Landscape processes and evolution

Physical Geographers at the University of Sydney investigate landscape processes over a range of spatial and temporal scales and have specific research interests in: geomorphology; hydrology; environmental change; environmental pollution; weathering; and, coastal and marine environments. This research utilizes data from a variety of sources including field sites, laboratories, satellite imagery and computer modeling and GIS.

Hydrological Processes

Rivers & Catchments
Australian Governments at all levels are placing an increasing emphasis on the sustainable use of our rivers. Such use, however, requires an understanding of how rivers respond to changes in flow and/or catchment landuse. Physical Geographers at the University of Sydney are currently involved in several research initiatives that have implications for the ongoing management of river systems in Australia. Mel Neave, for example, participates in a number of projects that aim to improve knowledge on the operation of Australian fluvial systems. Projects Mel is currently working on include:

• a Sustainable Rivers Audit funded by the Murray-Darling Basin Commission to develop a method for objectively defining river and floodplain condition at the reach scale using remote imagery (with colleagues from the University of Canberra);
• an investigation of the links between hillslope and river salinity, hillslope erosion and fluvial sedimentation; and,
• a study of how river channels evolve from initially straight to complex meandering planforms using a coupled form-flow model.

In addition, research into the condition of the River Torrens in South Australia by Stephen Gale has revealed it to be perhaps the most degraded urban river in Australia. The Torrens has suffered long-term and wide-ranging degradation. Its hydrology has been manipulated, its catchment has been massively modified, and its channel has been used as a sump for toxic materials and as a drain for the disposal of a wide range of pollutants. This degradation has had dramatic impacts on the river's ecology. This work has established for the first time the regional pattern of inorganic pollution in the sediments of the Torrens. The report has generated considerable media attention and played a major role in persuading the Adelaide City Council to set up an Urban Rivers Symposium and the State Government to establish the Torrens Taskforce. Stephen also has interests in the hydrology of carbonate aquifers and has studied groundwater quality on tropical islands, the groundwater chemistry of aquifers in far northwest Queensland and the archaeology of Aboriginal wells.

Soil erosion and sediment transfers
Work at sites in a range of environments by Stephen Gale has revealed that Australia's land surface was dramatically transformed by human activity within a few years of European contact. The extent of soil removal was so great that, for the last 150 years, denudation has been controlled not by human or environmental factors, but by the rate at which soil formation has been able to provide fresh material for erosion. This work has allowed the long-term impacts of land-use practices on soil loss to be judged, the effects of secular environmental variation to be evaluated, the antecedents of modern soil erosion problems to be established and the lag times between catchment modification and catchment response to be quantified. It has also enabled the impact of rare, high-magnitude environmental events to be placed in a meaningful temporal context, providing information on long-term recoveries and responses to environmental disruption.

Fire is an integral part of the Australian landscape and bushfires often lead to accelerated sediment transfer, in both temperate eucalypt forest and subalpine environments. Deirdre Dragovich has found that post-fire sediment transfer is linked to fire intensity, with bio-transfer from ant activity contributing to sediment availability. In subalpine Koscuiszko National Park, the effects of moderate intensity fire were minimised due to a dense root mat of snowgrass and the impact of low to moderate intensity control burns on sediment transfer are currently being investigated. In addition to considering the role of fire in systems of landscape change, Deirdre is interested in coupling hillslope-channel sediment delivery systems and patterns of dryland salinity.

Geomorphology

Desert Landscapes
Both A/Prof Deirdre Dragovich and Dr Mel Neave have extensive research interests in the evolution of arid and semiarid landscapes. In addition to her work on fire and salinity as agents of change in dry environments, Deirdre is a leading expert on the composition and formation of desert varnish and its role in the weathering of rocks in arid regions. Mel, on the other hand, is interested in interpreting links between runoff and erosion on semiarid hillslopes and investigates these using a combination of natural and simulated rainfall experiments and computer modeling. Identifying interrelations between water and sediment yields and the development of soil surface crusts, the percent cover of vegetation and the presence/absence of stone lags have been a focus of this work.

Biogeomorphology
In some systems, biological organisms (both plants and animals) significantly impact on geomorphic process functioning, contributing to effect landscape change. In the American southwest, for example, Mel Neave (in collaboration with researchers from the Jornada LTER Program) has revealed that historic changes in the type and distribution of vegetation across hillslopes have significantly altered runoff and erosion processes and that small mammal activities can be positively correlated with rates of fluvial erosion. In western New South Wales, Mel is also working to decipher the complex links between soil salinsation, vegetation cover and hillslope erosion.

