scholarly journals Deriving pedotransfer functions for soil quartz fraction in southern France from reverse modeling

SOIL ◽  
2016 ◽  
Vol 2 (4) ◽  
pp. 615-629 ◽  
Author(s):  
Jean-Christophe Calvet ◽  
Noureddine Fritz ◽  
Christine Berne ◽  
Bruno Piguet ◽  
William Maurel ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Land Surface ◽  
Geometric Mean ◽  
Sensible Heat Flux ◽  
Pedotransfer Functions ◽  
Quartz Content ◽  
Southern France ◽  
Weather Stations

Abstract. The quartz fraction in soils is a key parameter of soil thermal conductivity models. Because it is difficult to measure the quartz fraction in soils, this information is usually unavailable. This source of uncertainty impacts the simulation of sensible heat flux, evapotranspiration and land surface temperature in numerical simulations of the Earth system. Improving the estimation of soil quartz fraction is needed for practical applications in meteorology, hydrology and climate modeling. This paper investigates the use of long time series of routine ground observations made in weather stations to retrieve the soil quartz fraction. Profile soil temperature and water content were monitored at 21 weather stations in southern France. Soil thermal diffusivity was derived from the temperature profiles. Using observations of bulk density, soil texture, and fractions of gravel and soil organic matter, soil heat capacity and thermal conductivity were estimated. The quartz fraction was inversely estimated using an empirical geometric mean thermal conductivity model. Several pedotransfer functions for estimating quartz content from gravimetric or volumetric fractions of soil particles (e.g., sand) were analyzed. The soil volumetric fraction of quartz (fq) was systematically better correlated with soil characteristics than the gravimetric fraction of quartz. More than 60 % of the variance of fq could be explained using indicators based on the sand fraction. It was shown that soil organic matter and/or gravels may have a marked impact on thermal conductivity values depending on which predictor of fq is used. For the grassland soils examined in this study, the ratio of sand-to-soil organic matter fractions was the best predictor of fq, followed by the gravimetric fraction of sand. An error propagation analysis and a comparison with independent data from other tested models showed that the gravimetric fraction of sand is the best predictor of fq when a larger variety of soil types is considered.

scholarly journals Impact of gravels and organic matter on the thermal properties of grassland soils in southern France

2015 ◽  
Vol 2 (1) ◽  
pp. 737-765
Author(s):  
J.-C. Calvet ◽  
N. Fritz ◽  
C. Berne ◽  
B. Piguet ◽  
W. Maurel ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Organic Matter ◽  
Soil Moisture ◽  
Soil Organic Matter ◽  
Soil Temperature ◽  
Soil Thermal Conductivity ◽  
Volumetric Fraction ◽  
Southern France ◽  
The Impact ◽  
Conductivity Models

Abstract. Soil moisture is the main driver of temporal changes in values of the soil thermal conductivity. The latter is a key variable in land surface models (LSMs) used in hydrometeorology, for the simulation of the vertical profile of soil temperature in relation to soil moisture. Shortcomings in soil thermal conductivity models tend to limit the impact of improving the simulation of soil moisture in LSMs. Models of the thermal conductivity of soils are affected by uncertainties, especially in the representation of the impact of soil properties such as the volumetric fraction of quartz (q), soil organic matter, and gravels. As soil organic matter and gravels are often neglected in LSMs, the soil thermal conductivity models used in most LSMs represent the mineral fine earth, only. Moreover, there is no map of q and it is often assumed that this quantity is equal to the volumetric fraction of sand. In this study, q values are derived by reverse modelling from the continuous soil moisture and soil temperature sub-hourly observations of the Soil Moisture Observing System – Meteorological Automatic Network Integrated Application (SMOSMANIA) network at 21 grassland sites in southern France, from 2008 to 2015. The soil temperature observations are used to retrieve the soil thermal diffusivity (Dh) at a depth of 0.10 m in unfrozen conditions, solving the thermal diffusion equation. The soil moisture and Dh values are then used together with the measured soil properties to retrieve soil thermal conductivity (λ) values. For ten sites, the obtained λ value at saturation (λsat) cannot be retrieved or is lower than the value corresponding to a null value of q, probably in relation to a high density of grass roots at these sites or to the presence of stones. For the remaining eleven sites, q is negatively correlated with the volumetric fraction of solids other than sand. The impact of neglecting gravels and organic matter on λsat is assessed. It is shown that these factors have a major impact on λsat.

