Evaluating the stability and evolution of a proposed post mining landform.

<p>Evaluating the future stability and land denudation rates of natural or anthropogenic landforms is paramount for sustainable land use practices. Landform evolution models can be powerful tools in this endeavour.  In this study we used the well-established landform evolution model SIBERIA and the newly developed coupled soilscape-landform evolution model SSSPAM to simulate the evolution of a proposed post mining landform. SIBERIA uses a cellular digital elevation model to simulate annual average fluvial and diffusive erosion on landforms using annual average precipitation. However it does not simulate the soil profile evolution on the evolving landform. The new SSSPAM coupled soilscape-landform evolution model has the ability to assess the overall erosion rates of catchment scale landforms either using short term precipitation events, variable precipitation or time averaged precipitation rates. In addition, SSSPAM is able to simulate the evolution of the soil profile of the evolving landform using pedogenetic processes such as physical weathering and armouring.</p><p>            To assess the reliability of SSSPAM, model predictions at 100 and 10000 years were compared with SIBERIA predictions at the same times. During the long term (10000yr) simulation the effect of armouring and weathering on the landform evolution was also assessed. The results obtained from these different simulations were compared and contrasted. Comparison of the short term simulations revealed that SSSPAM results compare well with the simulation results of the more established SIBERIA model. Long term simulation showed that SSSPAM simulation results also compares well with SIBERIA simulations while the erosion rates predicted by both models are close to the land denudation rates measured in the field. The soil profile characteristics and channel forms simulated by SSSPAM long term simulations were examined using several landform cross-sections. This analyses revealed that SSSPAM produces deep incised channels with very low soil thickness in upper reaches of the catchment and shallow channels with relatively thick soil layers in the lower reaches of the catchment. These SSSPAM simulated channels match well with the channel forms and distribution of bedrock channels and alluvial channels observed in the field. The analysis of the catchment cross-sections also showed that SSSPAM is capable of reproducing complex subsurface soil evolution and stratification and spatial variability of soil profile characteristics typically observed in the field.</p>

Surface and sub-surface salinity in and around acid sulfate soil scalds in the coastal floodplains of New South Wales, Australia

Two-metre-deep soil profiles at 10 acid sulfate soil (ASS) scalds along the coast of New South Wales (NSW), Australia, were examined for salinity indicators. At 5 of the sites, permanently vegetated areas adjacent to the ASS-scalded land were also tested. Throughout the profiles, most sites had high soluble chloride (Cl−) concentrations (≤17 mg/g soil) and high soluble sulfate (SO42−) concentrations (≤17 mg/g soil). Very low Cl− : SO42− ratios (≤3) indicated active pyrite oxidation. Soil salinity (measured as electrical conductivity, EC) was extremely high in the top 2 m of most of the ASS scalds when related to the growth requirements of the typical introduced pasture species that were planted in these areas following drainage. This allows salinity, in addition to the extremely low pH of the surface soils, to contribute to land denudation, which can instigate or perpetuate pyrite oxidation and ASS-related land scalding. Although the sites had shallow watertables and soil-moisture content was high, the surface soil (top 0.10 m) of the scalds had consistently higher soluble Cl− and SO42− concentrations and EC than adjacent vegetated areas. All coastal ASS areas investigated, typically freshwater backswamps used for cattle grazing, were underlain by estuarine-derived sediments containing saline ground water. The results demonstrate that revegetation of ASS scalds must include investigation and management of salinity, in addition to acidity, within the soil profile and at the soil surface.

The Effects of Grazing on Plant Biodiversity in Arid Ecosystems

Conventional wisdom views heavy grazing as the major cause of desertification in semiarid and arid areas of Africa, Asia, and Australia (see, e.g., Acocks 1953, Jarman and Bosch 1973, Sinclair and Fryxell 1985, Middleton and Thomas 1997). Nowhere is the effect of heavy grazing more apparent than in the Sahel of Africa (Sinclair and Fryxell 1985). This land denudation has resulted in a negative feedback loop via decreased soil nutrient status and increased soil albedo (due to lower vegetation cover), causing increased evaporation and decreased precipitation, which in turn reduces the stocking capacity of the land, further exacerbating the negative effects of grazing (Schlesinger et al. 1990). A less dramatic result of overgrazing is a long-term decline in agricultural productivity. For example, the arid Karoo region of South Africa has experienced no climatic change over the last two centuries, yet there has been a 50% decline in stocking rates in seven of eight magisterial districts from 1911 to 1981 (Dean and McDonald 1994). These authors ascribe this decline to heavy grazing that reduced palatable plant populations and hence the carrying capacity of the vegetation in the long term. These examples of the negative effects of grazing in arid ecosystems lie in stark contrast with a large number of African studies that compared the effects of commercial (privately owned) and communal (subsistence, no private ownership) ranching on vegetation and soils (e.g., Archer et al. 1989, Tapson 1993, Scoones 1995, Ward et al. 1999a,b, reviewed by Behnke and Abel 1996). In spite of 5–10-fold higher stocking rates on communal ranches, few studies have shown differences in effects on biodiversity, plant species composition and soil quality between these ranching types (Archer et al. 1989, Tapson 1993, Scoones 1995, Ward et al. 1999a,b—fig. 14.1). Similarly, studies of grazing in Mediterranean semiarid grasslands (reviewed by Seligman 1996) and Middle Eastern arid rangelands (Ward et al. 1999b) show that the effects of grazing on biodiversity are relatively small. A consensus has developed in recent years that arid grazing ecosystems are nonequilibrial, event-driven systems (see, e.g., O’Connor 1985, Venter et al. 1989, Milchunas et al. 1989, Parsons et al. 1997).