Science results: special issues derived from EGU-Soil System Science sessions

Sunny day at EGU2014, by Antonio Jordán. Distributed by Imaggeo.

The impact of the oral, poster and PICO presentations of the Soil System Sciences Division of the EGU is greater and greater. Because of the relevance of research results, conveners and contributors often decide to promote the publication of journal special issues. This list is a compilation (probably not complete) of some of these special issues published in scientific journals, with links to the original sources. I’m sure some may be missing, so if you have information, you can send it to me or leave it in the comments. Continue reading

Snow deposits: A soil disturbance in urban areas

Snow stores a great amount of sediments during the winter. After this season snow melt transports a large amount of sediments to floodplains and water bodies. This natural process depends of the land-use, and is accelerated in urban areas, due soil sealing, which facilitates runoff and sediment transport. Here, sediments very often contain a high amount of sodium, due the salt spreading in the roads to break the ice. These sediments with high levels of sodium can induce an additional disturbance in the place where they are deposited. When leached into the soil, they will contribute to soil clay dispersion, sediment production and the increase of erosion potential. In urban areas as Vilnius, Lithuania (Figure 1), the sediment produced after the snow melt is a problem for the municipality and a cause of soil degradation in urban areas.

Featured image

Figure 1. Snow Deposits in urban parks.

Permafrost Research Group – University of Alcalá (Spain)

The permafrost team of the University of Alcalá is one of the world leading groups in the study of Antarctic permafrost. The first Antarctic campaigns of this group started in the 80’s when the Spanish Antarctic Program was being formed. Since then, the Research Group conducts research in the Antarctic Peninsula participating in the Spanish Antarctic expedition with the collaboration of the University of Lisbon. They focus on the study of the thermal state of permafrost through the CALM-S sites and the boreholes drilled in the South Shetland Islands (Antarctic Peninsula region).

Besides, during the last years the interest of the group turned towards the analysis of landscape in Mars and the possible distribution of permafrost there. The group participates in the Mars Sciences Laboratory NASA mission (MSL) collaborating in the Rover Environmental Monitoring Station (REMS), which is led by the Centro de Astrobiología (CAB-INTA). Mars Science Laboratory is a rover that will assess whether Mars ever was, or is still today, an environment able to support microbial life, basically on the permafrost system. In other words, its mission is to determine the planet’s “habitability.”


Meteo station and a 25 m deep borehole established to characterize the thermal state of permafrost and the active layer evolution in the top of Reina Sofia peak, close to the Spanish Antarctic Station (Livingston Island, Antarctica).

Soil wind erosion is influenced by soil inherent properties

Carlos M. Asensio Grima
Department of Agronomy
University of Almería, Spain

Soil wind erosion is influenced by soil inherent properties, different wind characteristics and surface vegetation cover. For a better understanding of this process is necessary to explain the effect and consequences of wind erosion on the ground and especially in agricultural areas of southern, eastern and northern Europe. In fact, this process usually occurs very slowly and its impact on soil quality and productivity fails to be detected until several years later. In addition, conventional farming practices may mask long term wind erosion effects on productivity by the intense and deep soil tillage and increased use of fertilizers.



It is true that in recent years there has been progress in the knowledge of the distribution of wind erosion in Europe, proving that in certain areas wind erosion rates are as high as those due to water erosion. It has already been noted, moreover, that in the case of the USA, while water erosion risk decreases, erosion wind one increases, with the added problem that damage and prevention costs are higher in this latter. This alerts us for the need to prevent and combat the problem and, for this, it is essential a better understanding of generated dust production mechanisms and emission by farming practices.

Effects, consequences and control of soil wind erosion will be discussed in the SSS.2.14 session of the EGU General Assembly, in Vienna, next April.




This post has been also published in the EGU Blog Network.

Lightening the clay (II)

According to the previous post, tetrahedral and octahedral sheets combine to form layers, and we can find two main types of clay structures: structure 1:1 (one tetrahedron sheet and one octahedral sheet) and 2:1 (two tetrahedral sheets and one octahedral sheet).

The basic structure of clays is this:

Basic structure of clays.
Basic structure of clays.

Substitutions between cations may occur in the tetrahedral and octahedral sheets, resulting in different charge deficits. These negative charges attract cations which are inserted between the layers, in the so-called interlayer space.

Depending on these substitutions, composition of the tetrahedral and octahedral sheets changes, and the resulting layer will have no charge, or will have a net negative charge. Depending on the amount of negative charge, the place where it occurs (the tetrahedral or octahedral sheet) and the type of cations, different mineral species may appear: kaolinite, serpentine, mica (muscovite, biotite, illite), smectite (montmorillonite), vermiculite, chlorite, sepiolite and vermiculite, mainly. Let’s have a look at them.

