procedures, which were trialled in two contrasting catchments (Border Rivers and Lower Richmond) in Australia. The field trials had mixed success, highlighting the potential for spurious seepage flux measurements due to these operational issues. [ABSTRACT FROM AUTHOR]

Fragmented populations of freshwater fish may develop genotypic and phenotypic differences as adaptations to local habitat conditions. These differences contribute significantly to biological diversity and may lead to speciation. In the Murray–Darling Basin, Australia, the Murray hardyhead Craterocephalus fluviatilis, listed as ‘endangered’ by the World Conservation Union, has a wide but fragmented distribution that is apparently related to salinity. To determine whether this pattern has a physiological basis, we compared osmoregulation in fish from two isolated populations in different salinity regimes (Wyndgate: 0.4–1.5‰; Disher Creek: c. 1.0–45‰). In laboratory trials, fish from both populations remained healthy at high salinities (5–65‰). The Disher Creek population maintained a significantly lower blood osmotic concentration than the Wyndgate population at salinities ≤1‰, suggesting that there is a physiological difference between them. The findings have implications for the conservation of C. fluviatilis and other fish populations whose distributions are fragmented by salinity. [ABSTRACT FROM AUTHOR]

Increasing salt concentration in tributaries from catchments and rising water tables are the prime contributor to environmental degradation of rivers, creeks, streams or other water bodies. This is especially true during periods of mid-and low stream flows in arid and semi-arid regions around the globe. Catchment scale studies suggest that management of stream salinity requires greater land use change than is economically viable. Therefore, rather than focusing on the opportunity cost of catchment scale interventions, exploring interventions that are potentially viable at farm scale could be an appropriate strategy for stream salinity management. This paper presents an analysis of alternative on-farm strategies, such as evaporation ponds and serial biological concentration of salts, aimed at developing an economically self-sustainable stream salinity management system for the Box Creek stormwater escape channel located in the Murray-Darling Basin (MDB), Australia. It is concluded that irrigation areas, with careful management of flows in tributary streams, may be able to play a role in safeguarding the Murray River against further salinisation from irrigation and dryland areas. The outcomes of this paper will be helpful, but not limited to, the MDB in addressing environmental, economic and social issues associated with management of salt concentration in tributaries. [ABSTRACT FROM AUTHOR]

Dryland salinity presents an overwhelming threat to terrestrial and aquatic habitats in Australia, and yet there remains very little empirical evidence of the impacts of secondary salinization on the biodiversity of riparian communities. Here we describe the response of a riparian plant community to stream and soil salinization, 25 years after the experimental clearing of a catchment in south-western Australia. Riparian plant species diversity was inversely related to soil salinity, and plant species composition was significantly altered by increased soil salinity. Despite the evidence for an impact of salinization on the taxonomic diversity and composition of the riparian plant community, there was little evidence for any effect of salinization on functional group diversity, or on ecological functioning, as measured by the percentage of above-ground plant cover. [ABSTRACT FROM AUTHOR]