Soil organic matter dominates the magnitude of porosity and bulk density in temperate soils, with important implications for land surface models

2021 ◽  
Author(s):  
Amy Thomas ◽  
Fiona Seaton ◽  
Jack Cosby ◽  
Bridget Emmett ◽  
Sabine Reinsch ◽  
...  
Keyword(s):  
Climate Change ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Land Surface ◽  
Pedotransfer Functions ◽  
Soil Porosity ◽  
Land Surface Models ◽  
Surface Models ◽  
Global Land ◽  
Temperate Soils

<p>Soil porosity controls the flow of mass and energy through soil, and thus plays a fundamental role in regulating hydrological and biochemical cycling at the land surface. Global land surface and earth system models commonly derive porosity from soil texture using pedotransfer functions. This does not allow for response to change in environment or management, or potentially important climate feedbacks. Furthermore, the approach does not fully represent the baseline spatial variation in this important soil property. Here we show that porosity, and bulk density (BD), depend on SOM in temperate soils, using two comprehensive national data sets, covering the full range of soil organic matter (SOM) (n=1385 & n=2570). Our novel use of analytical models with machine learning (ML) algorithms opens up new physical insight into controls on porosity and BD, while generalized additive mixed models (GAMMs) provide further insights and opportunities for prediction. Our models allow us to consider influence of management on soil compaction and recent observations that soil porosity responds to climate change. The dependence of soil porosity on SOM, more so than texture, indicates the need for a paradigm shift in the conceptualization and modelling of these soil physical properties. Broad habitat was also an important control, and explained some of the variance in the relationship between SOM and porosity. This highlights that changes in soil porosity may occur due to land use or climate change, and will create feedbacks to hydrological and biogeochemical cycling which should be represented in Global land surface models. This will also be important for other pedotransfer functions, e.g. the use of BD to determine carbon stock from concentration.  In addition, we found opportunities for improved representation of the spatial pattern of porosity, even in the absence of measured data on SOM, based on climate and earth observation data.</p>

scholarly journals Evaluation of Noah-MP Land-Model Uncertainties over Sparsely Vegetated Sites on the Tibet Plateau

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 458
Author(s):  
Guo Zhang ◽  
Fei Chen ◽  
Yueli Chen ◽  
Jianduo Li ◽  
Xindong Peng
Keyword(s):  
Heat Flux ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Tibetan Plateau ◽  
Sensible Heat Flux ◽  
Limiting Factors ◽  
Tibet Plateau ◽  
The Tibetan Plateau ◽  
Annual Total ◽  
The Impact

The water budget and energy exchange over the Tibetan Plateau (TP) region play an important role on the Asian monsoon. However, it is not well presented in the current land surface models (LSMs). In this study, uncertainties in the Noah with multiparameterization (Noah-MP) LSM are assessed through physics ensemble simulations in three sparsely vegetated sites located in the central TP. The impact of soil organic matter on energy flux and water cycles, along with the influence of uncertainties in precipitation are explored using observations at those sites during the third Tibetan Plateau Experiment from 1August2014 to31July2015. The greatest uncertainties are in the subprocesses of the canopy resistance, soil moisture limiting factors for evaporation, runoff (RNF) and ground water, and surface-layer parameterization. These uncertain subprocesses do not change across the different precipitation datasets. More precipitation can increase the annual total net radiation (Rn), latent heat flux (LH) and RNF, but decrease sensible heat flux (SH). Soil organic matter enlarges the annual total LH by ~26% but lessens the annual total Rn, SH, and RNF by ~7%, 7%, and 39%, respectively. Its effect on the LH and RNF at the Nagqu site, which has a sand soil texture type, is greater than that at the other two sites with sandy loam. This study highlights the importance of precipitation uncertainties and the effect of soil organic matter on the Noah-MP land-model simulations. It provides a guidance to improve the Noah-MP LSM further and hence the land-atmosphere interactions simulated by weather and climate models over the TP region.

scholarly journals Experimental Study on Thermal Conductivity of Organic-Rich Soils under Thawed and Frozen States

