Projecting the evolution of soil due to global change (original) (raw)
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Modelling soil evolution to assess soil system behaviour under global change
2016
Wasige John and my uncle Charles Okei, you all stood by me and kept encouraging me throughout, great thanks. Outside the academic arena, I am indebted to so many groups and friends! Ugandans@gent, Ugandans@obsg, my home away from home: OBSG and OBSG staff; I must say I always enjoyed nice and refreshing moments and big ups to you all. I and my family have enjoyed the company of and assistance from many families for which we are truly grateful. On behalf of my family, I would like to iii say great thanks to the families of
Evaluating SoilGen2 as a tool for projecting soil evolution induced by global change
To protect soils against threats, it is necessary to predict the consequences of human activities and global change on their evolution on a ten to hundred year time scale. Mechanistic modelling of soil evolution is then a useful tool. We analysed the ability of the SoilGen model to be used for projections of soil characteristics associated to various soil threats: vertical distributions of b2 μm fraction, organic carbon content (OC), bulk density and pH. This analysis took the form of a functional sensitivity analysis in which we varied the initial conditions (parent material properties) and boundary conditions (co-evolution of precipitation and temperature; type and amount of fertilization and tillage as well as duration of agriculture). The simulated scenario variants comprised anthroposequences in Luvisols at two sites with one default scenario, six variants for initial conditions and 12 variants for boundary conditions. The variants reflect the uncertainties to our knowledge of parent material properties or reconstructed boundary conditions. We demonstrated a sensitivity of the model to climate and agricultural practices for all properties. We also conclude that final model results are not significantly affected by the uncertainties of boundary conditions for long simulations runs, although influenced by uncertainties on initial conditions. The best results were for organic carbon, although improvements can be reached through calibration or by incorporating a dynamic vegetation growth module in SoilGen. Results were poor for bulk density due to a fixed-volume assumption in the model, which is not easily modified. The b2 μm fraction depth patterns are reasonable but the process of clay new formation needs to be added to obtain the belly shape of the Bt horizon.
Towards More Realistic Projections of Soil Carbon Dynamics by Earth System Models
Global Biogeochemical Cycles, 2015
Microbes influence soil organic matter decomposition and the long-term stabilization of carbon (C) in soils. We contend that by revising the representation of microbial processes and their interactions with the physicochemical soil environment, Earth system models (ESMs) will make more realistic global C cycle projections. Explicit representation of microbial processes presents considerable challenges due to the scale at which these processes occur. Thus, applying microbial theory in ESMs requires a framework to link micro-scale process-level understanding and measurements to macro-scale models used to make decadal-to century-long projections. Here we review the diversity, advantages, and pitfalls of simulating soil biogeochemical cycles using microbial-explicit modeling approaches. We present a roadmap for how to begin building, applying, and evaluating reliable microbial-explicit model formulations that can be applied in ESMs. Drawing from experience with traditional decomposition models, we suggest the following: (1) guidelines for common model parameters and output that can facilitate future model intercomparisons; (2) development of benchmarking and model-data integration frameworks that can be used to effectively guide, inform, and evaluate model parameterizations with data from well-curated repositories; and (3) the application of scaling methods to integrate microbial-explicit soil biogeochemistry modules within ESMs. With contributions across scientific disciplines, we feel this roadmap can advance our fundamental understanding of soil biogeochemical dynamics and more realistically project likely soil C response to environmental change at global scales.
Toward more realistic projections of soil carbon dynamics by Earth system models
2016
Soil carbon (C) is a critical component of Earth system models (ESMs), and its diverse representations are a major source of the large spread across models in the terrestrial C sink from the third to fifth assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Improving soil C projections is of a high priority for Earth system modeling in the future IPCC and other assessments. To achieve this goal, we suggest that (1) model structures should reflect real-world processes, (2) parameters should be calibrated to match model outputs with observations, and (3) external forcing variables should accurately prescribe the environmental conditions that soils experience. First, most soil C cycle models simulate C input from litter production and C release through decomposition. The latter process has traditionally been represented by first-order decay functions, regulated primarily by temperature, moisture, litter quality, and soil texture. While this formulation well capt...
Do we need to include soil evolution module in models for prediction of future climate change?
Climatic Change, 2010
Climate change induce increases in precipitation in Northern Europe that may in turn affect soil evolution by increasing the amounts of water flowing through soils. However, there is a general lack of consideration of the impact of climate change on soil evolution. We propose here to use agricultural soil drainage-that also increases the amount of water flowing through soils-as an analogy to climate change. We thus studied the impact of 16 years of agricultural drainage in one cropped plot of the most common type of soils of Northern Europe. To estimate the importance of the soil evolution induced by drainage, we compared it to the long term natural evolution of that soil. The recent increase in water fluxes by agricultural drainage (16 years) has resulted in an increase in the intensity and velocity of the natural pedological processes. The increased amount of water flowing thorough soils due to drainage is of same order of magnitude than that that would be induced by climate change in the next 50-100 years in northern Europe. Our results demonstrated thus that climate change will significantly affect soil evolution. This evolution induces losses of the finest particles involved in organic carbon sequestration and thus has a feedback effect on climate change. Therefore we consider that soil evolution in response to climate change has to be explicitly studied and included in models predicting global climate change.
