Energy, Resources and the Environment

Words on Wednesday: Remediation of degraded arable steppe soils in Moldova using vetch as green manure

ERE Matters July 8, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Wiesmeier, M., Lungu, M., Hübner, R., and Cerbari, V., 2015. Remediation of degraded arable steppe soils in Moldova using vetch as green manure, Solid Earth, 6, 609-620, doi:10.5194/se-6-609-2015, 2015.

Abstract:

In the Republic of Moldova, non-sustainable arable farming led to severe degradation and erosion of fertile steppe soils (Chernozems). As a result, the Chernozems lost about 40% of their initial amounts of soil organic carbon (SOC). The aim of this study was to remediate degraded arable soils and promote carbon sequestration by implementation of cover cropping and green manuring in Moldova. Thereby, the suitability of the legume hairy vetch (Vicia sativa) as cover crop under the dry continental climate of Moldova was examined. At two experimental sites, the effect of cover cropping on chemical and physical soil properties as well as on yields of subsequent main crops was determined. The results showed a significant increase of SOC after incorporation of hairy vetch mainly due to increases of aggregate-occluded and mineral-associated OC. This was related to a high above- and belowground biomass production of hairy vetch associated with a high input of carbon and nitrogen into arable soils. A calculation of SOC stocks based on equivalent soil masses revealed a sequestration of around 3 t C ha⁻¹yr⁻¹ as a result of hairy vetch cover cropping. The buildup of SOC was associated with an improvement of the soil structure as indicated by a distinct decrease of bulk density and a relative increase of macroaggregates at the expense of microaggregates and clods. As a result, yields of subsequent main crops increased by around 20%. Our results indicated that hairy vetch is a promising cover crop to remediate degraded steppe soils, control soil erosion and sequester substantial amounts of atmospheric C in arable soils of Moldova.

Bulk densities (BD) and soil organic carbon (SOC) contents
of topsoil horizons of control and experimental sites in Orhei
and Cahul after incorporation of HVW and harvest of the main crop. Error bars represent standard deviation (n = 10).

Words on Wednesday: Poroelastic responses of confined aquifers to subsurface strain changes and their use for volcano monitoring

ERE Matters July 1, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Strehlow, K., Gottsmann, J. H., and Rust, A. C., 2015. Poroelastic responses of confined aquifers to subsurface strain changes and their use for volcano monitoring, Solid Earth Discuss., 7, 1673-1729, doi:10.5194/sed-7-1673-2015.

Abstract:

Well water level changes associated with magmatic unrest can be interpreted as a result of pore pressure changes in the aquifer due to crustal deformation, and so could provide constraints on the subsurface processes causing this strain. We use Finite Element Analysis to demonstrate the response of aquifers to volumetric strain induced by pressurised magma reservoirs. Two different aquifers are invoked – an unconsolidated pyroclastic deposit and a vesicular lava flow – and embedded in an impermeable crust, overlying a magma chamber. The time-dependent, fully coupled models simulate crustal deformation accompanying chamber pressurisation and the resulting hydraulic head changes as well as porous flow in the aquifer. The simulated deformational strain leads to centimetres (pyroclastic aquifer) to meters (lava flow aquifer) of hydraulic head changes; both strain and hydraulic head change with time due to substantial porous flow in the hydrological system. Well level changes are particularly sensitive to chamber volume and shape, followed by chamber depth and the phase of the pore fluid. The Young’s Modulus and permeability of the aquifer, as well as the strength of pressurisation also have significant influence on the hydraulic head signal. While source characteristics, the distance between chamber and aquifer and the elastic stratigraphy determine the strain field and its partitioning, flow and coupling parameters define how the aquifer responds to this strain and how signals change with time. We investigated a period of pre-eruptive head changes recorded at Usu volcano, Japan, where well data were interpreted using an analytical deformation model. We find that generic analytical models can fail to capture the complex pre-eruptive subsurface mechanics leading to well level changes, due to aquifer pressure changes being sensitive to chamber shape and lithological heterogeneities. In addition, the presence of a pore fluid and its flow have a significant influence on the strain signal in the aquifer and are commonly neglected in analytical models. These findings highlight the need for numerical models for the interpretation of observed well level signals. However, simulated water table changes do mirror volumetric strain and wells can therefore serve as comparatively cheap strain meters that could provide important insights into pre-eruptive dynamics.