Glacial geomorphology and sedimentology
Stephen Gale’s investigations of glacial terrains are currently focussed on the alpine mountains of the Picos de Europa of northern Spain and the lowland basin of East Anglia in the United Kingdom. With Peter Hoare, he has shown that the complex assemblage of proglacial glaciofluvial landforms found along the northern fringe of East Anglia in the United Kingdom is the product of sediment transport along a series of subglacial valleys trenched across the southern North Sea Basin in Middle Quaternary times. Gale and Hoare have undertaken a comprehensive re-examination of the petrography of deposits of last glacial age in East Anglia and have recently completed a re-assessment of sites critical to the glacial stratigraphy of lowland southern and eastern Britain.

Ruiniform landscapes
Amongst the most dramatic and remarkable of Earth’s landforms are those lost cities of spires, towers and canyon-like corridors known as ruiniform landscapes. These landscapes occur widely across Australia but have been largely overlooked by academic geomorphologists, perhaps because their origins are apparently obvious. Yet even a cursory study reveals the inaccuracy of this assessment. Stephen Gale has undertaken case studies of ruiniform relief in Australia to clarify the mechanisms of its formation and to understand the global context in which such relief develops.

Weathering

Sandstone weathering in the Sydney environment is affected by high salt loads in near-ocean situations, with some buildings of heritage value being subject to accelerated deterioration from ocean-derived salts. Deirdre Dragovich is currently investigating potential desalination methods and management procedures for historic sandstone buildings located on islands and within 2 km of the ocean. In addition, Deirdre works in arid environments of western New South Wales where dust deposition processes have contributed to the development of desert varnish. Chronological relations between different varnishes, and between varnish and aboriginal rock engravings, are the subject of on-going study.

Environmental Change & Pollution

European impact on the Australian environment
Much early colonial activity in Australia, particularly that potentially relating to the environment, may have been clandestine, illegal and beyond the scope of government agencies. Its nature and chronology thus remain largely unrecorded. Non-documentary evidence may, however, provide valuable information on the character of the early colonial environment. Perhaps the most promising information source is that preserved in sediments laid down at and immediately prior to the time of initial colonisation. Investigations of such deposits by Stephen Gale has revealed the speed and magnitude of European environmental impacts, with soil, vegetation and erosional systems all apparently transformed within a few years of the arrival of hard-hooved stock. The sediments also reveal the fascinating possibility that the shadow of European culture preceded official settlement by decades, leaving its imprint clearly marked on the environment.

Dating the recent past
The last half millennium is a critical period environmentally. It saw the expansion of settler societies worldwide and the resultant transformation of the biophysical landscape of much of the Earth. It is ironic, therefore, that the only widely employed chronological tool capable of dating this period at a resolution adequate to tackle environmental issues at this timescale is 210Pb analysis. Yet this is a far from routine procedure and most applications of the method fail to meet even the most limited criteria for acceptability. Stephen Gale has sought to overcome this difficulty by applying the concept of event horizons, chronological markers of geologically instantaneous phenomena, to the recent past. Event horizons may be of local extent or may be global or continental in scale. They may be used both as a means of calibrating 210Pb chronologies and as a dating tool in their own right. A variety of markers has been employed to date sedimentary sequences. Of particular importance have been tetraethyl lead (first used in Australia as a petrol additive in 1932) and variations in the inclination of the Earth’s magnetic field (which have allowed the identification of a dramatic and short-lived inclination event immediately prior to official colonisation in 1788).

Environmental Pollution
In addition to his work on environmental change, Dr Stephen Gale is interested in identifying and quantifying the distribution and persistence of pollutants in the environment. Examples of research undertaken by Stephen in this field include: an examination of trace metal concentrations in playgrounds in the lower Hunter valley of New South Wales; exploration of sediment contamination of the River Torrens in South Australia; identification of the contribution made by cigarette butts to terrestrial pollution; the use of stratigraphic methods to investigate fallout from the lead–zinc smelter formerly operated by Pasminco at Lake Macquarie in New South Wales; and, a study of the contribution of tetraethyl lead from motor fuel in Australia to hemispheric lead pollution.