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Ruixia He ◽  
Ning Jia ◽  
Huijun Jin ◽  
Hongbo Wang ◽  
Xinyu Li
Keyword(s):  
Thermal Conductivity ◽  
Organic Matter ◽  
Soil Temperature ◽  
Land Surface ◽  
Phase Changes ◽  
Surface Processes ◽  
Organic Soils ◽  
Computational Formula ◽  
Soil Thermal Conductivity ◽  
Land Surface Processes

Thermal properties are important for featuring the water-heat transfer capacity of soil. They are also key to many processes in earth sciences, such as the land surface processes and ecological and geoenvironmental dynamics and their changes in permafrost regions. With loose and porous structures, the organic matter layer in soil strata substantially influences soil thermal conductivity. So far, thermal conductivity of mineral soils has been explored extensively and in depth, but there are only limited studies on that of organic soils. In this study, influences of soil temperature, soil moisture saturation (SMS), and soil organic matter (SOM) content on soil thermal conductivity were analyzed on the basis of laboratory experiments on the silt-organic soil mixtures of varied mixing ratios. Results show that soil thermal conductivity declines slowly with the lowering temperatures from 10 to 0°C; however, it increases and finally stabilizes when temperature further lowers from 0 to -10°C. It is important to note that thermal conductivity peaks in the temperature range of -2~0°C (silty and organic-poor soil) and -5~0°C (organic-rich soil), possibly due to phase changes of ice/water in warm permafrost. Under both thawed and frozen states, soil thermal conductivity is positively related with SMS. However, with rising SOM content, the growth rate of soil thermal conductivity with SMS slows gradually. Given the same SMS, soil thermal conductivity declines exponentially with increasing SOM content. Based on the experimental and theoretical analyses, a new empirical computational formula of soil thermal conductivity is established by taking into account of the SOM content, SMS, and soil temperature. The results may help better parameterize in simulating and predicting land surface processes and for optimizing frozen soil engineering designs and provide theoretical bases for exploring the dynamic mechanisms of environmental changes in cold regions under a changing climate.

The Relation between Stability of Aggregates on Surface and SOM of Red Bare Soil in the Karst Area of East Yunnan, China

2014 ◽  
Vol 1030-1032 ◽  
pp. 920-925
Author(s):  
Lei Zhang ◽  
Jia Xue Wang ◽  
Meng Jing Xiao ◽  
Bao Qiang Liu
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Aggregates ◽  
Geometric Mean ◽  
Physical Property ◽  
Significant Negative Correlation ◽  
Bare Soil ◽  
Karst Area ◽  
Structure Stability ◽  
Water Stable Aggregate

Red bare soil is a kind of soil remained on plateau from ancient ages. Researchs toward better understanding of the relationship between stability of surface aggregate and SOM (Soil Organic Matter) based on 14 typical samples indicate that red bare soil clay (<0.002mm) contents between 12.18% and 64.02% which belongs to poor cultivation performance soil. The number of macro-soil aggregates after dry sieving were far more than the number after wet sieving. Water-stable aggregate content (WSAC) informed the feature of red bare soil. The WSAC were between 28.77% ~ 52.87% at the size >0.25mm and the aggregates destruction rate (PAD0.25) were 34.28% to 68.10%, mean weight diameter (MWD) were at the size of 0.53 to 1mm, geometric mean diameter (GMD) were between 0.37 and 0.58mm, fractal dimension (FD) were between 2.79 and 2.92. The 5 index above indicated the structural stability, anti erodibility and physical property were both poor when compared with other typical soil samples in southwest karst area of China. The research also indicated that soil organic matter (SOM) and WSAC has more effect than mechanical aggregate. SOM has significant positive correlation with MWD and GMD, and significant negative correlation with PAD0.25 and FD. Lack of SOM and exposed led to soil structure stability deterioration. These can be the reason why soil erosion seriously and can’t grow vegetation in red bare soil area.

scholarly journals Warming and elevated CO2 promote incorporation of plant-derived lipids into soil organic matter in a spruce-dominated ombrotrophic bog

2021 ◽  
Author(s):  
Ofiti O.E. Nicholas ◽  
Zosso U. Cyrill ◽  
Solly F. Emily ◽  
Hanson J. Paul ◽  
Wiesenberg L.B. Guido ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Land Surface ◽  
Stable Carbon Isotopes ◽  
Specific Response ◽  
Microbial Decomposition ◽  
Short Period ◽  
Bulk Organic Matter ◽  
The Impact

