- Title
- Hydropedology, geomorphology and groundwater processes hold the keys to land degradation - case studies in SW Victoria, Australia
- Creator
- MacEwan, Richard; Dahlhaus, Peter; Fawcett, Jonathon
- Date
- 2006
- Type
- Text; Conference paper
- Identifier
- http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/43969
- Identifier
- vital:3750
- Abstract
- Soil is the component in the landscape along with land use management and vegetation that determines all the partitioning of water balance components that affect surface hydrology (runoff to waterways and wetlands) and recharge to groundwater. Most soil and land degradation processes are hydrologically driven or depend on hydrological conditions. Conceptual models and quantification of erosion processes (wind erosion is a result of lack of moisture), land salinisation, acidification, nutrient loss and impacts of nutrient movement, all require an understanding of the role of hydrology specific to the landscape under consideration. In Australia, salinity is a major problem for agriculture in irrigated and rainfed (‘dryland agriculture) land and has significant economic impacts in urban areas too. A general water balance approach has been used to conceptualise the processes and the problem. Large scale clearing of treed landscapes in favour of annual crops and pastures has been seen as the major change in the water balance of Australian landscapes since settlement. This change in vegetation and water use is frequently cited as the most significant factor in causing land salinisation, which is attributed to increase in groundwater recharge, mobilisation of salts, groundwater rise and discharge. We provide three case studies for landscapes that require quite different conceptual models and all of which are in some degree counter to the developed conventional wisdom regarding increased salinity. These case studies illustrate the importance of developing an appropriate conceptual model of hydrological processes in the ‘critical zone', in particular for implementation of policy and practice in land management. Case 1. South Eastern Dundas Tablelands, Victoria. In this landscape the apparent degradation of land by salinity is the result of changed hydrological conditions but has not resulted from increased groundwater discharge or increased salt accumulation. We have evidence that groundwater recharge and discharge have not increased since clearing of the landscape during European settlement. Laboratory hydrological studies in large diameter cores from soil and regolith, interpretation of redoximorphic features and functional horizons in the field and analysis of historical records of streamflow support this hypothesis. We also show that the degradation of salt affected areas is due to fluctuating waterlogging and drying of the soil causing cyclic redox conditions and changes in soil chemistry. Case 2. Dissected Coastal Plain, Victoria. In this landscape, slowly permeable marine clay overlain by coastal sand deposits provides a classic ‘layer cake' picture of differentially permeable material. The unconsolidated nature of the clays and the relatively deep dissection that exists presents a landslide prone landscape and one that also shows the effects of salting in low areas. In this region we show that upward pressure from a deep (200 m) confined freshwater aquifer maintains saturation in the marine clay and that waterlogging, landslides and salinity result from hydrological dynamics of the upper few metres of regolith and soil. Evidence has been collected from field survey, groundwater studies, geotechnical measurements and regolith mineralogy. Case 3. Granite Uplands, Victoria. In this landscape we have interpreted redoximorphic features of functional horizons and measurement of shallow groundwater salinities in a toposequence. Our conceptual model is of a regional saline groundwater system discharging in springs relatively high in the landscape. We show the role of shallow throughflow of water in the soil in spreading salt from these point sources, simultaneously diluting the effect of salinity in local drainage lines but increasing the area of salt affected land upslope from the drainage lines. In each case study area we have been compelled to develop an understanding that fits the landscape realities. We have used empirical observations and interpretation of soil morphology, regolith and groundwater characteristics, laboratory studies, soil chemistry and hydro-chemistry to support our work. We stress the importance of this approach integrating the sciences of hydrology, pedology, chemistry and geology in coming to appropriate conclusions about land degradation processes, especially if we are to advise on land management investment and policy to tackle degradation.
- Publisher
- Philadelphia, Pennsylvania, USA :
- Relation
- Paper presented at 18th World Congress of Soil Science, Philadelphia, Pennsylvania, USA : 9th-15th July 2006
- Rights
- This metadata is freely available under a CCO license
- Subject
- Geology; Land degradation; Soil; Victoria
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