2-sheet minerals (1:1 structure)

Some examples of 2-sheets minerals are kaolinite, dickite and nacrite (wich are polymorphs of Al2Si2O5(OH)4. Halloysite, a hydrated form of kaolinite, can be found in some Tropical soils.The structure of kaolinite is the following:

Kaolinite. 1 Å (from Swedish ångström) is 10−10 m (one ten-billionth of a metre) or 0.1 nm.

Layers of kaolinite are formed by a tetrahedral sheet of SiO44- on another sheet of AlOH66- octahedra, with shared vertices. The interlayer space is about 7.2 Å thick and non expandable due to strong hydrogen bonds. This union does not allow water molecules or ions to enter the structure. Particle size ranges from 0.2 to 2 µm and the effective surface area is limited (10 – 30 m2/g), as only external surfaces are available.

Kaolinite. Credit: M. Roe, Macaulay Institute. Click to see the original image and details at the Mineralogical Society website.
Halloysite (hollow tubes). Credit: Ömer Işik Ece, Istanbul Technical University. Click to see the original image and details at the Mineralogical Society website.
Kaolinite. Credit: Ray Frost, Macaulay Institute. Click to see the original image and details at the Mineralogical Society website.

In kaolinites, Si is never replaced. So, the elementary particle is electrically neutral and the cation exchange capacity (CEC) very low (1-10 cmol (+) / kg), which explains the low fertility of soils rich in kaolinite.

The name “kaolinite” is derived from Chinese Kao-Ling, a mountain from Jiangxi province (China) were this mineral was extracted.

Kaollinite-rich soil in Faro (Portugal). Credit: A. Jordán. Click to see the original image and details in Imaggeo.

3-sheet minerals (2:1 structure)


Smectites are a group of clay minerals including pyrophyllite, montmorillonite, nontronite, beidellite and saponite. Montmorillonite is hydrated sodium calcium aluminium magnesium silicate hydroxide (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O. Charge is very negative due to isomorphous substitutions of Si. Crystallization of montmorillonites is not stable, since the layers are bonded only by Van der Waals forces, weak O-O bonds and cation-O bonds, what makes the interlayer space very variable. This allows easy expansion of the crystal and the entry of water molecules and cations. On average, the spacing between adjacent layers is around 14.2 Å, but it may easily expand due to swelling in contact with water. During the dry season, water loss reduces the interlayer space, contraction of soil aggregates and development of cracks in the soil surface.As the internal surface of layers is available for interactions, the effective surface area is very high (up to 600 – 800 m2/g).

Montmorillonite. Credit: Emilia García-Romero, Universidad Complutense de Madrid. Click to see the original image and details at the Mineralogical Society website.
Smectite, nontronitic. Credit: Michael Velbel (Michigan State University) and William Barker, (University of Wisconsin-Madison). Click to see the original image and details at the Mineralogical Society website.
Summer cracks at the surface of a montmorillonite-rich soil from the Doñana Natural Park, Spain. Credit: A. Jordán. Click to see the original image and details at Imaggeo.


Micas are also three-layer minerals, but quite different from montmorillonites. Micas and illites (see below) are a group characterized the presence of trivalent cations in the octahedral sheet and potassium in the tetrahedral and octahedral seets. This allows them to have a greater CEC.

The unit cell is negatively charged, but is compensated by the entry of K+ ions. Mica crystallizes from magma, and isomorphous substitution of Al3+ for Si4+ is intense. Consequently, there is a highly net negative charge. K+ cations are strongly retained in the interlayer space, which can not expand or pick up other cations. CEC is low, and the interlayer spacing is constant (10 Å).

In addition to cations forming the crystal structure (Al, Si, Mg and Fe), there are also others between the layers, which confer give specific characteristics. These variations are the origin of muscovite (native of Moscow, Russia), biotite (in honour of the French physicist Jean-Baptiste Biot) and phlogopite (from a Greek word meaning “like fire”).

Structure of mica.
Structure of mica.


Illites are three-layer minerals derived from pyrophyllites, where the substitution of Si4+ by Al3+ is less intense, and the global negative net charge is smaller.

With less negative charge, K+ cations are not strongly bonded, so other cations of similar size (or smaller but hydrated cations) can enter the structure. Therefore, the space between layers is slightly variable (not as much as in montmorillonites), 10 Å on average. The effective surface area is smilar to montmorillonite’s, but CEC is smaller (20 – 40 cmol(+)/kg).

Fibrous illite. Credit: M. Roe, Macaulay Institute. Click to see the original image and details at the Mineralogical Society website.


The chlorite has many isomorphic substitutions in the tetrahedral and octahedral layers (Al3+ instead of Si4+ and Mg2+ instead of Al3+). The negative charge is compensated by a stable positively charged octahedral sheet of Mg, Fe and Al hydroxides sandwiched between the tetrahedral sheets. The expansion of the network is difficult, and the entry of water molecules and cations is limited. The effective surface area is small (70 – 100 m2/g).

