Abstract
Abstract. Humans have substantially altered soil and landscape patterns and properties due to agricultural use, with severe impacts on biodiversity, carbon sequestration and food security. These impacts are difficult to quantify, because we lack data on long-term changes in soils in natural and agricultural settings and available simulation methods are not suitable for reliably predicting future development of soils under projected changes in climate and land management. To help overcome these challenges, we developed the HydroLorica soil–landscape evolution model that simulates soil development by explicitly modeling the spatial water balance as a driver of soil- and landscape-forming processes. We simulated 14 500 years of soil formation under natural conditions for three scenarios of different rainfall inputs. For each scenario we added a 500-year period of intensive agricultural land use, where we introduced tillage erosion and changed vegetation type. Our results show substantial differences between natural soil patterns under different rainfall input. With higher rainfall, soil patterns become more heterogeneous due to increased tree throw and water erosion. Agricultural patterns differ substantially from the natural patterns, with higher variation of soil properties over larger distances and larger correlations with terrain position. In the natural system, rainfall is the dominant factor influencing soil variation, while for agricultural soil patterns landform explains most of the variation simulated. The cultivation of soils thus changed the dominant factors and processes influencing soil formation and thereby also increased predictability of soil patterns. Our study highlights the potential of soil–landscape evolution modeling for simulating past and future developments of soil and landscape patterns. Our results confirm that humans have become the dominant soil-forming factor in agricultural landscapes.
Highlights
Soils provide valuable functions for nature and society by supporting plant growth and agriculture, managing water and solute flow, sequestering carbon, preserving archaeological heritage, creating habitats for plants and animals and providing support for infrastructure (Dominati et al, 2010; Greiner et al, 2017)
The first step towards sustainable land management and a return to healthy, natural soils is a fundamental understanding of the development and characteristics of natural soil patterns and how these change under human influence
We developed a soil–landscape evolution model that can simulate natural soil and landscape evolution by incorporating dominant natural processes such as soil creep, tree throw, vegetation dynamics and infiltration-dependent pedogenesis driven by the soil-forming factors climate, organisms, relief, parent material and time
Summary
Soils provide valuable functions for nature and society by supporting plant growth and agriculture, managing water and solute flow, sequestering carbon, preserving archaeological heritage, creating habitats for plants and animals and providing support for infrastructure (Dominati et al, 2010; Greiner et al, 2017). Tree throw creates local pits and mounds, which temporarily change hillslope hydrology and act as local hotspots for soil development due to a larger influx of water (Šamonil et al, 2015; Shouse and Phillips, 2016) These seemingly random processes create a high degree of heterogeneity in soil patterns, which shows little to no correlation with relief (Vanwalleghem et al, 2010). Intensively managed agricultural landscapes show soil patterns that closely follow the relief (Phillips et al, 1999; Van der Meij et al, 2017) This reflects the fact that erosion processes are relief-dependent, and this propagates into the soil patterns, unless erosion and deposition patterns are affected by field margins such as hedges or banks. The switch from such natural to agricultural soil systems can occur abruptly, e.g., by deforestation or the implementation of highly mechanized agriculture in a few decades. Sommer et al (2008) described this switch in boundary conditions and its implications with a time-split approach: over a short time period – relative to Holocene soil evolution – the soil system changes from natural, progressive pedogenesis, where profile deepening and horizon formation dominate erosive processes, to regressive pedogenesis, where – vice versa – erosion and deposition dominate progressive pedogenic processes (Johnson and Watson-Stegner, 1987)
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