Salinization of soils and water is an increasing problem of land degradation in many countries, including large parts of Australia. Recognition of the problem has led to a number of government‐directed programs both nationally and regionally. Direct support has been provided by the Western Australian Government to manage secondary water salinization of rivers in what are termed Water Resource Recovery Catchments (WRRCs) of the state's south‐west. The goal of the WRRC approach is to maintain or restore the quality of water at the potential or existing damsites to potable levels.The research reported in this paper evaluated the merits and limitations of the WRRC approach by examining scientific and agency literature and data, surveying government agencies, and interviewing representatives of stakeholders directly involved in managing the WRRCs. It was found that substantial efforts have been made to encourage on‐ground implementation of fencing, revegetation, establishing perennials and other salinity‐management strategies. However, these strategies generally have been insufficient to prevent continuing degradation of the WRRCs due to lack of clearing control enforcement, the slow response of upper catchments to treatment, and the insufficient scale of the treatments. Objectives other than dealing with salinization in particular also need to be identified and pursued. A newly‐created government agency—the Department of Environment—is well‐placed to direct such a broadened approach. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The NSW Government commissioned catchment management boards (CMBs) to set the direction and process for catchment scale natural resource management. In the Lower Murray Darling, Rivers are highly regulated and water resources shared between three states. The Catchment Board only has jurisdiction over the northern bank of the Murray but salt and water enter the river from many locations upstream and along the area boundary. River salt and flow modelling has continually been improved to reflect and contribute to an increased understanding of salinity processes. The MDBC Salt Load study correlates 10 years of actual measured data with its modelled outputs, and estimates river salinities for 2020, 2050 and 2100. Routing models such as SALTFLO and MURKEY generate percentile salinity levels at different nodes in the River Murray downstream of the Lower Darling confluence. National, Murray-Darling Basin and NSW salinity management policy and legislative requirements were considered, MDBC model output was used to ensure the interim targets are achievable, auditable, and appropriate to the catchment. The method for an end-of-valley river based target for salinity is described. A target of less than 463 µS/cm for Lock 6, a point in the lower reaches of the Murray River is recommended for year 2010. Catchment management targets that express the main river salinity risk in five hydrologically distinct management zones are also recommended. Salinity management changes are needed in each zone to meet the end-of-valley target. [ABSTRACT FROM AUTHOR]

Improving irrigation efficiency (IE) is an approach used globally to help meet competing demands for water and facilitate reallocation of water between sectors. In the Murray–Darling Basin in Australia, the Australian government has invested heavily in IE projects to recover water for the environment. However, this approach has been seriously questioned, out of concerns that improved IE would reduce irrigation return flows to rivers and therefore offset water recovery. In this study, we use a water balance model to assess the impact of the IE projects on return flows and highlight sensitivities and uncertainties. The model enables the impact on return flows to be assessed on specific IE projects and regional characteristics. Overall, reductions in return flows are estimated to be less than 20% of the total proposed IE savings. The history of IE in the southern MDB has meant that most of the current reductions are in ground return flows. Our estimate is much lower than two previous studies, mainly due to different assumptions being used on groundwater connectivity between irrigation areas and major streams. While the IE projects significantly reduce seepage to groundwater (with off-farm and on-farm projects reducing seepage by 19% and 53% of total savings respectively), not all seepage reductions will translate to a reduction in ground return flows to rivers. A lower estimate is consistent with existing monitoring and groundwater modeling studies. In this paper, the study results are discussed in a broader context of impacts of IE projects on volumes and salinity of streams and groundwater resources. [ABSTRACT FROM AUTHOR]

Quantifying the magnitude and timing of groundwater returns to streams from irrigation is important for the management of natural resources in irrigation districts where the quantity or quality of surface water can be affected. Deep vadose zones and perched water tables can complicate the modelling of these fluxes, and model outputs may be biased if these factors are misrepresented or ignored. This study was undertaken in the Murray Basin in southern Australia to develop and test an integrated modelling method that links irrigation activity to surface water impacts by accounting for all key hydrological processes, including perching and vadose zone transmission. The method incorporates an agronomic water balance to simulate root zone processes, semi-analytical transfer functions to simulate the deeper vadose zone, and an existing numerical groundwater model to simulate irrigation returns to the Murray River and inform the management of river salinity. The integrated modelling can be calibrated by various means, depending on context, and has been shown to be beneficial for management purposes without introducing an unnecessary level of complexity to traditional modelling workflows. Its applicability to other irrigation settings is discussed. [ABSTRACT FROM AUTHOR]

