John Ruprecht

For thermal energy storage, the most promising method that has been considered is latent heat storage associated with molten salt mixtures as phase-change material (PCM). The binary salt mixture lithium chloride—lithium hydroxide (LiCl–LiOH) with a specific composition can store thermal energy. However, to the best of our knowledge, there is no information on their thermal stability in previous literature. The key objectives of this article were to investigate the thermophysical properties, thermal repeatability, and thermal decomposition behavior of the chosen binary salt mixture. FactSage software was used to determine the composition of the binary salt mixture. Thermophysical properties were investigated with a simultaneous thermal analyzer (STA). The thermal results show that the binary salt 32 mol% LiCl-68 mol% LiOH melts within the range of 269 °C to 292 °C and its heat of fusion is 379 J/g. Thermal repeatability was tested with a thermogravimetric analyzer (TGA) for 30 heating and cooling cycles, which resulted in little change to the melting temperature and heat of fusion. Thermal decomposition analysis indicated negligible weight loss until 500 °C and showed good thermal stability. Chemical and structural instability was verified by X-ray diffraction (XRD) by analysing the binary salt system before and after thermal treatment. A minor peak corresponding to lithium oxide was observed in the sample decomposed at 700 °C which resulted from the decomposition of LiOH at high temperature. The morphology and elemental distribution examinations of the binary salt mixture were carried out via scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). X-ray photoelectron spectroscopy was conducted for surface analysis, and their elemental composition verified the chemical stability of the binary salt mixture. Overall, the results confirmed that the binary salt mixture is a potential candidate to be used as thermal energy storage material in energy storage applications of up to 500 °C.

Salinization of land is a form of desertification; salinization of rivers is a global threat to biodiversity and compromises the ecosystem goods and services of rivers, wetlands, and lakes. Salinization is caused by flooding or inundation with saline waters, breaching of dykes, storm surges, tsunamis, or the drying of large inland water bodies. Salinization can result where irrigation waters are compromised by salinity. Salinity intersects with major global concerns, including food security, desertification, and biodiversity protection. Soil salinity results from an excess of salts in the soil that reduces plant growth and crop productivity and affects soil biological activity. Salinized soils impose an osmotic stress on plants, reducing water uptake and concentrating toxic level of sodium and chloride. Different plant species exhibit different degrees of salinity tolerance. Salinization removes arable land from production, causing abandonment globally of 0.3–1.5 million hectare year−1. With adequate drainage, salts can be leached and the soil recovered but where the water table remains near the surface, the salinity problem will remain. It may be possible to reverse the effects of salinization. A crucial consideration is whether the desired end point is stabilizing the soils against further change, or reversing the process and restoring soils to another state. Approaches include prevention, stabilization, active management, or land retirement or abandonment. Successful restoration of salinity at the landscape-scale relies on broadscale land-use change. This is problematic where the most profitable land-use is agriculture, thus there has therefore been considerable investigation of land-use systems that at least replicate the profitability of the current agricultural system. Recent approaches have explored how to make the higher water using farming systems acceptable by making the replacement plants profitable in their own right.

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.

Key message In a major Australian city, water supply has been decoupled from forests as a result of management and climate change. Water yield and quality are closely related to forest cover and have been manipulated through broad-scale intervention. The forests remain important for biodiversity protection and considering water as a forest product will fund interventions that maintain the forest’s environmental values. Context Perth, an Australian city of 2 million people and a potable water demand of 300 GL/year, occurs in a region that has experienced a decline in rainfall and a major reduction in surface runoff to water supply reservoirs over the last 40 years. This has led to a major impact on water policies, with the collapse of surface water supply from forested watersheds resulting in the almost complete substitution of Perth’s water supply with groundwater and desalinated water. Thus, water supply has been decoupled from forests and forest management processes. Aims In this paper, we review the interactions between forest cover and water supply in the drying environment of south-western Australia, exploring studies on the hydrological effects of extensive deforestation for agricultural development, widespread reforestation, forest management, and reduced annual rainfall. We draw conclusions applicable to other regions that are experiencing the combined impacts of climate change and pressures from land-use intensification. Results We find that streamflow and water quality are clearly linked to forest cover and this is affected by both climate and forest management. Streamflow increases with a reduction of forest cover (through deforestation or thinning) and decreases with reforestation and reduced rainfall. Stream salinity increases with deforestation and decreases with reforestation. Hydrological responses occur where forest cover treatments have been applied and maintained at watershed-scales. Surprisingly, where water yield or quality has been improved, this has not been rewarded financially and there is a need to develop methods of financing treatments to maintain streamflow. Conclusion Whereas forests were initially maintained for water and timber supply, with biodiversity protection as a co-benefit without a defined value, the decoupling of forests from water supply has substantially reduced the financial resources for any form of direct forest management. As the forests remain important for biodiversity protection, a key recommendation is to consider water as a forest product and thus provide funds for watershed-scale treatments, such as forest thinning, that maintain the forest’s environmental values in a drying climate.

