Richard Harper

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.

Carbon sequestration in soils is an issue of international significance, as soils represent a large carbon pool and can be a major sink for atmospheric carbon dioxide. In southern Australia, soil carbon under agricultural land uses has received attention, particularly in relation to the potential for perennial plants to sequester carbon. Although considerable attention has been applied to carbon sequestration associated with reforestation, there has been less work associated with perennial pastures. It can be argued that farmers are more likely to change pasture than undertake reforestation, thus if carbon mitigation via the land sector is to occur over large areas, the dynamics of carbon under perennial pastures needs assessment. Standard soil testing for carbon stocks extends to a depth of 0.3 m whereas perennial pastures have the potential to grow roots much deeper than this, and potentially can have impacts on soil carbon storage to the full depth of the root zone. In this research we measured soil carbon to a depth of 4.0 m under a replicated trial on a deep sandy soil including plots of Gatton panic (Megathyrsus maximus) and plots of a barley/lupin rotation, five years after commencement of the trial. Soil water measurements suggested a maximum rooting depth for the pasture of 3.5 m, and 1.5 m for the annual crops. Despite differences in root depth, there were no significant differences in soil carbon between the two land uses. However, total soil carbon storage was considerably higher (44 t C/ha) when measured to a depth of 4 m compared with the standard 0.3 m depth (23 t C/ha).

Multiple issues confront catchment managers including maintenance of water yield and water quality, preservation of soils and protection of remnant biodiversity. In many cases technical solutions exist but there is a lack of capital to implement solutions at the scale required to resolve the issues. Changes to land use such as reforestation and application of soil amendments can potentially provide a range of ecosystem services, such as carbon mitigation and biodiversity protection and also change water yield and water quality. The Australian Carbon Credits (Carbon Farming Initiative) Act 2011 (CFI) recently passed into law and while this is aimed at carbon mitigation it also provides a range of opportunities for widespread improvements in catchment management and water quality. This paper describes the potential benefits that could flow from the CFI using four case studies from south-western WA. They are (1) reforestation of catchments to achieve carbon sequestration and improve water quality, (2) soil amendments that are likely to sequester carbon and reduce nutrient leaching from sandy soils, (3) restoration of wetland vegetation to achieve carbon sequestration, and (4) biomass production from previously salinized land. For each the potential for carbon mitigation will be examined, the likely water co-benefits outlined and knowledge and policy barriers to implementation described.

The transition to a low carbon economy provides potential opportunities for Indigenous communities living in remote areas of Australia. Recent studies and trial projects indicate a potential range of benefits from early season fire management, biosequestration, bioenergy production, permaculture gardens and energy monitoring services. Remote Indigenous communities in Australia typically have few employment opportunities, and the health and socio-economic statistics of residents indicate several disadvantages compared to the average non-Indigenous Australian. Despite this many communities maintain a strong culture and a wealth of traditional knowledge, particularly in relation to natural resource management. Given the carbon profile in communities is highly influenced by their dependency on external factors such as energy, housing, food and general service supplies and lack of internal resources a model has been developed to investigate the effect of transitioning communities to a more self-sufficient 'sustainable livelihood' structure to address carbon emissions and also provide a suite of other benefits. The model being developed includes carbon sequestration opportunities for communities coupled with carbon emission reduction strategies for the six key sources including materials, construction processes, operating energy, transport, water and waste systems. The carbon sources and sinks are being measured using a life cycle analysis approach.

The transition to a low carbon economy provides potential opportunities for Indigenous communities living in remote areas of Australia. Recent studies and trial projects indicate a range of potential benefits from carbon management programs such as early season fire management, bio-sequestration, bioenergy production, and energy monitoring services. Remote Indigenous communities in Australia typically have few employment opportunities, and the health and socio-economic statistics of residents indicate several disadvantages compared to the average non-Indigenous Australian. Despite this many communities maintain a strong culture and a wealth of traditional knowledge, particularly in relation to natural resource management. These carbon management programs offer potential employment and business development prospects that utilise Indigenous knowledge and are in keeping with their caring for country preferences. There is little published information on the carbon profiles of these communities but they are expected to be highly carbon intensive due to their frequent reliance on diesel-powered electricity generators, fossil-fuelled vehicles that need to travel vast distances and housing that often requires energy-intensive thermal conditioning. Hence, efforts are also required to help reduce carbon emissions and associated costs, particularly rising electricity and fuel prices from direct use or those embedded in goods and services. To ascertain whether implementation of proposed carbon management programs can be combined to mitigate carbon emissions a method for estimating and comparing emission abatement across a range of scenarios is required. A carbon accounting model that quantifies the estimated carbon that can be mitigated from sources and sequestered in sinks for a given community has been developed. The model combines two methods of measurement: life cycle analysis and land use modelling techniques. LCA is an assessment of impacts throughout a product's life, or "cradle to grave", including raw material acquisition, through production, use and disposal. The AS/NZS ISO standard 14040:1998 Environmental Management- Life cycle assessment - principles and framework outlines the requirements and process for undertaking a life cycle impact assessment. The life cycle analysis is applied in the model to estimate key emission sources for greenhouse gases broadly categorised as follows: materials used for construction and maintenance, construction processes including transport, operating energy supply and demand, transport during the occupancy phase, water systems, and solid waste. Because a full life cycle analysis can be a time and data intensive undertaking only significant items in the community are included and some emissions related to transport and waste are based on annual inventory methods only. Embedded within the life cycle analysis is the model to estimate carbon sinks. The carbon sinks are modelled using a method in accordance with IPCC guidelines for land use, land use change and forestry (LULUCF). This takes into account conversions for a variety of land use categories and, where significant, sub-categories of biomass, dead organic matter and soil. This allows sinks to be estimated within defined limits of uncertainty and a total sequestration quantity to be approximated. The combination of the two measurement methods provides an overall carbon cycle for a community and an estimate of the potential to provide climate change mitigation capacity including a quantitative basis for further economic analysis.

