Effect of air turbulence on gas transport in soil; comparison of approaches

Geophysical Research Abstracts (GRA) is the conference series publishing the abstracts accepted for the General Assemblies of the European Geosciences Union (EGU). It links the annual conference programmes listing programme groups, included sessions, and their contributions. The abstracts underwent an access review by the session conveners.Xi'an Jiaotong-Liverpool Universit

Long-Term Grazing Intensity Impacts Belowground Carbon Allocation and Mycorrhizas Revealed by 13CO2 Pulse Labeling

Despite the importance of grasslands for carbon storage and climate regulation, there is uncertainty about the effect of livestock grazing intensity on aboveground carbon assimilation and belowground carbon partitioning. Furthermore, the relationship between belowground carbon allocation and arbuscular mycorrhizal fungi, which serve as a conduit for carbon movement through the plant and soil, is unclear. To investigate this, we used an in situ 13C stable isotope pulse-chase labeling approach in plots under seven rates of sheep grazing intensity in a steppe grassland in northern China. We quantified the allocation of carbon to plants, soil, and soil-respired CO2 along with measurements of mycorrhizal hyphal density in the soil. With increasing grazing intensity, carbon assimilation per unit shoot biomass increased significantly, whereas carbon allocation to roots marginally decreased. Soil-respired CO2 appeared to be independent of grazing intensity. Mycorrhizal hyphal density decreased with increasing grazing intensity and was correlated significantly with new carbon input to roots 2 d after labeling and marginally related to that of soil 1 d after the 13C-CO2 pulse. Our study suggests that grazing intensity alters the distribution of carbon among different carbon pools within the plant-soil system. The results also underscored the key role of mycorrhizas as a fast route for carbon transfer from plant to soil

Pilot study of method for constructing concrete seals and fracture grouts in deep boreholes, and cementitious backfills in tunnels, drifts and shafts in crystalline rock : Theoretical modeling and experimental study

Borehole sealing is required for different purposes, like permanent tightening of deep holesbored in conjunction with site investigations for location of radioactive waste repositories, andtemporary plugging of holes carrying water in deep mines. The holes will pass through low-permeablerock as well as through water-bearing fracture zones. Sealing can preferably bemade by use of concrete where such zones are intersected, while very low-permeable clayseals can be placed where the holes are surrounded by tight rock. This study focuses on withconcrete seals, and on grouts used for stabilizing intersected fracture zones before boreholesealing is started.The work on concrete comprised comparison of two recipes with different superplasticizers,i.e. organic Glenium which is currently used on a large scale, and talc being an inorganic,hydrophobic material. The study included determination of the compressive and tensilestrength as functions of time, and fluidity, pH and hydraulic conductivity of matured concrete.Part of the study concerned grouts for sealing of rock fractures. Two cement brands were usedas for the concrete study. The effect of adding palygorskite and talc to the silicious aggregatematerial for enhancing fluidity was tested. The work included determination of properties likestrength and fluidity.Validerat; 20120614 (anonymous

Can sealing of rock hosting a repository for highly radioactive waste be relied on?

Multibarrier systems are commonly proposed for effective isolation of highly radioactive waste (HLW). Presently considered concepts take the host rock as a barrier claiming it to retard migration of possibly released radionuclides from HLW containers to the biosphere. This capacity is small unless water-bearing fracture zones intersecting the blasted waste-containing tunnels and excavation-disturbance zones around them can be sealed by grouting and construction of bulkheads, but this is effective only for a very limited period of time as explained in the paper. The disturbed zones thence make the entire repository serve as a continuous hydraulic conductor causing quick transport of released radionuclides up to the biosphere. The dilemma can be solved by accepting the short-circuiting function of the disturbed zones along the tunnels on the condition that totally tight waste containers be used. Deep holes bored in the site selection phase through the forthcoming repository can be effective pathways for radionuclides unless they are properly sealed. They are small-scale equivalents of tunnels but do not have any ex-cavation damage and can be effectively sealed by using clay and concrete of new types. Applying this principle to very deep boreholes with a diameter of a few decimeters would make it possible to safely store slim, tight HLW canisters for any period of time.Godkänd; 2012; 20121030 (mohhat