&lt;p&gt;More than one third of global soil organic matter (SOM) is stored in peatlands, despite them occupying less than 3% of the land surface. Increasing global temperatures have the potential to stimulate the decomposition of carbon stored in peatlands, contributing to the release of disproportionate amounts of greenhouse gases to the atmosphere but increasing atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations may stimulate photosynthesis and return C into ecosystems. &amp;#160;Key questions remain about the magnitude and rate of these interacting and opposite processes to environmental change drivers.&lt;/p&gt;&lt;p&gt;We assessed the impact of a 0&amp;#8211;9&amp;#176;C temperature gradient of deep peat warming (4&amp;#160;years of warming; 0-200 cm depth) in ambient or elevated CO&lt;sub&gt;2&lt;/sub&gt; (2 years of +500 ppm CO&lt;sub&gt;2&lt;/sub&gt; addition) on the quantity and quality of SOM at the climate change manipulation experiment SPRUCE (Spruce and Peatland Responses Under Changing Environments) in Minnesota USA. We assessed how warming and elevated CO&lt;sub&gt;2&lt;/sub&gt; affect the degradation of plant and microbial residues as well as the incorporation of these compounds into SOM. Specifically, we combined the analyses of free extractable &lt;em&gt;n&lt;/em&gt;-alkanes and fatty acids together with measurements of compound-specific stable carbon isotopes (&amp;#948;&lt;sup&gt;13&lt;/sup&gt;C).&lt;/p&gt;&lt;p&gt;We observed a 6&amp;#8240; offset in &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C between bulk SOM and &lt;em&gt;n&lt;/em&gt;-alkanes, which were uniformly depleted in &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C when compared to bulk organic matter. Such an offset between SOM and &lt;em&gt;n&lt;/em&gt;-alkanes is common due to biosynthetic isotope fractionation processes and confirms previous findings. After 4&amp;#160;years of deep peat warming, and 2 years of elevated CO&lt;sub&gt;2&lt;/sub&gt; addition a strong depth-specific response became visible with changes in SOM quantity and quality. In the upper 0-30 cm depth, individual &lt;em&gt;n&lt;/em&gt;-alkanes and fatty acid concentrations declined with increasing temperatures with warming treatments, but not below 50 cm depth. In turn, the &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values of bulk organic matter and of individual &lt;em&gt;n&lt;/em&gt;-alkanes and fatty acids increased in the upper 0-30 cm with increasing temperatures, but not below 50 cm depth. Thus &lt;em&gt;n&lt;/em&gt;-alkanes, which typically turnover slower than bulk SOM, underwent a rapid transformation after a relatively short period of simulated warming in the acrotelm. Our results suggest that warming accelerated microbial decomposition of plant-derived lipids, leaving behind more degraded organic matter. The non-uniform, and depth dependent warming response implies that warming will have cascading effects on SOM decomposition in the acrotelm in peatlands. It remains to be seen how fast the catotelm will respond to rising temperatures and atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations.&lt;/p&gt;

scholarly journals Influence of organic matter on soil hydrothermal processes in the Tibetan Plateau: Observation and parameterization

2021 ◽  
Author(s):  
Jing Sun ◽  
Yingying Chen ◽  
Kun Yang ◽  
Hui Lu ◽  
Long Zhao ◽  
...  
Keyword(s):  
Organic Matter ◽  
Tibetan Plateau ◽  
Land Surface ◽  
High Surface ◽  
Sensible Heat Flux ◽  
Warm Season ◽  
Surface Energy Budget ◽  
The Tibetan Plateau ◽  
Undisturbed Soil ◽  
Soil Hydraulic