Salinization threatens up to 17 million ha of Australian farmland, major fresh water resources, biodiversity and built infrastructure. In higher rainfall (>600 mm yr-1) areas of south-western Australia a market-based approach has resulted in the reforestation of 250,000 ha of farmland with Eucalyptus globulus pulpwood plantations. This has had significant collateral environmental benefits in terms of reducing salinity and restoring landscape function in several key water supply watersheds. This success has not been replicated in the lower (300-600 mm yr-1) rainfall areas of this region, which is a global biodiversity hotspot. Wood yields are lower and there is often a land-holder preference to maintain existing agricultural activities. Several new forest products, such as sequestered carbon and biomass for renewable energy generation, are being evaluated as it is considered that a multi-product approach is more likely to be profitable than timber production alone. Carbon sequestration may occur both as an adjunct to wood production systems and also where restoration of biodiversity is the primary aim. The development of full markets for these products is dependent on the establishment of national emissions and renewable energy policies and targets, and in the case of liquid biofuels further technological development. Three broad approaches to integrating trees into the dryland farming systems are being assessed viz. (a) belts of trees with farming maintained in the alleys, (b) blocks of trees located on areas of water accumulation or of high recharge, and (c) short phases (3-5 years) of trees alternated with cropping. Both the alley and phase farming systems offer the prospect of producing biofuels from farmland without either using food-grains or displacing farming production. Paradoxically, for systems that are attempting to stabilize landscape hydrology, a major issue for reforestation is water management and this can be manipulated through species selection, tree placement and canopy management. If inappropriate species or planting densities are used, in relation to a site’s water supply, the trees will die. Although this is an aim of the phase farming system, for the other systems, avoidance of annual and periodic drought is a prime consideration.

The current agricultural systems of broad areas of Australia are unsustainable, with large projected increases in salinisation, decreases in water quality and losses of biodiversity. Increased concentrations of greenhouse gases have been linked to global warming. The international response to this warming, the United Nations Framework Convention on Climate Change and its Kyoto Protocol, include provisions that enable greenhouse sinks, or the sequestration of carbon in soils and vegetation to be used by Parties as one strategy to fulfil their obligations. The Kyoto Protocol, which is yet to be ratified by Australia, also allows for trading in emission reductions, and this opens the possibility that investment in carbon sinks may help underwrite broader natural resource management objectives. This paper describes a study that examined the possibilities for improved land management in Western Australia arising from the development of carbon sinks. This considered (a) the likelihood of a carbon market developing and the likely depth of that market as a result of current national and international policies, (b) the data available to provide estimates on different types of sinks and (c) the likely benefits of wide-scale sink investment. The study was designed to quantify an upper limit to sink potential. It was estimated that the total amount of carbon that could be sequestered by revegetating 16.8 Mha of cleared farmland was 2.2 Gt CO2-e, and 3.3 Gt CO2-e by destocking 94.8 Mha of Western Australian rangelands. It was considered that there were insufficient data to produce estimates of sequestration following changes in tillage practice in cropping systems or the revegetation of already salinized land. We conclude that carbon sinks are only likely to become profitable as a broad-scale stand-alone enterprise when carbon prices reach A$15/t CO2-e. However, below this price their value can be significant as an adjunct to reforestation schemes that are aimed at providing other products (wood, pulp, bioenergy) and land and water conservation benefits. Irrespective of this, carbon sinks provide an opportunity to both sequester carbon in a least-cost fashion and improve soil and watershed management.

Western Australia alone up to 450 species are threatened with salinity-induced extinction. The integration of woody perennials into farming systems is often advocated as a method of reducing recharge and remediating dryland salinity. Whereas complete revegetation is feasible in higher rainfall catchments where improved water quality is an outcome, such a planting strategy is impractical in lower rainfall areas due to the need to maintain cereal cropping. It is thus necessary to consider methods of integrating trees with agriculture that allow agricultural production whilst also improving the water balance. In low rainfall areas (<400 mm yr-1) two options for incorporating trees have been proposed, alley farming between belts of trees and short phases of trees rotate with agriculture. A survey of rooting depths of belts of farm forestry species (oil mallees (Eucalyptus spp.), Eucalyptus astringens, Acacia acuminata and Allocasuarina huegeliana) aged 4 to 11 years old found soil was dried to depths ranging from 4 to 10 m, with evidence of drying up to 15 m laterally. Phase farming with trees reduces recharge via the creation of a dry soil buffer to capture the leakage under subsequent annual crop rotations. In 2001, Eucalyptus globulus, E. occidentalis, Acacia celastrifolia, Pinus radiata and Allocasuarina huegeliana were planted at four densities 500, 1000, 2000 and 4000 stem ha-1, as well as 500 stem ha-1 plus fertiliser. Species survival and growth were predominately affected by site characteristics and slope location as well as density in the second year of growth. Soil water content under high density Eucalyptus plantings was depleted to depths of 4 m after 2 years. The implications of these results for the use of deep-rooted perennials for recharge reduction and salinity control are discussed.