Keith Smettem

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.

There is an established need to measure soil salinity, and wireless sensor networks offer the potential to achieve this, coupled with a suitable sensor. However, suitable sensors, up until very recently, have not been available. In this paper we report on the fabrication and calibration of a new low-cost, robust, screen-printed sensor for detecting chloride ions. We also report on two experiments using this sensor. The first is a laboratory-based experiment that shows how sensors can be used to validate modeling results by installing several sensors in a soil column and tracking the vertical migration of a chloride pulse in real time. The second is a trial of multiple sensors installed in a fluvarium (stream simulator) showing that distributed sensors are able to monitor real time changes in horizontal chloride flux in an emulated natural environment. We report on results from both surface flows as well as from sensors at a depth of a few mm in the fluvarium sediment, and differences and trends between the two are discussed. As an example of how such sensors are useful, we note that for the flow regime and sediment type tested, penetration of surface chloride into the river bed is unexpectedly slow and raises questions regarding the dynamics of pollutants in such systems. We conclude that such sensors, coupled with a distributed network, offer a new paradigm in hydrological monitoring and will enable new applications, such as irrigation using mixtures of potable and brackish water with significant cost and resource saving.

Short rotation energy crops have the potential to provide sustainable sources of biomass, but the efficient use of nutrients will be crucial to ensure that these systems are sustainable. In dryland environments 3- to 5-yr rotations of tree crops integrated with agriculture represent a major potential bioenergy feedstock and a means to restore landscape hydrologic balances, while maintaining food production. In soils with low natural fertility, the long-term viability of these systems is critically affected by site nutrient status and subsequent cycling of nutrients. A nutrient assimilation index (NAI) was developed to allow comparison of the nutrient assimilation between tree species and tree components, to optimise nutrient management, and to quantify different strategies to manage nutrients. Biomass, nutrient export, and nutrient use efficiency were assessed for three short rotation tree crop species (Eucalyptus globulus, E. occidentalis, Pinus radiata). Component NAI was generally in the order of leaf

Surface water and groundwater (SW-GW) interaction plays a key role in replenishing alluvial aquifers and sustaining the ecology, quality, and quantity of streams and rivers. The interaction, mainly through the hyporheic zone (HZ), also plays a role in the nutrient exchange between terrestrial and aquatic ecosystems. Hyporheic water exchange in many sandy coastal plain drains presents an intermittent hydrological regime, as often shifts occur in their hydraulic functioning from a losing to a gaining stream condition upon the position of the surrounding water table. This work documented the existence and the complex hydrodynamics of HZ water exchange in an artificial drain typical of a coastal plain area (Mayfield drain, Harvey River) in Western Australia (WA), which resulted from a combination of highly responsive water level regime in the drain and a seasonal-transient shallow water table developed in a duplex soil (sand over clay) setting. A novel hydrometric approach using a rugged field camera (water levels on the drain), automatic water level sensors (bores), and a set of temperature sensors (drain?s bed and bank) provided a robust data set to explore vertical water exchange (fluxes) under baseflow and storm event conditions for different hydraulic scenarios (water stages for drain and water table) across the wet season. Water fluxes and direction in the HZ were computed using the one dimensional (1D) heat transport model for pore water (VFLUX) from temperature data, and further verified by a standard hydraulic approach using Darcy?s law and hydrometric data. The results indicated that under baseflow conditions, vertical water flux estimates were directed downwards, of drain water into a shallow sandy layer (< 0.4 m), but with an upward flux from the underneath clay layer (0.4 - 0.7 m). The magnitude and temporal variability of the fluxes corresponded with the drain water stage as increasing downward fluxes due to higher drain stage resulted in decreasing upward fluxes from the clay layer. During storm event conditions, a similar water exchange direction was observed but a substantial increase in the downward flux (by an order of magnitude) of drain water occurred without any change on the upward flux. This dynamics showed a dependency on both mean drain storm water stage and the duration of high flow conditions. These results and the observations of high water table level at the bank indicated that the excess of water into the HZ was mainly mobilized to downstream locations along the drain bed. Further analysis of the gaining and losing water condition over a 620 m drain reach, using flow measurements and water quality surveys, supported VFLUX results. This work identified the presence of a shallow HZ confined vertically by a clay layer (typical feature of duplex soils in the area) and laterally by a high water table in the bank, under both baseflow and stormflow conditions present in the drain. The findings also highlighted the importance of flux estimation using thermal records to complement traditional hydraulic approaches due to lack of conclusive results provided by the latter.