AbstractIn the central-eastern Tibetan Plateau (TP) there is abundant organic matter in topsoils, which plays a crucial role in determining soil hydraulic properties that need to be properly described in land surface models. Limited soil parameterizations consider the impacts of soil organic matter (SOM), but they still show poor performance in the TP. A dedicated field campaign is therefore conducted by taking undisturbed soil samples in the central TP to obtain in-situ soil hydraulic parameters and to advance SOM parameterizations. The observed findings are twofold. 1) The SOM pore-size distribution parameter, derived from measured soil water retention curves, has been demonstrated to be much underestimated in previous studies. 2) SOM saturated hydraulic conductivity is overestimated. Accordingly, a new soil hydraulic parameterization is established by modifying a commonly used one based on observations, which is then evaluated by incorporating it into Noah-MP. Compared with the original ones, the new parameterization significantly improves surface soil liquid water simulations at stations with high surface SOM content, especially in the warm season. A further application with the revised Noah-MP indicates that SOM can enhance sensible heat flux but decrease evaporation and subsurface soil temperature in the warm season, and tends to have a much weak effect in the cold season. This study provides insights into the role of SOM in modulating soil state and surface energy budget. Note that, however, there are many other factors at play and the new parameterization is not necessarily applicable beyond the TP.

A numerical approach for understanding the main parameters and processes influencing the soil organic matter decay in wildfire events

2020 ◽  
Author(s):  
Sebastián A. Aedo ◽  
Carlos A. Bonilla
Keyword(s):  
Thermal Conductivity ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
High Temperatures ◽  
Pore Radius ◽  
Radiative Energy ◽  
Soil Response

&lt;p&gt;High temperatures reached at topsoil during wildfires can induce changes in physical, chemical, and biological soil properties. In the end, these changes are related to the loss of soil organic matter (SOM) and control the post-fire soil management decision. Therefore, the objectives of this study were: (1) to develop a numerical model to predict the SOM decay during wildfires, and (2) to study which are the main parameters that control the soil response. The model couples the energy balance for soil heating, and the species conservation for water and SOM using high temperature-induced vaporization and combustion kinetics. Fluid flow was neglected; however, radiative energy conducted through pores was included as a function of the volumetric pore radius. The soil thermal evolution showed values of r&lt;sup&gt;2&lt;/sup&gt;&gt;0.92 when the radiative term in the thermal conductivity was neglected, and r&lt;sup&gt;2&lt;/sup&gt;&gt;0.98 when the volumetric pore radius was adjusted. The results showed that the main parameters that control the soil response were soil texture, soil water content, volumetric pore radius, and oxygen availability. Also, soil response depends on the surface temperature and exposure time. Soil water content enhances the thermal properties and determines the amount of heat consumed during vaporization because of the high enthalpy of this endothermic reaction. On the other hand, neglecting oxygen flux leads to restricted oxidation, limiting the SOM decay. In terms of texture, silty soils showed the lower soil response, clay and loamy soils an intermediate response, and sandy soils had a higher response. Also, the volumetric pore radius enhances the soil thermal conductivity at high temperatures, leading to higher temperatures near the soil surface. These results suggest that the normalized SOM decay does not depend on the initial SOM content.&lt;/p&gt;

scholarly journals Spatial Estimation of Soil Organic Matter in Karst Peak-cluster Depression

2015 ◽  
Vol 9 (1) ◽  
pp. 1022-1027 ◽  
Author(s):  
Li Hui ◽  
Jiang Zhong-Cheng ◽  
Yang Qi-Yong ◽  
Yin Hui ◽  
Wang Yue
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Land Surface ◽  
Regression Kriging ◽  
Auxiliary Variables ◽  
Peak Cluster ◽  
Republic Of China ◽  
Spatial Estimation ◽  
Terrain Attributes ◽  
Karst Areas

In order to enhance the accuracy of spatial estimation of soil organic matter (SOM), spatial predictions of SOM in 0~20 cm depth were conducted in Guohua Ecological Experimental Area of Minister of Land and Resource of the People’s Republic of China. Analysis of multiple linear stepwise regressions showed that the two terrain attributes of relief degree of land surface (RS) and distance from ridge of mountains (DFR) entered into the regression equation. Therefore, RS and DFR were selected as auxiliary variables to predict SOM by MCOK and RK methods. The accuracy of spatial estimation of SOM was compared among methods of ordinary kriging (OK), multivariable cokriging (MCOK) and regression kriging (RK). Results showed that RK and MCOK methods with terrain attributes as auxiliary variables could enhance the accuracy of spatial estimation of SOM, and MCOK method could promote the accuracy notable by 31.33%. This study can provide a new idea and method for evaluation of soil quality in karst areas.

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