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.

Understanding how summer low flows in a Mediterranean climate are influenced by climate and land use is critical for managing both water resources and in-stream ecohydrological health. The Eucalyptus forest ecosystems of southwestern Australia are experiencing a drying and warming climate, with a regional step decline in rainfall in the mid-1970s. Reductions in catchment water storage may be exacerbated by the deep rooting habit of key overstorey species (>30 m has been reported), which can buffer against drought during dry years. Root exploitation of deep soil moisture reserves and/or groundwater can accelerate the long term decline in summer low flows, with a trend towards more ephemeral flow regimes. In contrast, conversion of forests to agricultural land in some catchments can lead to counter-trends of increased low flows due to a rise in groundwater pressure. These are invariably associated with an increase in stream salinity as regolith stores of salt are mobilized. There has also been extennsive reforestation of farmland in some catchments. In this study we perform a detailed analysis of changes to annual summer seven day low flow trends in perennial catchments and flow duration curves in ephemeral catchments across 39 catchments in south-western Australia that have long term records of runoff, rainfall and land cover. Results showed that 15% of catchments exhibited increased low flows and 85% decreased flows or decreased flow days since the 1970s. Significant downward step changes in low flows were observed in 17 catchments (44%). The earliest downward step changes occurred in three catchments between 1981-82 (a lag of one decade after the rainfall decline), with the most recent step changes for five catchments occurring in 2001-2004 (three decades after rainfall decline). Eleven catchments were already ephemeral in the 1970s, but exhibited continued declines in the number of annual flow days over subsequent decades. Step changes occur when groundwater becomes disconnected or reconnected to the stream invert, with disconnection associated with rainfall decline and vegetative water use. The statistical methods we used in this study can be applied to any catchment in order to aid land and water managers assess the impact of climate change and land cover manipulation on low flow response.

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.

Globally, forests cover 31% of the Earth’s land mass and are critical areas for water supply. In Australia, forested catchments provide 77% of urban water supplies to capital cities. However, recent studies have reported worldwide examples of forest damage resulting from drought or heat related events. The jarrah (Eucalyptus marginata) forests of south-west Western Australia (SWWA) have experienced both sudden and unprecedented forest collapse and profound reductions in streamflows. Projected further declines with climate change, reinforce the need to understand the hydrologic impact of forest disturbance and what management responses are needed to enhance forest resilience and productive capacity. The aim of this thesis was to understand the impact of disturbance and climate on the hydrology of the forests of SWWA, with objectives to: 1. Examine the characteristics of forest hydrology; 2. Evaluate the hydrologic response to forest disturbance and climate variability; and 3. Evaluate forest water management options in the context of forest disturbance and climate change. This thesis thus develops an understanding of the impact of disturbance and climate on the hydrology of the forests of SWWA. Using hillslope and paired catchment studies (Chapter 3), it develops an understanding of the process of infiltration and soil water dynamics and examines the hydrologic impact of forest disturbance. The studies demonstrate the important roles of infiltration, soil water dynamics, and groundwater on the forest water balance, and identify the major factors that impact forest disturbance and forest hydrology. These studies have improved understanding of factors contributing to catchment water balance, and streamflow generation processes. Four catchments underwent land use change and the impact on catchment hydrology was studied by comparing with a control catchment (Chapter 4). These paired catchment studies evaluated the impact of converting forest to agriculture and of timber harvesting. They explored the streamflow generation mechanisms for forested and cleared catchments, the streamflow generation and salinity export changes due to clearing for agriculture, and the hydrologic impact of intense timber harvesting for increased water production. The impacts of deforestation, forest thinning, bauxite mining, bushfires, dieback disease, and reforestation were evaluated using several paired catchment studies across SWWA (Chapter 5). The long-term implications for management of water yield, the impact of a range of disturbances at a catchment scale, and the impact of forest disturbances on stream salinity are also examined. The relationship between the drying climate observed in SWWA over the last 40 years and observed changes in rainfall, groundwater levels, streamflow volumes and flow duration were studied in Chapter 6. The changing relationship between rainfall and streamflow and the likely implications of recent climate change scenarios are also studied. The major forest water issues that have been identified in this thesis are the declining water values in forested areas, such as less water volumes, shorter flow periods, and declining groundwater levels. The adaptive strategies for forest ecosystems are identified to include resistance (protect highly valued areas), resilience (improve capacity to return to pre-disturbance conditions) and response (assist transition to new condition) are discussed in Chapter 7. Drivers identified (Chapter 7) by this thesis include (a) a drying climate with direct and indirect impacts on both the forest itself and on the overall water balance, (b) responses to historical forest management including forest harvest, deforestation and reforestation, (c) long-term impacts of bauxite mining and subsequent rehabilitation, and (d) the interaction of these forest disturbances at a catchment scale. The major findings from this study include: - The high saturated hydraulic conductivity of the sandy gravel topsoil overlies lateritic durcirust with a much lower saturated hydraulic conductivity; - The presence of large infilled “holes” within the lateritic duricrust; - Saturation above the lateritic duricrust was observed confirming subsurface flow concepts; - Presence of vertical preferential flow observed confirming soil water concepts; - The critical importance of the groundwater discharge area in streamflow generation; - Increase in stream salinity directly linked to groundwater levels approaching the surface; - The time to leaching of the salt from the catchment estimated at 200 years; - Forest disturbances such as clearing, timber harvesting and forest thinning led to increased streamflow but with significant delays related to the presence or lack of a groundwater discharge area; and - The extensive reduction in streamflow across the south west has ranged from 36 to 52% (1975 to 2000 compared to 2001 to 2012) seen as a delayed response to rainfall reductions from 1930 to 2000. The challenge for the future is for forest hydrology research to influence current and future forest management to improve environmental and water supply outcomes for the forests of not only SWWA, but globally. Understanding the impact of land-use change on hydrology, water quality and on water resources, and separating this from climate variability and change, is a recurring problem globally. Further understanding is thus needed of the causes of changing forest hydrology and of management options to ultimately improve forest outcomes.

Forests can contribute to climate change mitigation through (1) protection and enhancement of existing carbon stocks, (2) increasing carbon stocks and (3) substituting forest products for energy production or energy intensive building materials. Payments for forest carbon mitigation are occurring under various arrangements in different jurisdictions and the scale of future activity could be large. The likely impacts of broad-scale forest-mitigation on water yield and quality are not understood. Various approaches to water management using carbon mitigation have been examined in south-western Australia, a region with a drying Mediterranean climate and limited potable water supplies. The impacts on water yield and water quality of (1) deforestation and thinning of natural forests, and (2) reforestation of farmland have been studied. Approaches to reforestation have concentrated on Eucalypts and Pinus spp. and include total reforestation of watersheds, integration of strips of trees with farmland and 3–5 year rotations of trees interspersed with cereal cropping. Mitigation has been through both sequestration and bioenergy production and has occurred on both productive and abandoned land. Forest cover profoundly affects water yield and quality, not only through changes in watershed water balance, but also on the release of dissolved salts into the landscape.