title: Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil

authors: Salmanzadeh, Mahdiyeh

subjects: Science & Technology

abstract: Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δ¹¹⁴/¹¹⁰Cd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment.

text: Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δ¹¹⁴/¹¹⁰Cd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment.

year: 2017

title: Lagrangian relaxation schemes for calculating force-free magnetic fields, and their limitations

authors: Pontin, D.I.

subjects: magnetic fields

abstract: Force-free magnetic fields are important in many astrophysical settings. Determining the properties of such force-free fields—especially smoothness and stability properties—is crucial to understanding many key phenomena in astrophysical plasmas, for example, energy release processes that heat the plasma and lead to dynamic or explosive events. In the present work we discuss a serious limitation on the computation of force-free fields, within the context of a Lagrangian relaxation scheme that conserves magnetic flux and ∇ • B identically. This issue has the potential to invalidate the results produced by numerical force-free field solvers even for cases in which they appear to converge (at fixed grid resolution) to an equilibrium magnetic field. Error estimates are introduced to assess the quality of the calculated equilibrium. We go on to present an algorithm, based on rewriting the curl operation via Stokes' theorem, for calculating the current which holds great promise for improving dramatically the accuracy of the Lagrangian relaxation procedure.

text: Lagrangian relaxation schemes for calculating force-free magnetic fields, and their limitations Force-free magnetic fields are important in many astrophysical settings. Determining the properties of such force-free fields—especially smoothness and stability properties—is crucial to understanding many key phenomena in astrophysical plasmas, for example, energy release processes that heat the plasma and lead to dynamic or explosive events. In the present work we discuss a serious limitation on the computation of force-free fields, within the context of a Lagrangian relaxation scheme that conserves magnetic flux and ∇ • B identically. This issue has the potential to invalidate the results produced by numerical force-free field solvers even for cases in which they appear to converge (at fixed grid resolution) to an equilibrium magnetic field. Error estimates are introduced to assess the quality of the calculated equilibrium. We go on to present an algorithm, based on rewriting the curl operation via Stokes' theorem, for calculating the current which holds great promise for improving dramatically the accuracy of the Lagrangian relaxation procedure.

year: 2009

title: Whanaungatanga: an illustration of the importance of cultural context

authors: McNatty, William

subjects: Te reo Māori

abstract: The word 'whanaungatanga' is often used by people who lack an intimate understanding of the philosophical base in Māori culture out of which it emerges. Thus, it is sometimes used simply to describe the camaraderie that can be associated with team sports or with reference to the 'glue' that connects people to one another socially. This is not necessarily a problem in itself. After all, change and development in the lexicon is a characteristic of living languages. However, real problems can emerge where words become divorced from their cultural roots to such an extent that two speakers using the same word can completely fail to understand one another. It is argued here that this is what can happen when Māori words, such as 'whanaungatanga', are used in the context of modelling in the social sciences, particularly where that modelling is conducted in the context of Western social and cultural values. In particular, the essential spiritual dimension of whanaungatanga may be overlooked or misunderstood.

text: Whanaungatanga: an illustration of the importance of cultural context The word 'whanaungatanga' is often used by people who lack an intimate understanding of the philosophical base in Māori culture out of which it emerges. Thus, it is sometimes used simply to describe the camaraderie that can be associated with team sports or with reference to the 'glue' that connects people to one another socially. This is not necessarily a problem in itself. After all, change and development in the lexicon is a characteristic of living languages. However, real problems can emerge where words become divorced from their cultural roots to such an extent that two speakers using the same word can completely fail to understand one another. It is argued here that this is what can happen when Māori words, such as 'whanaungatanga', are used in the context of modelling in the social sciences, particularly where that modelling is conducted in the context of Western social and cultural values. In particular, the essential spiritual dimension of whanaungatanga may be overlooked or misunderstood.

year: 2002-02