The effect of global change on the soil body
Reference Module in Earth Systems and Environmental Sciences
Without soil, no life on land is possible because soil provides the means for plant growth and plays a crucial role in water and carbon cycling among others. Human-induced global changes related to climate, land use and management are altering soils. The concepts of ecosystem services and soil capital value them, their functions and prevent their degradation. A major challenge for soil science is to quantify the relationships better between global changes, and soil processes and properties. The aim is to predict soil changes and understand whether soils will continue to deliver the services required in the long-term and in what extent can soil management mitigate climate change. Key points/objectives Soil is a dynamic system characterized by feedback loops, linking external forcing variables (or factors of pedogenesis), pedological processes, soil properties and ultimately soil functions and services. As a result of the complex interactions between climate, land-use and or management changes acting on various spatial and time scales, the direction, intensity and spatiotemporal pattern of future soil changes remain largely unknown. First indications of the effect of global change on a range of soil types, processes and properties have been observed already. In the future, effects of global change on soils will largely exceed well identified situations such as the reduction of Cryosols, soil degradation processes (e.g. erosion or desertification) or manageable soil properties (e.g. soil organic carbon stocks). With the irreversibility of numerous soil processes, a changed climate that can increasingly remove primary minerals, clay particles and base cations from soil threatens soil fertility, quality and health. If land-use or land management changes could be used theoretically to counteract climate change, their practical implementation at the pace and spatial scales of climate change is doubtful and could have counterproductive effects. Soil management must be planned and implemented to limit the risk of mutual reinforcement of climate and land-use changes that are already inducing cataclysmic soil degradation under extreme weather events. To face these arising and mostly inevitable challenges, there is an urgent need to develop tools and methodologies able to capture the new evolution of soil under global changes. The feedback loops between external forcing variables and soil properties are currently insufficiently considered in global modelling approaches, in which the soil compartment is generally poorly described.
Modelling how carbon affects soil structure
Geoderma
This paper presents a mechanistic model, named Struc-C, which describes how the soil organic carbon (SOC) influences the dynamics of soil structure, and consequently, soil physical behaviour. The model is partly inspired from the Rothamsed Carbon model, RothC-26.3, divided into three sub-models; the first describes SOC dynamics, followed by how aggregates can be created from the combination of the SOC with the soil clay, and finally, how this process influences soil porosity. Soil aggregates are regarded as the elementary bricks building soil structure, which comprise of organo-mineral associations that are subsequently bound together by more SOC to form the skeleton of larger aggregates. This is modelled by using two plant material pools from the RothC-26.3 model to create four new pools; three for increasing physical protection (or increasing aggregation), and one for the non-protected SOC (or non-aggregated). Struc-C has been tested over a simulated time of 200 years with input data from Rothamsted (England) and the Australian Capital Territory (Australia), and the output from the carbon model compared with RothC-26.3 outputs for both datasets. Although the model is still in its infancy, the simulations look promising when compared to RothC. Further improvements are also contemplated.
Global Biogeochemical Cycles, 2015
Soil is the largest organic carbon (C) pool of terrestrial ecosystems, and C loss from soil accounts for a large proportion of land-atmosphere C exchange. Therefore, a small change in soil organic C (SOC) can affect atmospheric carbon dioxide (CO 2 ) concentration and climate change. In the past decades, a wide variety of studies have been conducted to quantify global SOC stocks and soil C exchange with the atmosphere through site measurements, inventories, and empirical/process-based modeling. However, these estimates are highly uncertain and identifying major driving forces controlling soil C dynamics remains a key research challenge.
Sensitivity of Global Soil Carbon to Different Climate Change Scenarios
2005
One of the most pressing questions in the current debate about global climate change is what will happen to organic carbon sequestered in organic matter in soils if global warming occurs. This paper aims to study the potential effect of changes in temperature and precipitation on organic carbon sequestered in global soils. Interpolated data from a General Circulation Model (GCM), predicting temperatures and precipitation as well as world vegetation data set were used in a soil organic carbon decomposition model to study the likely effects of climatic change on organic carbon in soils over the next 100 years under three different scenarios. Results show that levels of organic matter in global soils will decrease as a result of an increase in global temperatures and precipitation. Results also show that different climatic zones of the Earth appear to be affected differently by global warming. Results from the research, as with climatic change modeling itself, represent only one of man...