Lead Authors: Marco Bindi (Italy), Sally Brown (UK), Ines Camilloni (Argentina), Arona Diedhiou (Ivory Coast/Senegal), Riyanti Djalante (Japan/Indonesia), Kristie L. Ebi (USA), Francois Engelbrecht (South Africa), Joel Guiot (France), Yasuaki Hijioka (Japan), Shagun Mehrotra (USA/India), Antony Payne (UK), Sonia I. Seneviratne (Switzerland), Adelle Thomas (Bahamas), Rachel Warren (UK), Guangsheng Zhou (China)

Impacts of 1.5°C Global Warming on Natural and Human Systems

The saturated hydraulic conductivity of a soil can be predicted using empirical relationships, capillary models, statistical models, and hydraulic radius theories. A well-known relationship between...

On the use of the KozenyCarman equation to predict the hydraulic conductivity of soils

There is growing international interest in better managing soils to increase soil organic carbon (SOC) content to contribute to climate change mitigation, to enhance resilience to climate change and to underpin food security, through initiatives such as international ‘4p1000’ initiative and the FAO's Global assessment of SOC sequestration potential (GSOCseq) programme. Since SOC content of soils cannot be easily measured, a key barrier to implementing programmes to increase SOC at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) platforms, both for national reporting and for emissions trading. Without such platforms, investments could be considered risky. In this paper, we review methods and challenges of measuring SOC change directly in soils, before examining some recent novel developments that show promise for quantifying SOC. We describe how repeat soil surveys are used to estimate changes in SOC over time, and how long‐term experiments and space‐for‐time substitution sites can serve as sources of knowledge and can be used to test models, and as potential benchmark sites in global frameworks to estimate SOC change. We briefly consider models that can be used to simulate and project change in SOC and examine the MRV platforms for SOC change already in use in various countries/regions. In the final section, we bring together the various components described in this review, to describe a new vision for a global framework for MRV of SOC change, to support national and international initiatives seeking to effect change in the way we manage our soils.

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How to measure, report and verify soil carbon change to realize the potential of soil carbon sequestration for atmospheric greenhouse gas removal.

The paper focuses on investigating the destructuration process during time-dependent stress-strain evolution. For this purpose, various oedometer tests and triaxial tests on intact and reconstituted samples of soft sensitive Vanttila clay were carried out. Based on experimental observations, a new elastic viscoplastic model, extended from the overstress theory of Perzyna, is developed. The proposed model accounts for inherent and induced anisotropy, interparticle bonds and bond degradation, and viscosity. The determination of model parameters is discussed, demonstrating how all model parameters can be determined in a straightforward way and no additional test is needed for the proposed model compared to the modified Cam clay model. The model is implemented into a finite-element code, which enables coupled consolidation analyses. The model is used to simulate various strain-rate and creep tests under one-dimensional and triaxial conditions on the intact samples of Vanttila clay. The comparisons between experimental results and simulations show that the model has good predictive ability on the time-dependent behavior of a soft sensitive clay.

Modeling time-dependent behavior of soft sensitive clay

A microstructural insight into compacted clayey soils and their hydraulic properties

The paper examines the hydraulic conductivity of a nonplastic till from northern Quebec. It is shown that the hydraulic conductivity is strongly influenced by the compaction degree of saturation, a...

Influence of compaction conditions on pore-size distribution and saturated hydraulic conductivity of a glacial till

Long-term consolidation behavior interpreted with isotache concept for worldwide clays

[1] In this paper we present and discuss the role of the dynamics of suction, that is, negative pore water pressure relative to atmospheric air pressure, in the evolution of intertidal sandy flats. This is done through the combined use of field evidence, laboratory experiments, and a theoretical model. Field observations were performed in the estuary of Obitsu River located in the east coast of Tokyo Bay, Japan. Laboratory experiments were performed in a calibration chamber as well as in a laterally scaled model flat subjected to water/groundwater level variations. The present study demonstrates that the suction dynamics associated with the tide-induced groundwater level variations play a substantial role in the temporospatial evolutions of voids, stiffness, and surface shear strength in cyclically exposed and submerged soil. The suction-induced void state changes are a consequence of cyclic elastoplastic contraction of the soil and are accompanied by distinct morphological changes, despite the lack of significant surface shear stresses acting on the soil. Such soil behavior occurs in regions where suction develops above the groundwater level during low tides and strongly depends on the way in which such suction develops. Discussions are made on how these suction dynamics effects could contribute, via feedback involved in surface transport processes, to the overall morphological evolution of cross-shore intertidal flat soils.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006JF000575

Role of suction dynamics in evolution of intertidal sandy flats: Field evidence, experiments, and theoretical model

In this study, a series of incremental loading oedometer tests and microscopic observations is carried out in order to investigate the influence of sand/bentonite fractions on hydraulic conductivity and compressibility. If sand particles do not form a skeletal structure, and each particle is independent in the clay matrix, an additive fraction of sand causes a decrease in the compressibility; however, it does not affect the hydraulic conductivity under the same consolidation pressure. The additive fraction of bentonite contributes to a decrease in the hydraulic conductivity, even for clayey materials. In addition, the relationship between the pore-size parameter, which represents the pore entrance size distribution, and the hydraulic conductivity is discussed using a probabilistic model known as the general capillary model.

Hydraulic conductivity and compressibility of mixtures of Nagoya clay with sand or bentonite

Soil is a key compartment for climate regulation as a source of greenhouse gases (GHGs) emissions and as a sink of carbon. Thus, soil carbon sequestration strategies should be considered alongside reduction strategies for other greenhouse gas emissions. Taking this into account, several international and European policies on climate change are now acknowledging the importance of soils, which means that proper, comparable and reliable information is needed to report on carbon stocks and GHGs emissions from soil. It also implies a need for consensus on the adoption and verification of mitigation options that soil can provide. Where consensus is a key aspect, formal standards and guidelines come into play. This paper describes the existing ISO soil quality standards that can be used in this context, and calls for new ones to be developed through (international) collaboration. Available standards cover the relevant basic soil parameters including carbon and nitrogen content but do not yet consider the dynamics of those elements. Such methods have to be developed together with guidelines consistent with the scale to be investigated and the specific use of the collected data. We argue that this standardization strategy will improve the reliability of the reporting procedures and results of the different climate models that rely on soil quality data.

/pdf/accounting-for-carbon-stocks-in-soils-and-measuring-ghgs-5eih1bybkb.pdf

Yoichi Watabe

Papers

Influence of compaction conditions on pore-size distribution and saturated hydraulic conductivity of a glacial till

Long-term consolidation behavior interpreted with isotache concept for worldwide clays

Role of suction dynamics in evolution of intertidal sandy flats: Field evidence, experiments, and theoretical model

Hydraulic conductivity and compressibility of mixtures of Nagoya clay with sand or bentonite

Accounting for carbon stocks in soils and measuring GHGs emission fluxes from soils : do we have the necessary standards?