Chlorite structure
Structure of chlorite
Fe-rich chlorite from an alpine fissure. Credit: Michal Skiba, Institute of Geological Sciences, Jagiellonian University. Click to see the original image and details at the Mineralogical Society website.


Vermiculites are not very frequent. These clay minerals are intermediate froms between chlorites and micas. Intense weathering removed some  K+ cations, which are replaced by other hydrated cations. Expansion of the network is easy (10 – 15 Å), allowing the entry of water and cations replacing Mg2+. Net hegative charge is very high and CEC is . The effective surface area is 600 – 800 m2/g, similar to smectites.

Structure of vermiculite.
Structure of vermiculite.
Vermiculite. Credit: Steve Hillier and David Riley. Click to see the original image and details at the Mineralogical Society website. See video footage at the begining of the text, showing time lapse of hydrogen peroxide exfoliation process over 7 hours real time. Note bubbles in early stages when peroxide is still covering the particle, and relaxation as the process completes.

This post has been also published in the EGU Blog Network.

Mediterranean Environmental Research Group (GRAM)

The Mediterranean Environmental Research Group, (GRAM) from the University of Barcelona has over 20 years of working experience in the field of the effects of forest fires on soil properties. In 1998 the doctoral thesis entitled “Fire effects on soil properties, the role of fire intensity” carried out by Xavier Úbeda emphasized the importance of fire intensity impacts on soil physico-chemical properties and the consequent implications, as the increase of runoff and erosion in post-fire environments. From this thesis some papers were published in national and international journals. This work was funded by two European research projects related to forest fires, as the “Post fire soil and vegetation dynamics in natural and afforested areas in Southern Europe: The role of fire intensity.” The most important results were the reaffirmation of the importance of fire intensity impacts on soil properties, the increase of erosion and the implications on vegetation recuperation.

Plot located in a urban-forest interface area (see
Plot located in a urban-forest interface area (see

In the last twelve years, the GRAM members worked intensively in the study of prescribed fire impacts on soils.  Samples were collected before, immediately after and one year after the prescribed fire experiments in order to observe the impact of this type of landscape management on soil properties, mainly in nutrients behavior. This research was possible through collaboration with the GRAF (Grup de Recolzament to Actuacions and Forestry) from the Generalitat de Catalunya, which carries more than twelve years conducting controlled burns for forest management. Two projects from Spanish Ministry have funded this research: “Alterations of environmental quality in fire-affected soils in Mediterranean environments. The study of hydrophobicity, and development of new techniques to evaluate, and mitigate degradation“and the project: “Assessment of the quality of Mediterranean soils affected by the heat to medium and long term, applying an index of environmental quality“. From these projects, two theses were directed by the person who signs this petition (Dr. Xavier Ubeda). Both were defended in 2010. Luís Outeiro: “Geostatistics and environmental management; studies and applications of the spatial and temporal variability in soil and water “and Paulo Pereira:” Effects of fire temperatures on the chemical and physical characteristics of the Mediterranean species ash and their effect on water quality”. From the thesis of Luis the most relevant results were that based on geostatistical analysis, that low-intensity prescribed fires do not cause important variations on soil properties, but the repetition of this technique can be harmful, if carried out in a short time period. From the thesis of Paulo it was observed that fire temperatures and severity have an important effect on the ash physico-chemical properties, which will influence temporarily the type and amount of nutrients in the soil and available to landscape recuperation.

Studies on soil erosion (see
Studies on soil erosion (see


In the project funded by the Ministry of Environment of the Government of France with the title “Dynamique des paysages, érosion développement durable et dans les montagnes méditerranéennes” some interviews were carried out with stakeholders engaged in forest management. The stakeholder’s interviewed were staff from councils and consortia, councils, Forest Ownership Center and Forest Technology Centre of Catalonia. Using these interviews, Roser Rodriguez is currently doing a doctoral thesis entitled “Socioecology wildfire: an approach to environmental sociology wildfires central Catalonia.”

The GRAM has organized several national and international conferences, as the ‘ International Meeting of Fire Effects on Soil Properties “held in 2007 in Barcelona ( and in 2013 in Vilnius ( Other international congresses were organized by the group in several European Geoscience Assemblies.

The Members of the group have participated as “guest editor” in three special issues: “Fire Effects on Soil Properties” Catena. 2008 Vol 74 Issue 3, “Fire Effects on Soil Properties: Forest Fires and Prescribed Fires”. Environmental Research. 2011 Vol. 111. Issue 2 and “Incendis and Forestry” 2012. Treballs of the Catalan Society of Geography. Other three Special issues are ongoing, “The role of ash in fire-affected ecosystems: A physical, chemical and biological approach (Catena)”, “Soil processes in cold-climate environments (Solid Earth)” and “Soil mapping, classification, and modelling: history and future directions (Geoderma)”.