Dryland salinity is driven by excess water in the landscape resulting from clearing of perennial vegetation. The decrease in winter rainfall and virtual absence of ‘wet winters’ has caused a slowing in the process of salinisation, and in some cases groundwater levels have fallen. Deeper bores are continuing to rise while shallow (< 8m) groundwaters have flattened. In the north-eastern
Wheatbelt, the occurrence of summer storms has created an erratic response.

Stream salinities in many streams have continued to increase because of reduced fresh runoff which, in wet years, dilutes the saline groundwater discharge. However, in catchments where groundwater levels no longer intersect the valleys because of falling levels, runoff has freshened.

South-west WA can experience extreme rainfall in winter with frontal systems and in summer with tropical storms.

In the mid-1970s in south-west WA there was a shift to consistently drier conditions (see IOCI Climate Note 5/05) for annual and seasonal rainfall. Research sponsored by IOCI suggests that both natural climate variability and the enhanced greenhouse effect have played a role. However, it is much more difficult to determine if there has been a shift in extreme rainfall. At the relatively frequent level of extreme events, such as less than a one-in-10 year annual maximum rainfall event (20- 60mm recorded at various locations), observed statistics give us some insight, but for extremes at the rare or disaster level, there is very little understanding at this point in time.

The data for many rainfall stations in the south-west indicate that larger storms do not appear as often now in winter, but the magnitude of annual winter maxima is not significantly changed. There are also observations that summer rainfall events (one-in-10 year) are typically random and have not altered significantly over the last 100 years.

Continuing research by IOCI is building our understanding of factors driving these changes, but projections of change in rare events are perhaps only able to be investigated by modelling studies at the very edge of our current capability in climate science.

This is the first overview of stream salinity across the south-west of Western Australia since 1988. More than half of the rivers analysed in this study are now marginal in quality, brackish or saline, and only 44% of the south-west rivers are still fresh. Stream salinity was still rising at many of the sites analysed. Sixty-six percent of the analysed rivers had higher salinities in the last 10 years (1993–2002) than in the previous 10 (1983–92). Part of the reason for the higher salinity was lower rainfall over the last 10 years.

The wheatbelt of Western Australia largely corresponds to a zone of ancient drainage, characterised by highly variable rainfall, long dry summers, low hydraulic gradients, intermittent surface flows and high regolith salt loads. The accumulation and distribution of salt, the rudimentary aquifers with deep watertables, the intermittent flooding and subsequent transpiration of water from the valley sediments, and the low yields of water reaching the ocean were a product of the underlying physical environment and vegetation types capable of using deeply infiltrated water through the dry season. The hydrological and hydrogeochemical changes induced by widespread clearing of this vegetation for dryland agriculture are profound and enduring. Run-off onto and through the valley floors has increased by a factor of five; combined with local rainfall on these valley floors, the resulting increase in groundwater recharge is filling the deep sedimentary materials and bringing highly saline water to the surface. Diffuse recharge has also increased on the slopes and ridges, with saline watertables rising in these lateritic formations as well, providing additional hydraulic heads forcing groundwater towards the valleys. The resulting increase in the groundwater discharge areas is projected to greatly increase flooding risk downstream into the future. A variety of natural, built and agricultural assets are either already impacted or at risk to these phenomena. It is hypothesised that restoring the original hydraulic and hydrological functions of the system will lead to its recovery. This raises several issues: can we design remedies in terms of restoring the original rates of flux (recharge, runoff, etc) or in terms of the original balances (recharge less than aquifer discharge, input of salt into the root zone equal to output)? Secondly, to what degree can revegetation or engineering now restore these original conditions? Finally, we examine the potential for the landscape to recover to its original hydrological and hydrogeochemical state once salinised. Given the advanced state of saline watertable development, with its implications for successful revegetation and restoration of valley transpiration, the changes in soil structure and chemistry, and the immediate implications to valued assets, we posit that an aim of restoring the landscape solely with revegetation, either in terms of rates or balances, is not feasible or even possible. To a degree, one can only restore certain aspects of the original balance via revegetation combined with discharge enhancement and flood mitigation.

Saline water was common in south- west Western Australian aquatic systems prior to land- clearing because most streams and wetlands were ephemeral and evapo- concentrated as they dried, and there were high concentrations of stored salt in groundwater and soil profiles. Nevertheless, a 1998 review of salinity trends in rivers of south- west Western Australia showed that 20- fold increases in salinity concentrations had occurred since clearing in the medium- rainfall zone ( 300 - 700 mm). More recent data confirm these trends and show that elevated salinities have already caused substantial changes to the biological communities of aquatic ecosystems. Further substantial changes will occur, despite the flora and fauna of the south- west being comparatively well adapted to the presence of salinity in the landscape. Up to one- third of wetland and river invertebrate species, large numbers of plants and a substantial proportion of the waterbird fauna will disappear from the wheatbelt, a region that has high biodiversity value and endemism. Increased salinities are not the only threat associated with salinisation: increased water volumes, longer periods of inundation and more widespread acidity are also likely to be detrimental to the biota.