A talc-based cement-poor concrete for sealing boreholes in rock

Deep investigation boreholes in crystalline rock for site selection of repositories for high-level radioactive waste are proposed to be sealed by installing a series of dense concrete and clay plugs. These should prevent radionuclides from leaking canisters at depth to migrate to the biosphere through the holes. The concrete seals will be installed where the holes intersect water-bearing fracture zones to serve as stable and low-permeable supports for adjacent clay plugs. Low porosity and microstructural stability must be guaranteed for many thousands of years and ordinary Portland cement with organic superplastizer will not fulfil the requirements since the high pH will cause degradation of contacting clay and the organic additive can produce colloids with a capacity to carry radionuclides up to the biosphere. Very cement-poor concrete (<8 %) based on low-pH cement and with talc as plasticizer is an option but it matures more slowly, which requires that the construction of seals is made so that sufficient bearing capacity for carrying overlying clay seals is reached.Validerad; 2013; 20130104 (mohhat

Long-term grazing intensity impacts below-ground carbon allocation and mycorrhizas revealed by 13CO2 pulse labelling

Despite the importance of grasslands for carbon storage and climate regulation, there is uncertainty about the effect of livestock grazing intensity on above-ground carbon assimilation and below-ground carbon partitioning. Furthermore, the relationship between below-ground carbon allocation and arbuscular mycorrhizal fungi, which serve as a conduit for carbon movement through the plant and soil, is unclear. To investigate this, we used an in situ 13C stable isotope pulse-chase labelling approach in plots under seven rates of sheep grazing intensity in a steppe grassland in northern China. We quantified the allocation of carbon to plants, soil, and soil-respired CO2 along with measurements of mycorrhizal hyphal density in the soil. With increasing grazing intensity, carbon assimilation per unit shoot biomass significantly increased, whereas carbon allocation to roots marginally decreased. Soil-respired CO2 appeared to be independent of grazing intensity. Mycorrhizal hyphal density decreased with increasing grazing intensity and was correlated significantly with new carbon input to roots two days after labelling, and marginally related to that of soil one day after the 13C-CO2 pulse. Our study suggests that grazing intensity alters the distribution of carbon among different carbon pools within the plant-soil system. The results also underscored the key role of mycorrhizas as a fast route for carbon transfer from plant to soil

Talc-based concrete for sealing borehole optimized by using particle packing theory

The paper describes assessment of the performance of cement-poor concreteson the basis of packing theory. The concretes are intended for sealing segments of deep boreholes and have a small amount of cement for minimizing the mutual chemical impact on the contacting clay seals. The composition is examined by application of packing theory with respect to the cement/aggregate ratio and the gradation of the aggregate material which is crushed quartzite for providing high internal friction after maturation, as well as to talc added for fluidity and to the small amount of cement. Low porosity and micro-structural stability must be guaranteed for very long periods of time. The study exemplifies how packing theory assist designers in selecting optimal proportions of the various components. Optimum particle packing implies minimizing the porosity and thereby reducing the amount of cement paste needed to fill the voids between the aggregate particles. The use of talc as inorganic super-plasticizer since ordinary organic additives for reaching high fluidity at casting are undesirable, and since talc reacts with cement and provides high strength in along-term perspective.Validerad; 2013; 20130129 (nadhir)</p

Proportioning of cement-based grout for sealing fractured rock-use of packing models

Fractured, very permeable rock hosting repositories for radioactive waste will require grouting. New grout types of possible use where long-term performance is needed should have a small amount of cement for minimizing the increase in porosity that will follow from the ultimate dissolution and erosion of this component. They have to be low-viscous and gain strength early after injection and packing theory can assist designers in selecting suitable proportions of various grout components. Optimum particle packing means that the porosity is at minimum and that the amount of cement paste needed to fill the voids between aggregate particles is very small. Low porosity and microstructural stability must be guaranteed for long periods of time. Organic additives for reaching high fluidity cannot be used since they can give off colloids that carry released radionuclides and talc can be an alternative superplasticizer. Low-pH cement reacts with talc to give high strength with time while Portland cement gives early but limited strengthening. The clay mineral palygorskite can be used for early gelation because of its thixotropic properties. Once forced into the rock fractures or channels in soil it stiffens and serves as a filter that prevents fine particles to migrate through it be lost. However, its hydrophilic potential is too high to give the grout a high density and high strength. According to the experiments carried out most of the investigated grouts are injectable in fractures with apertures down to 100 μm.Validerad; 2013; 20130731 (mohhat