More information on the website of GRAM Group (


This post has been published also in the EGU Blog Network.

Wikipedia is evil

Yesterday, I had to write the exam questions for my students of Soil Science in the Faculty of Biology. As they are very more than 300, because of the facilities that my government gives to the fulfillment of the Bologna Process and the European Higher Education Area (ironic mode activated), I usually make multiple choice tests (if you do the same, have a look at this). However, I like to put some questions to see if students are able to solve problems, rather than selecting the correct answer from a number of possibilities.

To achieve this, one of the things I do is to display a picture and ask the student to give me all the information that can be extracted. For example, if I show a soil profile, I ask the student to say, only from the soil profile in the image, the geographical location, the type of climate, land use, geomorphological description of the area, etc.

Look at the soil in this hillslope. Can you tell me something about the exact location? Credit: Flickr user raindog808. Click to see the original image at Flickr.

So, for this case, I decided not to use a picture from my collection, but go into Wikipedia and seek for any image useful for my purpose. I typed “suelo” (soil, in Spanish) in the Spanish edition of Wikipedia and this is how one of the most funny times I’ve spent reading since I read “Lazarillo de Tormes” started. I hope someone has corrected the Spanish Wikipedia Suelo entry after December 11th 2013 (not me).

The Life of Lazarillo de Tormes and of His Fortunes and Adversities, anonymous (1554). Click to see the original picture at Wikimedia Commons.

I found statements such as the following:

  • In a simple way, it can be said that the steps involved in the formation of soil are: “mechanical disintegration of rocks and chemical weathering of regolitic materials, (comma) released“. And that’s all, folks. No more stages in soil evolution.
  • On colluvium materials, that thing commonly referred to as soil may develop“. That’s it, just on colluvium. And this is that thing commonly referred to as scientific language.
  • According to its function (?), soils can be “sandy, calcareous, humiferous, clayey, rocky and mixed“. In the case of clayey soils, these: “are formed by fine yellowish grains and retain water in ponds“. This guy has managed to see the color of clay particles!
  • Calcareous soils are white. What about terra rossa?
Calcareous soil. So white that can blind you. Credit: A. Jordán. Click to see the original picture at Imaggeo.
  • According to their physical characteristics, soil groups are: Litosols, Cambisols, Luvisols, Acrisols,  Gleysols, Fluvisols, Rendzinas and Vertisols. No more soil types according to their physical characteristics. My students are infinitely grateful.
  • There are detailed reviews of each case. Rendzinas, for example, are soils with “a horizon of about 50 cm deep“. Are you sure? More: Fluvisols are rich in calcium and Lithosols are soils that appear on rocky outcrops.
A Lithosol appearing? Credit: F. Cossu. Click to see the original picture at Imaggeo.

After this, a chapter is devoted to the classification of soils. According to Spanish Wikipedia:

  • Soils can be classified according to their texture: fine or coarse“. Have you heard about “silty clay loam soils”? Not me, the Super-Wikipedist.
  • Poorly developed soils are: “polar soils, deserts (rock and sand) and beaches“, and there are three types: Rankers, Rendzinas and steppe soils. Please, tell me: assuming that a beach is a soil, where are beaches included?
One of the three types of poorly developed soils in the world. Credit: E. Klimenko. Click to see the original picture at Imaggeo.
  • Among the wide variety of “developed soils“, there are soils of temperate forests, rainy regions, temperate climates (I guess these do not include temperate forests) and the Mediterranean red soil. Hey, hey, hey… they were not white?. But do not worry, because “if the weather is suitable and the place is accessible, most of these areas are now occupied by farms“.
  • One of the most important soil problems is “soil destruction“. According to Spanish Wikipedia, “very serious data claim that trees will be extinguished in twelve or thirteen years, and we will need to import all the wood“. This is frightening. Where will we import wood from? From Endor?
Sequoia forest in Redwood National Park (USA). Here the forest moon of Endor scenes were filmed for Star Wars Episode VI – Return of the Jedi. Click to see the original picture at the RNSP Photo Gallery.
  • More. Due to excessive sedimentation, we will end up with… navigable rivers! That’s the key issue, world!

After this, and discovering that the O horizon is the surface layer of A, the A horizon is a washed horizon and the C horizon is the subsoil “fragmented by mechanical and chemical action (but the chemical weathering does not exist)“, the reader finds a chapter about Soil Classification (yes, again, this is the third one in the same page). Here, you can read things like:

  • There are three main soil models, namely: the Podzol, the Chernozem and the latosol“.

Dear students: I hope this will serve to understand the difference between internet and books. Next time we will talk about Google Translator.

This post was also published simultaneously in the EGU Blog Network.