• Multiyear dry and wet periods affect the manifestation of dryland salinity. • We analyzed the role of GRACE total water storages in stream salinity variability. • The 2000–2009 millennium drought had a strong impact on stream salinity levels. • Stream salinity trends were partially explained by total water storage anomalies. By influencing water tables of saline aquifers, multiyear dry or wet periods can significantly delay or accelerate dryland salinity, but this effect remains poorly quantified at the large river basin scale. The Gravity and Climate Recovery Experiment (GRACE) satellite measures changes in the total water storage of river systems, providing a unique opportunity for better understanding connections between stream salinity and changes in catchment water storages at the large river basin scale. Here, we quantified the role of GRACE total water storage anomalies (TWSA) in stream salinity variability across Australia's Murray-Darling Basin (∼1 million km2), while also accounting for streamflow and rainfall. We used the MERRA-2 global land surface model to i) place our findings in the context of the longer-term hydroclimatology (1980-present) and ii) to decompose TWSA into groundwater storage as an alternative driver variable. Multivariate time series regression models (generalized additive mixed models or GAMM) showed that the driver variables could explain 20–50% of the variability in stream salinity across 8 sub-catchments in the Murray Darling Basin. TWSA commonly explained as much variability as streamflow, while groundwater storage and TWSA had very similar explanatory power and rainfall only negligible contributions. The 2000–2009 Millennium Drought and the subsequent La Nina Floods had a predominantly decelerating and accelerating effect on stream salinity respectively and these trends were partially explained by trends in TWSA. Our study illustrates that GRACE can be a useful addition for monitoring and modeling dryland salinity over large river basins. [ABSTRACT FROM AUTHOR]

• Restoration of water quality in watersheds is a major challenge in many parts of the world. • In south-western Australia stream salinity has been reversed in a 502 km2 watershed. • This was achieved through government planning and regulation and private sector investment in reforestation. Restoration of water quality in deforested watersheds is a major environmental and economic challenge in many parts of the world. In south-western Australia water quality issues manifest as salinisation, where reactivation of groundwater systems has occurred post-deforestation with the consequent discharge of salts stored in deep regolith into rivers. Prior to deforestation the stream salinity of the Denmark River (a forested watershed of 502 km2) was between 150 and 350 mg L−1TDS (Total Dissolved Solids) and was developed as a small water supply with potential for a much larger development. By the 1970s, 20% of deep rooted vegetation in the watershed was removed resulting in annual flow-weighted stream salinity of 1500 mg L−1TDS making the river unsuitable as a water supply. Two main policy approaches were used to restore this watershed: (1) the control of further deforestation on private land through regulation; and (2) a program to encourage private reforestation with eucalypt pulp-wood plantations. By 2010, 14.5% of the watershed was reforested leaving only 5.5% still deforested, with a strong relationship between streamflow and stream salinity and the amount of reforestation. River salinity had fallen to 500 mg L−1 TDS by 2017. Although streamflow had fallen from a mean 28.6 GL yr−1 in 1985–1990 to 13.6 GL yr−1 in 2012–2017 this was with water that was potable. The challenge into the future is to ensure the lower stream salinity is maintained through maintenance of forest cover. Importantly, this paper demonstrates that stream salinity can be reversed following deforestation if an appropriate scale of reforestation is deployed. [ABSTRACT FROM AUTHOR]

Sulfidic material commonly underlies coastal floodplains and in areas inundated by saline or brackish waters. A number of studies globally have quantified acidification risk in coastal environments and have identified potential coastal acid sulfate soil hotspots (CASS). Similarly, our knowledge of the geochemical processes and acidification risk which occur in inland acid sulfate soils (IASS) is also well established. In these environments in Australia, sulfidic material forms as a result of changes in river regulation or salinity which provides a source of sulfate. These studies on IASS have been largely been focused on floodplain environments, with sulfidic materials located on fluvial sediments.In some cases, sulfidic material can underlie peat swamps, which follow the same geochemical processes of oxidation as CASS and IASS to transport acidity and trace metals to degrade waterways and sediments. These peat swamps are commonly found in tropical areas and have rarely been studied in temperate catchments. This study identifies and characterises the acid sulfate soils and sulfidic material in two temperate peat swamps located in the upper reaches of a coastal catchment in southern Australia. Fish kills frequently occur downstream following rainfall events, most likely due to the initial flush of acidity from these peat swamps. We found that the acidification risk of these sulfidic peat swamps is very high largely due to the absence of any acid neutralising capacity. Reduced inorganic S concentrations were dominated by pyrite, suggesting that there is limited contemporary sulfide formation. Therefore, managing oxidation of sulfidic sediments and discharges of acidity in to these waterways is challenging as the environment surrounding the peat swamps is largely unmodified. [ABSTRACT FROM AUTHOR]