Challenging the food waste hierarchy.

Food waste is a multi-faceted and complex problem for urban circular economies with far-reaching environmental impacts. Effectively addressing this problem requires a comprehensive understanding of the food waste impacts on food, energy, water, and climate (FEWC) systems. Despite complex dynamics in the FEWC nexus, the most popular guidance for food waste management is the food waste hierarchy framework - which fails to account for ensuing impacts on all nexus elements. Aiming to optimise the framework, we adopt a participatory approach to develop the first comprehensive and replicable system dynamics model of the FEWC footprints of urban food waste throughout the agri-food supply chain. The quantitative model compares different food waste management options, and relevant policies in Bristol, UK (2018-2030). Unlike the guidance of the traditional waste hierarchy framework, our findings show that the preferability of each option can vary for each sector within the supply chain and for each FEWC element. Our results show that increasing food surplus redistribution in the supply sectors and reducing food waste in consumer sectors are the most preferable approaches to reduce the environmental impacts of food. Feeding food leftover to pets at household level also has a promising impact. Other options involve trade-offs between energy and carbon footprints, while having minimal impact on water footprint. We conclude that the traditional food waste hierarchy is too simplified to provide reliable guidance for environmentally sustainable food waste management and policy. Instead, we present an improved food waste hierarchy framework that accounts for the scale of preferability of each option for different sectors and different FEWC nexus elements. This novel framework thus provides more nuanced and more robust understanding of food waste impacts on the FEWC nexus in urban circular economies, thereby enabling the development of policy and management options that are optimised for environmental sustainability.

Calculating flux to predict future cave radon concentrations.

Cave radon concentration measurements reflect the outcome of a perpetual competition which pitches flux against ventilation and radioactive decay. The mass balance equations used to model changes in radon concentration through time routinely treat flux as a constant. This mathematical simplification is acceptable as a first order approximation despite the fact that it sidesteps an intrinsic geological problem: the majority of radon entering a cavity is exhaled as a result of advection along crustal discontinuities whose motions are inhomogeneous in both time and space. In this paper the dynamic nature of flux is investigated and the results are used to predict cave radon concentration for successive iterations. The first part of our numerical modelling procedure focuses on calculating cave air flow velocity while the second part isolates flux in a mass balance equation to simulate real time dependence among the variables. It is then possible to use this information to deliver an expression for computing cave radon concentration for successive iterations. The dynamic variables in the numerical model are represented by the outer temperature, the inner temperature, and the radon concentration while the static variables are represented by the radioactive decay constant and a range of parameters related to geometry of the cavity. Input data were recorded at Driny Cave in the Little Carpathians Mountains of western Slovakia. Here the cave passages have developed along splays of the NE-SW striking Smolenice Fault and a series of transverse faults striking NW-SE. Independent experimental observations of fault slip are provided by three permanently installed mechanical extensometers. Our numerical modelling has revealed four important flux anomalies between January 2010 and August 2011. Each of these flux anomalies was preceded by conspicuous fault slip anomalies. The mathematical procedure outlined in this paper will help to improve our understanding of radon migration along crustal discontinuities and its subsequent exhalation into the atmosphere. Furthermore, as it is possible to supply the model with continuous data, future research will focus on establishing a series of underground monitoring sites with the aim of generating the first real time global radon flux maps.