A coupled soilscape-landform evolution model: Model formulation and initial results

Abstract

22This paper describes the coupling of the State Space Soil Production and Assessment Model 23 (SSSPAM) soilscape evolution model with a landform evolution model to integrate soil profile 24 dynamics and landform evolution. SSSPAM is a computationally efficient soil evolution model which 25 was formulated by generalising the mARM3D modelling framework to further explore the soil profile 26 self-organization in space and time, and its dynamic evolution. The landform evolution was integrated 27 into SSSPAM by incorporating the processes of deposition and elevation changes resulting from 28 erosion and deposition. The complexities of the physically based process equations were simplified by 29 introducing state-space matrix methodology that allows efficient simulation of mechanistically linked 30 landscape and pedogenesis processes for catena spatial scales. The modelling approach and the 31 physics underpinning the modelled processes are described in detail. SSSPAM explicitly describes the 32 particle size grading of the entire soil profile at different soil depths, tracks the sediment grading of 33 the flow, and calculates the elevation difference caused by erosion and deposition at every point in the 34 soilscape at each time step. The landform evolution model allows the landform to change in response 35 to (1) erosion and deposition, and (2) spatial organisation of the co-evolving soils. This allows 36 comprehensive analysis of soil landform interactions and soil self-organization. SSSPAM simulates 37 fluvial erosion, armouring, physical weathering, and sediment deposition. The modular nature of the 38 SSSPAM framework allows integration of other pedogenesis processes in follow-on research projects. 39This paper presents the initial results of soil profile evolution on a dynamic landform. These 40 simulations were carried out on a simple linear hillslope to understand the relationships between soil 41 characteristics and the geomorphic attributes (e.g. slope, area). Process interactions which lead to such 42 relationships were also identified. The influence of the depth dependent weathering function on 43 soilscape and landform evolution was also explored. These simulations show that the balance between 44 erosion rate and sediment load in the flow accounts for the variability in spatial soil characteristics 45 while the depth dependent weathering function has a major influence on soil formation and landform 46

Evolutionary pathways in soil-landscape evolution models

“…SLEMs are numerical models that simulate a set of pedogenic and geomorphic processes that affect the spatial and temporal development of soils and landscapes (Minasny et al, 2015). Recent development in SLEMs enable a more accurate simulation of driving forces behind soil and landscape development (e.g., Van der Meij et al, 2018) and with that they become increasingly equipped to simulate soil and landscape development in a wide variety of settings, over long timescales (Bouchoms et al, 2017;Bock et al, 2018;Van der Meij et al, 2020;Welivitiya et al, 2019). These developments make SLEMs suitable not only to study past soil-landscape dynamics, but also to evaluate the effect of future changes in climate and land use on soil and landscape properties, such as carbon and nutrient stocks (Minasny et al, 2015).…”