Abstract
Abstract. This paper describes the coupling of the State Space Soil Production and Assessment Model (SSSPAM) soilscape evolution model with a landform evolution model to integrate soil profile dynamics and landform evolution. SSSPAM is a computationally efficient soil evolution model which was formulated by generalising the mARM3D modelling framework to further explore the soil profile self-organisation in space and time, as well as its dynamic evolution. The landform evolution was integrated into SSSPAM by incorporating the processes of deposition and elevation changes resulting from erosion and deposition. The complexities of the physically based process equations were simplified by introducing a state-space matrix methodology that allows efficient simulation of mechanistically linked landscape and pedogenesis processes for catena spatial scales. SSSPAM explicitly describes the particle size grading of the entire soil profile at different soil depths, tracks the sediment grading of the flow, and calculates the elevation difference caused by erosion and deposition at every point in the soilscape at each time step. The landform evolution model allows the landform to change in response to (1) erosion and deposition and (2) spatial organisation of the co-evolving soils. This allows comprehensive analysis of soil landform interactions and soil self-organisation. SSSPAM simulates fluvial erosion, armouring, physical weathering, and sediment deposition. The modular nature of the SSSPAM framework allows the integration of other pedogenesis processes to be easily incorporated. This paper presents the initial results of soil profile evolution on a dynamic landform. These simulations were carried out on a simple linear hillslope to understand the relationships between soil characteristics and the geomorphic attributes (e.g. slope, area). Process interactions which lead to such relationships were also identified. The influence of the depth-dependent weathering function on soilscape and landform evolution was also explored. These simulations show that the balance between erosion rate and sediment load in the flow accounts for the variability in spatial soil characteristics while the depth-dependent weathering function has a major influence on soil formation and landform evolution. The results demonstrate the ability of SSSPAM to explore hillslope- and catchment-scale soil and landscape evolution in a coupled framework.
Highlights
Soil is one of the most important substances found on planet Earth
To generalise the work of Cohen et al (2010), Welivitiya et al (2016) developed a new soil grading evolution model called SSSPAM (State Space Soil Production and Assessment Model), which was based on the approach of mARM3D and showed that the area–slope– d50 relationship in Cohen et al (2009) was robust against changes in process and climate parameters and that the relationship is true for all the subsurface soil layers, not just the surface
If the total mass of incoming sediment Lin is higher than the transport capacity of the sediment transport capacity Tc at the pixel (Table 1, scenario C) deposition of sediments occurs at the pixel
Summary
Soil is one of the most important substances found on planet Earth. As the uppermost layer of the Earth’s surface, soil supports all the terrestrial organisms ranging from microbes to plants to humans and provides the substrate for terrestrial life (Lin, 2011). To generalise the work of Cohen et al (2010), Welivitiya et al (2016) developed a new soil grading evolution model called SSSPAM (State Space Soil Production and Assessment Model), which was based on the approach of mARM3D and showed that the area–slope– d50 relationship in Cohen et al (2009) was robust against changes in process and climate parameters and that the relationship is true for all the subsurface soil layers, not just the surface These models predict the properties of the soil profile at an individual pixel, they do not model the spatial interconnectivity between different parts of the soil catena resulting from transport-limited erosion and deposition. In addition to the model development we present the initial results of coupled soilscape–landform evolution exemplified on a linear hillslope
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