INTERPRETATION OF SOIL FEATURES PRODUCED BY ANCIENT AND MODERN PROCESSES IN DEGRADED LANDSCAPES .1. A NEW METHOD FOR CONSTRUCTING CONCEPTUAL SOIL-WATER-LANDSCAPE MODELS

A pedo-hydrological method which involves interpreting features in soi ls that result from both ancient and modern processes along toposequen ces in a subcatchment of the Mt Lofty Ranges, South Australia, is used to construct conceptual soil-water-landscape models. This method link s soil-landscape features to soil-water processes with strong emphasis on: (i) soil water-flow systems and (ii) soil-forming and soil-change processes. The conceptual model illustrates the interactions between soil processes acting in soil water-flow systems. This model is able t o predict future modes of soil-landscape evolution under changing envi ronmental conditions. As well, it may be used by land and water supply managers to develop more efficient management strategies under condit ions of increasing land degradation (e.g. erosion and water pollution) . A typical Palexeralf-Natraqualf hydro-toposequence of soils (i.e. ca tena consisting of red-yellow-grey duplex soils) is used as an example to illustrate this new approach. The landscape selected is undergoing severe soil degradation (i.e. waterlogging, dryland salinity, erosion and water pollution). The constructed conceptual soil-water-landscape model is the result of detailed pedo-hydrological investigations alon g toposequences in a representative subcatchment in the high rainfall zone (>600 mm) of the Mount Lofty Ranges, South Australia. The model i llustrates in graphic form interactions between three soil water-flow systems (freely drained red soil system, hydromorphic topsoil system, hydromorphic subsoil system) and eight soil processes (saprolitization , ferralitization, glaebulization, redoximorphism, eluviation/illuviat ion, salinization/solonization, sulfidization/sulfuricization and wate r erosion). The study demonstrates that this whole ecosystem has been placed into disequilibrium thereby developing severe land degradation problems as a result of rising saline sulfatic ground watertables and perched watertables due to land-clearing since European settlement. Th e purpose of this paper is to provide a methodology framework and over all summary for other papers in a series dealing essentially with deta iled field and laboratory investigations of individual soil-water proc esses.