2-D axisymmetric model setup: a boundary load dP is applied on a cavity at depth, with the radius r for the spherical case or vertical semi-axis b for the ellipsoidal case, respectively. This changes the strain conditions in the surrounding linear elastic host rock (granitic crust), the poroelastic aquifer and the overlying linear elastic cap rock (clay). The watersaturated aquifer is modelled as either a vesicular lava flow or unconsolidated pyroclasts. An aquifer not covering the chamber but starting at some lateral distance L is realised by setting the darker grey region impermeable. The bottom boundary is fixed, the upper boundary is treated as a free surface, the lateral boundaries have a roller condition. There is no flow outside the aquifer, stress and displacement at the internal boundaries are continuous. An extract of the finite element mesh is shown only for illustration. The mesh density is finer around the cavity, at aquifer boundaries and the free surface.

Words on Wednesday: Effects of soil settlement and deformed geometry on a historical structure

ERE Matters June 24, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Yardım, Y. and Mustafaraj, E., 2015. Effects of soil settlement and deformed geometry on a historical structure, Nat. Hazards Earth Syst. Sci., 15, 1051-1059, doi:10.5194/nhess-15-1051-2015.

Abstract:

Protecting the historical character of a valued structure during the assessment and damage repair process is a very challenging task for many engineers. Heritage protection is complicated by a lack of design details and restrictions on sample extraction needed to obtain accurate material properties and limited studies on the restoration of certain types of historical structures. This study aims to assess the effects of soil settlement on a structure’s stress concentrations and the value of laser scanning techniques on structure analysis in obtaining correct data of settlement vs. deformation. Terrestrial laser scanner (TLS) data are used to analyse the 500-year-old historical structure of Naziresha’s Mosque. The obtained TLS data allow an accurate definition of the imperfect geometry patterns lying on every side of the structure. The soil profile and general crack formation together with TLS measurement proves that the structure deformed toward the south façade, where a railway and motorway are also located. Stress concentration and mode period results have a considerable difference, which highlights earthquake vulnerability and failure mechanisms and changes the strategy of possible retrofitting.

Cracks due to differential settlement (d = 18 cm) in the south façade (May 2012).

Words on Wednesday: The ocean carbon sink – impacts, vulnerabilities and challenges

ERE Matters June 17, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Heinze, C., Meyer, S., Goris, N., Anderson, L., Steinfeldt, R., Chang, N., Le Quéré, C., and Bakker, D. C. E., 2015. The ocean carbon sink – impacts, vulnerabilities and challenges, Earth Syst. Dynam., 6, 327-358, doi:10.5194/esd-6-327-2015.

Abstract:

Carbon dioxide (CO₂) is, next to water vapour, considered to be the most important natural greenhouse gas on Earth. Rapidly rising atmospheric CO₂ concentrations caused by human actions such as fossil fuel burning, land-use change or cement production over the past 250 years have given cause for concern that changes in Earth’s climate system may progress at a much faster pace and larger extent than during the past 20 000 years. Investigating global carbon cycle pathways and finding suitable adaptation and mitigation strategies has, therefore, become of major concern in many research fields. The oceans have a key role in regulating atmospheric CO₂ concentrations and currently take up about 25% of annual anthropogenic carbon emissions to the atmosphere. Questions that yet need to be answered are what the carbon uptake kinetics of the oceans will be in the future and how the increase in oceanic carbon inventory will affect its ecosystems and their services. This requires comprehensive investigations, including high-quality ocean carbon measurements on different spatial and temporal scales, the management of data in sophisticated databases, the application of Earth system models to provide future projections for given emission scenarios as well as a global synthesis and outreach to policy makers. In this paper, the current understanding of the ocean as an important carbon sink is reviewed with respect to these topics. Emphasis is placed on the complex interplay of different physical, chemical and biological processes that yield both positive and negative air–sea flux values for natural and anthropogenic CO₂ as well as on increased CO₂ (uptake) as the regulating force of the radiative warming of the atmosphere and the gradual acidification of the oceans. Major future ocean carbon challenges in the fields of ocean observations, modelling and process research as well as the relevance of other biogeochemical cycles and greenhouse gases are discussed.

Mean unweighted surface water fCO2 (μatm) for the years 1970–2002 (a) and 2003–2011 (b) using the SOCATv2
monthly 11 degree gridded data set (Bakker et al., 2014). The maps were generated by using the online Live Access Server.